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Canal configuration of the mesiobuccal root of the maxillary second molar
0099-2399/95/2101-0038/$03.00/0 JOURNALOF ENDODONTICS Copyright © 1995 by The American Association of Endodontists
Printed in U.S.A. VOL. 21, NO. 1, JANUARY1995
CLINICAL AID Canal Configuration of the Mesiobuccal Root of the Maxillary Second Molar Norman Eskoz, DDS, MS and Franklin S. Weine, DDS, MSD
type I, single canal from pulp chamber to apex; type II, two separate canals leaving the chamber, but merging short of the apex to form a single canal; type III, two separate canals leaving the chamber and exiting the root in separate foramina; and type IV, one canal leaving the chamber, but dividing short of the apex into two separate and distinct canals with separate foramina. Using a variety of methods to study canal configurations, investigators from 1972 to 1984 reported the occurrence of two canals (Weine types II, III, and IV) in the MBR of the maxillary second molar to range from 12% to 38% (2-4, 79). In a recent study in which a combination of methods was used, Kulild and Peters (10) found that 14 of 32 teeth (43.8%) had two canals in the MBR of the maxillary second molar when flies were placed in the orifices and radiographed. The number of two canals increased to 25 of 32 (78.2 %) when the orifices were counter-sunk with a bur before fries were placed in the canals. Finally, 30 of the 32 teeth (93.7%) had two canals when the roots were sectioned horizontally and examined histologically (Table 1). The purpose of this study was to determine the canal configuration percentages in the MBR of the maxillary second molar using a clinically oriented in vitro study.
The purpose of this study was to investigate the canal configuration in the mesiobuccal root of the maxillary second molar. The canal configuration of the mesiobuccal root of the maxillary second molar need not be the same as that of the maxillary first molar. Several studies have been attempted to clarify the configuration of the second molar, usually via postoperative evaluation, sectioning, or radiography. To follow more closely the clinical procedure, this study involved access cavity preparation and radiographs taken with files in place. Of the 73 extracted maxillary second molars investigated, 67 teeth (91.8%) had 3 roots whereas 6 teeth (8.2%) had 2 roots. In the three rooted teeth, the mesiobuccal roots of 40 (59.7%) were classified as type I (single canal from orifice to apex), 14 (20.9%) were type II (two canals merging short of the apex into a single canal at the apex), 11 (16.4%) were type III (two separate and distinct canals from orifice to apex), and 2 (3%) were type IV (single canal at the orifice, dividing in midroot into two canals exiting at the apex).
MATERIALS AND METHODS A major cause of endodontic failure when treating maxillary molars is the inability to locate, debride, and fill the frequently present second mesiobuccal canal. Before an article written by Weine et al. (1) in 1969, virtually all dentists thought of the mesiobuccal root (MBR) of the maxillary first molar as having only one canal. Since that article, many papers have been published concerning the types of canal systems present in that root and their percentages (2-5). However, few articles have dealt exclusively with the canal configurations in the MBR of the maxillary second molar, possibly because of the assumption that the root is very similar to the first molar. Some studies have grouped first and second molars together and reported combined results. Considering the difference in canal configuration between maxillary first and second premolars, it is reasonable to expect that a difference may exist between the MBR of the maxillary first and second molars. To categorize the canal systems in each root, Weine (6) described four different types of configurations as follows:
Seventy-three extracted human maxillary second molars were obtained from oral surgeons in the Chicago area. All teeth were known to be second molars absolutely. Ifa question existed, the oral surgeons were told not to include the teeth. They were stored in a 5.25 % solution of sodium hypochlorite. The distobuccal and palatal roots were resected to the base of the furcations and discarded so that unobstructed preoperative radiographs could be taken of the MBR from buccal-palatal and mesial-distal directions. Access cavities were prepared according to Weine (6). Size #8 files were placed into the canals until they just penetrated the apex. One millimeter was subtracted from that initial length, which became the working length. Glyoxide (Marion Laboratories, Lenaxa, KS) was used as a lubricant. If an orifice was found, but a size #8 frie could not be passed into it, a # 1 round long shank bur was used to a depth of 1 to 2 m m until the file could penetrate well into the canal. The canals were filed to a size #15 frie. Another set 38
Vol. 21, No. 1, January 1995
Second Maxillary Molar Configurations
39
TABLE 1. Studies of the canal configuration of the MBR of the maxillary second molar
Investigator
No. of Teeth
Type I
Type II
Post-op evaluation Post-op evaluation Post-op evaluation Radiographic Injected dye Access and bur penetration
161 29 33 294 100 32
68.9% 62.1 87.9 64.6 71.0 21.8
25.5% 5.6% 13.8 24.1 ,-12.1--, 8.2 12.8 17.0 12.0
Sectioning and microscopic exam
32
Method of Study
Nosonowitz and Brenner Pomeranz and Fishelberg Vande Vorde et al. Pineda and Kuttler Vertucci Kulild and Peters
Kulild and Peters
Type III
Type IV 0% 0
14.4 0 *
,-78.2--> 6.3
,--93.7--,
• Classification considered as accessory canals off main canal, could be off single (major) or second canal.
TAmE 2. Canal configurations of 73 maxillary second molars, determined by initial files placed to working length No. of Teeth
According to total no. of roots 3 rooted teeth 2 rooted teeth Total teeth Configuration of the MBR of the three rooted teeth Type I MBR Type II MBR Type III MBR Type IV MBR Total teeth
Percentage
67 6 73
91.8% 8.2%
40 14 11 2 67
59.7% 20.9% 16.4% 3%
of buccal-palatal and mesial-distal radiographs were taken with the files in place. Roots with type IV configurations were identified by placing files from the apex in any canal openings found palatal to a more buccally located apical foramen. If the second file penetrated and joined the first file away from the tip and further into the canal, it was categorized as type IV. The molars were categorized as to the number of roots, and the canal configuration of the MBR was determined using the classification according to Weine (6).
RESULTS The results of this study are summarized in Table 2. Of 73 molars, 67 (91.8%) had three roots and six (8.2%) had two roots. The MBR in the 67 three-rooted molars was further categorized as to canal configuration. Forty of the MBRs (59.7%) had a single canal only (Fig. 1). Fourteen roots (20.9%) had type II canal systems (Fig. 2), 11 roots (16.4%) displayed type III configurations (Fig. 3), and 2 (3%) were classified as type IV, based on the ability to place a second file from the apex (Fig. 4).
DISCUSSION The results of this study, as listed in Table 2, should be compared with the other studies of this tooth, as listed in Table 1. Differences that are noted may be related to methods of study. However, the use of radiographs on extracted teeth with fries in place is a clinically oriented, acceptable method for studying canal configuration, and has been used previously in a report on the mandibular second molar ( 1l). The results reported differ considerably with the study by Kulild and Peters (10), who found 78.2% of the MBRs had two canals after access preparation and bur penetration. Our study reported 40% with two canals, and the difference may be caused by the fact that they used their burs more aggressively for countersinking than we did, and we used a slightly different, more modest, method of classification. The even higher percentage, determined by sectioning and microscopic examination (93.7%), in the Kulild and Peters report would seem to be well beyond the ability of any clinician to reach. It is obvious to the clinically oriented endodontist that, in the past 25 yr, a considerable percentage of maxillary first molars have been treated with two canals filled in the MBR. However, it is rare to see this same occurrence in the maxillary second molar, even though most of the studies (Table l) have indicated that, in 30% or more of these teeth, two canals are present in the MBR. When treating this tooth, dentists should assume that there are two canals present in the MBR. Only after a thorough search for a second canal and after it is determined that further preparation would be fruitless or cause a perforation, should the operator accept treating only one canal. If therapy fails on the MBR, it may be because the second canal was not located and treated, and this should be considered carefully in the retrcatment, either by surgical or nonsurgical methods. When examining the views from the proximal (Figs. 1 to 3), it is evident that the MBR of the maxillary second molar is wide buccolingually. This is true even in teeth where only one mesiobuccal canal is present (Fig. IB). This indicates a morphological tendency for this root to be wide buccolingually on a consistent basis, whether one or two canals are present. The discovery of a wide root, by radiograph or manipulation, does not, by itself, indicate that two canals must be present.
40
Eskoz and Weine
FIG 1. A, Radiograph of maxillary second molar with type I canal configuration (single canal) buccal view, with size #15 file in place. From this view, it appears that the root is slender, probably similar in size and shape to the distobuccal root, which has been amputated in this photo. B, Mesial view of the same root shows the wide buccolingual dimension of this root, even in this case where only one canal is present.
Journal of Endodontics
FIG 2. A, Radiograph of maxillary second molar with type II canal configuration (two canals joining short of apex) buccal view, with size #10 file in the mesiobuccal canal and #8 file in the mesiolingual canal From this view the root is slender, but two files are visible. B, Mesial view; the wide buccolingual dimension of the root is apparent, but it is only slightly wider than the root with only one canal shown in Fig. lB.
Vol. 21, No. 1, January 1995
Second Maxillary Molar Configurations
41
FIG 4. All teeth that initially seemed to be type I configurations were explored from the apex with a small file for a second canal opening and radiographed from the mesial. In several instances, the two files merged almost instantly, so these were still classified as type I. In two roots, the two canals merged several millimeters from the apex, as shown herein, and were classified as type IV.
FIG 3. A, Radiograph of maxillary second molar with type III canal configuration (two separate canals) buccal view, with size #15 file in the mesiobuccal canal and size #10 file in the mesiolingual canal. This root also has a slender appearance in this view, but two files go to the apex in separate canals. B, Near the floor of the pulp chamber, where the clinician would search for the canals, the root is no wider than that found in the type I or II canal configurations (compare with Figs. 1B and 2B). It is a bit wider toward the apex to allow for separate exiting of the foramens.
To treat the maxillary second molar properly, an understanding of the morphogenesis of the mesiobuccal canal system is mandatory. Initially the canal in the MBR is the shape of a kidney bean. With a continued deposition of secondary dentin, the isthmus between the poles becomes narrower and eventually may even close, resulting in two canals. Because the mesiolingual segment of the canal surrounds the smaller of the poles of the kidney bean, it will close offleaving a small space, thus making it more difficult to locate. Figure 5 demonstrates the apex of an immature MBR. At first, there is one large ribbon-shaped apex, which, as the tooth matures, begins to constrict, eventually leaving one or more foramens. Therefore, depending on the age of the tooth, the MBR may have a variety of configurations. The percentage of two-rooted maxillary second molars has been reported to be anywhere from 0 to 12% (6). In this study, we found the occurrence to be ~8%. Obviously, 72 teeth are too few to use to derive this statistic accurately, but further studies could be considered using much larger numbers for clarification. When treating any tooth endodontically, statistics from nonclinically oriented studies could lead to erroneous conclusions. Also, when treating the maxillary second molar, statis-
42
Joumal of Endodontics
Eskoz and Weine
Dr. Eskoz is a former graduate assistant in Endodontics, and Dr. Walne is professor emeritus of Endodontics and former professor and director of Postgraduate Endodontics, Loyola University School of Dentistry, Maywood, IL. Address requests for repdnts to Dr. Franklin S. Weine, 30 North Michigan Avenue, Suite 1320, Chicago, IL 60602.
References
FIG 5. Apical view of the MBR of a maxillary second molar from a 14yr-old; apical development had not been completed. Note the kidney bean shape of the canal at this stage of development. With increase in dentin deposition, the isthmus will narrow (arrows). In some teeth, the wide canal will become squeezed into two canals, whereas in others a larger and wider single canal will be present.
tics from articles discussing the configurations of the roots of the maxillary first molar could be misleading.
1. Weine FS, Healey HJ, Gerstein H, Evanson L. Canal configuration in the mesiobuccal root of the maxillary first molar and its endodontic significance. Oral Surg Oral MealOral Pathol 1969;28:419-25. 2. Vertucci FJ. Root canal anatomy of the human permanent teeth. Oral Surg Oral Med Oral Patho11984;58:589-99. 3. VandeVorde HE, Odendahl D, DavisJ. Molar 4th canals: frequent cause of endodontic failure? III Dent J 1975;44:779--86. 4. PinedaF. Roantgenographicinvestigationof the mesiobuccal root of the maxillary first molar. Oral Surg Oral Meal Oral Pathol 1973;26:253-60. 5. Neaverth EJ, Kotler LM, Kaltenbach RF. Clinical investigation of in vivo endodonticallytreated maxillary first molars. J Endodon 1987;13:506-12. 6. Weine FS. Endodontic therapy. 4th ed., Chap. 6. St. Louis: CV Mosby, 1989. 7. Nosonowitz DM, Brenner MR. The major canals of the mesiobuccalroot of the maxillary 1st and 2rid molars. NY J Dent 1973;43:12-5. 8. Pomeranz H, Fishalberg G. The second mesiobuccal canal of maxillary molars. J Am Dent Assoc 1974;88:119-24. 9. Pineda F, Kuttiar Y. Mesiodistal and buccolingual roentgenographic investigation of 7,275 root canals. Oral Surg Oral Med Oral Pathol 1972;33:101 --20. 10. Kulild JC, Peters DD. Incidence and configuration of canal systems in the mesiobuccal root of maxillary first and second molars. J Endodon 1990;16:311-7. 11. Weine FS, Pasiewicz RA, Rice TR. Canal configuration of the mandibular second molar using a clinically oriented in vitro method. J Endodon 1988;14:207-13.
A W o r d for the W i s e There is a person who says the scientific literature contains two, and only two, types of studies. Those which provide equivocal answers to important questions and those which provide definitive answers to trivial questions. Zachariah Yeomans
Printed in U.S.A. VOL. 21, NO. 1, JANUARY1995
CLINICAL AID Canal Configuration of the Mesiobuccal Root of the Maxillary Second Molar Norman Eskoz, DDS, MS and Franklin S. Weine, DDS, MSD
type I, single canal from pulp chamber to apex; type II, two separate canals leaving the chamber, but merging short of the apex to form a single canal; type III, two separate canals leaving the chamber and exiting the root in separate foramina; and type IV, one canal leaving the chamber, but dividing short of the apex into two separate and distinct canals with separate foramina. Using a variety of methods to study canal configurations, investigators from 1972 to 1984 reported the occurrence of two canals (Weine types II, III, and IV) in the MBR of the maxillary second molar to range from 12% to 38% (2-4, 79). In a recent study in which a combination of methods was used, Kulild and Peters (10) found that 14 of 32 teeth (43.8%) had two canals in the MBR of the maxillary second molar when flies were placed in the orifices and radiographed. The number of two canals increased to 25 of 32 (78.2 %) when the orifices were counter-sunk with a bur before fries were placed in the canals. Finally, 30 of the 32 teeth (93.7%) had two canals when the roots were sectioned horizontally and examined histologically (Table 1). The purpose of this study was to determine the canal configuration percentages in the MBR of the maxillary second molar using a clinically oriented in vitro study.
The purpose of this study was to investigate the canal configuration in the mesiobuccal root of the maxillary second molar. The canal configuration of the mesiobuccal root of the maxillary second molar need not be the same as that of the maxillary first molar. Several studies have been attempted to clarify the configuration of the second molar, usually via postoperative evaluation, sectioning, or radiography. To follow more closely the clinical procedure, this study involved access cavity preparation and radiographs taken with files in place. Of the 73 extracted maxillary second molars investigated, 67 teeth (91.8%) had 3 roots whereas 6 teeth (8.2%) had 2 roots. In the three rooted teeth, the mesiobuccal roots of 40 (59.7%) were classified as type I (single canal from orifice to apex), 14 (20.9%) were type II (two canals merging short of the apex into a single canal at the apex), 11 (16.4%) were type III (two separate and distinct canals from orifice to apex), and 2 (3%) were type IV (single canal at the orifice, dividing in midroot into two canals exiting at the apex).
MATERIALS AND METHODS A major cause of endodontic failure when treating maxillary molars is the inability to locate, debride, and fill the frequently present second mesiobuccal canal. Before an article written by Weine et al. (1) in 1969, virtually all dentists thought of the mesiobuccal root (MBR) of the maxillary first molar as having only one canal. Since that article, many papers have been published concerning the types of canal systems present in that root and their percentages (2-5). However, few articles have dealt exclusively with the canal configurations in the MBR of the maxillary second molar, possibly because of the assumption that the root is very similar to the first molar. Some studies have grouped first and second molars together and reported combined results. Considering the difference in canal configuration between maxillary first and second premolars, it is reasonable to expect that a difference may exist between the MBR of the maxillary first and second molars. To categorize the canal systems in each root, Weine (6) described four different types of configurations as follows:
Seventy-three extracted human maxillary second molars were obtained from oral surgeons in the Chicago area. All teeth were known to be second molars absolutely. Ifa question existed, the oral surgeons were told not to include the teeth. They were stored in a 5.25 % solution of sodium hypochlorite. The distobuccal and palatal roots were resected to the base of the furcations and discarded so that unobstructed preoperative radiographs could be taken of the MBR from buccal-palatal and mesial-distal directions. Access cavities were prepared according to Weine (6). Size #8 files were placed into the canals until they just penetrated the apex. One millimeter was subtracted from that initial length, which became the working length. Glyoxide (Marion Laboratories, Lenaxa, KS) was used as a lubricant. If an orifice was found, but a size #8 frie could not be passed into it, a # 1 round long shank bur was used to a depth of 1 to 2 m m until the file could penetrate well into the canal. The canals were filed to a size #15 frie. Another set 38
Vol. 21, No. 1, January 1995
Second Maxillary Molar Configurations
39
TABLE 1. Studies of the canal configuration of the MBR of the maxillary second molar
Investigator
No. of Teeth
Type I
Type II
Post-op evaluation Post-op evaluation Post-op evaluation Radiographic Injected dye Access and bur penetration
161 29 33 294 100 32
68.9% 62.1 87.9 64.6 71.0 21.8
25.5% 5.6% 13.8 24.1 ,-12.1--, 8.2 12.8 17.0 12.0
Sectioning and microscopic exam
32
Method of Study
Nosonowitz and Brenner Pomeranz and Fishelberg Vande Vorde et al. Pineda and Kuttler Vertucci Kulild and Peters
Kulild and Peters
Type III
Type IV 0% 0
14.4 0 *
,-78.2--> 6.3
,--93.7--,
• Classification considered as accessory canals off main canal, could be off single (major) or second canal.
TAmE 2. Canal configurations of 73 maxillary second molars, determined by initial files placed to working length No. of Teeth
According to total no. of roots 3 rooted teeth 2 rooted teeth Total teeth Configuration of the MBR of the three rooted teeth Type I MBR Type II MBR Type III MBR Type IV MBR Total teeth
Percentage
67 6 73
91.8% 8.2%
40 14 11 2 67
59.7% 20.9% 16.4% 3%
of buccal-palatal and mesial-distal radiographs were taken with the files in place. Roots with type IV configurations were identified by placing files from the apex in any canal openings found palatal to a more buccally located apical foramen. If the second file penetrated and joined the first file away from the tip and further into the canal, it was categorized as type IV. The molars were categorized as to the number of roots, and the canal configuration of the MBR was determined using the classification according to Weine (6).
RESULTS The results of this study are summarized in Table 2. Of 73 molars, 67 (91.8%) had three roots and six (8.2%) had two roots. The MBR in the 67 three-rooted molars was further categorized as to canal configuration. Forty of the MBRs (59.7%) had a single canal only (Fig. 1). Fourteen roots (20.9%) had type II canal systems (Fig. 2), 11 roots (16.4%) displayed type III configurations (Fig. 3), and 2 (3%) were classified as type IV, based on the ability to place a second file from the apex (Fig. 4).
DISCUSSION The results of this study, as listed in Table 2, should be compared with the other studies of this tooth, as listed in Table 1. Differences that are noted may be related to methods of study. However, the use of radiographs on extracted teeth with fries in place is a clinically oriented, acceptable method for studying canal configuration, and has been used previously in a report on the mandibular second molar ( 1l). The results reported differ considerably with the study by Kulild and Peters (10), who found 78.2% of the MBRs had two canals after access preparation and bur penetration. Our study reported 40% with two canals, and the difference may be caused by the fact that they used their burs more aggressively for countersinking than we did, and we used a slightly different, more modest, method of classification. The even higher percentage, determined by sectioning and microscopic examination (93.7%), in the Kulild and Peters report would seem to be well beyond the ability of any clinician to reach. It is obvious to the clinically oriented endodontist that, in the past 25 yr, a considerable percentage of maxillary first molars have been treated with two canals filled in the MBR. However, it is rare to see this same occurrence in the maxillary second molar, even though most of the studies (Table l) have indicated that, in 30% or more of these teeth, two canals are present in the MBR. When treating this tooth, dentists should assume that there are two canals present in the MBR. Only after a thorough search for a second canal and after it is determined that further preparation would be fruitless or cause a perforation, should the operator accept treating only one canal. If therapy fails on the MBR, it may be because the second canal was not located and treated, and this should be considered carefully in the retrcatment, either by surgical or nonsurgical methods. When examining the views from the proximal (Figs. 1 to 3), it is evident that the MBR of the maxillary second molar is wide buccolingually. This is true even in teeth where only one mesiobuccal canal is present (Fig. IB). This indicates a morphological tendency for this root to be wide buccolingually on a consistent basis, whether one or two canals are present. The discovery of a wide root, by radiograph or manipulation, does not, by itself, indicate that two canals must be present.
40
Eskoz and Weine
FIG 1. A, Radiograph of maxillary second molar with type I canal configuration (single canal) buccal view, with size #15 file in place. From this view, it appears that the root is slender, probably similar in size and shape to the distobuccal root, which has been amputated in this photo. B, Mesial view of the same root shows the wide buccolingual dimension of this root, even in this case where only one canal is present.
Journal of Endodontics
FIG 2. A, Radiograph of maxillary second molar with type II canal configuration (two canals joining short of apex) buccal view, with size #10 file in the mesiobuccal canal and #8 file in the mesiolingual canal From this view the root is slender, but two files are visible. B, Mesial view; the wide buccolingual dimension of the root is apparent, but it is only slightly wider than the root with only one canal shown in Fig. lB.
Vol. 21, No. 1, January 1995
Second Maxillary Molar Configurations
41
FIG 4. All teeth that initially seemed to be type I configurations were explored from the apex with a small file for a second canal opening and radiographed from the mesial. In several instances, the two files merged almost instantly, so these were still classified as type I. In two roots, the two canals merged several millimeters from the apex, as shown herein, and were classified as type IV.
FIG 3. A, Radiograph of maxillary second molar with type III canal configuration (two separate canals) buccal view, with size #15 file in the mesiobuccal canal and size #10 file in the mesiolingual canal. This root also has a slender appearance in this view, but two files go to the apex in separate canals. B, Near the floor of the pulp chamber, where the clinician would search for the canals, the root is no wider than that found in the type I or II canal configurations (compare with Figs. 1B and 2B). It is a bit wider toward the apex to allow for separate exiting of the foramens.
To treat the maxillary second molar properly, an understanding of the morphogenesis of the mesiobuccal canal system is mandatory. Initially the canal in the MBR is the shape of a kidney bean. With a continued deposition of secondary dentin, the isthmus between the poles becomes narrower and eventually may even close, resulting in two canals. Because the mesiolingual segment of the canal surrounds the smaller of the poles of the kidney bean, it will close offleaving a small space, thus making it more difficult to locate. Figure 5 demonstrates the apex of an immature MBR. At first, there is one large ribbon-shaped apex, which, as the tooth matures, begins to constrict, eventually leaving one or more foramens. Therefore, depending on the age of the tooth, the MBR may have a variety of configurations. The percentage of two-rooted maxillary second molars has been reported to be anywhere from 0 to 12% (6). In this study, we found the occurrence to be ~8%. Obviously, 72 teeth are too few to use to derive this statistic accurately, but further studies could be considered using much larger numbers for clarification. When treating any tooth endodontically, statistics from nonclinically oriented studies could lead to erroneous conclusions. Also, when treating the maxillary second molar, statis-
42
Joumal of Endodontics
Eskoz and Weine
Dr. Eskoz is a former graduate assistant in Endodontics, and Dr. Walne is professor emeritus of Endodontics and former professor and director of Postgraduate Endodontics, Loyola University School of Dentistry, Maywood, IL. Address requests for repdnts to Dr. Franklin S. Weine, 30 North Michigan Avenue, Suite 1320, Chicago, IL 60602.
References
FIG 5. Apical view of the MBR of a maxillary second molar from a 14yr-old; apical development had not been completed. Note the kidney bean shape of the canal at this stage of development. With increase in dentin deposition, the isthmus will narrow (arrows). In some teeth, the wide canal will become squeezed into two canals, whereas in others a larger and wider single canal will be present.
tics from articles discussing the configurations of the roots of the maxillary first molar could be misleading.
1. Weine FS, Healey HJ, Gerstein H, Evanson L. Canal configuration in the mesiobuccal root of the maxillary first molar and its endodontic significance. Oral Surg Oral MealOral Pathol 1969;28:419-25. 2. Vertucci FJ. Root canal anatomy of the human permanent teeth. Oral Surg Oral Med Oral Patho11984;58:589-99. 3. VandeVorde HE, Odendahl D, DavisJ. Molar 4th canals: frequent cause of endodontic failure? III Dent J 1975;44:779--86. 4. PinedaF. Roantgenographicinvestigationof the mesiobuccal root of the maxillary first molar. Oral Surg Oral Meal Oral Pathol 1973;26:253-60. 5. Neaverth EJ, Kotler LM, Kaltenbach RF. Clinical investigation of in vivo endodonticallytreated maxillary first molars. J Endodon 1987;13:506-12. 6. Weine FS. Endodontic therapy. 4th ed., Chap. 6. St. Louis: CV Mosby, 1989. 7. Nosonowitz DM, Brenner MR. The major canals of the mesiobuccalroot of the maxillary 1st and 2rid molars. NY J Dent 1973;43:12-5. 8. Pomeranz H, Fishalberg G. The second mesiobuccal canal of maxillary molars. J Am Dent Assoc 1974;88:119-24. 9. Pineda F, Kuttiar Y. Mesiodistal and buccolingual roentgenographic investigation of 7,275 root canals. Oral Surg Oral Med Oral Pathol 1972;33:101 --20. 10. Kulild JC, Peters DD. Incidence and configuration of canal systems in the mesiobuccal root of maxillary first and second molars. J Endodon 1990;16:311-7. 11. Weine FS, Pasiewicz RA, Rice TR. Canal configuration of the mandibular second molar using a clinically oriented in vitro method. J Endodon 1988;14:207-13.
A W o r d for the W i s e There is a person who says the scientific literature contains two, and only two, types of studies. Those which provide equivocal answers to important questions and those which provide definitive answers to trivial questions. Zachariah Yeomans