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The C-shaped mandibular second molar: Incidence and other considerations
0099-2399/98/2405-0372503.00/0 JOURNALOF ENDODONTICS Copyright © 1998 by The American Association of Endodontists
Printed in U.S.A. VoL. 24, No. 5, MAY 1998
The C-Shaped Mandibular Second Molar: Incidence and Other Considerations Franklin S. Weine, DDS, MSD, and Members of the Arizona Endodontic Association
Although its most common configuration is two roots and three canals, the mandibular second molar may have many different combinations. Cooke and Cox were the first to describe a single-rooted mandibular second molar with a continuous slit connecting some or all of the canals. If sectioned horizontally through the main portion of the root, this slit had the shape of the letter "C." Other papers were written and lectures were presented on this and similar entities, but its frequency and significance have remained the object of speculation because large numbers of these teeth have not been categorized. By combining the efforts of an endodontic study club, 811 endodontically treated mandibular second molars were evaluated. Sixtytwo of these (7.6%) were identified as C-shapes. Other aspects of this configuration were also investigated.
was "closed" to the lingual. Subsequently, when this condition was described in clinical lectures, the speakers usually described the canal as being closed to the lingual (4). Several other papers were written in an attempt to quantify the frequency of occurrence of this condition among Mnd2M's (5, 6). Also, the presence of the C-shape was reported in teeth other than Mnd2M's, although as a very rare occurrence (7, 8). Cooke and Cox (3) claimed that 8% of the Mnd2M treated endodontically at Washington University School of Dentistry in the late 1970's had the C-shape, although no total sample size was indicated. Tamse and Kaffe (5), in 1981, investigated the incidence of conical Mnd2M, as opposed to those with two separate roots, using a radiographic study. They reported that 9% of 1049 Mnd2M's were conical, but did not comment on the possibility of the C-shape. In 1972, Pineda and Kuttler (9) investigated 7275 roots radiographically, including 300 Mnd2M's, but reported no C-shapes and, in fact, no single-rooted Mnd2M's. In a very exhaustive dye-injection study of all the human permanent teeth, including 100 Mnd2M's, Vertucci (10) (in 1984) failed to describe even one C-shape among 2400 extracted teeth studied. However, Weine et al. (6) examined 75 extracted Mnd2M's in 1988 by placing files into endodontic accesses and reported that two teeth (2.7%) had a C-shape. Melton et al, (1 l) reported on the internal anatomy of the C-shape by sectioning extracted teeth. They stated that three types of internal configurations were noted and that some roots were fused on the buccal portion, but others were fused on the lingual.
Of all the teeth in the human dentition, the mandibular second molar (Mnd2M) has the widest variation of canal configuration (1). The most common finding is two separate roots, with two canals in the mesial root and one canal in the distal (2), but many other combinations are possible. The existence of single-rooted Mnd2M with a continuous slit connecting two, three, or four canals was first described in the dental literature by Cooke and Cox (3) in 1979, although several clinicians had suggested its presence in lectures earlier. This original paper was in the form of three case reports of clinical treatment, including an endodontic failure that was extracted, apically filled with amalgam, and then intentionally replanted. During the extraoral period of that procedure, photographs were taken that confirmed the continuum and indicated that if horizontal sections were taken through the root area, the slit had the shape of the letter "C." The authors further observed that this C-shape consisted of a slit that went from the mesiolingual canal to the mesiobuccal canal, continuing around the buccal to the distal canal or canals. When the tooth was examined, there was a total fusion of the buccal portion of both the mesial and distal roots, so that the "C" form of the canal
M A T E R I A L S AND M E T H O D S One of the major problems in developing statistics on an infrequent variant in a canal configuration study is the difficulty in getting sufficient data to yield meaningful percentages. When using extracted teeth, another potential problem is the difficulty in knowing exactly which tooth is being examined. For instance, if a mandibular molar is examined, the classification is usually based on the number of cusps, so that a tooth with five cusps is considered to be a first molar, whereas a tooth with four cusps is classified as a second molar. This is not always correct. Also, some teeth in the present study had unusual root shapes that might have been classified as third molars had they not still been in the mouth. 372
Vol. 24, No. 5, May 1998
C-Shaped Molars
373
TABLE 1. Percentages of C-shaped Mnd2M's and directions of closure of the continuous slit Closed to:
Total Teeth
C-shapes (%) Lingual
Buccal
Unknown
399 412
25 (6.2) 37 (8.9)
11 26
5 11
9 0
811
62 (7.6)
37
16
9
Retrospective study Prospective study Total
To observe a large number of treated Mnd2M's and to know that all were positively Mnd2M's, the members of the Arizona Endodontic Association and the senior author (hereafter referred to as "the group") pooled their clinical cases over an --1-yr period. The participants were asked to make a retrospective investigation of the last 50 Mnd2M's treated in their offices to determine how many Mnd2M's were treated in that period and how many had a C-shape, as determined by the access view of a continuum between the canals. If possible, those in the group were asked to identify how many of the treated teeth had the slit closed to the buccal and how many were closed to the lingual. Then the participants were asked to prospectively gather the same statistics for the Mnd2M's that they would treat in the next 6 months. For these cases, the closure position could be identified quite accurately.
RESULTS The results of the retrospective and prospective portions of the study are available in Table 1. In the first stage of data development (retrospective), the group reported treating 399 Mnd2M's, of which 25 were C-shaped (6.2%). In the second stage (6 months after the instructions for the prospective study), 412 Mnd2M's were treated, of which 37 were C-shaped (8.9%). Combining the two time periods, 811 Mnd2M's were treated, of which 62 were C-shaped (7.6%). When compiling data for the first stage, not all of the contributors had noticed the closed segment of the " C " - - t o buccal or to lingual. Therefore, for this time period, the group reported 11 teeth with closure to the lingual, 5 with closure to the buccal, and 9 as unknown. For the second stage, the site of closure was always reported, with 26 teeth having closure to the lingual and 11 with closure to the buccal. Results were not submitted to statistical analysis. Radiographs of interesting cases were often included with the numerical reports. Most were the two common types of C-shapes already reported (Figs. 1 and 2). However, several of these films indicated configurations not previously reported as C-shapes, and some of these are seen in Figs. 2 through 4.
DISCUSSION To gain a large pool of endodontically treated Mnd2M's, the members of the Arizona Endodontic Association and Dr. Franklin Weine participated in a cooperative venture. The total sample pool of 811 Mnd2M's is extremely large, and the results obtained, therefore, should be meaningful. It is quite unlikely that such a number pool could be reached for clinical cases without involving a endodontic study club or state society.
FIG 1. Most common C-shape configuration has 2 or 3 canals merging toward a single site of exiting. However, differences may occur in the relationship of the canals to each other. In (A), the tooth seems to be quite wide mesiodistally. The canals are far from each other at their orifices, but curve toward each other to merge near the apex. In (B), the tooth seems to be narrower mesiodistally than in (It), the orifices are much closer, and the curving to merge near the apex is more gradual.
The teeth treated by the Arizona Endodontic Association were from a wide ethnic background. Many of the retirees living in Arizona are from families who had emigrated from eastern or central Europe; a Hispanic influence is still present in the area. Both African-Americans and Asians (Asians working for multinational companies, as well as Asian-Americans comprised this group) are also represented in the population of the state.
374
Weine et al.
FIG 2. Another common condition is the presence of 2 or 3 canals curving toward each other, but not merging, tn (A), the two mesial canals merge, but the distal canal is separate. In (B), the mesial and distal canals are wide slits buccolingually, curve towards each other, but do not merge.
Because of the education and clinical backgrounds of the members of the group, the statistics derived from the pool of treated teeth should have a high degree of reliability. However, it is interesting to note that when retrospective data were collected, only 25 C-shapes were reported among - 4 0 0 Mnd2M's (6.2%). When the group was made more aware of the existence of the C-shape in the second reporting period, with almost the same total Mnd2M's treated, 37 C-shapes were counted (8.9%). There are many other clinical situations that could be investigated by endodontic study clubs and state societies, where a large number of cases could be tabulated and reported upon with cooperative efforts. The senior author of this study respectfully suggests that these organizations consider such investigations as a part of their functions of disseminating worthwhile and dependable information to their fellow dentists. One might question the need to calculate the incidence of this variant. In the discussion section of the papers by both Cooke and Cox and by Melton et al., the authors made it clear that the clinical treatment of a C-shaped tooth is much more difficult than for the more routine Mnd2M. Unless the condition is considered before
Journal of Endodontics
FtG 3. More unusual C-shapes not already reported. (,4)Three canals with separate and distinct apices. The wide, knobby single-root tip seems to confirm that the tooth is a C-shape. (/3) Three separate, curved canals, also with a wide, knobby single-root tip.
the initiation of treatment or recognized very early in therapy, irreparable damage may result that puts the tooth in severe jeopardy. The orifice portions of the slit must be widened considerably early in treatment, but not too deeply toward the apex lest a perforation occur. Because of the large area of canal space, it is doubtful that intracanal instruments can reach and debride the entire portion of the continuum, making irrigation procedures more significant. The obturation of the final preparation must be given considerable thought as well, with deep penetration of condensation instruments in several sites necessary if cold condensation is performed. Otherwise, some type of thermoplastic sealing (12) might be appropriate. All dentists, both generalists and specialists, should be aware that fully one-twelfth of all treated Mnd2M's will be C-shaped. Because of the potential difficulty that they present, the clinician should always anticipate the possibility and take proper precautions if the condition is verified. This study further substantiates that the "C" may be in either of the two buccolingual directions. In one condition, the buccal portion of the mesial and distal roots are fused, the slit goes through
Vol. 24, No. 5, May 1998
C-Shaped Molars
375
FIG 5. Buccal view of the floor of the chamber in a C-shape. The photo was taken after access preparation, but before the placement of the rubber dam. The buccal (B) portion of the tooth is to the left, lingual (L) to the right, distal (D) to the top, and mesial (M) to the bottom. The slit starts at the mesiolingual, goes to the mesiobuccal, continues to the distobuccal, and stops at the distolingual. Thus, this canal is "closed" to the lingual, the more common condition as indicated by our study. Attempts were made to photograph Cshapes with closure to the buccal, but focusing was difficult and the kodachromes did not print well. Dr. Weine thanks the members of the Arizona Endodontic Association, and their president, Dr. Robert S. Roda, for their cooperation in providing most of the cases used in this study. Members of the Arizona Endodontic Association who participated in this study included: Drs. James C. Aten, James P. Deemer, David B. Foley, Bradley H. Gettleman, John W. Gillan, James F. Kramer, Robert A. Lees II, Scott Morrison, Robert S. Roda, and Charles L. Siroky. FIG 4. Another configuration in which a single canal is present on the mesial and two canals merge to the distal. (A) The clinician did not anticipate the mesial portion originally; but, after filling the distal canals, a file was placed into the mesial area, which seems to be separate and distinct. (B) After filling the mesial portion.
Dr. Weine is Professor Emeritus, Loyola University, Chicago, IL. Members of the Arizona Endodontic Association are affiliated with the American Association of Endodontists, Chicago, IL. Address requests for reprints to Dr. Franklin S. Weine, 20737 Alexander, Olympia Fields, IL 60461.
References the area of fusion, and so the "C" is closed to the lingual (Fig. 5). In the mirror image situation, the lingual portion of the roots are fused, and the "C" is closed to the buccal. Several newer configurations are demonstrated in this study, indicating that the operator should not assume a fixed spatial relationship if a C-shape is identified, but rather be aware of other possibilities. Based on the results of this study, the following conclusions are presented: 1. The C-shaped Mnd2M, probably requiring a different regimen of treatment than the more frequent two-rooted, threecanaled version, occurs in --8% of these teeth. 2. There are several variants of the C-shaped tooth, although the most common has two or three canals merging toward a single site of exiting. 3. The connecting slit that gives the tooth its name of "Cshaped" may have closure to the buccal or to the lingual. 4. Pooling of treatment modalities by endodontic study clubs or state societies is a logical means for obtaining a large sample size for clinically oriented research.
1. Weine FS. Endodontic therapy on the mandibular second molar: easiest to treat of the difficult, molar teeth. Comp Contin Educ Dent 1994;15:113040. 2. Ingle JI, Beveridge EE. Endodontics. 2nd ed. Philadelphia: Lea & Febiger, 1976:160-1. 3. Cooke HG, Cox FL. C-shaped canal configurations in mandibular molars. J Am Dent Assoc 1979;99:836-9. 4. Weine FS. Endodontic therapy. 5th ed. St. Louis: CV Mosby, 1996:289, 294 - 6. 5. Tamse A, Kaffe I. Radiographic survey of the prevalence of conical lower second molar. Int Endod J 1981;14:188-90. 6. Weine FS, Pasiewicz RA, Rice RT. Canal configuration of the mandibular second molar using a clinically oriented in vitro method. J Endodon 1988;14:207-13. 7. Rice RT, Gilbert BO. An unusual canal configuration in a mandibular first molar. J Endodon 1987;13:513-5. 8. Bolger WL, Schindler WG. A mandibular first molar with a C-shaped root configuration. J Endodon 1988;14:515-9. 9. Pineda F, Kuttler Y. Mesiodistal and buccolingual roentgenographic investigation of 7,275 root canals. Oral Surg Oral Med Oral Pathol 1972;33: 101-10. 10. Vertucci FJ. Root canal anatomy of the human permanent teeth. Oral Surg Oral Med Oral Pathol 1984;58:589-99. 11. Melton DC, Krell KV, Fuller MW. Anatomical and histological features of C-shaped canals in mandibular second molars. J Endodon t991;17:384-8. 12. Weine FS. A preview of the canal-filling techniques of the 21 st century. Compend Contin Educ Dent 1992;13:688-98.
Printed in U.S.A. VoL. 24, No. 5, MAY 1998
The C-Shaped Mandibular Second Molar: Incidence and Other Considerations Franklin S. Weine, DDS, MSD, and Members of the Arizona Endodontic Association
Although its most common configuration is two roots and three canals, the mandibular second molar may have many different combinations. Cooke and Cox were the first to describe a single-rooted mandibular second molar with a continuous slit connecting some or all of the canals. If sectioned horizontally through the main portion of the root, this slit had the shape of the letter "C." Other papers were written and lectures were presented on this and similar entities, but its frequency and significance have remained the object of speculation because large numbers of these teeth have not been categorized. By combining the efforts of an endodontic study club, 811 endodontically treated mandibular second molars were evaluated. Sixtytwo of these (7.6%) were identified as C-shapes. Other aspects of this configuration were also investigated.
was "closed" to the lingual. Subsequently, when this condition was described in clinical lectures, the speakers usually described the canal as being closed to the lingual (4). Several other papers were written in an attempt to quantify the frequency of occurrence of this condition among Mnd2M's (5, 6). Also, the presence of the C-shape was reported in teeth other than Mnd2M's, although as a very rare occurrence (7, 8). Cooke and Cox (3) claimed that 8% of the Mnd2M treated endodontically at Washington University School of Dentistry in the late 1970's had the C-shape, although no total sample size was indicated. Tamse and Kaffe (5), in 1981, investigated the incidence of conical Mnd2M, as opposed to those with two separate roots, using a radiographic study. They reported that 9% of 1049 Mnd2M's were conical, but did not comment on the possibility of the C-shape. In 1972, Pineda and Kuttler (9) investigated 7275 roots radiographically, including 300 Mnd2M's, but reported no C-shapes and, in fact, no single-rooted Mnd2M's. In a very exhaustive dye-injection study of all the human permanent teeth, including 100 Mnd2M's, Vertucci (10) (in 1984) failed to describe even one C-shape among 2400 extracted teeth studied. However, Weine et al. (6) examined 75 extracted Mnd2M's in 1988 by placing files into endodontic accesses and reported that two teeth (2.7%) had a C-shape. Melton et al, (1 l) reported on the internal anatomy of the C-shape by sectioning extracted teeth. They stated that three types of internal configurations were noted and that some roots were fused on the buccal portion, but others were fused on the lingual.
Of all the teeth in the human dentition, the mandibular second molar (Mnd2M) has the widest variation of canal configuration (1). The most common finding is two separate roots, with two canals in the mesial root and one canal in the distal (2), but many other combinations are possible. The existence of single-rooted Mnd2M with a continuous slit connecting two, three, or four canals was first described in the dental literature by Cooke and Cox (3) in 1979, although several clinicians had suggested its presence in lectures earlier. This original paper was in the form of three case reports of clinical treatment, including an endodontic failure that was extracted, apically filled with amalgam, and then intentionally replanted. During the extraoral period of that procedure, photographs were taken that confirmed the continuum and indicated that if horizontal sections were taken through the root area, the slit had the shape of the letter "C." The authors further observed that this C-shape consisted of a slit that went from the mesiolingual canal to the mesiobuccal canal, continuing around the buccal to the distal canal or canals. When the tooth was examined, there was a total fusion of the buccal portion of both the mesial and distal roots, so that the "C" form of the canal
M A T E R I A L S AND M E T H O D S One of the major problems in developing statistics on an infrequent variant in a canal configuration study is the difficulty in getting sufficient data to yield meaningful percentages. When using extracted teeth, another potential problem is the difficulty in knowing exactly which tooth is being examined. For instance, if a mandibular molar is examined, the classification is usually based on the number of cusps, so that a tooth with five cusps is considered to be a first molar, whereas a tooth with four cusps is classified as a second molar. This is not always correct. Also, some teeth in the present study had unusual root shapes that might have been classified as third molars had they not still been in the mouth. 372
Vol. 24, No. 5, May 1998
C-Shaped Molars
373
TABLE 1. Percentages of C-shaped Mnd2M's and directions of closure of the continuous slit Closed to:
Total Teeth
C-shapes (%) Lingual
Buccal
Unknown
399 412
25 (6.2) 37 (8.9)
11 26
5 11
9 0
811
62 (7.6)
37
16
9
Retrospective study Prospective study Total
To observe a large number of treated Mnd2M's and to know that all were positively Mnd2M's, the members of the Arizona Endodontic Association and the senior author (hereafter referred to as "the group") pooled their clinical cases over an --1-yr period. The participants were asked to make a retrospective investigation of the last 50 Mnd2M's treated in their offices to determine how many Mnd2M's were treated in that period and how many had a C-shape, as determined by the access view of a continuum between the canals. If possible, those in the group were asked to identify how many of the treated teeth had the slit closed to the buccal and how many were closed to the lingual. Then the participants were asked to prospectively gather the same statistics for the Mnd2M's that they would treat in the next 6 months. For these cases, the closure position could be identified quite accurately.
RESULTS The results of the retrospective and prospective portions of the study are available in Table 1. In the first stage of data development (retrospective), the group reported treating 399 Mnd2M's, of which 25 were C-shaped (6.2%). In the second stage (6 months after the instructions for the prospective study), 412 Mnd2M's were treated, of which 37 were C-shaped (8.9%). Combining the two time periods, 811 Mnd2M's were treated, of which 62 were C-shaped (7.6%). When compiling data for the first stage, not all of the contributors had noticed the closed segment of the " C " - - t o buccal or to lingual. Therefore, for this time period, the group reported 11 teeth with closure to the lingual, 5 with closure to the buccal, and 9 as unknown. For the second stage, the site of closure was always reported, with 26 teeth having closure to the lingual and 11 with closure to the buccal. Results were not submitted to statistical analysis. Radiographs of interesting cases were often included with the numerical reports. Most were the two common types of C-shapes already reported (Figs. 1 and 2). However, several of these films indicated configurations not previously reported as C-shapes, and some of these are seen in Figs. 2 through 4.
DISCUSSION To gain a large pool of endodontically treated Mnd2M's, the members of the Arizona Endodontic Association and Dr. Franklin Weine participated in a cooperative venture. The total sample pool of 811 Mnd2M's is extremely large, and the results obtained, therefore, should be meaningful. It is quite unlikely that such a number pool could be reached for clinical cases without involving a endodontic study club or state society.
FIG 1. Most common C-shape configuration has 2 or 3 canals merging toward a single site of exiting. However, differences may occur in the relationship of the canals to each other. In (A), the tooth seems to be quite wide mesiodistally. The canals are far from each other at their orifices, but curve toward each other to merge near the apex. In (B), the tooth seems to be narrower mesiodistally than in (It), the orifices are much closer, and the curving to merge near the apex is more gradual.
The teeth treated by the Arizona Endodontic Association were from a wide ethnic background. Many of the retirees living in Arizona are from families who had emigrated from eastern or central Europe; a Hispanic influence is still present in the area. Both African-Americans and Asians (Asians working for multinational companies, as well as Asian-Americans comprised this group) are also represented in the population of the state.
374
Weine et al.
FIG 2. Another common condition is the presence of 2 or 3 canals curving toward each other, but not merging, tn (A), the two mesial canals merge, but the distal canal is separate. In (B), the mesial and distal canals are wide slits buccolingually, curve towards each other, but do not merge.
Because of the education and clinical backgrounds of the members of the group, the statistics derived from the pool of treated teeth should have a high degree of reliability. However, it is interesting to note that when retrospective data were collected, only 25 C-shapes were reported among - 4 0 0 Mnd2M's (6.2%). When the group was made more aware of the existence of the C-shape in the second reporting period, with almost the same total Mnd2M's treated, 37 C-shapes were counted (8.9%). There are many other clinical situations that could be investigated by endodontic study clubs and state societies, where a large number of cases could be tabulated and reported upon with cooperative efforts. The senior author of this study respectfully suggests that these organizations consider such investigations as a part of their functions of disseminating worthwhile and dependable information to their fellow dentists. One might question the need to calculate the incidence of this variant. In the discussion section of the papers by both Cooke and Cox and by Melton et al., the authors made it clear that the clinical treatment of a C-shaped tooth is much more difficult than for the more routine Mnd2M. Unless the condition is considered before
Journal of Endodontics
FtG 3. More unusual C-shapes not already reported. (,4)Three canals with separate and distinct apices. The wide, knobby single-root tip seems to confirm that the tooth is a C-shape. (/3) Three separate, curved canals, also with a wide, knobby single-root tip.
the initiation of treatment or recognized very early in therapy, irreparable damage may result that puts the tooth in severe jeopardy. The orifice portions of the slit must be widened considerably early in treatment, but not too deeply toward the apex lest a perforation occur. Because of the large area of canal space, it is doubtful that intracanal instruments can reach and debride the entire portion of the continuum, making irrigation procedures more significant. The obturation of the final preparation must be given considerable thought as well, with deep penetration of condensation instruments in several sites necessary if cold condensation is performed. Otherwise, some type of thermoplastic sealing (12) might be appropriate. All dentists, both generalists and specialists, should be aware that fully one-twelfth of all treated Mnd2M's will be C-shaped. Because of the potential difficulty that they present, the clinician should always anticipate the possibility and take proper precautions if the condition is verified. This study further substantiates that the "C" may be in either of the two buccolingual directions. In one condition, the buccal portion of the mesial and distal roots are fused, the slit goes through
Vol. 24, No. 5, May 1998
C-Shaped Molars
375
FIG 5. Buccal view of the floor of the chamber in a C-shape. The photo was taken after access preparation, but before the placement of the rubber dam. The buccal (B) portion of the tooth is to the left, lingual (L) to the right, distal (D) to the top, and mesial (M) to the bottom. The slit starts at the mesiolingual, goes to the mesiobuccal, continues to the distobuccal, and stops at the distolingual. Thus, this canal is "closed" to the lingual, the more common condition as indicated by our study. Attempts were made to photograph Cshapes with closure to the buccal, but focusing was difficult and the kodachromes did not print well. Dr. Weine thanks the members of the Arizona Endodontic Association, and their president, Dr. Robert S. Roda, for their cooperation in providing most of the cases used in this study. Members of the Arizona Endodontic Association who participated in this study included: Drs. James C. Aten, James P. Deemer, David B. Foley, Bradley H. Gettleman, John W. Gillan, James F. Kramer, Robert A. Lees II, Scott Morrison, Robert S. Roda, and Charles L. Siroky. FIG 4. Another configuration in which a single canal is present on the mesial and two canals merge to the distal. (A) The clinician did not anticipate the mesial portion originally; but, after filling the distal canals, a file was placed into the mesial area, which seems to be separate and distinct. (B) After filling the mesial portion.
Dr. Weine is Professor Emeritus, Loyola University, Chicago, IL. Members of the Arizona Endodontic Association are affiliated with the American Association of Endodontists, Chicago, IL. Address requests for reprints to Dr. Franklin S. Weine, 20737 Alexander, Olympia Fields, IL 60461.
References the area of fusion, and so the "C" is closed to the lingual (Fig. 5). In the mirror image situation, the lingual portion of the roots are fused, and the "C" is closed to the buccal. Several newer configurations are demonstrated in this study, indicating that the operator should not assume a fixed spatial relationship if a C-shape is identified, but rather be aware of other possibilities. Based on the results of this study, the following conclusions are presented: 1. The C-shaped Mnd2M, probably requiring a different regimen of treatment than the more frequent two-rooted, threecanaled version, occurs in --8% of these teeth. 2. There are several variants of the C-shaped tooth, although the most common has two or three canals merging toward a single site of exiting. 3. The connecting slit that gives the tooth its name of "Cshaped" may have closure to the buccal or to the lingual. 4. Pooling of treatment modalities by endodontic study clubs or state societies is a logical means for obtaining a large sample size for clinically oriented research.
1. Weine FS. Endodontic therapy on the mandibular second molar: easiest to treat of the difficult, molar teeth. Comp Contin Educ Dent 1994;15:113040. 2. Ingle JI, Beveridge EE. Endodontics. 2nd ed. Philadelphia: Lea & Febiger, 1976:160-1. 3. Cooke HG, Cox FL. C-shaped canal configurations in mandibular molars. J Am Dent Assoc 1979;99:836-9. 4. Weine FS. Endodontic therapy. 5th ed. St. Louis: CV Mosby, 1996:289, 294 - 6. 5. Tamse A, Kaffe I. Radiographic survey of the prevalence of conical lower second molar. Int Endod J 1981;14:188-90. 6. Weine FS, Pasiewicz RA, Rice RT. Canal configuration of the mandibular second molar using a clinically oriented in vitro method. J Endodon 1988;14:207-13. 7. Rice RT, Gilbert BO. An unusual canal configuration in a mandibular first molar. J Endodon 1987;13:513-5. 8. Bolger WL, Schindler WG. A mandibular first molar with a C-shaped root configuration. J Endodon 1988;14:515-9. 9. Pineda F, Kuttler Y. Mesiodistal and buccolingual roentgenographic investigation of 7,275 root canals. Oral Surg Oral Med Oral Pathol 1972;33: 101-10. 10. Vertucci FJ. Root canal anatomy of the human permanent teeth. Oral Surg Oral Med Oral Pathol 1984;58:589-99. 11. Melton DC, Krell KV, Fuller MW. Anatomical and histological features of C-shaped canals in mandibular second molars. J Endodon t991;17:384-8. 12. Weine FS. A preview of the canal-filling techniques of the 21 st century. Compend Contin Educ Dent 1992;13:688-98.