| Contents | Post-Test |
A fixed prostodontic is any set of fixed crowns, ranging from two crowns side by side to sixteen crowns, with or without pontics (spaces). (If you are not familiar with the basic techniques of crown preparations, you should first take the prerequisite course on ‘Crowns.’) Fixed prostodontics is the process of extending the crown preparation to include more then one tooth. The teeth included in the fixed prostodontic (bridge) will be thought of as a whole. Thus, we are extending the principles of a single crown to include two to sixteen teeth, de¬pending on the size of the fixed bridge.
To treat the bridge as a whole, the walls of the preparations must all be slightly convergent, in order to allow the fixed bridge to seat upon insertion. One wall that is slightly undercut will cause the fixed bridge to fail. A single tooth has four walls to consider, but a sixteen-unit bridge has sixty four walls, and if any one of these is slightly off, the bridge will fail. Dedi¬cated precision is a necessity.
It is recognized that dentistry is an art form. Each dentist will acquire a technique that works well for him or her. This course is not meant to replace this technique but to supplement it. A basic technique will be given for clarity, but each dentist’s ability to problem solve will ultimately be of greater value. This course will present the normal problems one encounters in fixed bridges and the methods of solving these problems, which were learned during forty years of experience and well over twenty-five thousand units of crowns and bridges.
A medical form should be filled out by the patient before any procedures are started. There are many of these available. The medical form should be thought of as an outline of the pa¬tient’s medical history. The medical history is completed after an extensive oral review of the medical form.
A medically compromised patient may need a medical clearance from his or her physician. This can be accomplished by a fax to the patient’s physician using any number of forms. A basic form will be provided at the end of this course. The physician will fax back a medical clearance, or he will advise what precautions will be necessary when treating the patient.
Usually this is not enough when you are treating patients with severe problems. In these cases, I would suggest talking with the physician personally. This will allow you to discuss treatment goals and coordinate your treatment with his goals. He can assist in your long range-treatment planning, and he can help you keep the patient out of severe problems.
Occasionally a physician will refuse to give a medical clearance for legal reasons. I would not treat a medically compromised patient without a medical clearance. In these cases, you could suggest that the patient see another physician.
If a patient checks the communicable diseases box, extensive questioning should follow to see if you wish to continue the treatment. You need to protect your other patients, your per¬sonnel, and yourself.
Basically, you need to know what you are getting into before you start the dental treatment. The more you can learn before the treatment starts, the fewer surprises you will have later.
Planning the treatment is the most critical phase of constructing a fixed bridge. Before a fixed bridge can be constructed, the condition of the mouth needs to be considered. Any basic form can be used to identify a few of the problems you might encounter, but the form should be thought of as an outline. It should be a way of taking your mind through a thought process to avoid missing important information. When you see something abnormal or unusual, it needs to be noted on the form.
The condition of the alveolar bone support is critical for constructing a bridge. If the abut¬ments for the fixed bridge exhibit extensive alveolar bone loss, the fixed bridge will need additional abutments to work.
It is also important to know how the patient lost the tooth you are replacing. If the tooth was lost to periodontal infection, you should investigate the possibility that the patient clenches his teeth. This needs to be considered when you plan the fixed bridge.
The fixed bridge should not be constructed into an inflamed or damaged gingiva. Usually, a fixed bridge is not an emergency treatment, so you may allow time for the gingiva to regain its health before undertaking the procedure. This is a good time to re-contour the alveolar bone around the abutments with a reverse bevel gingival flap. The gingiva tissue will heal back with a tight gingiva. This may also leave the abutments’ roots exposed allowing the crown preps to cover them.
If you see a red ring of inflamed tissue around an anterior tooth, and the rest of the gingiva is okay, you should suspect that the tooth is under stress. You should not place an abutment on a tooth with this condition. The bridge is doomed to failure. This condition may or may not ex¬hibit severe bone loss. It will all depend on the length of time the tooth has been under stress.
This condition can occur on a posterior tooth, but here the tissue usually swells and be¬comes inflamed. The tooth will lose its bone support, and eventually the tooth will show mobility. The cause of the problem is the same. The tooth is under stress, and a fixed bridge placed under either of these stresses will fail.
No amount of periodontal treatment will cure this condition. The tissue can be put through a scaling and curettage, a gingivectomy, or a reverse bevel, but the tissue will heal back with the same red ring. The problem is stress. The tooth is under stress from the opposing occlu¬sion, tongue thrusting, or the lips pressing against the tooth or teeth.
If this condition occurs after the fixed bridge is cemented into place, the fixed bridge needs to be evaluated for the source of the stress. Occasionally the abutments are too long, forcing the lips to reach over them and creating stress on the tooth or teeth.
The only cure is to relieve the stress on the tooth or teeth. If this cannot be done, the fixed bridge should be reconsidered as option. If the fixed bridge is already in place, then the sources of the stress need to be found.
ANECDOTEA female patient of sixty years was in my office to correct a malocclusion of her anterior teeth. We had done her posterior bridges years ago with no stress problems. I had avoided her anterior malocclusion, thinking nothing could be done for her. Tooth number six pro¬truded and extended labially. Tooth number eight was protruding labially five millimeters and bunched with seven and nine. Teeth number seven and ten were in extreme over bite, and all six teeth were too large for her mouth. Amazingly, she had a class one occlusion. She had been living with this condition for her whole life and seldom smiled. She should have had orthodontic treatment years ago, when she was a child. Then, looking at her case, I began to see a way to correct her malocclusion. Since she was older, the pulp chambers in her teeth had shrunk, allowing more reduction of tooth num¬ber eight. It was possible to correct the malocclusion. I reduced teeth five through eleven, bringing them all into a fixed bridge position. The preparations would pull, but I decided to leave them as individual crowns to give a better esthetic look. She was not a clencher. She tolerated the long posterior fixed bridges I had placed years ago. I did not see a need to splint the anterior crowns. I cemented the teeth in place. The look was simply amazing. Her anterior teeth were straight. The crowns were smaller, but they fit her small frame. Teeth eight and nine were long and slender to give a nice feminine look. It changed her whole appearance. She could smile and be pleased with herself. A week later, a red ring developed around teeth number seven, eight, nine and ten. The teeth were under stress. The bite was adjusted, but I hesitated removing any of the beauti¬ful porcelain. The condition persisted, so I constructed a bite appliance to take the anterior teeth out of occlusion, but the condition did not improve. Then I built a tongue thruster appliance to force her tongue away from her teeth because I thought she might be trying to push her anterior teeth forward. But now teeth eight and nine were developing a space. The Hawley appliance attached to the tongue thruster appli¬ance brought them back, but the red ring remained. She said her father had the habit of pursing his lips. I examined this, but the tongue thrust¬er appliance prevented stress from this direction. Finally, I attacked the crowns themselves, reducing the beautiful slender anterior teeth by shortening their lengths and taking the lingual portion of the crowns out of occlusion. Yet the red ring remained on the gingival, so I removed the crowns. Since the preparations would pull, I placed an eight unit (splinted) fixed bridge from tooth number five to tooth number twelve. This gave the teeth the needed support, and the red ring finally disap¬peared. The crowns remained shorter, and careful attention was placed on the bite in all functions. The patient may have unintentionally placed undo stress on her crowns because of psycho¬logical reasons. She went from being ashamed of her smile to a very beautiful smile. This may have been more then she could handle all at once. |
Always pay careful attention to the alveolar bone support for the abutments. If the abut¬ment has vertical alveolar bone lost, it is not a good candidate for an abutment. The bridge is doomed to failure unless the alveolar bone is corrected and the cause of the stress is found. If the abutment is already under stress, it will not tolerate more stress.
A reverse bevel flap will give you access to the alveolar bone and allow the vertical alveolar bone defect to be corrected. This will weaken the abutment and may require additional abut¬ments to take the stress of the fixed bridge.
Anterior teeth with extensive bone loss are not good candidates for abutments. An abutment tooth with a third of its alveolar bone missing is doomed to failure. The tooth is under stress and is losing alveolar bone support. To place more stress on it will only increase the speed the bone recedes from the abutment tooth.
You may have to anchor the fixed bridge to the cuspids to find good alveolar bone support. This is better then replacing the bridge when it fails.
The mandibular anterior teeth are the most difficult to replace with a fixed bridge. The teeth are small and the alveolar bone has usually progressed apically on the labial. When a tooth is lost in this area, it is usually necessary to take the fixed bridge to the cuspids to find support.
The small, thin mandibular anterior teeth are difficult to match in shape and color. The exten¬sion to the cuspids makes a difficult procedure easier.
This should not be an automatic decision. Some mandibular anterior teeth are large, and the bone support is good. These can be handled with a three unit fixed bridge, and they often look very aesthetically pleasing.
When a fixed bridge is being considered and one of the mandibular anterior teeth is not aligned to facilitate the fixed bridge, the tooth can be extracted. The fixed bridge needs to reach both cuspids. If a thin mandibular tooth out of alignment compromises this, then it should be removed because it is very difficult to shape a thin anterior mandibular tooth out of alignment and make it look good.
Anterior mandibular teeth with extensive bone loss may or may not be included in the fixed bridge. If the tooth is aligned in a good position and the gingiva and alveolar bone are free of disease, it would be good to keep the extra bone support for the bridge.
When the four anterior mandibular teeth are removed and the bridge extends from cuspid to cuspid, the mandibular ridge shrinks. This leaves the bridge high off the ridge. This can be avoided if you are willing to wait a year for all the shrinkage to take place.
However, there is another way. The mandibular ridge can be preserved if two or three of the mandibular anterior teeth are free of periodontal disease. This would be the case, for exam¬ple, when the roots are good but the crown portions are fractured or decayed off. The teeth cannot be saved, so it is decided to remove the teeth.
But instead of removing the remaining roots, they can be root-canaled and sealed into the alveolar bone. This will keep the mandibular ridge intact.
The root-canalled roots are reduced below the cortical alveolar bone. The gutta percha is sealed with a hot instrument to insure closure. The tissue is numbed with the painless infiltra¬tion method, and a tissue flap is laid on the buccal and lingual. The alveolar ridge incision needs to go down the center line of the ridge across the root-canaled roots. Labial and lingual vertical release incisions in the gingiva are made on each side of the root-canalled teeth.
The labial and lingual tissue flaps are released with the two periosteal instrument technique. Using a surgical scissor, the tissue is made fresh where the buried roots are located, and the tissue is sutured in place. This will allow the tissue to heal over the buried roots.
I used to do this procedure without burying the roots, but this eventually led to additional decay, infection, and loss of the root and ridge. Mandibular teeth buried in the alveolar bone will hold the ridge.
Tooth positioning is especially important in the posterior region where the second and third molars tend to drift into the voids left from the extraction of the first molar. If the second mo¬lar drifting has not extended too far into the first molar void, a preparation can still be made on the tooth.
The angle of the occluding force needs to be evaluated. Is there enough vertical root sup¬port for the abutment? If there is some doubt here, the second molar needs to be straightened before the abutment is used.
If the patient is young (under thirty), the abutment could be moved into the void by using or-thodontics. In this case, the fixed bridge would not be needed. This works well when the first molar is missing and the third molar has erupted. The second molar has already moved into the space left by the first molar extraction. It requires tipping the second molar up and bring¬ing it into contact with the second bicuspid. The third molar will follow behind the second molar and become the second molar.
You are already using orthodontics to straighten the second molar. Why not bring it forward and close up the space? I have done this on many occasions. It works very well. If the tooth remains tipped after the forward movement, it can always be crowned to straighten the occlusion.
ANECDOTEAn eighteen-year-old young man was genetically missing teeth thirty-one and thirty-two. Teeth one and two were present. Tooth number one was still impacted, but tooth number two was dropping into the space left by the missing number thirty-one tooth. The options were either to place the number two and three teeth into a fixed bridge splint to prevent tooth number two from dropping, or to move tooth number thirty distally and place a fixed bridge. We opted for the latter. Working with the orthodontist, tooth number thirty was moved distally, and a fixed bridge was placed. The temporary was the key to this success. It had to be very strong and rigid. The occlusal and contact areas of the temporary bridge had to be correct to prevent any relapse of the tooth. This technique would work well for older patients, but the tooth may drift in the tempo¬rary. Stability would also be a concern. Teeth can move through alveolar bone, but the stability of the tooth decreases with age. This condition could be a stress factor. We tend to increase our clenching as we grow older. |
These are teeth the patient has been grinding on for a number of years, leaving very flat teeth and in some cases exposures. The patient usually has lost several millimeters of the vertical dimension between the mandible and the maxilla. Instead of the alveolar bone giving way to the constant pressure, it has become stronger, and the teeth become short and flat. The patient is usually male and exhibits strong masseter and other facial muscles.
The difficulty in placing a fixed bridge in this situation is the lack of occlusal space. The patient really needs a full mouth bridge work to open the vertical space. This may be beyond the scope of the patient.
If so, you must place a fixed bridge into the existing condition. It has to be assumed that any crown placed in this situation is going to take a beating. It also has to be assumed that the occlusal surface will be metallic and relatively flat. Any high area on the abutment disrupt¬ing the movement of the mandibular teeth across the maxillary teeth will cause the abutment to become inflamed. This can result in lost of alveolar bone support and failure of the fixed bridge.
A fixed bridge cannot be placed in this condition without taking into consideration the patient’s need to grind his teeth. If the bridge in any way disrupts this, the fixed bridge will fail.
Occasionally a patient will exhibit worn teeth and loss of alveolar bone. This is not a favor¬able situation for a fixed bridge. A removal, partial denture, or denture may be the treatment of choice.
Contemporary Fixed Prosthodontics- Rosenstiel, Land, Fujimoto
This law proposes a relationship between the root surface areas of the missing teeth and those of the potential abutment teeth.
The following numbers represent root surface area percentages:
| Maxillary: | ||
| Central | 10 | |
| Lateral | 9 | |
| Canine | 14 | |
| First Premolar | 12 | |
| Second Premolar | 11 | |
| First Molar | 22 | |
| Second Molar | 22 | |
| Mandibular: | ||
| Central | 8 | |
| Lateral | 9 | |
| Canine | 15 | |
| First Premolar | 10 | |
| Second Premolar | 11 | |
| First Molar | 24 | |
| Second Molar | 23 | |
"If the first molar (22) and the second premolar (11) are missing, the abutments for a four-unit FPD will have slightly greater total root surface area (33%) than the teeth being re¬placed. Then, in the absence of other detrimental factors, an FPD’s prognosis will be favor¬able.
However, if the first premolar (12) is also missing, the loss of potential abutment root surface area will comprise 46%, whereas the remaining abutments have only 36%, which is much less favorable."
This is assuming the alveolar bone support for the abutment is not compromised by bone loss or a lack of the normal number of roots. A single rooted molar should be treated as a premolar when calculating the percentages.
Other factors also need to be taken into account before making the final decision to place a fixed bridge. The loss of alveolar bone support will lower the surface area percentage. Even though the bone loss is horizontal, the tooth will not be as strong and the surface area per¬centage number should be reduced accordingly.
A three unit fixed bridge is good anywhere on the mandibular except on lower anterior teeth twenty-three through twenty-six. This is assuming the bone support is adequate. There are exceptions. Some lower anterior teeth are large enough to accept a three-unit bridge.
A four-unit fixed bridge is used when one abutment is weak. An example of this is when the patient has a missing first molar. The distal second molar is adequate for an abu- ment, but the second bicuspid may need the support of the first bicuspid.
A five-unit fixed bridge is used when two teeth are missing. This usually includes the cuspid as an abutment. An example of this is when the second bicuspid and first molar are missing. The fixed bridge will extend from the second molar to the cuspid. This is assuming there is adequate alveolar bone support.
A missing first and second molar usually means a patient is not a good candidate for a fixed bridge. The third molar usually has curved roots to the distal, making the vertical occluding forces very detrimental to the tooth. The mesial abutments can extend to the cuspid, but the failure will come with the third molar abutment. Again, there are excep- tions to the rule. If the patient’s facial muscles are fragile and the patient is not a clench- er, the bridge could work. This is even more likely if the third molar has two roots with the mesial root extending to the mesial.
A six-unit fixed bridge can be constructed from tooth twenty-two to tooth twenty-seven. The two cuspids can be the only abutments in most cases. You can pick up a few more abutments if the lower anteriors are available and they are aligned. If the cuspids are a little weak, or the patient is clencher, I would take the bridge back to the first bicuspids and make it an eight-unit bridge. This is especially important if any lower anteriors have bee lost due to periodontal disease.
A fixed bridge with two pontics should take three abutments. A bridge with three pontics should take four abutments. 10 Fixed Prosthodontics and the Sixteen Unit Bridge
It does little good to use an abutment that will not give the fixed bridge the support it needs. To extend a fixed bridge to a small lateral incisor to acquire another abutment is not practical. There is not enough gain in strength, and the added tooth brings more prob¬lems with it.
If the fixed bridge needs another abutment and the cuspid is available, it should be used. This will give you the strength you need. It is not good treatment planning to leave a mandibular bicuspid as the only mesial abutment for a fixed bridge with two or three pontics. The distal abutment is secured with one or two molar abutments, but the mesial abutments need strength to make the bridge work. The cuspid will give you this strength.
A third molar distal abutment with a single cuspid mesial abutment will not work in most cases. The exception may be a frail older woman who does not place a great deal of pres¬sure on her teeth, for example if she eats oatmeal as her regular diet.
7. If the mandibular first and second molars and first bicuspid are missing, the abut ments need more then the second molar and the cuspid. The third molar might be a consideration to increase the strength on the distal side. This would depend on where the third molar is located, and whether it is aligned.
The strength on the mesial side could be increased by taking the bridge abutments across the mandibular anterior teeth to the other cuspid. If the second molar roots are well de¬veloped with good alveolar bond support and free of periodontal disease, it could support the distal side of the bridge. Again, the patient’s clenching habits should be considered before this decision is made.
The condition of the existing teeth needs to be evaluated, and the reason for the missing teeth needs to be investigated. A patient with excessive wear on his or her teeth or with extensive periodontal alveolar bone lost will need more abutments. Both of these condi¬tions are indications that the patient clenches or grinds his or her teeth. The success of the fixed bridge will be determined by the amount of support the fixed bridge can give with the addition of more abutments.
In these cases, the occlusion has to be perfect to avoid trauma from the opposing teeth. A slight high spot on the fixed bridge can lead to a failure of the bridge. The high spot becomes the focal point of all the force applied to the teeth.
ANECDOTEA middle-aged woman with a comfortable weight came into my office with a periodontitis condition around all of her maxillary teeth. Her periodontal pockets averaged five mil¬limeters, and the gingiva tissue had a slight inflammation. Most of her teeth from tooth one to tooth sixteen exhibited class one to two mobility. But she wanted to save her teeth, and expense was not an issue. The periodontal treatment consisted of three quadrants of gingiva curettage and three quadrants of reverse bevel. The tissue healed back with three to four millimeters of buc¬cal root showing. This was not attractive. She was especially concerned with the anterior teeth and the exposed labial roots. I suggested full crowns to cover the teeth. Since the teeth exhibited class one to two mobility, it was decided the teeth would be splinted together to give them more strength. Two fixed bridges were constructed splinting teeth two to eight and splinting teeth nine to fifteen. Two months later the patient came back to the office. A two-millimeter gap had developed between the two splints. The splinted fixed bridges were under stress and moving apart. The patient had spent a great deal of money, and the bridges were a failure. I had plenty of root support, but the patient’s jaw was stronger. To fix the problem, I removed the two splints and constructed a fourteen-unit fixed bridge going from tooth number two to tooth number fifteen. The extra strength gained by the horseshoe construction gave the fixed bridge enough strength to resist the occlusal forces. The patient continued to do well for many years. Judging from the occlusal forces the patient was applying to her teeth, the prognosis for her teeth would have been less then a year without the fourteen-unit bridge. |
The length of the pontic span is an important consideration when analyzing a bridge place¬ment. Even if there are enough abutments to hold the bridge sufficiently, the length of the bridge is a consideration because of the long pontic’s flexibility. The following should be taken into consideration:
The width of the pontic will determine its flexibility. A long, narrow pontic is some times used with third molar abutment to reduce the stress on the third molar. 12 Fixed Prosthodontics and the Sixteen Unit Bridge
An older, fragile woman would not tolerate a long thick pontic. The thick pontic itself would put undo stress on the small abutments. The abutments should fit the size of the patient. Small teeth need small abutments. Large teeth require large pontics.
The stress factor is very important. A patient who clenches his teeth would stress a small narrow pontic. A patient who clenches needs a solid pontic to stand up to the stress it will undergo.
Some laboratories like to place a solder joint where the pontic connects to the abutment. A solder joint is the weakest point on the bridge. If one needs to be placed, it should be placed between two abutments. It is best to cast the framework as one piece to avoid the problem.
Before the preparation is started, alginate impressions are taken of the maxillary and man¬dibular teeth. These impressions are wrapped in a wet paper towel and placed in a zip-lock bag. This allows the laboratory to see the original state of the abutments before the reduc¬tion takes place. It also allows the dentist to make a temporary restoration after the prepa¬ration of the abutments is completed.
It is good to take a second impression of the tooth or teeth you are preparing. The first impression distorts during the process of making the temporary restoration leaving a poor impression for the laboratory.
The primary impressions are taken with the fast acting alginate impression material. This still gives you a minute to three minutes of working time, depending on the amount of moisture in the air. Warm and dry air will cause the alginate impression material to set faster. If the water you use with the alginate is warm, the material will set faster. When the air is warm and dry, you can control the setting time by making the water very cold.
The impression trays should be tried in the patient’s mouth before the impressions are taken to allow the dentist to fit the impression tray to the patient’s mouth. This also allows the patient to learn what he is supposed to do once the impression material is in his mouth. Example: The patient learns to lift his tongue to allow the tray to slip beneath it.
Disposable plastic trays can be fitted to the patient’s mouth. The trays come in three sizes: small, medium, and large. The tray that fits the patient’s mouth the closest is selected. If a small tray fits the maxillary arch except for the posterior teeth, the wings of the tray can be heated over a Bunsen burner and pushed out to fit. This does not take a lot of heat. You do not want a melt down of the plastic. The plastic tray should move back and forth over the flame to warm the tray enough to make it flexible.
The tray should always be cooled with running water before it is placed back into the patient’s mouth. To avoid burning your own fingers when working the hot tray, you should allow the tray to cool slightly before touching it. I use a paper towel to push the tray’s poste¬rior wings out. The tray is placed under water until it is cooled. The cool tray is placed in the patient’s mouth to check the fit. If the tray needs more adjustment, it can be heated a second time.
The lower tray is handled in a similar manner. The lingual wings of the tray may need to be adjusted for the mandibular tori.
The tray may be too long. If so, the plastic tray can be cut to fit with a pair of scissors after it is heated over the Bunsen burner to soften the plastic. The remaining sharp edges should be smoothed with your finger after the tray is made pliable by heating it a second time.
When the alginate is mixed, the following should be considered:
The consistency should be on the thicker side to hold its position in the tray.
It should be pliable to allow the material to flow over the teeth easily.
It should be mixed thoroughly to ensure an even consistency.
Cold water should be used unless speed is a consideration.
Hot water will accelerate the setting time.
The lower impression should be taken first to allow the patient to become acquainted with the procedure before the more difficult maxillary impression is taken. The mandibular tray is loaded with the alginate mixture.
A portion of the alginate mixture in the bowl is taken out with a gloved finger and placed on the labial side of the lower anterior teeth. This will insure enough material flows in this area. Additional alginate impression material is placed in any critical areas where you want to avoid bubbles. I usually coat the occlusals of posterior teeth and the preparation area with the alginate impression material.
The tray full of the alginate impression material is placed over the teeth and below the tongue. The lower lip is pulled free of the tray and held until the impression material flows out from beneath the tray. The cheeks are pulled free to allow the impression material to flow. The tongue is lifted and moved side to side. The impression material should flow up through the holes in the tray.
The impression tray full of alginate should remain in place until the impression material sets to a rubbery consistency. Then the lip of the tray impression should be lifted from the poste¬rior section first to break the seal. Both sides should be free before the anterior portion of the tray is lifted free of the teeth.
Excessively dry teeth will cause the impression material to stick to the teeth. This is especially important with older patients. It is good to have the patient rinse his mouth with water before the impression is taken.
There is a tendency for the impression material to pull loose from the tray in the anterior section. If this occurs, the impression is distorted and must be retaken. If the impression material is allowed to flow through the holes in the tray in the anterior section, the im pression material will lock in better.
There is a tendency to place your fingers on the anterior portion of the tray. This removes the impression material coming through the holes. The fingers should hold the tray by the handle or over the posterior portion of the tray in difficult impressions. The excess impression material can then be pushed up over the holes to increase the locking effect of the holes.
The maxillary impression can be very difficult or very easy depending upon the reaction of the patient to the impression material. The patient and the chair should be sitting forward. Two fingers full of impression material are placed behind the maxillary anterior teeth to insure the palate will be in the impression. The impression tray full of impression material is inserted over the posterior teeth first and then brought over the anterior teeth. This will prevent the excess impression material from being pushed out the back of the tray.
It is very important that the impression material have a thick consistency, but the impression material should still be pliable to flow over the teeth. Impression material with a thin consis¬tency will not remain in the tray, allowing the material to overflow into the patient’s mouth.
A person gags because he believes he will die from the lack of air to his lungs. He panics and feels he must clear his mouth immediately to breathe.
To correct the situation the patient must be aware he can breathe through his nose any time he wishes. Have the patient hold his breath for a few seconds to calm himself, and then tell the patient to breathe slowly through his nose.
I usually go through this with an apprehensive patient. I tell him exactly what I will do if he panics and start to gag. I will yell at him: "Hold your breath and count to five! One, Two, Three, Four, Five, Now breathe slowly through your nose!"
This usually works very well even when the patient is in an immediate crisis. Sometimes when the impression material and tray are inserted, the patient will take a deep breath. This allows the impression material to flow into the patient’s throat. The patient will begin a gag¬ging reflex, attempting to remove the impression material.
The patient can still breathe through his nose. If you can keep the patient calm with the above technique, the impression material will harden in place. Then the hardened impression mate¬rial and tray can be withdrawn.
The setting time of the impression material in the patient’s mouth can be controlled in two ways:
As has already been mentioned, the warmer the water used to mix the alginate material, the faster the alginate material will set.
The tray filled with the impression material can be held outside off the patient’s mouth un¬til it is ready to set. Then when the tray filled with impression material is inserted, it will set in seconds instead of a minute or more. One has to be aware of the setting time of the mate¬rial to make this an effective method.
The swing-on bridge has a pontic supported with abutments on only one side. This is usually used with a single abutment, like on a cuspid, but sometimes it is used with several abut¬ments. In these cases, the swing on pontic is on the end of the fixed bridge.
This is usually used to replace a lateral incisor. The crown is made to fit over the cuspid, and the pontic attaches on the mesial side of the cuspid crown.
The following should be considered when placing a cuspid swing-on bridge:
The cuspid should be well supported with a long root and good crown-length to root ratio.
Sometimes it is good to place a lingual rest on the central incisor to stabilize the pontic.
The swing-on bridge is preferred over the three-unit bridge when the central incisor does not make a good abutment.
The swing-on bridge is preferred when the central incisor shade is difficult to match.
Rule of thumb: It is always good to crown teeth eight and nine at the same time to match the shade and shape. When this is not possible, then a swing-on fixed bridge from the cuspid is preferable.
A swing-on bridge is used when the second molar has moved into the first molar space. This leaves a small gap for the pontic between the second molar and the second bicuspid.
The following should be considered when placing a molar swing-on bridge.
The second molar should be fairly upright to avoid undo pressure on the curved mesial root.
2. If the second molar is leaning too far to the mesial, an occlusal rest can be placed on the second bicuspid. This will give the extra needed support to compensate for the additional occlusal pressure.
3. This is the preferred treatment when the third molar is pushed up tight to the second molar, making an upright procedure difficult.
4. It is good to use a swing-on bridge when the space between the second molar and second bicuspid is relatively small. All you really want is a wide second molar crown, or a swing-on bridge.
This technique works well for first or second mandibular molars when there is extensive bone loss in the bifurcation between the mesial and distal roots.
The diseased tissue in the bifurcation can be removed, but the tooth is usually doomed for an extraction. The patient cannot keep the area clean, and the disease condition returns to the area. The smaller mesial root in these cases is usually more involved then the buccal root.
The technique also works well for teeth where large portions of tooth structure have been destroyed by decay activity, or the combination of bone loss in the bifurcation and decayed tissue. The problem with the molar is the space between the roots. A crown over the tooth will still leave the space. At this stage, extraction is the only alterative to remove the problem. The alveolar bone will not heal back. The space will only be filled with tissue that will become necrotic.
The distal root needs to be viewed as cuspid. Ask yourself if the bone support around the distal root is strong enough to be an abutment and whether the distal root can be used as an abutment if the mesial root is removed.
The tooth is numbed with a painless inferior alveolar injection. The occlusal is opened and the distal root is endodontically treated. Gutta percha seals the canal. Undercuts are placed in the distal portion of the pulp chamber, which is made ready to receive the amalgam.
A 557 bur places a groove through the floor of the pulp chamber buccal-lingually. A wide bone chisel is placed in the groove and twisted. The roots are split, and the smaller mesial root is removed with a pedodontic forceps. This is an easing of the mesial root out of the socket.
A small elevator should be used to apply pressure on the mesial side of the root, pushing it distally. The elevator is placed between second bicuspid and the mesial root. The cutting edge of the elevator on the mesial root is twisted distally. This will loosen the root. The root should not be extracted with the anterior pedodontic forceps until the root is loosened with the eleva¬tor first. You may need to remove some of the mesial root’s occlusal surface to accommodate the extraction. The mesial root needs to miss the distal root upon extraction.
Once the mesial root is loose and ready to be extracted with the pedodontic forceps, the distal root should be filled with amalgam. If the amalgam is filled after the extraction, there is a risk of the amalgam pieces falling into the mesial root socket.
The mesial root is eased out of the socket and the site is held under pressure with two-by-two gauze. The patient is sent home.
When the site has healed enough to prevent the amalgam shaving from entering the mesial socket, you are ready for the preparations. The distal root is treated like a small cuspid in the preparation, the extracted mesial space is the pontic, and the distal root of the mandibular molar and second bicuspid are the abutments. When the bridge is placed, it will look from the surface like a two-unit bridge with a full mandibular molar crown and a bicuspid crown, but below the surface it is a three-unit bridge.
The walls of the distal root abutment take precedence over the mesial bicuspid abutment. The mesial bicuspid is shaped to accommodate the long mesial wall of the distal root. The preparation is taken to the alveolar bone, keeping the diverging walls on the distal root very conservative.
The mesial wall of the distal abutment will be an amalgam wall until the preparation reaches the alveolar bone. It is important to take the preparation below the amalgam margin if it is possible. The preparations are packed with gingi-pak and treated as regular crown prepara¬tions. The impression is taken, and the temporary bridge is placed. This is a good technique for treating a mandibular molar with bifurcation bone resorption.
The following need to be taken into consideration:
The bone support for the distal root needs to be adequate to support the bridge.
You may want to use a composite instead of amalgam to fill the distal root after the root canal therapy. This will depend on the conditions at the time. A wet area will not lend itself well to a composite restoration.
The teeth are numbed with the inferior alveolar injection using the pain-free technique.
Before the bridge is started, the path of insertion needs to be determined. If the mesial abut¬ment comes up next to the distal contact of a cuspid, the path of insertion needs to avoid the obvious undercut.
The path of insertion is established in the preparation, when the contacts are opened with a long, thin, round-ended diamond. The mesial and distal walls of the preparation should be slightly convergent.
The buccal and lingual walls of the preparation are placed with a long, medium, round-ended diamond bur. The buccal wall of the distal abutment must be slightly convergent from the lingual wall of the mesial abutment. The cut is not taken to the free gingiva. These are guide¬lines for the preparation.
The mesial wall of the distal abutment and the distal wall of the mesial abutment are estab¬lished with a long, medium round-ended diamond. These need to be slightly diverging from each other.
Once the path of insertion is established on all of the walls, the teeth are ready for reduction. If a tooth is leaning toward the lingual, you may not need to remove excessive tooth structure on the buccal, but the lingual may require extensive reduction. When the path of insertion is established at the start of the preparation, over-reduction of the teeth is avoided.
Retention of the bridge is established by the length and convergence of the prepared walls. Excessively converging short walls will lead to poor retention. A good bridge will hold its position in the mouth without cement.
After the path of insertion is established, the reduction of the teeth is started with the occlu¬sal surface. A flame-shaped diamond is used to reduce the occlusion. The preparation should clear the opposing teeth by a millimeter and a half. On a mandibular cuspid and bicuspid preparation, the buccal wall usually has two angles. The incisal portion of the teeth should clear the opposing teeth by a millimeter and half when the teeth are taken into account.
Grooves can be placed to help in establishing the amount of reduction. The reduction is taken from one groove to another. The reduction can be checked by placing a mirror beside the tooth and observing the preparation when the tongue moves out of the way.
The bite is not critical at this point of the preparation. We are mainly interested in a gross reduction of the occlusal to give shorter walls for the preparation reduction.
The walls of the preparation are reduced with the long medium round-ended diamond bur un¬til the free gingiva is reached. The reduction follows the path of insertion already established. The long diamond bur is used like a parallelogram. The hand rests on the jaw, and the long diamond bur moves through the path of insertion on both abutments. All of the walls should be in the path of insertion when the preparation reaches the free gingiva.
The long, thin, round-ended diamond bur takes the preparation below the free gingiva. This will reduce the amount of damage to the gingiva, though healthy gingiva will grow back with healthy tissue after it has been damaged.
Once the preparations are established below the free gingiva, the long, medium, round-ended diamond bur is used to finish the preparation. The occlusal is checked by placing a warm piece of wax over the preparation. The patient bites. The wax is removed and observed. The thin areas will show up in the wax. The areas can then be reduced with a flame-shape dia¬mond bur to give the necessary millimeter and a half to two millimeters of clearance. The sharp and rough edges are removed and the occlusal is smoothed with a white flame-shape stone.
The long, large, round-ended diamond is used for extensive reduction on the wall of the preparation. The bur is also used for placing a smooth finished on the prepared walls. This requires a light touch. The finished preparations will converge slightly to accommodate the path of insertion, and they will be out of occlusion from the opposing teeth by a millimeter and a half to two millimeters.
The further toward the posterior the bridge extends, the more critical the bite becomes and the more difficult to reduce. It is very difficult to see the reduction is this area. The tongue does not move enough to give a good visual of the area. A wax bite is the only sure way to see this reduction.
A patient with a tight bite will not have much room for a reduction of his occlusal. The most critical area will be the distal half of the distal abutment. This is especially critical when third molars are used for abutments. The distal wall of the third molar is jeopa- dized when the occlusal is reduced to the millimeter and a half. A short wall not have enough retention for the bridge, or the occlusal will not be able to be reduced enough to give adequate clearance. One or the other will be lost in the preparation.21 Fixed Prosthodontics and the Sixteen Unit Bridge
The opposing tooth can be reduced in the critical area to give the clearance needed.
The distal wall can be lengthened by removing alveolar bone below the gingiva.
A metal occlusal is placed on the crown in the critical area. The metal occlusal does not require the full millimeter and half of clearance.
The mesial and distal walls of the preparation need to be at least three millimeters high to give adequate retention. Some would say only two millimeters are necessary, but I would suggest another abutment to hold the bridge in place. Short abutments need be only slightly convergent to assist in retention.
The x-ray will show the amount of tooth below the tissue. The short abutment can be taken to the alveolar bone to pick up more length.
b. The preparation can be taken below the alveolar bone. This can be done with a surgical procedure (laying a flap and reducing the alveolar bone around the tooth), or with the long medium round-ended diamond bur, if only a millimeter is necessary.
Large fillings or excessive tooth decay need to be evaluated before the preparations are started.
Healthy existing amalgam or composite fillings can be used in the preparation, but the margins must be tight with no discoloration.
If you suspect that the amalgam or composite restoration may be leaking or decay exist, then the restoration should be replaced before the preparation is started.
Large restorations in the abutments should NOT be considered part of the retention. The tooth structure below the restoration is the only area to be considered for retention.
Sometimes pins are used to support restorations. Pins placed at different angles do not add greatly to the retention ability of the abutment. Over the years, I have seen many abutments fail due to reliance on pins for retention.
A large amalgam or composite may come out of the abutment during the preparation. This is the best time for this to happen. All of the restorations in the abutment should be thoroughly tested for retention before the impression is taken.
If the retention for the preparation is dependent upon the tooth structure below the restoration, then the loss of the restoration is not serious. The undercuts are removed from the cavity left by the restoration, and the sharp edges are rounded off. Sometimes a wall left by the loss of the restoration can be used for retention.
If the retention depends upon the restoration, then a new retention will need to be found. One should never depend on the restoration to give retention. The new retention may be found from a wall left by the loss of the restoration, or more retention can be found by extending the margin into the alveolar bone. If possible, another abutment should be considered.
The maxillary incisors are good candidates for a porcelain margin preparation. The teeth need to be evaluated to insure there is enough bulk on the labial wall and the tooth is long enough to accommodate a porcelain margin. Thin walled or short teeth should be prepared with a shoulderless margin.
It is usually very difficult to match teeth eight and nine in shape or shade. It is best to use both teeth for abutments or be willing to send the patient to the laboratory.
A fixed bridge on the lower anterior teeth is difficult because of the shape and small size of the teeth. There are not many laboratory technicians who can create a good match. The small, narrow roots of the mandibular teeth usually do not lend themselves well to good alveolar bone support for a fixed bridge. Therefore, it is usually best to extend the bridge to the cuspid for better bone support.
When a porcelain margin is used, the number of walls necessary for preparing the bridge increases by three times.
A porcelain margin should NOT be used when any of the following conditions exists:
A maxillary lateral incisor usually is not used for an abutment unless it is a large tooth with excellent bone support. It is usually better to make it a four-unit fixed bridge by including the cuspid in the abutments.
If the teeth are mobile or there is alveolar bone loss on the central and laterals, it is best to extend the bridge to the cuspids. If there is a problem with clenching, it is better to extend the fixed bridge to the premolars. It does little good to replace a missing anterior tooth only to see the bridge fail a few months later.
In this procedure, first, the path of insertion is determined, and contacts are removed with a long thin round-ended diamond bur. All of the contacts are opened keeping the path of inser¬tion in mind. You may find you need to adjust the path of insertion.
The smallest tooth or the tooth slightly out of alignment is selected for the first cut. Usually this is the lateral. It will be this tooth determining the path of insertion. All of the other teeth will be set to this tooth. The long diamond bur moves between the abutment contacts. As you do this, keep the initial embrasure cut through the lateral contact in mind.
Using a flame-shaped diamond bur, two millimeters are removed from the incisals of the teeth being prepared. If a cuspid is involved, the incisal reduction should include the whole incisal and not just the tip.
The flame-shaped diamond bur should be used to reduce the lingual portion of the maxillary anterior teeth to give a millimeter to a millimeter and a half of clearance from the mandibu¬lar anterior teeth when they are in centric occlusion. This is especially important when there is a steep over bite. The whole labial surface of the mandibular anterior teeth must clear the lingual of the maxillary teeth.
It is important to leave enough gingiva lingual wall to keep the retention. You can leave too much gingiva lingual wall, though the mandibular teeth usually dictate the length of this wall. There is a tendency to leave a sharp edge on the lingual wall. The flame-shaped diamond can be used to remove this.
A long, medium, round-ended diamond bur is used to reduce the bulk of the labial wall. The reduction is not taken below the free gingiva, but it does extend into the embrasures and up to the lingual wall. The labial wall of one abutment needs to be slightly converging from the lingual gingiva wall of the other abutment.
The long, narrow, round-ended diamond finishes all the margins except the labial. The abut¬ment should be finished except for placing the labial 90-degree shoulder. The short lingual wall should be slightly converging from the labial wall. Using the long, narrow, round-ended diamond bur, a hand parallelogram can be used to check the short lingual walls of all the abutments with their corresponding labial walls.
Another method is to use a Boley gauge instrument to check the mesial and distal walls of the abutments to insure they are converging. One beak of the Boley gauge is placed on the lingual of one abutment, and the other beak is placed on the labial of another abutment. Us¬ing the Boley gauge to measure each abutment will show which walls need more reduction. Remember, it is the lateral or the misaligned tooth that the path of insertion must follow.
When the lingual, mesial, and walls are finished, the 90-degree shoulder can be placed for the porcelain margin. A number of burs can be used, including a 557-carbide bur. Here we will use a long, medium, flat-ended diamond bur. The 557-carbide bur has a tendency to slip into the labial wall, creating an exposure or at the very least an undercut.
The 90-degree shoulder is approximately one millimeter in width. This width can vary de¬pending on the size of the tooth. It needs to be smaller for a small tooth and larger for a large one. It should not extend over a millimeter and a half. The possibility of exposure here is high.
The 90-degree shoulder is placed slightly below the free gingiva. The preparation is started above the free gingiva and then taken below the free gingiva after the width is established. There is less chance of damaging the free gingiva this way. The labial wall is again checked with the Boley gauge to insure that no undercuts are incorporated in the procedure.
There is a technique of packing the sulcus of the free gingiva to retract the tissue while the preparation is being made. I usually catch the bur in the packing material. Using a little care, there will be no damage or very little damage to the free gingiva using either method.
The 90-degree shoulder is taken into the mesial and distal embrasures, where it blends with mesial and distal margins already established. The labial wall ends with a cut-out portion extending to the mesial and distal embrasures.
The placement of the 90-degree shoulder leaves a box form that includes the gingiva shoul¬der, the mesial vertical shoulder and the distal vertical shoulder. The shoulderless lingual margin extends into the embrasures and stops at the mesial and distal vertical shoulders. The mesial and distal walls of the vertical shoulder should converge to match the existing walls. These need to be checked with the Boley gauge or with the long diamond bur and the hand parallelogram.
It is sometimes suggested that the 90-degree shoulder should back up to the labial wall with a sharp 90-degree angle. I do not believe this is necessary. It is the best place to create an exposure, and a sharp cut only serves to create an undercut in the preparation. A round angle protects the pulp chamber, and laboratories prefer the round angle.
I usually use a long, medium, round-ended diamond bur to make the 90-degree shoulder. This leaves a round angle at the labial wall. A light touch with the bur takes the shoulder below the free gingiva. Others use a flat-ended diamond bur to establish the 90-degree shoulder.
In either case, the gingiva edge of the 90-degree shoulder has a tendency to leave unsup¬ported enamel (ragged edges). The unsupported enamel can be removed with a flame-shaped diamond bur moving lightly over the enamel edge, or a sharp chisel can scrape the edges.
The main disadvantage of the porcelain margin (the 90-degree angle) is the chance of leaving a cement margin. The restoration is made to fit the preparation, but it is not an exact fit. Labo¬ratories tend to make the crown restoration slightly larger to avoid the small undercuts in the preparations. This will leave a small gap between the 90-degree shoulder and the crown restoration.
Cement fills this gap, but cement can wash out, allowing exposure to the labial wall. The thin labial wall is very close to the pulp chamber. A slight decay in this location will leave an exposure. Fortunately, the pressure applied to the crown upon insertion creates a very hard cement margin.
To eliminate the problem entirely, a small bevel can be placed on the 90-degree shoulder. This will remove the unsupported enamel rods and provide a one-millimeter margin to cover the 90-degree shoulder. Then a slight discrepancy in the crown restoration will not expose the 90-degree shoulder. This is especially a concern where the 90-degree shoulder meets the shoulderless margin in the mesial and distal embrasures.
The angle and location of the tooth will determine the bevel size and whether you use a long, medium, round-ended diamond or a flame-shaped diamond. The bevel blends in with the lingual shoulderless margin when it approaches the mesial and distal embrasures. This mar¬gin moves in a continuous flow around the tooth, and the mesial and distal sharp 90-degree margin breaks in the embrasures are also removed with the bevel.
There is a tendency to leave the incisals too long. A good look at the preparations should be taken. The crowns covering the abutments will be at least two millimeters longer then the abutments. It is also good to remove any sharp edges on the abutments. It is difficult to make good impression of thin sharp incisal edges.
The lingual surface of the maxillary abutments should be at least a millimeter from the labial surface of the mandibular anterior teeth. A metal lingual may be necessary in this area.
If one of the abutments is very close to becoming exposed from being out of alignment, a porcelain margin preparation may not be possible. Instead of leaving the porcelain thin over the gingiva margin of the crown, a small mass of porcelain could be placed to hide the metal. The gingiva tolerates the porcelain well, and the margin will remain tight.
Care needs to be taken when placing the 90-degree shoulder to avoid an exposure. A good indication the tooth is close to an exposure is the color of the tooth: the enamel is lighter than the dentin, and a light-reddish color says you are in the pulp chamber or very close to it.
A slight exposure does not always translate into a root canal. There is no infection. If the exposure can be sealed and covered, there is a good chance the tooth will recover.
The 90-degree angle can create an undercut in the preparation. A round-ended long diamond can be used to avoid this.
When removing the unsupported enamel with a diamond bur after the 90-degree shoulder is placed, a light touch is required. If this is difficult, then a sharp chisel should be considered. This will give you more control and feel when removing the ragged edges.
The 90-degree porcelain margin preparation has more walls to consider, so guarding against the possibility of undercuts becomes more critical. The gingiva portion of the box form in the labial wall is the most likely place for an undercut. A rounded angle here will prevent the undercut.
The size and length of the tooth needs to be considered before the 90-degree shoulder is placed. A short tooth may need the extra length a shoulderless preparation will give, after the incisal is reduced for adequate retention.
Diamond scratches should be removed with a flame-shaped white stone for occlusal or lingual surfaces and a long, medium, round-ended diamond bur should be used for the preparation walls. A light touch and plenty of water will remove most scratches. A nice satin finish on the preparation will allow the final restoration to seat properly.
Sometimes it is necessary to remove a previous crown or bridge if the abutments need to be brought into the fixed bridge abutments. The path of insertion cannot be determined until the previous bridge is removed because the abutment under the crowns may determine the path of insertion.
When dealing with both multi-crowns splints and crowns with pontics attached, the process is the same. The path of insertion is determined by looking at the smaller tooth or the tooth out of alignment.
Using the long, large, round-ended diamond bur, a groove (cut) is made on the labial portion of the crown, centering it in the middle of the tooth. The long axis should be the approximate angle of the path of insertion. The possibility of making a groove in the labial surface is very high, but if this groove is in the path of insertion, it will not be a problem.
The cut continues over the incisal or occlusal, remaining in the center of the tooth, and it extends down the lingual to the gingiva margin. The cut usually has to be completely through the metal on both sides of the tooth and the occlusal.
When cement is detected beneath the metal, the cut is through the metal. This becomes tricky when an amalgam exists beneath the crown. It is very difficult to observe the difference be¬tween the amalgam and the metal of the crown. Sometimes your first indication that you have cut through the metal is the sudden drop in the depth of the groove. This is why the groove should be in the path of insertion.
A good mirror and air will reveal the large groove so that you can determine if the cut is deep enough. Another test is to try pressuring the two sides apart. The medium size spoon is placed in the groove on the labial wall of the crown. Pressure is applied to the distal. If the groove is through the crown, the distal half of the crown will move. If the distal half did not move, then the groove is not deep enough somewhere.
When cutting off a bridge, the process is the same. The groove is placed on the most distal crown first because of the difficulty. The grooves are placed through the center of the crowns on the abutments. I would not become too concerned when the distal portion of the distal abutment remains in place. It will loosen further when the groove on the mesial abutment is placed and pressure is applied.
Once the distal portion is removed, a small groove is placed on the mesial occlusal or inci¬sal portion of the crown. The spoon is inserted and pressure is applied. If the tooth does not move, the methods below should be tried.
The following methods should be attempted when you are sure the groove is through the metal on all three sides of the abutment.
Apply pressure with the medium spoon toward the distal.
Using a long thin round-ended diamond bur, place a small groove under the incisal or occlusal of the distal half of the mesial abutment. This small groove is placed below the metal of the crown. Place the spoon in the groove and apply pressure. It should move the distal half of the crown. If you are dealing with an anterior crown, the Hollenbeck instrument can be used. A little care is needed. The Hollenbeck can snap under excessive pressure.
A pedodontic forceps can be used to rock the cut half of the crown loose. The beaks are placed on the buccal or labial side and on the lingual side of the distal split half of the crown. Pressure is applied by rocking the distal half mesial-distal and buccal-lingually. You are not trying to extract the tooth. This is only light pressure to move the distal portion of the crown.
ANECDOTEA patient in her late forties came into the office a year after I opened my office, forty years ago. She was missing teeth 1, 2, 3, 5, 13, 14, 18, 19, 30, and 32. She had extensive periodontal problems. Teeth 6-11 had 4-7 millimeter pockets, tooth 15 had a 4-millimeter pocket, and teeth 21-28 had 4 to 5 millimeter pockets. Teeth 8, 9, 24-26 had class two mo¬bility. She was destined for a denture. A reverse bevel periodontal flap was done on maxillary teeth 6-11 and on mandibular teeth 21-27. This left extensive labial root exposure. A maxillary bridge was placed from tooth 4 to tooth 15. It was soldered in two locations: the junctions between teeth 6-7 and 10-11. The laboratories at that time did not have the capacity to cast the metal framework in one piece, so a mandibular bridge was placed from pontic 19 to tooth 31 with two solder locations. The thirteen-unit bridge remained in place until year 2000 when the remaining portions of the bridges were removed and maxillary and mandibular dentures were placed. The bridges did not begin to break down until 1990. Root canal therapy and crown repairs allowed another ten years of wear. The patient was clencher. This was evident in her extensive loss of bone support before the bridge was placed. It was the horseshoe effect of the bridge that allowed her to keep her teeth the thirty-two years. I had diagnosed her for maxillary and mandibular dentures as an alternate plan to the thirteen-unit bridge, but she wanted to keep her teeth. She did for thirty-two years. |
A sixteen-unit bridge follows the same principles as a three-unit bridge, except it is longer and has more walls to consider. The converging walls start to change position as the bridge moves around the anteriors to the other side. Then the distal walls of the molars and bicus¬pids need to be convergent with the labial walls of the anteriors. This is usually the most dif¬ficult area of the sixteen-unit bridge. The converging buccal walls of the molar and bicuspids usually fall in easily, and the lingual walls seem to follow simply by being convergent to the buccal walls.
An arch with missing teeth may lend itself to the sixteen-unit bridge. The additional support of the anterior arch will give the bridge more strength. It seems the horseshoe effect of the sixteen-unit bridge is worth at least two more abutments. If a patient clenches his teeth, you will want the additional support of the horseshoe. The rationale for the sixteen-unit bridge can be used for a twelve-unit or fourteen-unit bridge as well. It is the horseshoe strength that is important.
The patient who has undergone full-mouth reverse-bevel periodontal surgery leaving exposed roots on the teeth is probably the best candidate for the twelve to sixteen-unit bridge. This patient placed extreme pressure on his or her teeth to put them in this condition. Now he is disfigured from the surgery. The roots of his teeth are showing, but the periodontal pockets are gone.
He will not be stopping his clenching, and some of his teeth are loose from all the pressure he or she is placing on them. He needs full crowns to cover the roots, but the weakened teeth will not tolerate more bone loss. He is not missing teeth particularly, but the prognosis is not good without some method of supporting the teeth. The horseshoe sixteen-unit bridge is the treatment of choice.
The bridge will cover the exposed roots of the teeth giving a good aesthetic result.
The splinted teeth no longer will be able to move, which will prevent them from destroying periodontal alveolar bone.
The horseshoe effect of the bridge will give the splint the strength it needs to resist the extreme occlusal forces from the clenching.
We will assume the patient is not missing any teeth, but the procedure is the same for a bridge with pontics. The sixteen-unit bridge is the treatment of choice for a patient with peri¬odontal pockets of five and six millimeters. The periodontal treatment needs to be completed before the sixteen-unit bridge is started. This will probably involve reverse-bevel periodon¬tal surgeries or gingivectomies on the maxillary and mandibular arches. A person with deep periodontal pockets (five to six millimeters) will usually finish the periodontal treatment with three to four millimeters of root exposure on most of his or her teeth.
The sixteen-unit procedure is the same for a twelve-unit or fourteen-unit bridge using the horseshoe technique. When the sixteen-unit bridge is discussed, it is assumed the principles apply to the twelve or fourteen-unit bridge. This is also assuming the third molar is fully erupted and in line with the other molars. If this is not the case, then the fourteen-unit bridge is the treatment of choice.
Before the sixteen-unit bridge is started, a temporary bridge should be considered. There are two options.
An alginate impression of the arch to be prepared can be taken and sent to the laboratory. The laboratory can make a sixteen-unit acrylic bridge shell. The shell is filled with acrylic after the preparations are completed and formed to the abutments. The excess is removed, and the bridge is trimmed.
An alginate impression can be taken at the time of the appointment before the prepara - tions are started. This impression is filled with acrylic and placed over the abutments after the preparations are completed. This technique is discussed in detail below.
A preliminary impression can be taken, poured and placed on a parallelometer. I use a Har¬vey Surveyor Parallelometer. The stone model is placed on the parallelometer and locked into place. Using the movable arm, the stone teeth are analyzed. Problem areas are noted and recorded. All sixteen teeth are viewed as one tooth with converging walls that allow a path of insertion. The labial walls of the anterior teeth must be convergent with the distal walls of the second molars.
The teeth out of alignment will need to be brought into the path of insertion. One must ask whether this be done without exposing the teeth. If not, performing a root canal is one option.
Since the roots are exposed, the walls of the teeth will be long. One must ask whether enough reduction be done to bring the teeth into the path of insertion. This is especially important for the lower anterior teeth where the teeth are small and the labial walls need to be convergent with the distal of the posterior molars.
The vertical is checked by placing a piece of tape on the nose and a piece of tape on the chin. Using the Boley gauge, a measure is taken between the two pieces of tape with the moist lips barely touching. The Boley gauge measurement is reduced three millimeters. This measure should reach the two pieces of tape when the teeth are in occlusion. This will be an indication of the amount of wear on the teeth. The vertical measure should be fairly close to the teeth in occlusion, though this is not critical.
It should be noted whether the teeth protrude over the lip line or remain under it. Some teeth sit high on the gingiva when a person has very small lips.
The lips over the bridge should be slightly pinched to see how much excess tissue exists.
Are the lips tight against the teeth?
Are the lips loose over the teeth?
Teeth with three to five millimeters of root showing will need very long crowns. It is important to see if the length of the anterior teeth can be reduced.
Teeth with spaces between them will require larger teeth in the bridge. Can the soft tissue tolerate this?
The size of the tongue needs to be evaluated. Is the tongue pressing on the lingual of the anterior teeth? Can the teeth be brought in slightly closer to the lingual?
The laboratory will need an impression to make the acrylic temporary bridge a few days before the sixteen-unit bridge is started. There usually is a high cost to this, but the laboratory temporary will look nicer then the one you can construct at the time of the appointment. It will save you an hour of chair time.
If you decide to make the temporary in the office, then you will need an alginate impression before the preparations are started. You will also need maxillary and mandibular alginate impressions for the laboratory. The alginate impression for the temporary bridges needs to be good. The following are areas of concern:
After the alginate is mixed, a finger full of alginate can rub the impression material over the teeth to remove any dry areas that may cause bubbles.
The anterior teeth need a finger-full of impression material over the labial walls to insure the lips are pushed away from the teeth when the impression tray is placed.
There is a tendency to leave gaps in the alginate impression on the palate behind the maxillary anterior teeth. This can be avoided by placing a finger-full of alginate here before the tray is inserted.
The alginate impressions are placed on a wet paper towel and put in a zip-lock bag.
Usually, both arches will require a fixed bridge to correct the exposed roots following peri¬odontal surgery. It is best to complete one sixteen-unit bridge before starting the second one. The sixteen-unit bridge usually take three weeks or more to complete. This includes a metal try-in and a biscuit bake try-in. It is very difficult to keep a patient in a full mouth temporary for any period of time. There is little sense in complicating this with two sixteen-unit tempo¬raries.
All of the abutments will have a shoulderless margin. This includes the maxillary anteriors. The additional walls of a porcelain margin only complicate the difficulty of the sixteen-unit bridge, and porcelain margins should not be placed on the exposed roots.
The patient needs to be numbed with the painless technique using the inferior alveolar or the infiltration method. Since this is a five-hour procedure, the numbing needs to be carefully controlled to avoid toxic effects from an overdose of anesthetic. Read the label of the anes¬thetic to learn the toxic levels.
Until the preparations are taken below the gingiva, the gingiva does not need to be numbed. Usually the gingiva will not remain numbed for more then an hour to an hour and a half. Sometimes, when the gingiva is hemorrhaging, the time can be reduced to fifteen to twenty minutes. If the gingiva is numbed early, it will need to be numbed a second or third time before the preparation is completed. This may lead to an overdose of the anesthetic. Always remember there is another day.
The first phase of injections is given to numb the teeth. This will allow the initial preparation of the abutments. The second phase of injections is given before the preparations are taken below the gingiva. An evaluation of the patient should be taken before this second phase is started. The process can be stopped at this juncture and the temporary can be made.
The path of insertion is established with a long, thin, round-ended diamond. Usually the most critical teeth of the sixteen-unit bridge are the distal walls of the molars and the labial walls of the anterior teeth. If no other teeth are out of alignment, the next most critical areas are the mesial and distal walls of the lateral incisors.
These lateral incisors will dictate the placement of the path of insertion. Using the long thin round-end diamond bur, the mesial and distal contacts of the lateral incisors are opened. The angle established on the walls will be the path of insertion for the rest of the teeth in the sixteen-unit bridge. This does not require excessive angles to the walls. Slightly converging walls are all that is needed.
When the other contacts are opened, the angle must be convergent to the walls of lateral inci¬sor (path of insertion). The two anterior lateral incisors’ walls become the guide for the path of insertion. The labial walls of the lateral incisors are established before the contacts are open posterior to the cuspids. The angles of the distal walls of the posterior teeth need to be convergent to the lateral incisor walls. This includes the distal, mesial and labial walls.
The long diamond bur is used as a parallelogram. Keeping the hand supported, the bur is moved from the labial wall of the lateral incisor to the distal walls of the posterior teeth and then back again. This will allow you to keep the walls converging.
The initial cuts are not excessive to allow a change in the angle of the cuts as the path of insertion is established. The medium sized, round-ended diamond bur is used to further estab¬lish the path of insertion.
Once the path of insertion is established for the contacts and distal walls of the molars, the labial walls of the teeth can be brought into the path of insertion. The labial walls of the ante¬rior incisors are reduced with each cut slightly convergent to the distal walls of the molars.
This is not the final reduction, but enough needs to be reduced to give some indication of where the problems are going to be.
The buccal reductions on the left posterior teeth need to be slightly convergent to the buccal reductions on the right posterior teeth. Usually this is not a problem for mandibular teeth. The normal shape of the mandibular teeth will dictate this angle, creating a convergent angle un¬less a tooth is out of alignment.
Buccal reduction on the posterior maxillary teeth may need a steep angle to obtain the con¬vergence necessary for the path of insertion. A Boley gauge can be used to check this angle. The reduction is not severe until the path of insertion is established and the occlusal has been reduced. The bridge is done as a single tooth. All of the walls are checked for convergence.
The occlusal reduction can start on either side of the mouth. It is usually best to start on the side that will be the most difficult. Since I am right handed, I start on the left side and take the reduction on around the arch. All of the partially completed walls are in the path of inser¬tion.
Two occlusion points are located on the left side of the bridge abutments. The distal point should be on the most distal molar in occlusion, and the anterior point should be on the cus¬pid or bicuspid in occlusion.
Occlusion reduction is done on the posterior teeth between these two points. A millimeter and a half of reduction is done and visually checked. Keeping the path of insertion, the walls of the abutments are reduced and taken to the edge of the free gingiva. The walls should be continuous around each tooth between the two points.
The occlusals are checked with a wax bite, and the small corrections are made. The abut¬ments are completed, except for taking the walls below the free gingiva. An acrylic bite regis¬tration is made before the mesial and distal points are reduced.
A bench cure acrylic is used to make the bite registration. Liquid monomer is placed in a dappen dish. Then, acrylic powder is added to the liquid until the liquid is saturated. The excess powder is removed by tapping the upside down dappen dish against the bench. The correct amount of powder remains in the liquid. The acrylic mixture is mixed thoroughly and allowed to set.
When the mixture is a doughy consistency, it is kneaded and formed into a small loaf of acrylic. The small loaf of acrylic is placed over the abutments between the two occlusal points. The opposing teeth close on the acrylic. The buccal side of the small acrylic loaf is pushed against the abutments. A bite registration is taken.
The small loaf of acrylic is removed with the bite indentation. The excess acrylic is removed with a pair of scissor leaving the incisal of the abutments and the occlusal tips of the cusps from the opposing teeth intact. The excess of the lingual is removed, and the loaf is reinserted over the abutments. Then, the opposing teeth are closed to correct for any discrepancies.
The acrylic loaf is removed to trim any overhangs into the mesial or distal contact points. The acrylic loaf must be clear of any undercuts. The buccal pushed-in portion can be trimmed, but enough needs to remain to give a guide for the insertion of the acrylic loaf. The acrylic loaf is removed and inserted many times while the acrylic is curing to insure the bite is accurate.
Once the bite is secured, the points still in occlusion can be removed. The occluding teeth are reduced a millimeter and a half, and a wax bite is used to check the clearance. The wax bites are retained for a backup. The walls of the two teeth that are holding the contact points are reduced to the free gingiva following the path of insertion.
The incisals of the anterior teeth are reduced two millimeters with a long, medium, round-ended diamond bur. The reinsertion of the acrylic bite on the left side keeps this accurate.
The lingual reduction is done with a flame-shaped diamond bur. Enough is removed to ensure the lingual portion of the teeth are clear of the mandibular teeth by at least a millimeter. The walls of the incisors are then reduced further. Pay close attention to the distal wall of the sec¬ond molar until the walls touch the free gingiva.
All four walls of the six anteriors are reduced and aligned with the mesial and distal walls of the laterals (the path of insertion). A Boley gauge can be used to check the convergence of the walls. All of the anteriors are now completed, except for taking the walls below the free gingiva.
An acrylic bite is taken of the anteriors with the left acrylic bite in place. This will give an¬other registration of the bite before the right side reduction is done.
It may be necessary to bring the distal walls of the molars more into convergence with the anterior labial wall of the incisor. This does not need to be a radical procedure. The walls need only be slightly convergent.
The maxillary incisors may be extremely long because of the extensive alveolar bone resorption. This makes a converging wall very difficult to make. To solve this problem, the incisal reduction may need to be four or five millimeters. One needs to be aware of the location of the pulp chamber to avoid an exposure.
This is done in a similar manner as the left side reduction. Two occlusion points are located on the right side of the bridge abutments. The distal point should be on the most distal molar in occlusion, and the anterior point should be on the cuspid or bicuspid in occlusion.
Occlusion reduction is done on the posterior teeth between these two points. A millimeter and a half of reduction is done and visually checked. Keeping the path of insertion, the walls of the abutments are reduced and taken to the edge of the free gingiva. The walls should be continuous around each tooth between the two points.
The occlusals are checked with a wax bite, and any necessary small corrections are made. The abutments are completed, except for taking the walls below the free gingiva.
The acrylic bite registration is taken with both the left and anterior bite registrations in place as well. This will avoid a tilting of the bite on the right side. A flame-shaped diamond bur is used to reduce the mesial and distal occlusal points.
Using the hand piece and a long diamond bur as a parallelogram, the distal walls of the mo¬lars are checked with the labial walls of the anteriors. The buccal walls of the right and left molars should be convergent. The molar lingual walls of the right and left sides should be divergent from each other but convergent with the buccal walls.
The lingual wall of the second molar should be convergent with the buccal wall of the first molar. The buccal and lingual of all the molar teeth should be checked for convergence.
At this point the patient has been in the chair a couple of hours. More anesthetic will need to be given to continue the process. The full mouth temporary will take approximately an hour to make. A laboratory temporary will take approximately thirty minutes to adapt to the exist¬ing abutments.
The gingiva will need to be numbed before the preparations can be taken below the free gin¬giva. The patient needs to be evaluated. Is the patient able to continue? Is the gingiva strong enough to take push below the free gingiva?
Whether the process is continued or not, this is a good opportunity to take an alginate impression of the abutments. The alginate is poured in a quick-setting plaster and stone combination and allowed to dry. The stone model is pulled from the alginate and placed on the parallelometer.
The long arm of the parallelometer is used to check for any undercuts in the abut¬ments. All of the walls need to be convergent. The distal walls of the molars should be checked with the labial walls of the anteriors. All of the mesial and distal walls should be checked. The buccal and lingual walls of the molars should also be checked.
Any walls out of convergence can be corrected before the walls are taken below the free gingiva. However, once the final reduction takes place, the correcting of the walls be¬comes very difficult.
This procedure can be done after the temporary is made and the patient is sent home. When the patient comes back for the second appointment, the corrections can be made before the final reduction takes place.
Whether you wish to continue immediately or another day, when the patient returns to continue, he needs to be numbed. The teeth are numbed with the painless technique, using the inferior alveolar or the infiltration method. The gingiva around the abutments needs to be numbed with the blanching technique. The toxic effect of the anesthetic needs to be considered if you are continuing the process.
Keeping the path of insertion, the abutment walls are taken below the gingiva with the long, thin diamond bur. The process should start on the left second molar and be taken to the first bicuspid. The abutments should be finished below the free gingiva with the long, medium, round-ended diamond bur.
Then, the occlusal should be analyzed. If the abutments appear to be too long because of the excess alveolar bone loss, the occlusal may need to be reduced one or two millime¬ters. The shorter abutment will improve the path of insertion, allowing the bridge to pull easier.
The sharp edges are rounded over. The white flame-shaped stone is used to give a satin finish to the occlusal, and the large, long diamond bur lightly touching the walls will smooth over the bur cuts.
The acrylic bite blocks for the anterior and right molar teeth are placed to check the occlusal. A new loaf of acrylic is mixed and placed over the left molar’s finished abutments. The ex¬cess acrylic is removed, and the new acrylic bite is created with the right and anterior acrylic bite blocks in place. It is important not to lose the bite in the finishing of the abutments.
The walls of the anterior abutments are taken below the free gingiva with a thin, long, round-ended diamond bur. The long, medium, round-ended diamond bur is used to finish the reduc¬tion unless the teeth are very small. Then the long, thin, round-ended diamond bur is used to finish them. Using the hand parallelogram technique, the labial walls are checked with all the molar distal walls to make sure the labial walls of the anterior teeth are convergent.
The lingual reduction of the anterior teeth should be slightly concave mesio-distally and gingivo-incisally and extending from the incisal plane to the top of the cingulum. The gingi¬val third regions are convergent to the labial walls.
The bite is checked on the lingual of the maxillary anterior teeth and on the labial of the mandibular anterior teeth for one millimeter of clearance. The incisal is smooth of any sharp points. It is recommended that the mandibular incisal plane be at approximately a 45-degree angle to the occlusal plane, in order to meet the forces of mastication at right angles. This is not always possible, but a flat incisal edge can withstand the occlusal forces better then a sharp edge. There is also a tendency for sharp edges to fracture in the stone dies.
Further reduction of the incisal may need to be done to make the path of insertion easier. The anterior teeth should not be left with excessively long walls.
The white stone places a satin finish on the lingual. The long, medium, round-ended diamond bur is used with a light touch and plenty of water to give the walls a smooth finish. The long, large, round-ended diamond bur can be used with larger teeth.
Keeping the right and left bite blocks in place, the final anterior bite block is made. A loaf of acrylic is placed over the anterior abutments. The bite is closed to the posterior bite blocks, and the labial portion of the acrylic loaf is pushed into the labial wall of the anterior teeth. The excess is trimmed, leaving a small amount of the pushed-in portion of the acrylic loaf in place for alignment.
The right molar abutments walls are taken below the free gingiva with the long, thin, round-ended diamond bur. The walls are finished with the long, medium, round-ended diamond bur. The path of insertion is maintained by using the long diamond bur with the hand parallelo¬gram technique. The right side becomes the key to the sixteen-unit bridge. It brings all the walls into the path of insertion.
The occlusal is reduced two to three millimeters depending on the length of the abutments. Long walls are difficult to bring into the path of insertion and should be shortened. All of the sharp edges are smoothed. A white stone and water will give a satin finish to the occlusals.
When all the final reductions are completed, the path of insertion is checked with the Boley gauge. All of the walls are checked by running the Boley gauge through all the angles. The medium, long, round-ended diamond bur is used to correct any walls out of the path of inser¬tion. This should not be more than a slight adjustment at this stage. It is important to observe the known difficult areas.
The buccal walls of the right molars and bicuspids need to be in convergence with the buccal walls of the molars and bicuspids on the left side. The lingual walls of the molars and bicus¬pid on the right side need to be in divergence with the lingual walls of the molars and bicus¬pid on the left side.
When all of the angles are correct, the abutments are air-dried. Using a mirror, all of the mar¬gins are checked to be sure they are below the free gingiva. Areas of special concern are the central incisors and the mesial of the first molar. These areas tend to remain above the free gingiva.
The right bite block is made using the left side and anterior bite blocks for reference. The acrylic loaf is placed between the teeth, and the patient bites down. The excess is cut away to give a clear view of the bite. The acrylic loaf tends to distort when it cures, so the distorted acrylic needs to be removed from all three bite-blocks. The acrylic bite blocks should move easily on and off the abutments and the opposing teeth.
Impressions of the sixteen-unit bridge can be a challenge, but with the help of your assistant, the process can be done efficiently. The patient may need more anesthetic for the gingiva tis¬sue around the abutments.
This is the most critical phase of the impression. If the gingiva around the abutments is hem-orrhaging severely, it might be better to delay the process a few days to allow the tissue to heal. This is not a time to be persistent.
I use the gingi-plain soft twist non-impregnated cord. There are many cords available, but this course will not be evaluating them. The gingi-pak cord is cut into sixteen pieces and soaked in the hemodent solution.
The cut pieces of gingi-pak cord are removed from the hemodent and placed on the tray. This allows the hemodent liquid to drain from the cord. A cut piece of cord is pushed into a loop and picked up with the cotton pliers. The loop of hemodent-impregnated cord is placed over the left third molar and pressed into place with the plastic instrument.
The idea is to pack the cord snugly around the abutment, but heavy pressure is not necessary. This is especially important in the lower second molar area where the buccal gingiva may be non-existent. A heavy push of the gingi-pak will detach the tissue from the alveolar bone.
Once the gingi-pak is placed snugly around the abutment, a two-by-two gauze is pressed against the tissue to absorb the excess hemodent liquid. The process continues around the arch, packing all the abutments. Several two-by-twos are placed over the packed abutments, and the patient closes his mouth until the impressions are taken.
The patient is advised to swallow his saliva to avoid soaking the two-by-twos and drawing the bitter hemodent liquid to his tongue. If the patient allows his saliva to fill his mouth, the packing material will need to be removed for the patient to rinse. When the patient learns to swallow, the process can continue.
I routinely pack the abutments a second time. There may not be any hemorrhaging, but the tissues are pressed again with the hemodent gingi-pak to insure the tissue remains clear. If the abutments are packed more then three times in an attempt to stop the hemorrhaging, another day should be considered. The hemorrhaging will remove the anesthetic, complicating the problem.
This will be a full metal tray impression. The metal tray is preferred because it has better stability against distortion. It should cover all of the abutments. If this becomes a problem, a special acrylic tray can be constructed off of the abutment study models taken earlier. If the acrylic tray is necessary, please refer to the appendices for the construction of the acrylic tray.
The impression material will not be debated in this course. There are many good impression materials available. It is good to use an impression material with a lighter (wash) consistency for the syringe and a heavy consistency for the tray material. If two different manufacturers are involved, you should be sure the two materials are compatible.
Two inches of the light impression material and its accelerator are placed on one of the glass slabs for the syringe. If the amount of the accelerator is decreased or increased, it will alter the setting time of the impression material. It is better to delay the setting time for this bridge.
Two five-and-a-half-inch by eight-inch pieces of twenty-pound paper (one half of an 8x11) are folded to form a tip like one would use in cake decorating. Starting with the five-and-a-half-inch edge, each paper is folded, leaving a quarter-inch hole at one end and an inch-and-a-half hole at the other end. The folds continue one upon another, maintaining the holes at the end of the each paper. It usually takes four to five folds. The sixteen-unit bridge will take two folded pieces of paper and two syringes.
The heavy impression and the accelerator material are placed on the other glass slab. The amount of material is determined by the metal tray periphery. The material needs to cover the teeth, but it is not necessary to cover the palate. The light and heavy impression materials are mixed simultaneously.
The mixed heavy impression material is loaded into the metal tray. It does not need to fill the tray completely. In fact, it is necessary to leave room for the light impression material. The heavy impression material is not placed on the maxillary palate of the metal tray. This will avoid a gagging problem.
At the same time, the light impression material is mixed and placed on the first fold of the folded piece of paper. The paper is folded over the material. The folding continues, closing all four to five paper folds. The large inch-and-a-half end is folded over to seal the material. The small quarter-inch paper tip is rounded to allow the material to flow. The paper tip is placed in the open tube of the syringe. The light impression material is squeezed into the tube until the excess comes out the syringe tip.
The paper tip is removed and placed in the other syringe. The remaining light impression ma¬terial is squeezed in the tube. A small scoop of material is placed in the second folded paper, in case there is a need for it later. The remaining light impression material on the glass slab is scooped up and placed over the heavy impression material, filling in any voids.
The plungers are placed in the syringes. The preparation is air-dried, and the light impression material in the syringe is squeezed into the free gingiva sulcus. It is best to start the syringe material the on buccal of the left distal abutment and work your way forward. This allows a better view of the process.
The syringe tip is placed in the distal gingiva sulcus. The light material is squeezed into the sulcus. The tip of the syringe moves mesially, filling the gingiva sulcus with the light im¬pression material. The tip enters each embrasure and fills the sulcus until the material flows through to the lingual side. The tip then returns to the left side, and impression material fills in the gingiva sulcus on the lingual and embrasure areas. The tip never leaves the gingiva sulcus when going from one embrasure to another.
The distal wall of the last molars needs special attention to be sure enough material reaches this area. In a small mouth, the process continues all the way around the anteriors and is car¬ried to the right side. In large mouths, the impression process may need to be made in two or three parts.
One assistant holds the cheeks out while the other one is refilling the first syringe with the extra light impression material in the second folded paper. When the syringe material is in place, the tray with the heavy impression material is inserted and held. The excess light im¬pression material in the syringe is emptied on the tray.
It is good to remove the plastic tip and push the plunger on through each syringe. This cleans the walls of each syringe. A two-by-two cleans the end of the plungers. The plunger is re¬moved and wiped clean. The excess at the end is wiped, and the syringe is ready for another impression.
The plastic tip is not touched until the material is set. Then the excess material is wiped clean. A ‘C’ explorer is used to push the set impression material from the small tip end and to pull the set impression material from the large end. The impression material usually pops out after it is loosened.
When this excess material is set, the impression tray is removed. The impression is rinsed, air-dried, and examined. If there is a discrepancy in the impression, it will need to be retaken. Sometimes when the impression sets, it sucks in a portion of the material, creating a defect in the impression.
A second metal tray impression should be taken even though the first impression is good. If there are defects in either impression, a compressed impression is taken. The compression impression can be done over the tray impression once. A third attempt with the same tray impression should not be done because the material becomes too thick and distorts.
The defective metal tray impression is rinsed, dried, and examined. If there is a discrepancy, the impression can be taken again using the defective impression. All of the undercuts in the defective impression are removed with a pair of scissors. This includes any overhanging impression material, pontics, and embrasures.
The paper folds and syringes are the same as the original impression. No tray material is necessary for this impression. It will be the light impression material and the two syringes. If more time is needed to complete the syringe application, then less accelerator should be used.
Two-inch portions of the light impression material are mixed and placed in the two syringes. Both syringes are filled with the folded-paper technique. It may require two folded pieces of paper. The tray impression of the abutments is lightly filled with the syringe light impression material. This does not need to be excessive. It should take no more then half of a syringe to flow over the impression of the abutments.
The light syringe material must also flow over the area void of abutments (pontic) if you are replacing missing teeth with the bridge. Essentially, you will be placing a layer of impression material over the previous impression.
The abutments are rinsed and dried. Using the syringe, the light impression is poured into the distal gingiva sulcus of the last molar on the left side. Keeping the syringe tip in the buccal gingiva sulcus, the light material flows from embrasure to embrasure. The embrasures are filled until they overflow into the lingual.
When the buccal is completed, the tip is placed on the distal lingual of the last molar of the left side. The light impression material is pushed into gingiva sulcus and taken into each embrasure, connecting the two sides all the way around the arch. The process is made faster by staying on the buccal-labial side until it is completed and only then moving to the lingual side.
The impression tray with the two millimeters of light impression material is inserted and pressed home. You should feel the impression seat itself over the abutments. Once the im¬pression tray feels mostly seated, it should be rocked slightly to be sure it seats completely. The tray is held with a fair amount of pressure.
If the tray doesn’t seat, it should be removed and reinserted. It is sometimes difficult to find the correct relationship. This can be avoided by inserting the tray before the light impression material is added. This will allow you to see if there are any undercuts holding the impression from seating.
When the light impression material is set, the tray is removed from the mouth. The impres¬sion should be correct. If the tray did not align, the impression will be lost. The pressure technique cannot be used a second time for the same impression. The impression material becomes too thick to take more material without misaligning the abutments with the ridge.
The one to two millimeters of impression material needs to go the full length of the arch after the impression of the preparation is filled. Otherwise, when the impression is poured, the abutments will be further off the ridge, giving an incorrect relationship.
The impression material should be mixed thoroughly. This includes the unmixed material on the spatula that tends to find its way into the syringe.
The syringe tip and plunger should be removed before the light impression material sets. Also, the excess light impression material should be pushed out of the syringe with the plunger after the tip is removed. This will make the clean-up easier. Only those with very strong muscles can remove a plunger once the impression material has set in the syringe. If this should occur, the syringe should be placed in hot water to expand the metal. Even then, you may still have to work hard at pulling the plunger out.
The mandibular tori may prevent the mandibular tray from seating correctly. A cut-away plastic tray may be necessary. The area on the plastic tray to be removed or bent is lightly heated over the Bunsen burner. While the tray is still warm, the tray is bent or cut to fit the mandibular preparation. The tray is then cooled with water before it is tried in the patient’s mouth.
Sometimes the maxillary tray will not fit properly because the mouth is narrow at the orifice and expands in the posterior. This forces the use of a large maxillary tray that may not fit the preparation adequately. A mandibular metal tray may work better. We do not need an impression of the palate.
If you are taking an impression of bridge abutments other then the sixteen-unit bridge, it is sometimes difficult to remove the impression tray from the patient’s mouth once the impression material has set.
This usually happens when a bridge with a pontic is involved in the impression. To prevent this problem, the pontic undercut of the bridge should be blocked out with wax before the impression is taken.
The embrasures may be open, allowing the impression material to flow between the teeth. To keep this from happening, the tray with the hardened impression material is removed by lifting the impression tray in the posterior section of the mouth first to break the seal. If the impression material remains stuck, the impression tray is lifted first on the side that the seal is broken on and then lifted on around the arch. It is best to break the seal on the opposite side of the preparation to avoid damage to the impression material over the preparation, even though it is usually easier to break the seal on the preparation side.
The compression technique is used commercially for some brands of impression material, but there is no attempt to obtain an accurate impression on the first attempt. The heavy material is used for the base and first impression and then the lighter material is used for the second and final impression.
Usually the first attempt is accurate using the heavy and light impression material at the same time. The compression technique is used when the first attempt leaves a discrepancy. The im¬pression is wrapped in a wet paper towel and placed in a zip-lock bag until it can be poured.
The laboratory temporary is a shell of acrylic with a glazed finished surface. The idea is to preserve this finish in the process of making the temporary useable. The sixteen-unit labora¬tory temporary is tried on the abutments. In some areas, the temporary will rock back and forth on a high abutment. A large #2 round bur is used to relieve the acrylic keeping the tem¬porary from seating. This may require hollowing the temporary until only a very thin veneer of acrylic remains.
Once the laboratory temporary seats, the occlusion is checked. The opposing teeth should be able to hold the laboratory temporary in place. This may require thinning out the acrylic more with the large round bur. All of the major adjustments are made on the inside of the labora¬tory temporary to preserve the surface finish.
When the laboratory temporary seats with the opposing teeth in place, the temporary is ready for the addition of more acrylic. There may be several millimeters of space between the laboratory temporary and the free gingiva. The acrylic used to fill the temporary can be any acrylic that bench cures. The shade can be adjusted with light and dark acrylic, or a shade can be selected to match the laboratory temporary acrylic.
The acrylic monomer and powder is mixed in a dappen dish or porcelain jar to a smooth creamy mixture. The size of the teeth will decide the amount of acrylic you will need. The acrylic mixture is poured into the hollow laboratory temporary, filling from one side to the other.
The excess acrylic is poured over the lightly dried abutments going from one side to the other side. The acrylic will flow into the gingiva sulcus. This should not be a detailed time-con¬suming procedure. You need to move along.
The laboratory temporary filled with soft acrylic is placed over the abutments and pressed into place. The patient closes and seats the temporary with the opposing teeth. The soft acrylic will begin to set almost immediately under pressure. The excess acrylic is trimmed with a Hollenbeck. It is good to wipe the soft acrylic off the surface finish with a two-by-two piece of gauze before the acrylic sets to preserve the glaze.
The laboratory temporary should be removed from the abutments before the soft acrylic sets, in order to insure it will come off. It is immediately replaced to keep the bite correct. Taking the laboratory temporary off and on continues until the acrylic is set. After the acrylic sets, the laboratory temporary is removed, and the excess acrylic is trimmed with a large, flame-shaped acrylic bur.
If a large space existed between the laboratory temporary shell and the free gingiva, it may be necessary to polish the acrylic addition. Care should be exercised to avoid removing the glazed portion of the temporary.
The trimmed laboratory temporary is seated over the abutments. The bite is checked with blue paper and adjusted with a flame-shaped green stone using plenty of water. The labora¬tory temporary is cemented to place with temporary cement.
The temporary may not fit the abutments correctly. This can be corrected by hollowing out the inside of the temporary.
The laboratory temporary may extend too far labially, or the abutments may not line up with the temporary teeth. Room for the abutments can be found by relieving the mesial and distal walls inside the temporary. This will weaken the temporary until the new acrylic is added. You may find that only the labial or buccal walls are workable.
If all else fails, the impression technique below is still available.
This technique uses the alginate impression taken prior to the reduction of the teeth. If the al¬ginate impression was poured with laboratory stone, then an alginate impression of the stone study model can be used.
The alginate impression is trimmed of excess alginate. This includes the extended alginate beyond the hard palate and in the mandibular sulcus. Any areas of the alginate impression that might interfere with its insertion need to be removed. If this is not a full-arch bridge, the alginate between the remaining teeth and under the pontics of existing bridges needs to be removed.
The alginate impression is tried in the mouth. If the alginate impression seats properly, we are ready to make the temporary. A mental note of some of the alginate locations in the mouth will help you to guide the alginate impression when it is filled with the acrylic.
The acrylic used to place in the alginate impression can be any acrylic that bench cures. A light cure acrylic will not work. Some acrylics come in varies shades. A trubyte bioform acrylic shade 65 is the same as vita A-3. A trubyte bioform shade 62 is the same as a vita A-2.
Some acrylics come with a dark shade and a light shade. This allows you to mix your own shade. After some experience using the acrylics, this may be your preferred method.
The alginate impression is air-dried. Where the restoration was prepared is especially impor¬tant. The drying should not be overdone. Only the excess moisture needs to be removed.
The acrylic shade is selected. If you are mixing your own shade, the powders should be mixed in a porcelain jar before the liquid is added. Otherwise, the acrylic will come out in different color stripes. Two dappen dishes can be used instead of the porcelain jar, but this increases the problem of keeping the mixture consistent.
The liquid is slowly added to the powder in the porcelain jar with an eyedropper until all of the powder is incorporated into the liquid.
If you are using one acrylic shade, the powder is added to the liquid in the porcelain jar or dappen dishes until the powder over saturates the liquid. We are not concern with color stripes. The excess powder is shaken off by turning the porcelain jar over and lightly tapping it to the bench. The excess powder will fall off. You will find the remaining liquid and pow¬der ratio produces the correct consistency.
The liquid and powder are mixed thoroughly. This is especially important if you are mixing two shades. Using the spatula, the mixture is eased into the alginate impression of the teeth before the reduction. The acrylic mixture needs to fill the crown-tooth impression of the abut¬ments. The excess should be removed. The process should move along before the material starts to set.
The abutments are dried of excess moisture. A portion of the acrylic mixture is allowed to flow over the abutments and into the contact areas. The spatula or the plastic instrument works well for this procedure. This will prevent voids in the contact margin areas.
The alginate with the acrylic mixture in the abutments’ impressions is seated in the mouth and held in place. It may take some adjustment to find the correct location. It needs to seat all the way to insure a good temporary. A little rocking motion may be necessary to insure the impression is seated properly.
The spatula and the porcelain jar are cleaned. The excess acrylic is placed on the tray. Once the impression is in place, the excess acrylic is tested with the fingers. When the acrylic mix¬ture snaps when it is pulled apart, the impression tray is removed. The acrylic mixture will usually stay in the alginate impression unless the abutments are excessively dry.
The Hollenbeck is used to pry the acrylic temporary loose from the alginate impression. This should be done over the tray. If the acrylic temporary remains on the abutments, the Hollen¬beck is also used to ease it off. This takes light pressure to avoid damage to the temporary. Once the acrylic is free from the alginate or abutments, the excess acrylic is removed with curved scissors. This is most easily done by turning the temporary upside-down. The scissors can follow the margins around the temporary.
The temporary is placed back on the abutments, and the patient bites the temporary into oc¬clusion. Minor repositioning of the temporary can be done at this time also. A cuspid can be pushed into a better shape, etc. Using the Hollenbeck, the temporary is loosened while it is still pliable and removed.
The embrasures are checked for undercuts. These are removed with the scissors if the mate¬rial remains soft or a hand piece and flame-shaped (football) diamond bur if the material has hardened. The temporary is again placed over the abutments and seated.
The acrylic temporary is removed once it is hard. A large, football-shaped acrylic bur in a slow-speed hand piece is used to reduce the excess from the acrylic temporary. Again, turn the acrylic temporary upside down to view the margins. This makes it easier to trim and prevents taking the margins off the temporary. All of the undercuts are removed. The acrylic temporary needs to freely move off and on the abutments in the patient’s mouth.
Once the temporary seats and the occlusion is corrected, additional acrylic can be added to the acrylic temporary. This is usually the buccal or labial surface. A small amount of acrylic is mixed. The surface of the acrylic temporary is air-dried, and the wet acrylic is added with a double-ended plastic instrument or the spatula.
The acrylic temporary is reinserted over the preparation and seated. The plastic instrument works the wet acrylic to place. If this is not a full arch temporary, care needs to be exercised to avoid creating undercuts in the embrasures,
Another way is to add the wet acrylic while the acrylic temporary is seated in the patient’s mouth. This allows missed margins to be covered. Always remove the acrylic temporary before it set in the patient’s mouth. It can be immediately reinserted if the undercuts are re¬moved. This is especially important for a temporary that is not a full arch temporary.
The occlusion is checked and reduced where necessary with a flame-shaped diamond bur. The acrylic temporary is removed from the mouth. The excess acrylic is trimmed. The tem¬porary’s labial and lingual surfaces are shaped with the large, flame-shaped acrylic bur and a slow-speed hand piece.
When the shaping is completed and the occlusion is adjusted, the acrylic temporary is pol¬ished with a rag wheel and pumice. The rag wheel and pumice is used wet. Using a slow speed, the rough surfaces are removed by pushing the acrylic temporary into the moving, wet rag wheel. This requires a firm grip, and you must keep the acrylic edges pointed away from yourself.
Once the rough spots are removed, the wheel can be turned to high speed. A light touch of the rag wheel will place a nice shine to the acrylic. The rag wheels should be cleaned and steril¬ized before they are reused.
The acrylic temporary is rinsed and tried in the mouth. Sometimes a piece of acrylic will chip off during the polishing. It may need to be repaired. If everything looks good, the acrylic temporary is cemented with temporary cement.
When the cement is dry, the excess is removed with a Hollenbeck and a "C" explorer. The bite is checked. If everything is good, the patient is sent home.
The patient may bite all the way through the soft acrylic when he or she closes to establish the bite.
The acrylic bite registrations can be placed in the patient’s mouth. A piece of tape on the tip of the patient’s nose and chin can be measured with a Boley gauge before the temporary is started. The bite registrations are removed and the patient is told to bite slowly into the soft temporary until the measurement is reached.
The acrylic should be allowed to set more before the bite is taken.
There may be some problems in seating the alginate impression after it is filled with the wet acrylic. If it does not seat all the way, the temporary will not work. It is better to start over. The following should be checked:
Usually you are off a tooth. Establishing guiding marks during the try-in phase will help to prevent this.
All of the alginate undercuts should be removed with the scissors. This includes the alginate over the pontics, and the alginate between the teeth for a temporary that is not a full arch temporary.
The acrylic temporary may be difficult to seat after it is removed and the material has hardened.
The embrasures need to be checked. The undercuts can be removed with a flame- shaped diamond bur.
The preparation may carry an undercut where the decay existed. This undercut will need to be removed with the flame-shaped diamond before the temporary will seat.
All of the abutment walls may not be convergent. The acrylic temporary is a good test for this. You may need to readjust for this and retake the impression.
The acrylic temporary should be removed while the wet acrylic is in its pliable stage. This should be done during the initial insertion and upon each addition of wet acrylic. This will prevent an undercut developing in the embrasures.
If the hardened acrylic temporary encounters an undercut and cannot be removed from the abutments, the temporary can be cut free with a 557 bur. A diamond bur cannot be used here because it will quickly fill with acrylic and stop. The procedure for removing the temporary is similar to removing a bridge or crown. A groove is cut on the center of the buccal wall of each abutment using plenty of water. The groove goes across the occlusal, and down the lingual wall. Care is necessary to avoid injury to the abutments. Sometimes a spoon can be used to lift the acrylic slightly off the abutment.
Heat generated from the curing process of the acrylic material may cause injury to the nerves in the pulp chamber. I have not experienced this high heat problem using the modern acrylic products. The chemical reaction from the monomer and powder does produce heat, but not enough to cause damage. However, the older products did produce enough heat to burn your fingers or do severe damage to the nerves in the pulp chamber. This can be avoided by removing the acrylic material from the patient’s mouth in the later stages of the curing when the heat is generated. This will also prevent the acrylic material from developing undercuts in the embrasures for bridges other then a full arch.
Plenty of water and a light touch should be used whenever the diamond or carbide burs are placed against acrylic surfaces. This will keep the acrylic material from burning and adhering to the surface of the burs.
The stone poured into the impression material should be the same kind that the laboratory you are working with uses. Each brand of stone mixture has a different texture and works a little differently. It makes little sense to handicap the laboratory man. Usually the stone sets up hard.
It is good to wear gloves when mixing the stone. It will make for an easy clean-up later, and keeps the moisture in your hands. The stone has a tendency to draw moisture to itself.
The impression should be thoroughly rinsed to remove any debris and blood. It is also good to run the impression through a sterilizing solution. The impression is removed from the ster¬ilization solution, rinsed and air-dried.
The size of the impression will dictate the amount of stone you use. Usually half a bowl of stone is adequate. You will not be placing a base on the impression pour. The impression tray will remain on the lab bench after the pour. If you turn the impression over to place the base, you run the risk of creating bubbles or distortions in the die or study model.
Water is added to the stone mix while the mix is stirred in the bowl. It is easy to place too much water in the mixture. More of the dry stone mix can be added to the bowl to compen¬sate if it becomes necessary. The attempt here is to have a creamy mixture of the stone mix and water. All of the stone mix needs to be incorporated in the creamy mixture. This will avoid bubbles later.
The creamy mixture of stone and water is emptied onto three paper towels. The towels are patted over the creamy mixture removing the water until the mixture is dry enough to be lifted off the towels.
The stone mixture is still pliable and will flow when vibrated. Using gloves, the mixture is held in one hand and the impression is held in the other. It is important to pour the prepara¬tion in the impression first. This will avoid a bubble in the critical area.
The impression is vibrated as a small amount of the stone mixture is worked into the prepara¬tion. The stone mixture needs to flow into the impression. It is important to work the stone mixture around the impression to insure every crevice is covered.
The stone mixture is added at one location on the impression and made to flow slowly through the impression using the vibrator. To use more then one location invites a bubble. The small amount of excess water and bubbles flows in front of the stone mixture. The prepa¬ration fills in behind the flow.
The excess stone mixture flowing over the tray should be removed before it sets. Enough bulk should be retained above the tray for the laboratory to make a stone base. The tray filled with the stone mixture is not turned over. It is left in the position it was in when it was poured.
Regular yellow stone can be used for pouring the alginate impressions. The stone mixture is mixed and dried in a similar manner using the paper towels. When you are comfortable with the procedure, more then one impression can be poured from the same mixture.
The maxillary impression is poured from the post dam and palate. The maxillary tray is vibrated as the stone mixture flows over the palate and into the impression of the teeth. The stone mixture is added slowly to allow the bubbles and excess water to move out of the im¬pression.
The base of the maxillary and mandibular study model can be made with the same mixture, as long as you wait for the stone mixture to set slightly before turning the impression and stone mixture to the bench.
It is usually easier to make the base with a separate mixture. The stone mixture in the impres¬sion is set enough by the time the base stone is mixed to keep the stone mixture from running out of the impression.
It is usually better to place a separating medium between the bench and the stone mixture. I use the zip-lock bag that the impressions were placed in earlier.
The bowl and spatula are cleaned with the paper towels before they are rinsed in the sink. This will avoid the expensive plumbing job that sending the stone down the drain would cre¬ate later.
Once the stone mixture is on the zip-lock bag, it can be trimmed with a spatula after it begins to set. The time will vary according to the dryness in the air. Usually by the time the bowl and spatula are cleaned, the stone mixture is set enough.
The spatula runs along beside the impression tray to separate the excess stone from the tray. If this is done carefully, there is very little need to use the model trimmer later. The undercuts on the lingual portion of the mandibular tray can also be shaped with a spatula before the stone mixture sets completely. This will reduce cleanup time on the study model later.
The alginate impression to be used for the temporary is not poured. This impression should be wrapped in a wet paper towel and kept in a zip-lock bag until you are ready to make the temporary crown.
The excess post dam alginate should be trimmed from the maxillary impression before the stone mixture is vibrated in. This will give a good finish to the stone model.
Some laboratories recommend mixing the impression stone mixture in a vacuum bowl after the water is added in order to remove the bubbles. Bubbles are created from the excess water and the lack of incorporating all of the stone mixture into the water. If initially the stone mixture is kept creamy, all of the dry stone will be incorporated into the water. The paper towels can remove all of the excess water, leaving a pliable stone mixture free of bubbles.
The impression should be poured immediately to avoid any distortions. Do not send wet impressions to the laboratory! You can expect some distortion fifteen minutes after the impression is taken.
The laboratory will send back a metal framework of the sixteen-unit bridge. This will allow you to check the abutments to see if the bridge will seat before the porcelain is added. The metal framework is carefully removed from the study model and placed in the cold sterilizer.
The patient is numbed enough to take the sting out of the exposed dentin. You will not need to numb them more unless the metal framework does not fit. Some patients can tolerate this try-in procedure without any numbing. You need to know your patients.
The temporary is removed with a spoon applying pressure on the distal buccal on one side and then on the other side. To further loosen the temporary, pressure is applied to the cuspid areas. The surrounding mucosa needs to be protected from the sudden release of the spoon. The patient may not appreciate a suture in his cheek
The temporary is removed after it is loosened. The excess temporary cement is carefully removed from the abutments to avoid pain and injury to the gingiva. This is usually an excit¬ing moment, but all of the hard and loose temporary cement needs to be removed from the abutments.
The metal framework is placed over the abutments. The metal framework should reach the abutment margins. If this is not the situation, the following should be checked.
The metal framework may be slightly bent.
An undercut may exist in the abutments. The parallelogram can be used to check the framework stone’s dies. The undercut has probably been removed from the stone die, but you may be able to see where the possible problem might be. It is usually the distal wall of the posterior molars or the labial walls of the anterior teeth. This needs to be corrected.
If a slight diverging wall exists, a long, round-ended diamond bur on the occlusal third molar can be used to make the wall more converging. You cannot reduce the abutment wall in the gingiva third without creating a weak point (leakage) in the bridge. The impression will need to be retaken and the metal framework redone.
The metal framework may not seat more then half way over the abutments. The abutments may be correct, but the impression and stone dies are distorted from pouring the impressions late. The impression will need to be retaken and the metal framework redone.
One of the abutments may be out of alignment slightly because the temporary was under stress, or the temporary cracked causing one of the abutments to move. If this cannot be ad¬justed out, then the impression needs to be retaken.
When the framework seats correctly, it can be sent to the laboratory for the biscuit bake. The temporary is cleaned with a toothbrush, soap and water. It may need to be polished again with the wet cloth wheel and pumice to remove some of the stains.
The biscuit bake finishes the bridge, except for the glazing. If the metal framework seated at the previous appointment, the biscuit bake will also seat. The biscuit bake gives you the op¬portunity to evaluate the bridge in the mouth before the glazing. The first glaze brings life to the porcelain. Each glazing after the first one takes life out of the porcelain. Therefore, all the corrections should be made in the biscuit bake.
The vertical is checked by placing a piece of tape on the nose and a piece of tape on the chin. Using the Boley gauge, a measurement is taken between the two pieces of tape with the moist lips barely touching. The Boley gauge measurement is reduced three milli- meters. This measure should reach the two pieces of tape when the teeth are in occlusion. This is not critical, but the vertical should be fairly close to this measure.
The bite is checked with blue articulating paper. Usually the posterior teeth are holding the occlusion open. This should not be a major adjustment. The teeth are brought into centric occlusion first. Reduction of the porcelain is done until all of the porcelain teeth are in occlusion, unless this is a class two malocclusion.
The porcelain teeth are taken through their functions with the blue articulating paper in place. Reduction of the porcelain continues until the porcelain bridge can move through the functions easily. All of the occluding porcelain teeth should display extensive blue markings.
The porcelain may be lacking in some areas on the bridge. A wax bite is taken with the bridge in place. The wax bite and porcelain bridge are placed on the stone model. The opposing stone bite is readjusted to fit the new bite. This may involve resetting the articulator. All of this is sent to the laboratory. It is recommended to check the new bite registration in a biscuit try-in a second time before the final glazing.
The margins are checked. If there is some recession, or the die preparations are cut short, more porcelain may need to be added. This is critical in the anterior region. The bridge is loosened slightly, and an alginate impression is taken. The porcelain bridge needs to come with the alginate impression. This will allow the laboratory to see where the bridge is short or lacking porcelain.
The opposing teeth may be flat plane teeth. If the opposing arch is not going to be bridged, then the bridge needs to match them. If the opposing arch is going to be bridged, then anatomy can be added. It is still recommended to keep a relatively flat anatomy because if the patient is used to moving heavily through the functions, anything in his way is going to become a problem.
The overall look is evaluated.
Did the bridge accomplish its goals?
Are the anterior crowns balanced in size, length, and shape? Is the lip line of the crowns the same as the original teeth? Is there a reason for making the crowns longer or shorter? Sometimes reducing the length of the teeth will make them look better.
Are the interproximals correct? Do the anterior crowns show enough definition? The interproximals may need to be deepened.
Has the tissue beneath the interproximals receded, leaving spaces? Are the pontics touching the ridge? If either of these are the case, an alginate impression is taken with the porcelain bridge in place. The porcelain bridge needs to come with the impression. The impression will show the recession of the gingiva.
You may need to make the patient another temporary bridge. An alginate impression of the biscuit bake could be used for this. This should be a consideration if the biscuit bake needs to corrected. A fractured temporary will allow the abutments to drift, and the patient would appreciate a nice temporary matching his or her new bridge.
If the bridge is satisfactory, the temporary is replaced and the bridge is returned to the labora¬tory.
This is usually a very exciting moment. The patient will need to be numbed with the painless injection. The gingiva usually is not numbed unless the patient is very sensitive to the proce¬dure. The bridge is removed from the study model and placed in the cold sterilization solu¬tion.
The temporary is removed and the excess cement is cleaned away. If the patient is a clencher, some of the abutments may be very sensitive to the touch or air. These abutments will need to be numbed thoroughly before the bridge can be tried in.
This should be an easy appointment. The occlusion should be checked for any changes. Sometimes the metal will warp when heat is applied.
ANECDOTEI had completed the sixteen-unit bridge for a man in his late forties and placed it on the tray along with my instruments. I left the room after I had given the man the initial injections. When I came back to the room, I removed the temporary and tried in the bridge. The bridge was bent slightly. I could not believe what I was seeing. Everything fit perfectly at the biscuit bake appointment. I tried the bridge back on the stone model. It would not fit. The bridge had a definite bend between the central incisors. The patient finally confessed that he had looked at the bridge and dropped it on the base of the chair. He said he tried to unbend it, and offered to try again. Needless to say, we had to redo the bridge. Never, I repeat, never leave the bridge on the tray where the patient can reach it. |
The bridge will not seat all the way to the abutment margin. The areas the laboratory corrected after the biscuit bake try-in should be checked first.
The porcelain cracked upon insertion. The metal is caught in an undercut below the abutment margin. When the metal moved, the porcelain fractured. The undercut needs to be removed in the metal or the abutment before the crack is repaired.
The bridge is removed from the abutments, and air-dried. It is important that the consistency of the cement be on the thin side of whipped cream. The cement powder and liquid is placed on a glass slab. It will take a fair amount of cement. The cement powder and liquid is mixed with long strokes across the glass slab to be sure no debris is in the cement.
The cement is added to the crown from the lingual side and spread over the remaining por¬tion with a plastic instrument.
The abutments are air-dried. The bridge is inserted and pressed home. The opposing teeth are used to seat the bridge once it is in place. A margin should be checked on the right and left sides to be sure the bridge seated. If the bridge is not going down all the way, it needs to be removed immediately and cleaned. Some debris has lodged itself inside the one of the crowns.
The bite is checked with blue articulating paper before the cement sets. It is another way to check the seating of the bridge. If the bridge needs to be pushed tighter on one side or the other, a cotton roll between the bridge and the teeth can be used. I do not like using this method because the possibility of cracking porcelain is very high.
When the cement is dry, the excess cement can be removed with a Hollenbeck and a "C" ex¬plorer. A wet two-by-two will remove the cement from the porcelain and gingiva. Do not use a dry two-by-two on the mucosa. It will take away tissue and leave sores.
The above discussion took us through the process of building a horseshoe sixteen-unit (all abutments) fixed bridge. The procedure also works well for twelve or fourteen-unit bridges, with or without pontics. The horseshoe bridge brings the anterior labial walls and the distal molar walls into play. The converging walls change as the bridge rounds the corners. The total bridge should be thought of as single crown with all the walls converging.
There is a tendency to over-cut the walls to be sure they converge. This is not necessary. If the path of insertion is kept in mind, the abutments will work with a slight convergence of the walls. This will keep the retention intact and allow a good seal for the horseshoe fixed bridge. Nothing is more disheartening then to see a portion of the bridge come loose from the abut¬ments for lack of retention.
The undercuts of the abutments or teeth on the study model need to be blocked out with pieces of a wet paper towel before they can be used for constructing acrylic trays. We will be using Coe Tray Plastic to make the trays. One full measure of the powder is placed in a porcelain jar, and the liquid is added until the mixture is smooth and wet.
The Coe mixture will change from a creamy mixture to a doughy mixture. Make sure your hands are wet before touching the doughy mixture. If the mixture sticks to your fingers, you need to wait longer. When the mixture can be manipulated without sticking to your fingers, take the doughy mixture from the jar and split it in half. Your hands must remain wet to keep the mixture from sticking to your fingers.
One half of the doughy mixture is placed on a flat wet surface. A small piece of the doughy mixture is snapped off for the handle, and the rest is flattened, and shaped to fit over the WET maxillary stone model.
The doughy mixture is pulled from the stone model and the excess material is cut off with a pair of scissors. The doughy mixture is placed back on the stone model and pressed to place. The idea is to keep a uniform thickness throughout the tray, and extend the tray into the pe¬riphery and post dam of the maxillary mold.
The small piece pinched off earlier is added to the maxillary anterior ridge for the handle, and smoothed into the tray. It is important to keep the handle high on the ridge.
The other half of the doughy mixture is placed on a flat wet surface, flattened and shaped to fit the wet mandibular plaster stone model. A small piece of the doughy mixture is snapped off for the handle. The handle is placed on the mandibular anterior incisal and smoothed into the tray portion of the doughy mixture.
The doughy tray is pulled from the plaster stone model and trimmed with a pair of scissors. The tray will distort in the process. This is corrected by placing it back on the model and pushing it into place.
Once the trays are hard, they are removed and trimmed with the emery cloth arbor band. The maxillary tray is trimmed back anterior to the soft palate.
Using a #2 round bur, holes are punched through the plastic trays. The holes are spaced three millimeters apart and should cover the entire tray. This will allow the impression material to flow through the holes and lock to the tray.
A large acrylic round bur is used to remove any undercuts to allow the tray to seat easily. The tooth impressions in the tray need to be burred well to remove the undercuts.
If you wish to make the handle separately, it can be added to the hard acrylic. A portion of the soft material directed onto the surface where the handle will be placed. The handle is rolled, shaped, and placed into the soft material on the tray. Then it is shaped and allowed to dry.
The handle does not need to be extended straight out. The handle usually works better slant¬ing downward from the maxillary ridge or extending more upward and outward from the mandibular ridge. The handles need to be fairly large. They will be your main point of thrust to remove the impression from the mouth.
From: Your name (Doctor’s)
Phone number and Fax number
To: Doctor’s name
Phone number
We need a medical clearance before we can do the dental treatment on the following patient:
Patient‘s Name: ____________________________________
Date of birth: ______________________________________
The plan procedure may consist of extractions, soft tissue surgeries, prophylaxes, endodon¬tics (root canals), fillings, crowns, or dentures.
We are concerned about the following areas:
Is the patient physically able to withstand the above-mentioned dental work? Yes or No
Can we administer epinephrine 1/100,000 in 1.8ml capsule of local anesthetic? Yes or No
Do we need to pre-medicate (antibiotic) before each dental appointment? Yes or No
Is the patient is on a blood thinner (coumadin, plavix)? Yes or No
If yes, can we stop it for three days? Yes or No
Please list any other comments pertinent to this patient.
Sign:_________________________
We greatly appreciate your help in providing us with this information.
Thank you