Current Endodontic Treatment

Current Endodontic TreatmentContents

Learning Objectives1 Current Endodontic Treatment Introduction Use of Tapered, Rotary Instruments - Initiation of Changes in File Design Need for Early Enlargement of the Orifice Area The "Zip" and the "Elbow" and Their Significance in Curved Canal Preparation Introduction of Nickel-Titanium Instruments Other Excellent Files for Use in Curved Canals No-No's When Using NiTi Files Step-By-Step Use of .04 Files in Curved Canals Conclusion2 Recent Studies of Canal Configuration Introduction Terminology for Canal Configuration Studies Early Studies on the MBR of Maxillary Molars Further Studies of the MBR Retreatment of Failing MBRs Names of the Canals in Maxillary Molars Studies of the Maxillary Second Molar Studies of the Mandibular Bicuspids Studies of the Mandibular First Molar Studies of the Mandibular Second Molar -A Tooth With Multiple Variations Studies of the Maxillary Bicuspids Studies of the Mandibular Incisors Studies of Teeth With Five or More Canals Role of Ethnicity in Configuration Studies Effect of Preparation Methods on Configuration Studies Future for Canal Configuration Studies3 Endodontics of the Future Newer Types of Canal Filling Materials Use of Single-Appointment Treatment Conclusions References Legends Post Test

1. Current Endodontic TreatmentIntroduction

Current treatment procedures in endodontic therapy have undergone almost a complete changeover in the last ten years. Teeth that were formerly considered to be hopeless now may be saved on a very high percentage basis using procedures and instruments recently introduced. The net result is that teeth that were extracted not long ago now have an outstanding chance for being retained. The following pages will deal with many of these innovations and illustrate how they may be used for best results. Even so, the author wishes to inform the reader that some of the views listed here are not universally accepted by endodontic experts and there are many outstanding textbooks and publications which can be consulted for excellent discussions of alternative methods of therapy. The areas of discussion will be accompanied by appropriate case radiographs, some with extensive follow-up views (Figs. 1 and 2), to illustrate the methods of treatment and healing.

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Figure 1

Figure 2 - 27 Years Post- Op

The subjects to be discussed will be the following: (1) use of tapered, rotary instruments, (2) recent studies of canal configuration, and (3) areas of future interest.

Use of Tapered, Rotary Instruments - Initiation of Changes in File Design

Prior to 1958, there were many varying types of intracanal instruments for use in endodontics. Although all were designed with the intent to clean and widen the canal, differences in instrument length, width, degree of taper, and rake angle were constant. Then, John Ingle decided to introduce a standardized system for the use of canal preparation, with a clear demarcation in the relationship of the instruments(1). Ingle then was Departmental Chairman at Washington University Dental School and later became Dean at University of Southern California School of Dentistry. His contributions vaulted endodontics into a new era where canal preparation became easier to perform and results were more predictable.

There were many differing file shapes available at that time. Long-handled instruments, useful only on maxillary anterior teeth (where much of the endodontic treatment of that time was performed), were

grasped by the entire hand and conducive for use with reaming action. There were numerous file systems available with short handles, for use with the fingers, but there were variations in length, width, taper, and length of flutes among them. The instruments were designated #1 through #12, but, for instance, a #3 Union Broach might be totally different than a #3 Kerr file in flute length, width, and/or taper. Even files by the same manufacturer could be different from year to year. Ingle’s system changed this. He standardized the files to have similar total lengths, length of flutes, degree of taper, and widths, and also assigned a lettering/numbering system to use for identification of these sites on the new instruments. The International Standardization Organization (ISO) had control over file dimensions, but immediately recognized the improvement offered and accepted Ingle’s principles.

Ingle standardized the total length of the files to 21 mm, 25 mm, or 31 mm in length, eliminating the long-handled instruments. Of these lengths, 16 mm of the apical portion was fluted to provide for dentin removal. The tip area of the file where the first rake-angle was formed was called “diameter 1”, or D1 and the flutes’ end site (16 mm up the shaft) was called “diameter 2”, or D2. At that time, flute length commonly ranged from 15 mm to 25 mm. He fixed the width of the files to widen from the first rake- angle (at D1) to the rake-angle at D2 at a rate of approximately 1 mm of length to enlarge the file width by .02 mm.

Several alterations were made within the next few years. Some manufacturers had their flute level ground between a length of as little as 15 mm to as long as 19 mm. The D1 and D2 indicators were changed, D1 (the first rake-angle) to D0. The D2subscript was changed to indicate the exact length of the flutes, which usually was 16 mm, but could be anywhere from 15 mm (referred to as D15) to 19 mm (referred to as D19) up the shaft (Fig.3). In all cases, the flute width still increased by .02 mm of width per one mm of length—still a .02 taper.

Figure 3

These changes were welcomed by virtually all dentists involved in endodontic therapy, even those who treated a minimal number of teeth. This innovation was especially valuable when reordering files because files purchased at varying times would still fit into the standardized system. Previously, older files, that were still usable, had to be discarded to maintain tip and taper degree relationships.

Need for Early Enlargement of the Orifice Area

The standardized use of .02 for taper degree opened up an entirely new horizon for endodontic instruments. It had been assumed for many years that most teeth treated endodontically were widest at the orifice and then tapered down to a much narrower width near the apex. This might be true in teeth that required treatment due to trauma or from incorrect dentin removal during restorative procedures. However, Leeb(2) wrote an eye-opening paper indicating the error of such views (Fig. 4). He showed that teeth that were heavily restored or had extensive decay (which included most teeth requiring treatment) had very narrow orifices that widened to a larger diameter in midroot and then narrowed again toward the apex.

Figure 4. Schematic representation of Leeb’s study. Dentists have an erroneous idea of the shape of canals in heavily restored teeth (center, mesial canal enlarged at right). It has been assumed that the canal is widest near the orifice and then tapers down to the apex. In truth ( left), the canal is narrow at the orifice due to the deposition of reparative dentin in response to the restoration. Away from the orifice, the canal widens in midroot and then tapers down to the apex. (From: Weine FS: Endodontic Therapy, 6th ed. Elsevier Publishing, with permission)

Since all endodontic files had some degree of taper, this finding meant that in many teeth the small orifice area could cause premature binding of the instruments and result in much less apical enlargement than was anticipated. Whereas many clinicians believed that the narrowness of the canal preventing the penetration of the entire canal was from the apical area, it was obvious that the coronal site was largely responsible. This transferred the need for early enlargement of the canal in the orifice area in order to gain more effective cleaning towards the apex.

With this in mind, changes in the files had to be made so that the orifice area could be widened quickly and safely without any damage to the apical portion. This was accomplished by the introduction of rotary engine driven files of tapers greater than the standard .02 taper developed by Ingle. The areas at the upper portion of flutes were made to be wider so that the orifice could be enlarged early in the preparation. At this time, the apical portion (minimally enlarged) merely provided a pathway for directing the instrument but did little, if any, enlargement.

The “Zip” and the “Elbow” and Their Significance in Curved Canal Preparation

For many years, it was assumed that canal preparation in anterior teeth and posterior teeth were very similar. Of course, posterior teeth almost always had more canals, many of which were quite curved as compared to the straighter anterior teeth, but no severe alteration was drawn in the facets of treatment. Then, in a landmark study by Weine, Kelly and Lio in 1975(3), the difficulties encountered in treating teeth of greater curvature were elucidated and new words were added to the endodontic glossary of terms.

In their analysis, Weine, et al. determined that in curved canals the files did not cut dentin equally in all directions, but instead took more off from the inside portion of the curve than the outer side except nearer to the apex where the opposite occurred. This meant that the desirable canal long-section view of a gradual taper from the orifice to the apex was not obtainable in curved canals by using the techniques then in vogue. Because of the files working to the inner portion from the orifice and then to the outer portion near the apex, the tapered funnel really was never present when a sharply curved canal was prepared, but the shape in long-section was really more of an hourglass. From the orifice it was wide and tapered to the center of the curve, but then widened again (Fig. 5).

Figure 5

The authors of the study attached names to the two most significant changes in canal shape. The narrowest area was called the “elbow,” which is a plumbing term at the turning site of plumbing equipment which may fill with debris and cause blockage in the system. The area at the very apex of the preparation was called the “zip,” because this site was wider than expected and ragged. The “elbow” generally occurred in the middle of the curve in a canal with an apical curvature of 30 degrees or greater and usually is noted from 2 to 5 mm from the tip of the preparation. “Zipping” occurs from that point to the apex (Fig.5). The article went on to suggest that modification of the flutes should be performed and use of files of greater flexibility be used to lessen the zipping problem.

Many endodontists refused to accept these findings and believed that their preparation methods were useable in any canal configuration. However, within a few years most endodontists were compelled to agree with the study and began to make changes in their preparation techniques, which also included their choice of files. Newer files were evaluated which were more flexible than those in common use and several styles were found to be useable and able to minimize the elbow and zipping. However, most dentists felt that flute removal was a tedious and, perhaps, unnecessary procedure. But, the best was yet to come!

Introduction of Nickel-Titanium Instruments

Another important innovation pertained to the metal used in the instruments. Originally made from carbon steel blanks, at this time most endodontic files were being made from stainless-steel blanks and thus were less susceptible to corrosion. Stainless-steel was at least mildly resistant to breakage and could be cleaned and resterilized after use. Then, a newer metal was introduced into endodontic treatment after previous use in other areas of grinding. This metal was Nickel-Titanium, which had been used in industry since 1960 and was at first referred to as Nitinol—“ni” for nickel, “ti” for titanium and “ol” for the Naval Ordinance Laboratory in Maryland, where it was first used. The initial dental use was orthodontic wiring and shortened to be called “NiTi.” Endodontic files of this material have increased flexibility due to a low modulus of elasticity and therefore retain its general shape even when strained within the canal. Too much strain can still be responsible for breakage, but requires a much higher level of stress than does carbon or stainless-steel. While the Ni-Ti instruments are more expensive than stainless-steel, they retain their shape much longer, a phenomenon known as pseudoelasticity (4). The metal has different properties when stressed, but returns to the original shape when the stress is relieved. There is a limit to the amount of stress that NiTi files can resist and this is an important consideration when the file is used in conjunction with mechanical handpieces, as compared to use by hand(5).

The metal may go through any of three transformations, to detwinned martensite, to austenite, or to twinned martinsite via heating and cooling(6). It appears that the phase of transformation between austenite and martinsite is where the greatest elasticity occurs and thus is the best time to work under some stress.

To obtain even more advantage to these newer file systems, they were modified to be used in conjunction with mechanical handpieces. Mechanical handpieces had been introduced in endodontic treatment many years earlier for use with carbon steel as well as stainless-steel. When used in straight canals, which were by far the minority found in the teeth being treated, they seemed to work quite well. However, in the more curved canals many files fractured within the tooth and posed many difficulties in attempts to retrieve them. When used in conjunction with the NiTi instruments, this was much less of a problem. Thus a very useful series of instruments that could complete routine canal preparation in much less time than hand filing and allow for considerable increase in orifice size to promote more effective canal cleaning and filling were then available.

Immediately after their introduction, the NiTi systems became quite popular. In fact, they probably were used more quickly than any of the endodontic systems for the past 50 years. For many manufacers introduced varying systems, combining the use of NiTi instruments and .04 tapers. Some of the systems still have wide usage (Fig. 6a and b) whereas others came into the market and in a short period of time were withdrawn (Fig. 6c).

Figure 6A

Figure 6B

Figure 6C

The combination of NiTi files with mechanical handpieces as rotary instruments delivering an extraordinary type of flexibility alone was greatly responsible for diminishing zipping. However, file separation did occur if these new instruments were stressed to a great level and this caused a serious problem. Cantatore, an excellent endodontist practicing in Rome, with great skill in the removal of separated instruments in the apical third of the canal (where a huge majority of separations will occur), has stated that even with much time, effort, experience and auxiliary instruments, only approximately one-third of the files separated at this level could be retrieved(7).

With more dependable instruments and the knowledge that the mechanical handpieces could give a better shape to the canal preparation, another innovation was introduced. This was the making of some of the files to double the width that Ingle had promoted and with even greater than double—to triple or quadruple them (Fig. 7). This meant that the orifice area could be widened more quickly and the areas toward the apex also could be made wider. Personally, I am not an advocate of those files which are much wider, such as the .08 tapers or larger, and I rarely even use the .06 instrument. I fear that these wider files have a greater chance of getting stressed in narrow, curved canals and thus lead to possible separation. I much prefer using only the .04 tapered instruments, even though they may require some additional time for completion of the preparation, but this is more than balanced by the greater safety afforded to the narrower files. In fact, my preference is to use only the .04 tapered instruments, and then never even use them past the elbow, which virtually assures very low chance for separation, and completing the apical portion (past the elbow) with hand files, usually the most flexible obtainable. This aspect of treatment has

been followed by me in virtually every complex case that I have had in the last 10 years without any separation whatsoever.

Figure 7

Other Excellent Files for Use in Curved Canals

Several files were developed in order to gain safely the wideness of the canal orifice, as per Leeb’s instructions. The file that I find to be most advantageous for this important step is the “SX” file (Fig. 8). Instead of the file having a taper of .04 or larger it has a taper that is quite wide at D 16, but then decreases much more than the routine files to the apex and is a shorter file—19 mm in length. When placed into the canal orifice, only the set of flutes highest on the shaft will cut, with the tip portion of the file merely indicating the direction of the canal. To be extra-sure that the file will not separate nor cut into the sides of the canal, I often cut the apical 2 mm off the file prior to use. The resultant instrument is shorter and, thus, easier to insert and the safety is increased.

Figure 8

The importance of the use of SX files, particularly in molar teeth, is demonstrated in Figure 9. It shows how the instrument may be used to place pressure on the outer surfaces of the molar canals to allow the exterior triangles to be reduced and result in decreasing the angle of entry—a very desirable condition. There are other mechanical handpieces that are used in endodontic treatment—the Gates-Glidden drills and the Peeso reamer. However, they are centering files and when pressed against the outside of curved canals may result in instrument breakage. The manufacturers of these instruments acknowledge this but state that the broken portions of the instrument are not difficult to remove. This may be true, but it never is fun to have to remove a separated instrument.

Figure 9

The most difficult canal in the dental arch to prepare is the mesio-buccal of the maxillary 2nd molar. This tooth has a distal inclination and the files must be inserted from the disto-lingual direction. This is an extremely difficult file placement. As will be discussed later in this report, there is a high incidence of two canals in this root. By early use of the SX file and pressure on the mesial aspect of the orifice with the SX, a much straighter access is obtained to the root. Pressure to the mesio-lingual wall will allow for examination for the mesio-lingual canal.

No-No’s When Using NiTi Files

As excellent as the NiTi files are, the instruction booklet that may come with them may be incomplete or inaccurate. Also, some of the speakers who discuss them at dental meetings may give erroneous information. I have used these instruments for over ten years with outstanding results, but I have modified and added information to make their use better and safer. My advice for safety follows.

When using the NiTi files, the operator must distribute the rotation of the stress throughout the canal and, therefore, must NOT stop preparation in this area. To accomplish this best, the file rotation must be started prior to the insertion into the canal and use of light pressures to obtain deeper insertion. If the file starts to rotate more slowly as it goes down the canal, it is best to withdraw the file, still rotating, and go back to smaller sizes nearer the orifice.

The handpieces that are typically used with the NiTi files are made with controls that are different

than those used for routine preparation for operative dentistry, that is cavity, crown, or onlay preparation. The best handpieces for use with these files are those with torque control electric engines that allow for 300 to 450 rotation per minute. The readout for the machines are indicated on the control box and the operator is free to utilize the desired speed. I prefer something in the neighborhood of 350 to 400 revolutions per minute (Fig. 10).

Figure 10

As stated earlier, the best safety for rotary instruments involves using them ONLY to the center of the apical curvature and using hand instruments for the remaining distance. Therefore, place the marker on the NiTi file to indicate no more deeply than the center of the curve and do NOT allow for the marker to

go past this length. In most mandibular molars, this calculation is easily made by placing the file along the long axis of the tooth on the radiograph. In maxillary molars and bicuspids with unusually placed curvatures, a working-length file of small diameter (no wider than a #15 file) may be placed and measured to indicate the position of safety.

When starting out to use the NiTi instruments, the operator should select easier cases—even anterior teeth that do not ordinarily require complex methods of therapy, merely to adjust to the “feel” of the files within the canal. Once these are mastered, it is best to use extracted teeth or plastic blocks (available from companies selling these NiTi products) and examine the result to be certain that mastery has been obtained.

Step-By-Step Use of .04 Files in Curved Canals

In order to allow the reader to follow the step-by-step use of the instruments described, I am utilizing three cases of expanded complexity that will serve to demonstrate the techniques.

CASE ONE: Mandibular second molar with recurrent decay, acting as posterior abutment of 5-unit fixed bridge, with adjacent tooth replaced by an implant in place for over one year. The involved tooth had a periapical lesion at the apex that was draining along the distal portion of the distal root, a condition thought never to be treatable some 25 years earlier. The preparation of the mesiolingual canal is given, and the radiographs and file use are presented in Figs. 11 and 12.

The curvature of the mesiolingual canal (Fig. 11, b) is approximately 50 degrees. A size #10 file of a flexible file system is passed to the working length and the tooth is radiographed to verify length, which was calculated to be 19 mm. If an apex locator is being used along with the radiographs to calculate working length, it too may be used at this time. The distance to the center of the curve is approximately 4 to 5 mm from the apex.

Use the *SX file in the mechanical handpiece to widen the orifice area to allow for ease of placement of the files which will be inserted to the apex.

Figure 11A Figure 11B1. Place the #10 file to 19 mm and using rasping action by hand widen the apical portion of the

canal until the file is loose. 2. Clip 1 mm from the size #10 file (making it a size #12) and widen the apical portion of the

canal. 3. Set the stop on the smallest rotary file at 14 to 15 mm (distance to the center of the curve) and

widen the canal. Do not worry if the file does not go to the stop, but BE CERTAIN that it does not go BEYOND the stop.

4. Use the #12 file to the full working length. 5. Set the stop on the second smallest rotary file at 14 to 15 mm and widen the canal. 6. Repeat step 5. 7. Set the stop on the third smallest rotary file at 14 to 15 mm and widen the canal. 8. Repeat step 5. 9. At this point, if you took a radiograph with the size #12 file a file in the ML canal, the angle of

the canal is now 30 degrees, a much easier preparation than a curvature of 50 degrees (Fig. 11, c).

The two mesial canals merge and the ML is made the master canal with the mesiobuccal merging several mm from the apex and the preparations of the three canals are completed. Be certain to keep the canals heavily irrigated with sodium hypochlorite or similar irrigant during the completion of the preparation.

The distal canal is very straight and may be prepared easily after the mesials. In the 30-month post-operative film, complete healing of the lesion is seen. (Fig 11G)

Figure 11C Figure 11D

Figure 11E Figure 11F

Figure 11G

* In the case shown, I was only rarely using the SX files and was not sufficiently understanding their excellent use. Now I would use them more aggressively, after each file to the full working length. The .04 tapered files were used as indicated. No tapered, rotary instrument was used past the site of the elbow—only hand instrumentation.

Figure 12

CASE TWO: Mandibular first molar with periapical and lateral lesion associated with the mesial root and drainage into the furcation. Preparation of the mesial and distal canals is provided. I was using the SX files actively at this time.

The working length of the mesial canals was calculated to be 21 mm and the distal was 20.5. The apex locator may be used at this time to verify the length. The curvatures on the mesial canals were approximately 35 degrees, close to the root tips. The curvature of the distal, which was wide bucco- lingually, was approximately 45 degrees, also close to the root tip. The preparation of the three canals is presented in Figs. 13 and 14.

Use the SX file first in the mechanical handpiece to widen the orifice area to allow for ease of placement of files which will be inserted to the apex.

Figure 13A Figure 13B


Mesial canals:

1. Insert the size #10 file to 21 mm and using rasping action by hand widen the apical portion of the each canal until the file is loose.

2. Clip 1 mm from the size #10 file (making it a size #12) and widen the apical portion of the canal.

3. Use the SX file in the mechanical handpiece after cutting off 1 mm at the tip and widen the orifice portion of the canal, slightly deeper than it had been in the first use. The clipped portion of the tip keeps the file at 18 mm or less, not long enough to do any preparation at the tip.

4. Set the stop on the smallest rotary file at 19 mm (distance to the center of the curve) and widen the canal. Do not worry if the file does not go to the stop, but BE CERTAIN that it does not go BEYOND the stop.

5. Use the #12 file to the full working length. 6. Set the stop on the second smallest rotary file at 19 mm and widen the canal. 7. Repeat step 5. 8. Set the stop on the third smallest rotary file at 19 mm and widen the canal. 9. Repeat step 5. 10. At this point, the size #20 should go the full working length without any

problem. The canal curvatures should now be approximately 25 degrees, much easier than 35 degrees. The canals should be widened to size #30 easily.

Figure 14

Distal canal: This canal is wide bucco-lingually, so the SX file used should make an oval shape in the orifice instead of round as was done on the mesials. Use the SX in this manner now to start the preparation.

1. Place the initial size (size #10 or #15) into the disto-buccal and disto-lingual portions of the canal using rasping action and widen the apical portion of the canal. Set the stop at 20.5 and use rasping action at that length.

2. The SX file length is normally 19 mm, just about the length to the middle of the curve, so it is safe to place it into the canal and allow it to go to the full length and no damage to the apex will occur.

3. Set the stop on the second or third smallest rotary file at 18 mm and widen apical portion of the canal. Do not worry if the file does not go to the stop, but BE CERTAIN that it does not go BEYOND the stop.

4. Use the SX file to widen the occlusal portion of the canal. 5. Use the next size hand file and widen the canal at 20.5 mm. 6. Repeat step 4. 7. Go up one more size with the next larger rotary instrument and file no farther than 18 mm. 8. Repeat step 4 then step 7. 9. Go up one more size with the next larger rotary instrument and file no farther than 18 mm. 10. At this point, the canal curvature should be approximately 30 degrees, much easier than 45

degrees. Little more preparation is required at the apex and some further use of the SX may be employed.

As before, use the irrigant and lubricant constantly and ensure that the path to the apex remains clear by using a smaller-sized file (size #12) at any time.

CASE THREE: Maxillary second bicuspid with double curves of almost 90 degrees each. Large periapical lesion, slightly behind the implant, often making the apical area difficult to see. The working length of the tooth (with the crown removed) was 17 mm. NOTE: This case is presented to illustrate the

excellent possibilities afforded by the .04 tapered and SX instruments. This case is VERY difficult and I tried treating similar teeth without these burs with limited success. The final results here were very gratifying but not always predictable. They should ONLY be attempted after a considerable number of teeth has been successfully treated.

The SX file was used short of the first curve to widen the orifice. Second bicuspids are wide buccolingually, but much narrower mesio-distally, a condition not often realized. Therefore, the SX file is used to the buccal and lingual initially to give more access to the canal portion in the curved area. The size #8 file was used to the apex, with minimal clips made and heavy use of irrigant and lubricant. Then the size #10 was used to the apex (Fig. 15, a). The SX file was placed more deeply into the canal, but kept short of the initial curve. A small amount of the tip of the size #10 was removed, making it a size #11 and passed to the apex. Much irrigant and lubricant are used. Continue gradually working the hand files and SX files toward the apex, using minimal clip on the hand files and the SX files short of the first curve. When the apical portion has reached size #25, it is safe to attempt to fill the canal (Fig. 15, b). The four-year postoperative film indicates excellent healing (Fig. 15, e).



Figure 15E

Conclusion

The use of tapered, rotary instrument of sizes .04 taper plus files to open the canal orifices quickly and safely is a huge step for endodontic treatment even on very complicated cases. It is anticipated that more file systems will be introduced in the future and it is up to the individual dentist to assess these newer products and determine their usefulness. Just because something is new does not mean that it is better. Use extracted teeth and plastic blocks to verify the abilities of the newer products before initiating treatment based on advertisements or poorly designed studies.

2. Recent Studies of Canal ConfigurationIntroduction

In 1925, Hess, a German dentist, wrote a book on the internal anatomy of human permanent teeth, by taking vulcanite impressions of the cleared canals and decalcifying the surrounding dentin. One of his most interesting findings was the presence of two canals in some mesiobuccal roots (MBRs) of the maxillary first and second molars. He also demonstrated that some of the canals in that root displayed anastomoses that made several curves before joining another canal near the apex. Hess made observations on other teeth as well, including the possibility of complex canal anatomy in the roots of teeth that were wider bucco-lingually than mesio-distally(8). Although it was hardly appreciated at the time, his work was truly an immense achievement which is verified by the fact that no one had ever attempted a similar compilation on the subject of tooth internal anatomy. When one realizes that from the 1970s to the present, hundreds of papers have been published that use aspects of his work, enabling clinicians to better treat endodontically involved teeth. The result of Hess’ efforts is that many millions of teeth have been saved, starting with his text.

As interesting as these conclusions were, very little attention was directed to them. At that time, endodontic treatment was firmly positioned on the lowest rung of the dental ladder. There were three reasons for this: 1) problems with the focal infection theory were centered around pulpless teeth, 2) teeth that were treated before the development of proper radiological principles but then were judged some years later radiographically to have latent infections, 3) there was a pervasive attitude by both physicians and dentists against saving teeth.

On the rare occasion when endodontic therapy was performed, it was usually for anterior teeth and some bicuspids with teeth, but curved canals and molars were almost never treated. Endodontics as a specialty was still 40 years away. Some of the pioneers of endodontics—Grossman, Rhine, Hine, Healey, Sommer, and others attempted to convince their contemporaries of the value of retaining involved teeth, but it was a difficult task. Molar teeth with necrotic pulps required four to eight, often difficult, appointments and there were frequent failures.

Terminology for Canal Configuration Studies

To understand the potentially different anatomy of the canals of the various teeth, some general terminology is necessary. According to Weine, there are four frequent configurations or pathways that canals may take as they traverse from the crown through the root to the apex (Fig 16). They are:

(1) type I—a single canal from the crown to the apical site of exiting

(2) type II—two canals in the crown which merge short of the apex to form a single exit site

(3) type III—two canals which remain separate and distinct to their sites of exiting

(4) type IV—a single canal in the crown that divides well short of the apex into two separate canals at the apex(9).

Figure 16A

Types I, II, and III are found in many teeth and have been referred to in many articles. Type IV, however, was first discussed when studies on the mandibular first bicuspid were undertaken. This pathway has also been reported in maxillary second bicuspids, and MBRs of maxillary molars.

There are at least three other systems that have been proposed to classify canal configuration, but this is the most simple to understand and covers over 99.5% of human teeth. The remaining 0.5% usually will fit into this system, although not perfectly. For instance, a single canal that divides in midroot into two canals that merge short of the apex into a single canal again is very rare, perhaps 0.5%, but does exist. It would be classified as a Type I canal in this system. It is important to understand that this classification, as well as the others, takes into account only the main canals within the tooth. Auxiliary and lateral canals and small branches are not considered. Also, the comparatively few configuration studies in this review using other systems have been converted and listed according to the method stated above.

Figure 16B Figure 16C Figure 16D

Early Studies on the MBR of Maxillary Molars

For over 40 years following the Hess study, few articles on canal configuration were published, generally in minor journals and with minimal attention. Then, in 1965, Rankine-Wilson and Henry of the Perth Endodontic Study Club, a group of sophisticated restorative dentists who were forced to perform endodontics on their own patients in the absence of specialists in southwestern Australia, published a study on mandibular anterior teeth in the JADA, indicating that incisors bifurcated in 40.5% of the teeth in the study and remained separate to the apex in 7.5%(10). With the interest in endodontic therapy now on the rise, the report did generate interest, but mandibular incisors did not require treatment very frequently so it had little effect on clinical procedures.

Figure 16E

Weine and Rankine-Wilson met shortly thereafter when both were on the faculty of Northwestern University Dental School and discussed possible future studies in configuration. Although neither had ever read Hess’ work, both agreed that the MBR had more failures than any other roots treated endodontically. At that time, sophomore students radiographed, accessed, filed, and filled extracted teeth while mounted in a block, practicing for treating patients in the clinic. The Class of 1970, 52 students,each drilled down the mesial portion of the MBR on four teeth until the canal system was totally exposed. Obviously, in some cases the inexperienced sophomores drilled past the canals and not far enough in others. However, compilation of the data revealed that two canals were present in 51.5% (Type II and Type III) of the total of 204 teeth, an astonishing and unexpected total! Also noted was that 14% of the MBR had two canals that were separate and distinct to the apex (Type III), an even more significant finding(11).

The study was published in Oral Surg, Oral Med, Oral Pathol in 1969 and created immediate reactions among educators as well as clinicians, many of them quite negative. Ingle had published the first edition of his textbook, Endodontics, in 1975(12), with triple the number of pages than in the older endodontic textbooks and many large, appealing drawings. However, the maxillary first molar was listed and drawn as having three roots and three canals. The books on root anatomy written by Wheeler, probably the most widely used texts in dental education, including the edition printed in 1976(13), listed the MBR as having a single canal, even though the drawing of the root from the proximal was over 50% wider than that of the distobuccal root (Table 1).

Further Studies of the MBR

Many subsequent studies(14-35) have been undertaken on the maxillary first and second molars and they have had more articles in the dental literature than any other teeth. If anything, the results seem to indicate that the number of two canals in the Weine et al. study was too low. This is especially true of the more recent reports which incorporated magnifying equipment for identification.

Figure 16F Figure 16G Figure 16H

Two other studies, both from Europe, deserve additional discussion, those by Evenot from France, and by Zill from Germany. Both were the basis of theses for Ph.D. degrees and have many more pages and much more information than the other studies. Evenot reported on a great number of teeth (378) in his study and his use of the microscope in addition to radiographs had not been used in other studies until recently. He also reported the lowest number of a single canal in the MBRs studied up to that time and, hence, the highest number of teeth with two canals in the MBR (18). Zill used a different type of classification system than used by most of the studies referred to in this review and thus his statistics are a bit difficult to state. He did find two interesting statistics not proposed up to that time. They were that male patients had more teeth with two separate and distinct canals than did females (41.5% vs. 25.0%) and that the percentage of MBRs with two canals increased with the age of the patient(24).

Table 1. Configuration of MBR of Maxillary Molars, (1925-2002)

Author(s)(Year) Number of

Teeth

Method of study %Type I Type II Type III Type IV

Hess8 (1925) 513 Vulcanite Impressions

47.0 <-------------- 53.0 ------------>

0

Weine et al.11(1969)

208 Vertical sectioning 48.5 37.5 14.0 0

Pineda14 (1973) 262 Proximal radiographs

39.3 12.2 35.7 12.8

Green15 (1973)** 100 Vertical sectioning 64.0 22.0 14.0

Seidberg et al.16

(1973)100 Horizontal

sectioning38.0 37.0 25.0

100 Clinical cases 66.7 <-------------- 33.3 ------------>

Pomerantz and Fishelberg17 (1974)

71 Decalcified and dyed

71.8 16.9 11.3 0

100 Clinical cases 69.0 16.0 15.0 0

Evenot18 (1980) 178, 208

Radiographs, several microscopic

28.8 23.5 38.8 8.8

Hartwell and Bellizzi (l982)19

538 Clinical cases 81.4 <-------------- 18.6 ------------>

0

Vertucci20 (1984) 100 Decalcified and dyed

45.0 37.0 18.0

Bjorndal and Skidmore21 (1987)

85 Acrylic casts 41.1 40.0 18.9

Weller and Hartwell22 (1989)

835 Clinical cases 61.0 <-------------- 39.0 ------------>

Fogel et al.23 (1994) 208 Clinical cases 28.9 39.4 31.7 0

Zill24 (1997) 105 Radiographs and some sections

1.0 41.0 39.0 19.0***

Weine et al.25

(1999)300 Radiographs, files

in teeth42.0 24.2 30.4 3.4

Stropko26 (1999)* 1732 Clinical cases with operating microscope

16.5 31.9 44.3

Wolcott et al.27

(2002)**1193 Clinical cases,

initial<-------------- 58.8

------------>

Clinical cases, retreatment

<-------------- 67.4 ------------>

*MBR studied in first, second, and third molars, only 72/92 4-canaled teeth could be filed**MBR studied in first and second molars ***German, “sonstige,” means “otherwise”

While the first finding does not offer a clear rationality, the second may be explained by the canal in the MBR after eruption having a single, figure-eight shaped canal. With age, there is increased dentin deposition and the center point of the figure-eight eventually squeezes off the single canal into two in the MBRs.

After the first few studies were published on the MBR of the maxillary first molar, many more were undertaken using different methods of investigation and reporting different results. It is possible that some of these investigations were undertaken to disprove the frequency of two canals in the MBR, since it had been noted in precious few studies in the preceding years. However, the finding of over 50% of the teeth examined having two canals was a constant of in vitro reports. The early in vivo reports indicated fewer bicanaled MBRs. However, several of the very recent studies, including that by Stropko using an operating microscope and a large number of cases, have indicated that two canals may occur as often as in 80% or more of the teeth (Table 1)(26).

Retreatment of Failing MBRs

The first determination to make when treating a failure of endodontic therapy on a maxillary first molar is the root(s) involved. By far, the MBR is the most frequent, perhaps by a ratio of 5 to 1, or more. The distobuccal, smallest of the three roots, usually has a gentle curve that is prepared and filled rather easily. The palatal is more curved than the distobuccal but not as much as the MBR, generally to the buccal direction. However, the canal is much wider than the buccals and, therefore, easier to prepare and fill than the MBR. But the keys to determination in evaluation of the MBR root are the preoperative radiographs. In addition to the normal straight-on view, another view must be taken from the distal so that the distal and palatal roots overlap or the distal is mesial to the palatal. This puts the MBR into a mild profile, and, if present, will show the canal filling not centered in the root, but to the mesial. Post-filling films must include an angle from the distal (Fig. 17, a).


Although not as reliable an indicator as the film from the distal, another hint that two canals are present in the MBR and should be located is that the tooth is shorter than average from occlusal to apex, that is less than 19 millimeters. Such teeth have a tendency to be wider bucco-lingually than teeth that are longer, thus permitting essentially similar periodontal ligament attachment regardless of length (Fig. 17, b). It is usually best to attempt location and position of the mesiolingual canal before making a decision on the retreatment of the mesiobuccal canal. If the latter is obviously inadequate, both canals in that root should be treated. If the mesiolingual canal merges with the mesiobuccal canal, some advise that the latter may be left alone. Weine advises retreatment of the mesiobuccal and treatment of the mesiolingual whenever retreating a failure of the MBR and has demonstrated cases where a type II canal system was shown to be present, but a sinus tract did not clear up until both canals were prepared(9).

Names of the Canals in Maxillary Molars

Some authors and/or clinicians have referred to the second canal in the MBR as the “MB2.” This is neither an accurate nor a correct name and has no basis as compared to the references to any of the other canals in the dental arch. The teeth with multiple canals have always had an important basis in common—the direction for entering the root is the opposite to the name of the canal. In bicanaled bicuspids, the buccal canal is entered from the lingual and the lingual canal from the buccal. In the three-canaled mandibular molars, the distal canal is entered from the mesial, the mesiobuccal from the distolingual, and the mesiolingual from the distobuccal.

In the maxillary molars, the palatal canal is entered from the buccal, the distobuccal from the mesiolingual, and the mesiobuccal from the distolingual. Examination of the typical mesial roots from the 1969 report(11) indicated that the correct path towards entering the second canal in the mesial root is from the distobuccal, hence it should be referred to as the mesiolingual. As was mentioned and will be discussed in the next section, the maxillary second molars very rarely may have two palatal canals. These would never be called P1 and P2, but, more properly, the mesiolingual and the distolingual. The same conditions apply to the mesiobuccal root.

In the first English edition of his text, Castellucci states that rather than using MB2 as the name of this canal, it is “more appropriately named the mesiolingual canal”(28). Failure to gain entrance to this canal often occurs because the operator fails to consider this initial curve to the distobuccal and the small file continuously bends when pressure is exerted as the instrument tip bypasses the angle of the orifice. Weller and Hartwell(22) and Fogel(23) et al. also refer to the second canal in the mesial root as the mesiolingual.

Studies of the Maxillary Second Molar

With so many multicanaled MBRs found in maxillary first molars, it was not too long before this root in second molars started to receive attention. Several of the earlier reports on the first molar had concomitant results listed for the second molar, too (Table 2). Subsequent studies on the second molar only are listed in Table 2(17,30-33,36). Many endodontists started finding a second mesiobuccal canal in the first molar, but had great difficulty in locating an additional canal in the second molar, probably due to the position as most posterior tooth and inclination to the distal. However, the statistics are probably correct. Still, the in-vitro investigations depict a much higher percentage of average number of canals than do the in-vivo reports. At this time, when many maxillary first molars have four canals filled frequently, the percentage of treating four canals in the second molar still lags far behind.

The maxillary second molar has many more canal configurations than does the first molar. One, two, three, or four roots may be present with two, three, or four canals, whereas the first molar has three or four roots in virtually every instance, always with three or four canals. The spread of the roots in the first molar is much greater than in the second molar and the position of the canal orifices also may differ, particularly the distobuccal in the second molar being more to the mesiolingual in some teeth.

Table 2. Configuration of the MBR of Maxillary Second Molar, (1972-2002)



Teeth

Pineda and Kuttler29 (1972)

294 Proximal radiographs

64.6 8.2 12.8 14.4

Nosonwitz and Brenner30 (1973)

161 Clinical cases 68.9 25.5 5.6 0

Pomeranz and Fishelberg17 (1974)

29 Clinical cases 62.1 13.8 24.1 0


71.0 17.0 12.0 0

Kulild and Peters31

(1990)32 Access and bur

penetration21.8 <-------------- 78.2

------------>0

32 Sectioning and microscope

6.3 <-------------- 93.7 ------------>

0

Eskoz and Weine32

(1995)67 Radiographs, files

in place59.7 20.9 16.4 3.0

Wolcott et al.27

(2002)689 Clinical cases,

initial <-------------- 35.3

------------>

Clinical cases, retreatment

<-------------- 43.6 ------------>


The maxillary second molars also may have two palatal roots, in one of two distinctly differing formations, a condition almost never seen in the first molar. In one of the types, the palatal roots are rather far from each other and the tooth resembles an upside down card-table, easily discernible on the radiograph (Fig. 18, a). In the other condition, the palatal roots are much closer together, difficult to see on the radiograph, and often are noticed only when examining the floor of the chamber of the tooth (Fig. 18, b).

Table 3. Configuration of the Mandibular First Bicuspid (1972-1992)


Teeth




69.3 1.5 1.5 0.9

Green15 (1973)** 50 Vertical sectioning 86.0 <-------------- 10.0 ------------>

Zillich and Dowson33 (1973)***

1393 Radiographs 69.3 <-------------- 2.7 ------------>


70.0 4.0 1.5 0.5

Baisden et al.34 106 Transverse 76.4 0 0 23.6

(1992) sectioning

*reported 0.9% had 3 separate canals**did not report on 3 canaled teeth***reported on first and second bicuspid; 0.4% of the teeth had 3 canals

Studies of the Mandibular Bicuspids

Next to the MBR of maxillary molars, the configuration studies on the mandibular first bicuspid have been the most illuminating and useful. (Table 3)(15,20,29,33,34). For many years it was thought that the mandibular first bicuspid had only a single canal, although there were a few examples of those teeth being bicanaled in rare instances. Of all the teeth studied for additional canals, this tooth seems the most mystifying for failure to diagnose that more than a single canal is present immediately upon examining properly angled radiographs. The key sign is that the occlusal portion of the canal seems large and well developed, but suddenly disappears in midroot (Fig. 19, a). That site is obviously the point of separation of the canals into two, and, sometimes, even three canals to their apices.

Figure 19A

The older studies on this tooth listed Type I systems on 69%-86% of the teeth examined and some percentage of Types II, III, and IV. A recent study, by Baisden et al.(34), reported that the tooth only had either a single canal or a bifurcated canal system. The net result of these studies indicates that more and more mandibular first bicuspids being treated are found to have more than a single canal, but rather a Type IV system, the most complicated of the systems to treat. This finding occurs in a much higher number than had been assumed—perhaps as high as 30%—and the Baisden study certainly should result in fewer failures in the future. In 1973, Zillich and Dowson reported on this tooth, studying 1393 teeth—a huge number—and reported that 69.3% had a type I system. Of the remaining bicuspids, 22.7% had 2 canals and 0.4 had three canals(33). Both mandibular bicuspids may have two or three canals, but this finding occurs much less frequently in the second bicuspid than it does in the first.

All of the studies indicating two canals in this tooth stress the need for a wide preparation buccolingually. The buccal canal is penetrated from the lingual whereas the lingual canal is found from the buccal. The height of the division from one canal to two usually will determine the outlook for the treatment. When the division is towards the occlusal, the treatment is not complicated. However, in cases where the site of division approaches the apex, treatment is very difficult.

In general the mandibular second bicuspid is one of the easiest teeth to treat endodontically, with a single canal well centered in the crown and extending to the apex. Even in single-canaled mandibular first bicuspids the access

is more difficult because it is the only tooth in which the long axes of the crown and the root meet at an angle (Fig. 19, b).

Figure 19B Figure 19C Figure 19D

Studies of the Mandibular First Molar

Shortly after the first study of the MBR of the maxillary first molar, Skidmore and Bjorndal reported on the canal configurations in the mandibular first molar(35). Bjorndal had investigated many of the human teeth and, with aid from his graduate students, reported not only the configuration but also the lengths and widths of the permanent teeth in a booklet, Anatomy and Morphology of Human Teeth, second edition(35). Many hours were invested in this complex undertaking. Bjorndal and Hess probably should be given co-credit as the fathers of modern canal configuration reporting (Tables 4-7 and 9).

Table 4. Configuration of the Mesial Root of the Mandibular First Molar (1971-1988)


Teeth


Skidmore and Bjorndal35(1971)

45 Acrylic casts 6.7 55.6 37.7 0



12.8 30.2 50.4 6.6

Green15 (1973)* 100 Vertical sectioning 12.8 48.5 37.7 1.0


27.0 38.0 26.0 9.0

*sections of both mandibular first and second molars

Table 5. Configuration of the Distal Root of the Mandibular First Molar (1971-1973)


Teeth


Skidmore and Bjorndal35(1971)

45 Acrylic casts 71.1 17.7 11.1 0



73.0 12.7 5.7 8.6


89.3 4.9 2.9 2.9

Table 6. Configuration of the Mesial Root of the Mandibular Second Molar (1972-1988)


Teeth




58.0 20.6 13.8 7.6


27.0 38.0 26.0 9.0


60 Acrylic casts 25.0 43.0 32.0 0

Weine et al.36

(1988)*72 Radiographs, files

in place4.0 52.0 40.0 0

*4.0% C-shaped teeth were found

Table 7. Configuration of the C-shaped Mandibular Second Molar (1972-1998)

Author(s)(Year) Number of Teeth

Method of study % of Second Molars that were C-shaped

Pineda and Kuttler29 (1972) 300 Proximal radiographs none noted

Cooke and Cox37 (1979) * Clinical cases 8%

Tamse and Kaffe38 (1981) 508 Radiographic 10.9

Bjorndal and Skidmore21

(1987)60 Acrylic casts 13

Melton et al.39 (1991) 15 — known to be C-shaped

8—polyester resin casts 7—cross sectioned, 3 levels

100

Weine et al.40 (1998) 399 Retrospective—clinical cases 6.2

412 Prospective—clinical cases 8.9

*no number reported

In their evaluation, Skidmore and Bjorndal stated that four canals were present in the mandibular first molar in 28% of the cases, separate and distinct in 11% and merging short of the apex in 17.5%. They listed three roots to be present in 2.2% of the teeth studies and recommended a larger, more rectangular access preparation than had been shown in Ingle’s first edition(12), which was largely adopted by the endodontic community soon thereafter. This change from a smallish triangular form allowed for the added room to locate the fourth canal, if present (Fig. 20).

Figure 20

The mandibular first molar, being the first permanent tooth to erupt, probably is the most common tooth to have pulpal damage but early in the 20th century it was usually extracted when involved. For the past 40 years, it has been treated more and more as endodontic techniques have become more predictable. For this reason, it is important for any dentist treating this tooth to be well informed as to the configuration possibilities and some excellent studies have been reported(20,29).

According to the studies on human teeth, the mandibular first molar is one of the few teeth where the normal configurations differ between the European/American and the Asian population. Most of the studies reported in this review are from the former group. A further discussion of some of the types prevalent in the Asian population will be presented later in this report.

Studies of the Mandibular Second Molar—A Tooth With Multiple Variations

The mandibular second molar has the greatest variation of configurations among the molar teeth. One of the most egregious errors is the often-felt opinion that the mesial root has a fairly high percentage of only one canal (Table 6)(20,35,36). In the study of Weine et al.(36) this was clearly stated as a source of failure on this root and, furthermore, when only one canal is located, radiographs of several angles with files in place, mesial and distal, should be taken to verify that only one centered canal is present. In addition, the distal root may have several variations and, in some more rare cases, a completely different variant is present, the so-called C-shape. This will be discussed in further detail in the next section.

One of the major reasons why researchers were content to believe that only one canal in the mesial root is a dominant feature of the mandibular second molar is that there is a high percentage of two canals which merge short of the apex in that root (Type II system). In that case, if only one of the two canals is found, generally the mesiolingual, but it is prepared and filled adequately, that root will have a decent chance for success. But in case the two canals are separate to the apex (Type III), then the chances of success are severely decreased.

The mandibular second molar has a few very unusual configurations, including a second canal in the distal root and, very rarely, a second distal root (Fig. 21). Viewing the preoperative radiographs of this tooth with magnification is mandatory because of the many variants that are possible.

Figure 21

The C-shaped configuration of the mandibular second molar (CMnd2M) was first reported by Cooke and Cox(37) in 1979, who stated that of the second molars treated in the late 1970 at the Dental School of Washington University (St. Louis), 8% were CMnd2Ms. This was quite a surprise because of 300 mandibular second molars investigated by Pineda and Kuttler in 1972(29), no CMnd2Ms were reported and no single-rooted teeth were seen. Similar results were reported by Vertucci(20). In succeeding years, other studies were reported noting the CMnd2Ms, with similar frequencies to the original Cooke-Cox report(38-41). There have been a few papers indicating the finding of a C-shape on other teeth beside the second molar(43,44).

The tooth is referred to as C-shaped because the canals present (usually three, but may be two or four, on occasion) have a continuous septum at the orifice area that may or may not extend to the apex. If cut in cross section, the septum is that of the letter “C.” Generally the closed area of the “C” is to the lingual, but it may be to the buccal. The canals are usually far from each other at the orifice, but merge near the site of exiting. In some cases only two of the three canals merge (Fig. 22).

Figure 22A Figure 22B Figure 22C

In 1981, Tamse and Kaffe reported on conical mandibular second molars in 10.9% of 508 teeth surveyed, demonstrating radiographs that did indicate some, but perhaps not all, as being CMnd2Ms (38). Melton et al.(39) studied only 15 mandibular second molars, but all were known to be C-shaped and made a number of interesting findings. In general, C-shaped teeth have one of two root configurations, a single root or two roots with an attached segment to allow for the septum to traverse from the mesial to the distal. They also found that not all of the “C” sections were continuous, but that some had interruptions. Also, not all of the canals merged at the apical portion, but instead one canal was separated from the others at the site of exiting.

The study involving the most teeth was reported by Weine and Members of the Arizona Endodontic Association(40). Three hundred ninety-nine second molars were evaluated retrospectively by radiographs and 412 were examined while they were being treated, including radiographs with files in place and postoperatively. It is of interest to note that fewer CMnd2Ms were recorded retrospectively (25/399, 6.2%) than prospectively (37/412, 8.9%). This probably occurred because the operators were looking for the specific variant in the prospective portion of the study.

It is obvious that this variant—the C-shape—has multiple shapes and configurations, easily the most complicated of any single tooth. For this reason, Weine et al.(40) suggested that larger sample sizes should be obtained and studied to clarify some of the situations noted and examine for more possibilities. They recommended that endodontic study clubs or other smaller organizations pool their

cases to gain larger number of teeth for study, just as the mandibular incisors were investigated by a small group.

The configuration offers some difficulty in filling because of the slit-like canal present, as opposed to the normally occurring oval or roundish canal. Several of the reports warned that the condition should be considered early in treatment, lest irreparable damage occurs in the narrow slits present (43,44). Manning wrote two papers on the variants in the C-shape and gave two interesting conclusions. He said that the slit portion of the C-shape should be filed and filled with great care to avoid perforation through the narrow walls. He further stated that studies of the Chinese and the Hong Kong Chinese had greater number of C-shaped roots than did Caucasians.

Studies of the Maxillary Bicuspids

The maxillary bicuspids have a number of potential configurations, but somehow do not present as much of a problem during treatment as do the MBRs, C-shaped molars, or bicanaled mandibular incisors. Perhaps it is because the teeth are easier to radiograph or that the patients are able to open widely enough to allow for better examination than with the maxillary molars. The first bicuspid often has only a single root, usually with Type II or III configurations, but rarely just a single canal. It may have two roots, each with a single canal. It also may have three separate and distinct roots, although rarely, which may be difficult to recognize and thus cause difficulties early in the treatment (Fig. 23). The three-rooted tooth resembles the common maxillary second molar which has three separate canals. Two types of this condition are seen, one where the buccal canals separate near the end of the crown with the other, more difficult type, having canals separating further toward the apex, similar to a Type IV system, making preparation and filling more complicated.

Figure 23

The maxillary second bicuspids also may have one or two roots, but with this tooth the two canaled combination may be slightly more common than in the first bicuspid. Type I, II, and III canal systems may be present in the tooth with a single root. However, this tooth may have two complex configurations—a Type IV canal system that has the position of division fairly deeply in the root (Fig. 24) and three separate and distinct canals. The latter is even more rare than in the first bicuspid (Table 8).

Table 8. Configuration of the Maxillary Second Bicuspids (1972-1976)


Teeth


Pineda and Kuttler29


98.9 0 1.2 0

Vertucci et al45

(1974)*100 Decalcified and

dyed48.0 27.0 17.0 6.0

*2 teeth had 3 canals

Figure 24A Figure 24B Figure 24C Figure 24D

Vertucci(20,45-47) has been the most prolific investigator of configuration in these teeth. He has also described combinations of canal systems that are more complex than the Type I, II ,III, IV description used in this review. Vertucci obtained his specimens from exodontists in the southeastern portion of the US and many were extracted to allow for replacement with dentures, rather than with restorative and/or pulpal problems. Even so, the specimens are quite beautiful and have interesting curvatures and anastomoses.

Table 9. Configuration of Mandibular Incisors (1965-1997)


Teeth


Rankine-Wilson and Henry10 (1965)

111 Radiographs, files in place

59.5 35.1 5.4


356 Radiographs, proximal view

98.3 0.5 1.2 0

Vertucci47 (1974) 100 centrals

Decalcified and dyed

92.0 5.0 3.0 0

100 laterals

93.0 5.0 2.0 0


277 Acrylic casts 63.9 25.9 2.2 7.9

Miyashita et al.48

(1997)1085 Decalcified and

dyed87.6 9.3 1.4 1.7

Studies of the Mandibular Incisors

Most dentists, and even many endodontists, do not realize that it was on these teeth that the first definitive study of canal configuration was performed. Many general dentists, similarly, do not appreciate the difficulty that these teeth offer during endodontic treatment, thinking that they are “merely small maxillary centrals.” Nothing could be further from the truth and can only lead to disaster. As stated earlier in this review, because these teeth are not treated endodontically very often, the complexities of the bi-canal possibilities coupled with the narrowness and depressions on the proximal surfaces are not considered during therapy (Table 9). Miyashita et al.(48), reported on the types of canal systems in these teeth as an introduction to their article on general aspects of mandibular incisors shape, canals, external appearance, and accessory canals, which is of considerable interest to anyone treating these complex teeth. Furthermore, the difficulty in taking useful angled radiographs to indicate the possibility of more than a Type I systems is very difficult to obtain because of the mesio-distal narrowness of the teeth and the ease with which they appear overlapped in angled views. The study by Rankine-Wilson and Henry emphasized the need for placing the access in the incisal edge to give best approach to the two canaled teeth (Fig. 25)(10). The mandibular incisors should always be treated with great care.

Figure 25

Studies of Teeth With Five or More Canals

Periodically, reports crop up in the endodontic literature demonstrating teeth with five, and sometimes even more, filled canals. Because these cases are in-vivo and the teeth were treated in the hope that they may remain in the mouth, no sectioning to verify individual canals is ever made. Demonstration of five and more canals in-vitro with file placement has been reported only very rarely.

In 1982, Weine published an article in which three canals were filled in the mesial root of a mandibular first molar(49). He stated that although it would appear that the mesial root had three definite canals, such was not the case. The tooth had been treated originally when the patient was only 10 years old and the canals obviously quite large. The preoperative radiographs appeared to show two (poorly) filled canals that had merged short of at the apex. After opening the tooth, he found that the two canals that had been filled were both in the mesiobuccal segment of the tooth. Opening the chamber floor further, a definite path to the mesiolingual was opened and enlarged. Both of the previously filled canals were prepared, as was the last-found mesiolingual and all three separate canals filled into a common site of exiting near the apex. He postulated that this did not constitute three separate canals in the mesial root, but rather a single, very wide canal that permitted preparation and filling in more than two sites. In 1997, DeGrood and Cunningham published a case report that demonstrated three canals filled in the mesial root that was identical(50). This was a Type II canal in the system used for this review. In 1989, Fabra-Campos also published a similar paper, except that one mesial canal had a separate exit but the other two had a common exit(51). This was a Type III canal. In 2004, Baugh and Wallace described the treatment of a mandibular first molar with two separate and distinct canals in the distal root and two separate mesial roots, one of which showed two canal fillings, merging short of the apex(52). Pomeranz et al. were early investigators on wide canals in the mesial roots of mandibular molars which were able to be filled as three canals(53). In a recent case report, Ferguson et al. described the filling of three canals in the MBR of a maxillary first molar for the first time(54). The postoperative angled radiograph shows only two sites of exit, one to the buccal and one to the lingual, clearly a Type III system. The patient was young—only 18 years old—and a photo of the access to the canals indicated the two orifices to the lingual much closer than the middle orifice to the buccal.

Most of the radiographs demonstrating five or more filled canals show four or less sites of exiting at the apex. This can be explained as a canal being quite wide or the pulp becoming necrotic when the patient was quite young and allowing for multiple sites of filling. These reports are interesting to read and we all should endeavor to treat any canal that can be located. However, these findings of an unusual number of canals (five or more), as compared with the total number of teeth treated, still remain an extremely small group.

Role of Ethnicity in Configuration Studies

Most of the studies listed in Table 1 through 9 have statistics derived from teeth accumulated from two ethnic groups. They are from the Europeans, largely Caucasians, and the African-Americans. Both of these groups have large populations in Europe, the Americas, and Australia, and, in the case of the African-Americans, Africa as well. However, this leaves out a very huge percentage of the world

population, particularly the Asians. In these days of multi-national companies and super-sonic travel, dentists and especially endodontists should be aware of the deviations from Tables 1 through 9 that might occur when a patient of an alternative ethnic group seeks treatment.

Walker(55-57), who was on the Dental Faculty in Hong Kong, and, therefore, had access to the Chinese population from the southern portion of China, wrote several illuminating articles, listing some of the differences that this group had as compared to other groups. In general these studies were on mandibular molars and bicuspids. Other studies of Asians were also reported (58,59). Weine et al.(25)

investigated the MBR of maxillary first molars of an exclusively Japanese sub-population and reported few differences from those with the European/African background.

It still would seem that studies of Asians, including Asian Indians, the people of the eastern former Russian republics, and Oceania, would be interesting and useful to anyone whose patients from those areas require endodontic treatment. Perhaps these groups will be studied in the future.

Effect of Preparation Methods on Configuration Studies

Tables 1 through 9 not only supply statistics on the numbers and configuration of the canals indicated, but they state the methods used in the investigations. The easiest, useful technique is the sectioning method. A high number of teeth may be investigated and evaluated relatively quickly. The technique may be by vertical or horizontal cutting and it may be used to grind away tooth structure (11) or cut through it horizontally(16). In the latter case with various levels of cutting, for example every 1 millimeter, there is the allowance for repositioning the segments to demonstrate the variance at any level. The disadvantage for the grinding method, as stated earlier, is that it is possible to grind through too far, removing the most, or even the entire canal, or grind too little. In either error, the critical midcanal area is lost for demonstration.

Another popular method has a clinical orientation, using radiographs with files in place to demonstrate the relationship of the files in any canal, in vitro. The extracted tooth may be rotated in several planes to disclose positions not always available in vivo. This method was used in the Rankine-Wilson and Henry study(10) and works well when study clubs combine results for large numbers of teeth. The possible disadvantage is that the files have stiffness and, if traversing a very curved canal, will tend to take a central path rather than detail the true curvatures. The injection methods demonstrate this condition very well. Another radiographic technique combines the use of x-rays and sectioning of roots to allow for views from the proximal without the placement of files. Other than the palatal root of the maxillary first molar, all of the other roots in the mouth are either wider bucco-lingually or roundish. By taking radiographs of sectioned roots from the proximal, the wider dimension, the more significant view is obtained and there is no overlap of adjacent roots. This method was used by Pineda and Kuttler (29) to survey a very large number—7,275—of teeth. Many teeth may be examined in a relatively short period of time, but the assessment of the interior of the teeth—where the canals are—may not be accurate.

A very frequent, but time-consuming technique, is the decalcifying and dyeing method, which probably gives the best results for student use and for long-range retention of the specimens. The contrasts seen in the preserved roots show examples of the unusual relationship of the curving canals, not seen in either the grinding or files-in-place methods. Vertucci(20, 45-47), who studied most of the teeth in the arches, including anteriors, used this method and because of the many anastomoses picked up by the dyes, applied a different and more complicated configuration coding. Hess’ studies used a vulcanite impression technique, which differs from the decalcifying-dyeing method, but his results look very similar(8) to Vertucci’s.

The major problem for the articles by Vertucci is that because many of the patients supplying the teeth were young and had extractions for prosthetic rather than pulpal/periapical disease, the canals were relatively wide. This is not typical of the types of cases seen in most endodontic practices because of the absence of reparative dentin that occurs in response to decay and/or restorations. The canals in his specimens show many exotic curvatures. Several other reports using the dyeing mechanism also are replete with multiple lateral canals and curvatures. These are rarely demonstrated following treatment of patients, especially of middle-aged or older, using any of the popular canal filling techniques.

In vivo clinical cases may be correlated, although they may yield fewer complicated canal arrangements due to the difficulty in locating all of the canals. Recent use of the surgical operating microscope (26) has improved the results for this method and probably will be the basis for studies of the future.

Future for Canal Configuration Studies

In the 1970s, when canal configuration studies reached their zenith, every tooth in the dental arches was investigated. Except for the maxillary incisors and cuspid, unexpected and unusual results were obtained in every instance. Anyone attempting a study of depth really hopes to uncover new material or refutation of a previously accepted condition. However, after the publication of the findings in the MBRs of the maxillary molars, the mandibular molars, and the bicuspids, repeated studies have been uneventful.

It is possible that future studies, particularly those performed in vivo with the aid of magnification, may produce results that increase the frequency of the variants from the most typical Type I configuration. Studies of other population groups and use of other fixatives may be fruitful. However, the vast differences from the expected types probably will not occur as they did in the 1970s, truly the hey-day for canal configuration studies.

3. Endodontics of the FutureNewer Types of Canal Filling Materials

The most challenging aspect of endodontics for the immediate future is the canal filling material to be utilized. This subject has taken up a huge amount of space in the endodontic journals of the past few years and shows no signs of subsiding.

Gutta-percha, the trans isomer of polyisoprene, has dominated the canal filling scene for well over 100 years and the results obtained, in combination with exacting canal preparation efforts, have been quite positive. Gutta-percha itself has been around for a long time. It was used in the 18 th century as a component of golf balls and was used for many years in the manufacture of chewing gum. The cis isomer has been used in many rubber products, such as tires, rubber gloves, and other similar products. It has many desirable qualities as a canal filling material, including nonsupport of bacteria and substrate, compactibility into the canal, and has been used in several different forms in endodontics. These include packing of room-temperature gutta-percha, insertion of warmed injection-molded gutta-percha, and filling in conjunction with such solvents as chloroform, eucalyptol, and xylene. Its few disadvantages are its lack of rigidity to be placed deeply into curved canals and lack of length control(60).

Another mild problem is that gutta-percha for use in endodontics is naturally occurring, coming from the sap of the Indian rubber tree and, for many years, was taken from trees in the Malaysian peninsula. Because the use of rubber products has been more significant than the uses of gutta-percha, the preponderance of the yields has been away from the dental use. For the last 10 years, or so, the product has been taken from trees in the western region of Brazil where the temperatures and humidity are similar to those in Malaysia.

Despite the excellent results that it has delivered for many years in many, many cases, periodically there have been efforts to replace it with other materials. In l941 Jasper introduced silver wires or points(61). This material could be placed into canals with curvatures and had good length control, the two deficiencies associated with gutta-percha. However, there were also some problems. If the point was overextended and entered the periapical tissue, the extended portion could become corroded because of the silver content. Perhaps even more importantly, the ease of insertion led many dentists to minimize the critical factor in gaining endodontic success by failing to clean the canal properly, leaving behind bacteria and substrates. Also, the silver wires were strongly radiopaque and would give the illusion on the post-operative radiograph of a density that was deceivingly good. After a brief period of expanded use, silver points gradually went out of favor and gutta-percha was back in vogue.

Now efforts to replace gutta-percha are gaining advocates and a new product has reached the market recently as a replacement. Called Resilon, it is a synthetic, semi-crystalline aliphatic polyester named polycaprolactone which has been approved by the FDA for use in several areas of medicine and dentistry. Because it is synthetic, the material may be produced in the laboratory in accordance with the determined volume needed rather than in far away areas which require specialized delivery systems to the manufacturer.

The initial studies were published by Trope and his colleagues at the University of North Carolina (62,63). These studies usually included a specific sealer, Epiphany Primer (Pentron Clinical Technologies) and the combination of the two were reportedly responsible for a stronger root structure after canal filling. In an in vitro study, Torabinejad, et al.(64) reported 50 percent penetration along the entire canal 30 days after filling using gutta-percha and a sealer other than Epiphany. In their articles, Shipper and Trope(64,65)

seem to suggest that following canal filling with presently accepted procedures, bacteria are able to infiltrate the root and potentially may be responsible for treatment failure. Ray and Trope (66) have suggested that the quality of the restoration following endodontic treatment may have more to do with treatment success than the canal filling procedure. They further recommended that resins be used for better sealing of the canal.

These statements have been accepted by a significant number of endodontists. I have particular problems with much of the data. First of all, Trope has a financial interest in Resilon and although he has been a highly recognized researcher for many years, his results are subject to question. A spate of papers and programs endorsed the Resilon material, several suggesting the use of other resin products, including resin posts for the restoration. Then Tay, originally from the University of Hong Kong, and his cohorts, at the Medical College of Georgia and the group that he developed there, undertook a number of studies( 67-70) that cast considerable doubt about the efficacy of the materials. The group in Georgia included David Pashley, who has authored or co-authored a slew of excellent papers investigating endodontic interests, including initial studies on the smear layer and the effectiveness of apical seal. For the most part, these articles did not agree with the Trope studies. The assertion concerning the claim of increased root strength has been essentially discarded.

Obviously the jury is still out on the subject of whether or not Resilon/Epiphany will replace gutta-percha as the dominant filling material used. However, it appears that the ice-jam of reliance on the old favorite probably has been broken and other synthetic materials will be investigated very soon. In my opinion, these newer and, perhaps, better substitutes will require intensive investigation before gutta-percha use is discontinued. Furthermore, it is hoped that the newer materials, yet unknown, will be reported upon by investigators without financial interest to eliminate any chance of personal bias.

Use of Single-Appointment Treatment

Another subject that should be investigated is the proper place of one-sitting treatment. Such therapy is far from recent, with an article on the subject by Kells published in Dental Cosmos in 1887(71). Certainly the practice is very frequent among a number of dentists and it is my contention that it occurs very close to 50 per cent of the time, thus with virtually an even distribution as compared to multiple-appointment therapy. There can be no question that there are times when any practitioner leans heavily toward single-visit treatment, as when a patient suffers a clean horizontal break of a maxillary anterior tooth with minimal exposure of the pulp and no history of pain prior to the incident. By the same token, treating a tooth endodontically in a single visit when the tooth has been left open for a long period without having more than minimal canal preparation would seem to be asking for a serious exacerbation, if attempted. Even prescribing strong antibiotics probably would not offer sufficient coverage to prevent an undesirable response. The greater problem here is that endodontists have found that limiting cases to one appointment can be very remunerative, even if they decrease the total fee for the service, which few have done. Because the tooth need not be opened and then subsequently reopened to complete, the total office time is significantly decreased(72).

What is needed is a wide-ranging study of a large number of patients with efforts made to clarify the problems of single-visit treatment. Also, a clear definition of single-visit treatment must be made. Some dentists have patients in for a preliminary visit but, except for those in pain, only radiographs and an evaluation of the patient’s problem take place. The patient then is rescheduled for a future time when the tooth can be completely treated. Thus, it may take two scheduled appointments to treat a single tooth.

I know that in my own experience it is rare that I can locate and prepare the fourth canal in a maxillary molar, if present, in a reasonable appointment time (1 ½ hour or less). Merely attempting to locate it, even with magnification, may take 30 minutes or more. Mandibular first bicuspids with two canals may also be time consuming. It is my opinion that extending the appointment time (to 3 hours, for example) is counterproductive as patients do not like the very long time of keeping their mouths open with the rubber dam in place.

Even though I rarely finish a tooth in one appointment, I readily agree that there are some cases, perhaps many, when the tooth may be treated safely in a single visit. Most older studies on the subject have endorsed single-visit treatment(73-75), but most of them were reported by dentists who prefer that

method of treatment. Many older articles discussing the subject from both sides of the controversy have been poorly designed and only were listing of cases that enforced the author’s position. A more recent report by Holland et al. (76) was carefully planned, but healing in dog’s teeth is much superior to that in humans.

Recently, there have been several interesting reports dealing with this situation. Many have implicated failure to successfully remove microorganisms as more responsible for healing failure than the number of appointments utilized. Trope et al. (77) studied the results of 556 cases that exhibited periapical lesions prior to treatment. The teeth were divided into 3 groups, one group treated in a single visit, a second treated in two visits, and the third treated in two appointments with calcium hydroxide placed in the canal for at least one week. After one year, evaluated by culture samples, the calcium hydroxide-treated cases were judged to be successful in 74 per cent of those teeth whereas the one-visit cases were successful in 64 per cent. The group treated in two appointments without calcium hydroxide had the poorest results. However, the authors stated that due to the differing teeth treated, no statistical analysis could be offered. However, the total percentages of success were much lower than reported in many other reports.

Saleh et al. (78) prepared canals, verified sterility, and then placed a suspension of Entoerococcus faecalis prior to canal filling at that appointment. Those teeth using sealers with strong antibacterial properties gave the best results. However, the authors warned that sealers high in antibacterial contents may be cytogenic or even mutagenic. AH Plus and Grossman’s sealer were considered the most reliable for antibacterial action with safety. Insertion of calcium hydroxide decreased the number of bacteria in the canals, but did not kill all the bacteria in the tubules.

Nair et al.(79), in an impressive study with beautiful color sections, evaluated treatment of 16 MBRs of maxillary first molars (a low number) with two canals and periapical disease in vivo. Immediately following the single-appointment therapy, the treated roots were surgically removed and evaluated microscopically. Multiple areas of canals revealed complex configurations with sites uninstrumented and many microbes. The authors speculated that treatment of this type of root in a single appointment with impressive decrease of bacteria is highly questionable. They quoted a study by Bystom and Sundqvist in 1981 that reported considerable debris, and microbes were noted in treated MBRs after five appointments. The conclusion by Nair was that the development of a bacteria-free MBR with presently used techniques is doubtful, particularly if using a single-treatment technique.

Waltimo et al. (80) reported in 2005 on an extension of the Saleh study (78) with several coauthors of the previous work. The study divided 50 teeth with chronic apical periodontitis into 3 groups. One group had one-visit treatment, the second had calcium hydroxide used as a medication for one week and the tooth treated in two appointments, and the third leaving the canal empty but sealed for one week. Only minor differences were found in the groups after one year, but the teeth where sodium hypochlorite was used as irrigant rather than calcium hydroxide being placed showed much better results. Calcium hydroxide has been recommended as intracanal medicament for the last 10 years, but this study had a different finding.

A widely informative study, with clear delineations and a proper cross section with ample post-operative follow-up evaluations, could be extremely valuable to every dentist who performs endodontic treatment and will allow the decision-making to be based on suitable criteria (81).

Conclusions

Endodontic therapy has reached a very high level of knowledge and usage in the past 10 years, even though the number of teeth requiring the treatment has probably decreased. The new instruments make treatment easier and the increased knowledge concerning the number and direction of the canals in each tooth is more apparent by recent studies and better radiology. It is very likely that newer replacements for gutta-percha involving synthetic materials is just over the horizon. Very few areas of dental treatment have had as much progress in evaluation and treatment in the last few years than has endodontics. I hope that this will continue for the near future, as well.

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LegendsFigure 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.

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