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Figure 1. a, Mandibular second molar, immediate post-filling view, canals filled with laterally condensed gutta-percha and Wach’s Paste. Note periapical radiolucency present. Although I did not know it at that time, this tooth probably was a C-shaped second molar, a difficult tooth to treat, especially when I didn’t realize what I was dealing with. Note that the mandibular first molar has furcation involvement. b, Twenty-two years later, periapical lesion is perfectly healed, and treated tooth supports a fixed bridge. The first molar had been extracted for periodontal reasons and if the second molar was not treated properly, the patient certainly would have masticatory difficulties.
Figure 2. a, Preoperative radiograph of mandibular second bicuspid, indicating poor canal filling performed 5 years early and periapical involvement. b, Tooth was treated and canal filled with gutta-percha and Wach’s Paste. c, Radiograph taken 27 years later, indicating perfect healing. d, Radiograph taken 34 years after treatment, still excellent healing.
Figure 3. Present landmarks for standardized endodontic files as determined by Ingle and International Standardization Organization after many years with total lack of conformity among the manufacturers. The tip of the file at the first rake angle is referred to as D0 (had been called D1 initially by Ingle) and 16 mm up the shaft from that site is referred to as D16 (was referred to as D2), where flutes are often halted. Depending on how far up the flutes cease, that number is combined with D—sub whatever the distance to the rake angle. The width of the flutes between D0 and D16 expands by .02 mm per mm of length. Therefore, every mm of length equals .02 mm of width, meaning that the file had a .02 taper of flutes. Other lengths still used the .02 taper, but might have a different subscript determined by the length of flutes on the given file.
Figure 4. Leeb2 stated that the conception that canals are wide at the orifice and then become more narrow towards the apex is erroneous. He determined that often the width at the canal orifice was responsible for the difficulty of small files reaching the apex rather than the width at the apex. This was due to narrowing of the orifice due to deposition of reparative dentin in heavily restored teeth. Apical to this site, the canal gradually widens and then narrows closer to the tip. He advised that the orifice area be widened early in the canal preparation phase to give more coronal room for the files to penetrate.
Figure 5. Weine, et al., introduced “zip” and “elbow” as new endodontic terms in their paper in 19753. The study showed that canal preparation in relatively straight canals and those with canal curvatures of 30 degrees or more was totally different. In the canal with greater degrees of curvature, when the preparation was completed, the narrowest level was not at the apex, but in the middle of the curve—usually 2 to 5 mm from the apex—which they called the “elbow.” The canal then widened towards the apex and the end of the preparation was called the “zip” because of the irregularity that developed. The files removed more tooth structure on the inside of the curve above the elbow, but attempted to straighten there and thus took off more tooth structure on the outside of the curved between the zip and the elbow.
Figure 6. a, Differing types of NiTi files: Style manufactured by Denstply/Tulsa, using a slight change in colors of the shaft as compared to colors used in regulation-type instruments and a different tapering system. b, Style manufactured by Dentsply/Maillefer with a striped color as used with regulation files and a tapering systems with smaller total increments. c, Mc-Xim files as made by New Technology. The first 2 sets of instruments are still made and popularly used. The Mc-Xim system had files with differing degrees of taper and a large number of basic files. However, it did not receive good acceptance by clinicians and has undergone several changes in design and shape.
Figure 7. Other types of NiTi instruments. After the popularity of the .04 tapered instruments was established, many new designs were introduced. One system had tapers greater than .04, (top to bottom) .10 taper, .08 taper, .06 taper, and comparison to the .04 taper. Note that the wider tapers have a shorter length of flutes than the .04 taper to concentrate cutting in the orifice area. The wider tapers should be used with great care, because they work quickly and make a larger hole.
Figure 8. The SX file (bottom) as compared to finishing files (two top files). The finishing files have 21 mm flute lengths, whereas the SX has a 19 mm flute length. Instead of a uniform taper, these instruments have a wider taper at the top of the flutes and the degree of taper decreases toward the tip. In very curved canals, I prefer to clip an additional 2 mm off the tip of the SX to lessen any chance of breakage in the elbow area.
Figure 9. Clinical action of SX files in the decreasing of canal curvatures. a, Maxillary first molar with initial files (#10s in the buccal canals) placed to the apex. The curvatures are approximately 45 degrees in the MB and 35 degrees in the DB. Note that the files cross within the access opening. b, After only minimal use in the buccal canals with the SX file, against the mesial wall of the MB and the distal wall of the DB, note that the same files have decreased curvatures. Now the files in the canals cross outside of the access cavity.
Figure 10. Torque control electric engine for use with tapered, rotary files. The rpm readout is on the control box and should indicate a speed of 300 to 450 rpm.
Figure 11. Treatment of mandibular second molar with NiTi instruments. a, Mandibular second molar with pocket to the apex on distal surface of distal root with moderate mobility. b, Initial files in place, #15 in distal root and #10 in mesiolingual root. Note that the curvature of file in mesial root is approximately 45 degrees. c, Mesiolingual canal was enlarged as indicated in Fig. 12 and file in place now has a curvature of approximately 30 degrees or less, much easier to treatment than 45 degree curvature. d, Files in place in all 3 canals. e, Canals filled with gutta-percha, post room prepared in distal canal. f, The referring dentist was unsure of the outcome for the tooth due to the distal pocket (I was not worried), so a temporary bridge was made. This radiograph, taken 6 months after treatment, indicated excellent healing of the tooth, now very tight. g, The radiograph taken 30 months after treatment indicates perfect healing.
Figure 12. Files used between Fig. 11 b and c. From top, size #10 file, clipped #10 now #12, #2 NiTi tapered, rotary file to middle of curve, back with #12 to apex, #3 rotary file, back with #12 to apex, #4 rotary file, back with #12 to apex. Rotary files were manufactured by Dentsply/Tulsa. Exact use of files listed as Case One.
Figure 13. Treatment of first molar with NiTi instruments. a, Maxillary first molar with pocket to the apex of mesial root. Distal canal has curvature of approximately 45 degrees, mesial canals have lesser curvatures. Tooth treated according to text, Case Two, with ample use of SX file. b, Angle view of canal filling, post room in distal root. c, Radiograph taken 6 months after completion of treatment, lesions healing very well. d, Radiograph taken 4 years after treatment, excellent healing, no lesion associated with mesial root and no probing possible.
Figure 14. Files used in initial treatment of case shown in Fig. 13. From top, size #10 file, clipped #10 now #12, SX file clipped 2mm, #15 rotary file to center of curve, SX file, back with #12 to apex, #20 rotary file, SX file, back with #12 to apex, #25 rotary file, SX file, back with #12 to apex, regular #20 file drops in easily. Exact use of files listed as Case Two.
Figure 15. Treatment of double curvature. Extremely difficult case, requiring exhaustive use of SX filing to widen access in a buccal-lingual direction, heavy use of irrigation and lubricants, and clipping to make intermediate files.
Figure 16. a, Diagrammatic representation of 4 types of canal configurations that depict 99.5% of the conditions found in human teeth, views from the proximal (views rarely seen in most clinical cases). The major canals only are shown, not auxiliary or lateral canals, or apical delta. From left to right, Type I canal system, single canal from orifice to apex. Type II canal system, 2 canals at orifice merging to form a single canal short of the apex. Please note that left canal appears to be straighter and will be the “master canal”, with the right canal filled into it. Type III canal system, 2 separate and distinct canals from orifice to apex. Type IV canal system, single crown from orifice, dividing into 2 separate canals short of the apex. b, Vertical ground section of maxillary 1st molar with a single canal (Type I). c, Vertical ground section of maxillary 1st molar with 2 canals at orifice merging into a single canal at the apex (Type II). d, Vertical ground section of maxillary 1st molar with 2 canals at orifice, separate and distinct to apex (type III). (No type IV canals were found in 1969 study.) e, Radiograph of Type I canal in maxillary 1st molar. f, Radiograph of Type II canal in maxillary 1st molar. g, Radiograph of Type III canal in maxillary 1st molar. h, Radiograph of Type IV canal in maxillary 1st molar. Figs. e through h had roots other than MB root removed for clarity. (Obviously file placement in Fig. h could not occur in a clinical case, but merely shows that a Type IV in this tooth is possible.)
Figure 17. a, Key radiograph of maxillary first molar to know if two canals in the mesiobuccal root is from the distal. Post-filling radiograph clearly demonstrates two canals filled in MB root. Note that the distobuccal canal is mesial to the palatal canal. b, Working lengths on the first molar canals were 18 to 19mm. One-year post-operative film taken from the distal clearly shows 2 canals in MB root and periapical lesion, present before treatment, almost completely healed. Note that DB canal is also mesial to palatal canal.
Figure 18. Maxillary second molars with 2 palatal roots. a, Sixteen-year postoperative film of maxillary posterior area. Second molar has 4 filled canals, one to the left is the mesiobuccal, one to the right is distobuccal, and two palatal canals between them. Both the second molar and second bicuspid (to left) had large lesions before treatment. b, Four canals in maxillary second molar. From right to left (viewed slightly from distal), mesiobuccal, mesiolingual, distobuccal, and distolingual.
Figure 19. Mandibular first bicuspid with 2 canals. a, Preoperative straight-on radiograph indicates a large canal in crown of the tooth, but it almost disappears in the root. This site of disappearance is where the canal divides into a Type IV system. b, Lateral view of an extracted maxillary first bicuspid of a similar tooth, indicating a dividing canal system. c, One-year postoperative film of tooth shown in a. d, Ten-year postoperative film.
Figure 20. Most endodontic textbooks through the 1960s advised that the access cavity for entry into the maxillary first molar be triangular in shape. Such an access makes location and preparation of the distal portion of the tooth, which contains one wide, kidney-bean shaped canal or two canals, quite difficult. The correct access is a trapezoid with rounded corners for better access to the distal root or roots.
Figure 21. Mandibular second molar with 4 distinct canals. Note the second separate and distinct canal to the distal with a sharp curve that would be difficult to locate and very difficult to prepare and fill. (Endodontic treatment by Dr. Brad Gettleman, Glendale, AZ.)
Figure 22. C-shaped mandibular second molars, first reported by Cooke and Cox 37. a, Two canals, one to the mesial and one to the distal. b, Three canals merging at the apex. c, Three canals, two distals merging and mesial canal separate and distinct.
Figure 23. Maxillary first bicuspid with three canals. Most often when this condition occurs, the three canal orifices can be found on the floor of the chamber and the configuration is similar to a small maxillary second molar. The configuration in this tooth, however, is much more difficult because only two orifices can be found on the floor of the chamber and the canals divide in midroot, similar to a Type IV system.
Figure 24. Treatment of maxillary second bicuspid with Type IV canal system. a, Preoperative film of posterior maxillary teeth with periapical areas on second bicuspid and second molar. Please note that the canal in bicuspid seems to disappear toward the apex, typical of Type IV canal system. b, Initial files placed seemed to indicate a Type II canal system because the file in palatal canal seemed to engage the file in buccal canal near the apex or vice versa. However, further manipulation proved that the wide canal split into 2 canals near the apex. c, Immediate postoperative film, slight angle from the distal, shows 2 canals filled near the apex, a Type IV system. d, Six years after treatment of both teeth, excellent healing of both.
Figure 25. Angled radiograph of mandibular incisors treated after locating two separate and distinct canals. A straight-on preoperative radiograph would never pick this up and the lingual canal probably would be missed. Note the access to the roots with this configuration goes through the incisal edge.