0099-2399/90/1607-0311/$02.00/0 JOURNAL OF ENDODONTICS Copyright 9 1990 by The American Association of Endodontists
Printed in U.S.A. VOL. 16, NO. 7, JULY 1990
Incidence and Configuration of Canal Systems in the Mesiobuccal Root of Maxillary First and Second Molars James C. Kulild, DDS, MS, and Donald D. Peters, DDS, MS
Acosta and Trugeda (10) have stated that the ML canal orifice is usually covered by a dentinal rounded growth which conceals the funnel-shaped structure of this canal from view. Textbooks generally mention the use of endodontic explorers and/or chemicals to locate the ML canal. Sampeck (15) and Weine (1) have stated that burs should never be used in the floor of the pulp chamber to find canal orifices. Weine (1) has advocated using a safe-tipped bur on the sides of the pulp chamber. However, clinically, it often appears that only an end-cutting bur can reach and remove portions of the dentinal "growth" and some of the other calcifications. Pomeranz and Fishelberg (9) have recommended using a #1 round bur to follow the orifice 1 m m below the floor of the chamber. Slowey (14) has discussed using a bur in the tacky area found by a sharp endodontic explorer. Although authors have stated that the use of burs can lead to perforations, no specific evidence has been presented (1, 15). If burs do increase the incidence of perforations, their use should be discouraged. The ideal would be to develop techniques which would increase the efficiency of locating the canal without increasing the chance of perforation. The purposes of this study were: (a) reconfirm the actual incidence of a ML canal in both first and second maxillary molars; (b) determine whether the careful use of a bur to remove the dentinal overgrowth and follow the subpulpal groove apically in the floor of the chamber would increase the incidence of locating ML canals; (c) report if the careful use of burs increases the incidence of perforations; (d) determine the positional relationship of the ML canal to the MB canal when orientated to the entire tooth; (e) determine the relationship of the MB and ML canals to the mesial and distal surface of the root; and (f) develop a more complete classification of the canals' configurations.
The anatomy of the mesiobuccal (MB) root of 51 maxillary first and 32 maxillary second molars was studied. Initially, an attempt was made to locate all canals using a standard access and hand instruments. A bur was next used carefully to locate any additional second mesiobuccal (mesiolingual (ML)) canals. Finally, after crown removal, the teeth were reduced horizontally in 1-mm increments and examined by microscope. A second ML canal was located in the coronal half of 95.2% of the roots: by hand instruments in 54.2%; bur in 31.3%; and microscope in 9.6%. There were no root perforations when the bur was used as described. The ML canal orifice averaged 1.82 mm lingual to the MB canal orifice. The difference in incidence of ML canals between the first and second molars was not statistically significant. The canal systems were type 1, 4.8%; type 2, 49.4%, and type 3, 45.8%.
Weine (1) has stated that the frequent failure of endodontic treatment of the maxillary first permanent molar is likely due to the failure to locate and fill the second mesiobuccal (mesiolingual (ML)) canal. This second canal in the mesiobuccal (MB) root has been observed at least since 1925 and 1927 when Hess (2) and Okumura (3) discussed it. However, it was not until 1969 that its significance appeared to be recognized by Weine et al.(4). Since then, its incidence has been reported and discussed by several authors (5-l 5). According to Weine et al. (4), the MB and ML canals generally either join 1 to 4 m m from the apex and exit with a common foramen (type 2), or remain separate and exit through two foramen (type 3). Obviously, before the practitioner can clean, shape, and obturate the ML canal, it must be located. This has proved to be a difficult in vivo procedure for many dental practitioners (8). Hartwell and Bellizzi (11) demonstrated this when they reported treating a second canal in only 18% of 538 maxillary first molars and 9.6% of 176 second molars. However, Neaverth et al. (12) located and treated a much higher percentage, 77.2% (176 of 228), in maxillary first molars.
MATERIALS AND M E T H O D S Fifty-one first molars and 32 second molars were collected and stored in 10% formalin. A standard access was made in each molar and an attempt was made to locate the MS and ML canals utilizing only an endodontic explorer (group 1). Next, new long-shank endodontic round burs were used sequentially (# 8 - 6 - 4 - 2 ) to open the subpulpal groove to locate the ML canal. Dentin was removed carefully at the expense
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of the mesial wall away from the trifurcation area, moving the entire access mesially and apically. The burs were used until the M L canal was located (group 2) or until the subpulpal groove and discolored dentin, appearing to be a calcified canal, was reduced 2 to 3 m m below the pulpal floor. Once a ML canal was located, fine instruments were placed in the MB and M L canals and 35-mm photographs taken (Fig. 1). Radiographs were made of each tooth with files in place. Each tooth was mounted in clear orthodontic resin with the mesial of the MB root perpendicular to the horizontal plane as shown in Fig. 2a. Using a rotating sandpaper disk on a polisher/grinder (Buehler Ltd., Evanston, IL), the crown o f each tooth was removed perpendicular to the long axis of the MB root down to the floor of the chamber (Fig. 2b). Two dots were placed with indelible ink on the superior surface of the base of the acrylic block below the apex of the MB root (Fig. 2a). The dots were placed on a line (B) parallel to a line (A) connecting the center of the lingual (L) canal with a point equidistant between the MB and distobuccal (DB) canals (Fig. 3a). The dots and flat acrylic base allowed the resin block to be reoriented in precisely the same position during measurements using a measuring microscope (Nikon Microscope; Nikon, Inc., Garden City, NY). Evaluation and measurement of the anatomy was then done as the tooth was reduced in 1-mm increments (Fig. 3b). The presence or absence of the M L canal was recorded (Fig. 4), resulting in groups 3 and 4 (Table 1). Ten measurements were made as shown in Fig. 3a (xl-8; yl-2). They gave dentin thickness, mesial and distal of each canal, canal diameters,
and distance between the MB and ML canals. The measurements also allowed evaluation of the movement of the ML canal in respect to the MB canal at each level. RESULTS Table 1 shows that 95.2% of the MB roots of both the first (96.1%) and second (93.7%) maxillary molars had two canals in the coronal half o f the root. The difference between first and second molars was not statistically significance. Fiftyfour percent were located by normal access preparation. Thirty-one percent were located with careful use o f a bur. The microscope revealed M L canals in 8 of the remaining 12 teeth. Only four MB roots (4.8%) did not demonstrate a second canal in the coronal half of the root. Two of the four did manifest a definite M L canal in the apical 3 to 4 m m of the root (type 1A, Fig. 5b).Pearson's chi-square evaluation showed no significance relative to numbers of M L canals located by use of a bur between the first and second molars (p < 0.12). However, for both molars the use of a bur was significant in locating a ML canal at a p < 0.01 incidence. One tooth, a maxillary first molar, had a second M L canal, or three canals, in the MB root (Fig. 3b). The root contained
'
a
FIG 1. Six of the maxillary molars in the study showing characteristic broad configuration of MB root. Note fused DB and L roots of tooth in center bottom row, a second molar.
MB ROOT
2-~- .~
FIG 2. a, Diagram of side view of tooth embedded in acrylic base. Reference dots below apex level allowing reorientation of block during total sectioning of tooth. Perpendicular line (PL) placed on MB root to orientate to acrylic base. b, Cut through chamber of maxillary molar showing lip of dentin over ML canal (arrow).
Vol. 16, No. 7, July 1990
Canal Anatomy in MB Roots
a
At
313
tB I
MB ROOT
X;
x4X3 i.
o|
ROOT
L
(
ROOT .D
i I ACRYLIC BASE
REFERENCE DOTS
J
FIG 3, a, Diagram of occlusal view of section with crown and portion of roots removed. Apices of roots embedded in acrylic base. Reference lines (,4 and B) used to establish reference dots which allowed precise reorientation of acrylic base and tooth to microscope after each section was removed, b, Photograph of sectioned specimen of only tooth in the study that had a second ML canal. Note two orientation dots countersunk below apices of tooth.
a type 3 canal system, and all measurements used were from the buccal and lingual canals. Figure 5 shows the 10 variations observed of the three basic root canal configurations and Table 2 shows the incidence of their occurrence. Pearson's chi-square test showed no significance (p < 0.36) in difference in the incidence of type 2 or 3 canal systems in the MB root of first or second molars. Table 3 shows the average canal separation at each level where two canals were-observed in roots with either the type 2 or 3 canal configurations. The first evidence of an orifice of the ML canal was an average distance of 1.82 m m lingual to the orifice of the MB canal (Table 3). It originated slightly distal to the MB but as it progressed apically it moved immediately mesiolingually relative to the MB canal. At approximately level six, the M L area of the root moved distal in respect to the MB area of the root. In cases where the canal was located without extensive use of the bur, there was often evidence of the dentinal growth over the area where the ML canal orifice was located (Fig. 2b). Table 4 shows the average thickness of dentin mesial and distal to each canal at each level and the average diameter of the canal at each level. Each measurement, except for the area of dentinal growth over the M L orifice, was significantly smaller for the M L area of the root compared with the MB area of the root. There were no cases where the dentin mesial or distal to the M L canal was less than 0.5-mm thick in any sections at the levels where the burs were used. No perforations were identified. Apical to this area of bur use, there were sections of the canal that microscopically appeared to be completely occluded (type 2B and 3B roots) (Fig. 4a). Finally, one or more additional "accessory canals" were observed in the final one or two levels of nine additional MB roots.
DISCUSSION In this investigation, two patent canals could be demonstrated from the chamber to the apical area, exiting via either one or two foramina, in 71.1% (types 2, 2C, 2D, and 3) of the MB roots. Additionally, remnants of canals, or partial canals, were located clinically in an additional 14.4% o f the roots and microscopically in an additional 12%. In some of these roots the point where the canal turned either buccally or lingually was apparently so acute that it was lost during sectioning, resulting in the type 2A and 3A canal configurations. The type 2B and 3B roots appeared to have ML canals that were occluded by calcifications (Fig. 4a) for an extensive portion of their length. This occurred in seven cases or 8.9% of all M L canals. It appeared that the occlusal portion o f these canals was the space created by the bur following the discolored calcified "dot." This was followed by an additional 2 to 3 m m o f calcified canal. The apical portion of the canal was the only truly patent portion of these canals. In two of the type 1 roots, canals were observed only in the apical third (type 1A). Weine (1) has referred to these as type IV canal configurations. However, in this study they were also seen to occur in type 2 canal configurations (type 2D). Therefore, it was decided to consider both as variations of the three basic canal configurations. These apical second canals could have been only accessory canals. However, definite accessory canals, shorter and not necessarily lingual to the MB canal, were seen in nine (10.8%) additional MB roots. One of these accessory canals was present in the apical two sections o f one of the two MB roots with only one primary canal (type 1). The high incidence of two canals in the coronal half o f the MB root strongly supports the hypothesis that two canals are
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FiG 4. a, Photomicrograph of section through roots (level 5) showing remnant of canal between MB and ML canals of maxillary first molar. Note calcified remnant of ML canal (arrow). b, Higher magnification of another mesial root at level with both M B and ML canals patent. TABLE 1. Mesiolingual canals located by each technique
MesiolingualCanals Located Tooth First molars Second molars Total
51 32 83
Group 1
Group 2
Group 3
Group 4
No Bur
Bur
Microscope
1 Canal
3 (5.9%) 5 (15.6%) 8 (9.6%)
2* (3.9%) 2* (6.3%) 4 (4.8%)
31 (60.8%) 15 (29.4%) 14 (43.8%) 11 (34.4%) 45 (54.2%) 26 (31.3%)
* Onecanalin eachgroupwas of the type 1A, or had a secondmajorapicalcanal.
normal in this root in fully developed teeth. This hypothesis also is supported by the basic oblong, "bean-shaped," configuration of the root (Fig. 1). Evaluation of the photomicrographs of the MB roots in this study suggests a developmental pattern. Originally a ribbon bean-shaped canal which conforms to the external anatomy develops within the root. During maturation, the isthmus area between the MB and ML areas closes, leaving a larger MB canal and a smaller ML canal (Fig. 4b). It is proposed that this is the manner in which two canals form in all bean-shaped roots. It is feasible that one or more of the four teeth with only one canal in the MB root became pulpally involved and was extracted prior to final closure of the isthmus.
This investigation found a very low incidence of type 1 canal systems compared with previous studies. One reason could be that this sample of teeth was skewed. However, two other reasons appear more likely. First, the use of the bur and microscope helped identify the highly calcified ML canals which could have been easily missed in previous in vitro studies. Second, previous in vitro studies may have included more pulpally involved teeth from very young patients. It may be that a decrease in caries incidence and an increase in endodontic treatment have significantly reduced the incidence of molars from young patients. Pineda and Kuttler (5) found 48.5% of their maxillary molar cases demonstrated two apical foramen. This study's finding of 51.8% closely approximates their finding. Obviously, with present clinical techniques the second apical foramina of the type IA, 2D, and 3B roots would most likely not be located in present in vivo studies. The authors feel that a combination of factors is responsible for the difficulties encountered in locating the ML canal. First, the ML canal is the smallest canal during normal development (Table 4 and Fig. 4b). Second, during normal development, the ML area of the MB root first moves slightly mesially and lingually (Fig. 3a). This mesial position of the ML canal has been well diagrammed previously (12, 16). Third, these molars often become pulpally involved due to mesial caries. This means that, prior to endodontic therapy, the area most adjacent to this canal experiences the greatest chronic irritation due to caries, deep restorations, leakage, and so forth, prior to the irreversible pulpitis. These irritants could stimulate irritational dentin formation, whether the "dentinal growth" of Acosta and Trugeda (10), pulp stones in the chamber, or the other canal calcifications which appear to add to the difficulty in locating the canal. The MB, DB, and L canals in each tooth were located after standard access preparation and use of an endodontic explorer in the floor of the chamber. These canals were all patent to the apex. However, only 45 of 79 ML canals (60.0%) were located without additional use of a cutting instrument within the pulp chamber, and only 26 of the 34 remaining canals observed were located with use of the bur. Almost 10% (9.6%) of the ML canals were occluded occlusally to such a degree that they were not located even with use of a bur. This study supports the finding of Neaverth et al.(12) that with careful access and opening of the canals, a significant additional number of ML canals can be located. In fact, under ideal in vitro conditions, 90.2% of first molars and 78.2% of second molars had a locatable ML canal. The most important step in successfully locating the ML canal is to establish excellent access to the entire pulp chamber. After the chamber is well cleansed and the three main canals located, the growth needs to be removed so the mesiocentral area of the chamber can be well visualized. This study indicates that at this point, about 50 to 60% of the teeth should contain a ML canal easily entered by an instrument. However, most of the remaining ML roots will contain partially calcified ML canals. Careless search with burs to locate these canals may lead to perforations. However, an indication of their presence is usually noted as a discolored dot area about 1.8 m m lingual to the MB canal. Clinically, it appears that the greatest danger lies in a trifurcation perforation. This occurs when the orifice is lo-
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Canal Anatomy in MB Roots
315
Type 1A
Type 1
b
Type 2
Type 2A
Type 28
Type3
Type 2C
d
Type3A
Type 3B
Type 2D
f
FIG 5. a, Radiographs of one of each type 1 canal configurations observed. Tooth on left had no second canal (type 1) and tooth on the right had a second canal in apical third to fourth levels (type 1A). b, Diagram of type 1 canals, c, Radiographs of five type 2 canal configurations observed: top left, ML canal unites with MB canal at midroot (type 2); top middle, microscopically ML canal appeared to turn toward MB canal but actual point of contact apparently was in area sectioned (type 2A); top right, occlusally, canal appeared to be created by bur following calcified canal. Microscope showed continued calcification in midroot area, but patent apically (Fig. 4a) (type 2B); bottom left, ML canal unites with MB in apical area (type 2C); bottom right, using radiograph only would classify as type 3, but microscope showed canals united in midroot (type 2D). d, Diagram of type 2 canals, e, Radiographs of three type 3 canal configurations observed: top left, two canals from chamber to apex (type 3); top right, canal appeared to turn and exit to lingual about midroot level (type 3A); bottom, occlusally, canal appeared to be created by bur following calcified canal, continued calcificed in midroot area, but patent in apical area (type 3B). f, Diagram of type 3 canals.
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Kulild and Peters
three, four, and six, it had diameters of 0.511, 0.391, and 0.334 mm. A #2 round bur with a diameter of 0.92 m m could not have reached this level (17). The ML canal in this root at the fifth level was 0.246 m m in diameter. With the technique described, ML canals were located in vitro 85% of the time. In each case, use of the described technique resulted in the "heart" rhomboidal shaped access preparation described by Neaverth et al. (12). Three other points can be made re 1ative to the anatomical variations of the M L canal observed in this study. First, as indicated by the standard deviations in Table 3 for the initial three to four levels, the M L canal was generally 1 to 3 m m lingual to the MB canal in both type 2 and 3 canal systems. It was rare for the canals to be over 3 m m apart. Second, in this sample of teeth there were no cases of two lingual canals. Third, while there were cases of fusion between the DB and L roots (Fig. 1) (18), there were no cases of second molars with only two canals (1).
cated beneath the dentinal growth but the dentist does not recognize the initial ML movement of the canal as it progresses apically. In this case, using the bur directly at the initial orifice opening may allow the bur to cut into the floor of the chamber and result in a trifurcation perforation. As described, initially the canal apical to the dentinal growth moves mesiolingually (4, 9). If the dot is followed indiscriminately to the mesial by the bur, the position at which it stops moving to the mesial can be missed, resulting in a mesial surface perforation. However, if the whole mesial wall occlusal to the dot is planed to the mesial as the bur opens the canal apically, the turning of the calcified canal can be observed and followed. In all of the measurements through the first levels, there were no perforations and only one canal with dentin thinner than 0.5 mm. In this canal the dentin was thinner on both the mesial and distal of a MB canal at the fifth level. It appeared to be an area of internal resorption, since, at this level, the canal had a diameter of 1.284 m m whereas at levels
CONCLUSIONS
TABLE 2. Number of teeth in each mesial root configuration Root Type
No. %
1
1A
2
2A
2B
2C
2 2.4
2 2.4
22 26.5
7 8.4
1 1.2
2 2.4
Totals* 4.8
2D
3
9 26 10.8 31.3
49.4
3A
3B
6 7.2
6 7.2
This study demonstrated that the normal anatomy of both the first and second maxillary molars is two canals in the MB root. Careful use of a bur increased the incidence in locating the ML canal, in vitro, from 54.2 to 85.5%.This study also showed that the careful use of a bur in the floor of the chamber should not lead to an increase in perforations. Relative to a plane bisecting the lingual canal and a point midway between the MB and DB roots, the M L canal orifice is initially slightly distal of the MB canal orifice but moves immediately mesiolingually relative to the MB canal. Then, at about the midroot level, the ML canal moves, relative to the MB canal, buccodistally i r a type 2 canal system is present and distally if a type 3 canal system is present. Both the MB and M L canals have thicker dentin on the mesial than on the distal and the MB canal is consistently larger than the M L canal. Microscopically, there were 10 primary variations of the three basic root canal systems. Microscopic evaluation also revealed only 4.8% of the roots as a true type 1 canal system, 49.4%, type 2, and 45.8%, type 3.
45.8
* Total percentage of each type of root.
TABLE 3. Mean distance at each level between centers of MB and ML canals (in millimeters) for type 2 and 3 roots Level Root Type 1 2
3
2
3
4
5
6
7
8
9
mm 1 . 8 0 1.85 1.99 1.78 1.47 1.07 1,01 0.74 1.03 SD 0.69 0.82 0.72 0.71 0.61 0 . 5 9 0.51 0.54 0.62 No.* 41 41 41 41 39 27 20 19 11t mm 1 . 8 4 1.88 1.96 1.82 1.83 1.72 1.75 1.48 0.74 SD 0.85 0.94 0.79 0.76 0.64 0.64 0.51 0.99 0.45 No.* 38 38 38 33 30 28 29 26 5
* Number of roots with two canals available at each level. t Relates to type 2D's (apical second canal).
TABLE 4. Mean thickness of dentin (mesial and distal) of each canal and mean diameters of each canal* Level
Wall mesial to MB canal Wall mesial to ML canal Diametert MB canal Diameter? ML canal Wall distal to MB canal Wall distal to ML canal
mm SD mm SD mm SD mm SD mm SD mm SD
1
2
3
4
5
6
7
8
9
2.30 0.33 2.4610.41 0.68 0.55 0.38 0.25 --w
2.08 0.35 2.07 0.37 0.61 0.25 0.35 0.11
1.76 0.25 1.57 0.32 0.52 0.18 0.44 0.08 1.50 0.28 1.11 0.26
1.52 0.20 1.27 0.20 0.44 0.09 0.30 0.09 1.40 0.38 1.21 0.28
1.39 0.28 1.21 0.22 0.45 0.21 0.25 0.08 1.28 0.31 1.13 0.28
1.37 0.26 1.1 8 0.30 0.39 0.07 0.25 0.10 1.33 0.31 1.15 0.32
1.33 0,31 1,11 0,33 0,37 0,03 0,25 0,16 1,35 0,34 1,12 0.30
1.20 0.34 1.17 0.36 0.31 0.08 0.20 0.07 1.23 0.25 1.13 0.45
1.13 0.39 0.95 0.35 0.26 0.08 0.15 0.05 1.06 0.38 0.94 0.40
* Comparison was made in all measurements between type 2 and type 3 canals. There were no significant differences at the p < 0.05 level. t Area of remnant of dentinal growth over first location of orifice of ML canal. 1: Measurements used in occlusal three levels only from canals where no bur was used to locate canals. w Dentin trifurcation area,
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Canal Anatomy in MB Roots
The authors wish to thank Dr. Patrice D. Primack and Dr. Jerome C. Donnelly for their help in classifying each tooth, Mrs. Mary Scovill for her assistance in preparation of the manuscript, Dr. Richard Guerin for helping design the study, and Dr. Lewis Lorton for helping with the statistical analysis. The opinions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense. Dr. Kulild, a Colonel, US Army Dental Corps, is presently assistant director, Endodontic Residency Program, Ft. Gordon, GA. Dr. Peters, a Colonel, US Army Dental Corps, is commander, US Army DENTAC, Ft. Gordon, and former director, Endodontic Residency Program, US Army Institute of Dental Research, Walter Reed Army Medical Center, Washington, DC.
References 1. Weine FS. Endodontic therapy. St. Louis: CV Mosby, 1982:210-35. 2. Hess W. The anatomy of the root canals of the teeth of permanent dentition. London: John Bale, Sons & Danielsson Ltd., 1925. 3. Okumura T. Anatomy of the root canals. J Am Dent Assoc 1927;14:6326. 4. Weine FS, Healey NJ, Gerstein H, Evanson L, Canal configuration in the mesiobuccal root of the maxillary first molar and its endodontic significance. Oral Surg 1969;28:419-25. 5. Pineda F, Kuttler Y. Mesiodistal and buccolingual roentgenographic investigation of 7,275 root canals. Oral Surg 1972;33:101-10.
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6. Pineda F. Roentgenographic investigation of the mesiobuccal root of the maxillary first molar, Oral Surg 1973;36:253-60. 7. Green D. Double canals in single roots. Oral Surg 1973;35:689-96. 8. Seidberg BH, Altman M, Guttuso J, Suson M. Frequency of two mesiobuccal root canals in maxillary permanent first molars. J Am Dent Assoc 1973;87:852-6. 9. Pomeranz H, Fishelberg G. The secondary mesiobuccal canal of maxillary molars. J Am Dent Assoc 1974;88:119-24. 10. Acosta Vigouroux SA, Trugeda Bossans SA. Anatomy of the pulp chamber floor of the permanent maxillary first molar. J Endodon 1978;4:2149. 11. Hartwell G, Bettizzi R. Clinical investigation of in vivo endodonticatly treated mandibular and maxillary molars. J Endodon 1982;12:555-7. 12. Neaverth EJ, Kotler LM, Kaltenback RF. Clinical investigation (in vivo) of endodontically treated maxillary first molars. J Endedon 1987; 13:506-12. 13. Nosonowitz DM, Brenner MR. The major canals of the mesiobuccal root of the maxillary 1st and 2nd molars. NY J Dent 1973;43:1215. 14. Slowey RR. Root canal anatomy road map to successful endedontics. Dent Clin North Am 1979;23:555-73. 15. Sampeck BS. Instruments of endedontics: their manufacture, use, and abuse. Dent Clin North Am 1967;579-601. 16. Bower RC. Furcation morphology relative to periodontal treatment: furcation root surface anatomy. J Peddonto11979;50:366-74. 17. Kessler JR, Peters DD, Lorton L. Comparison of the relative risk of molar root perforation using various endodontic instrumentation techniques. J Endodon 1983;9:439-47. 18. Cecic P, Hartwell G, Bellizzi R. The multiple root canal system in the maxillary first molar: a case report. J Endodon 1982;8:113-5.
Printed in U.S.A. VOL. 16, NO. 7, JULY 1990
Incidence and Configuration of Canal Systems in the Mesiobuccal Root of Maxillary First and Second Molars James C. Kulild, DDS, MS, and Donald D. Peters, DDS, MS
Acosta and Trugeda (10) have stated that the ML canal orifice is usually covered by a dentinal rounded growth which conceals the funnel-shaped structure of this canal from view. Textbooks generally mention the use of endodontic explorers and/or chemicals to locate the ML canal. Sampeck (15) and Weine (1) have stated that burs should never be used in the floor of the pulp chamber to find canal orifices. Weine (1) has advocated using a safe-tipped bur on the sides of the pulp chamber. However, clinically, it often appears that only an end-cutting bur can reach and remove portions of the dentinal "growth" and some of the other calcifications. Pomeranz and Fishelberg (9) have recommended using a #1 round bur to follow the orifice 1 m m below the floor of the chamber. Slowey (14) has discussed using a bur in the tacky area found by a sharp endodontic explorer. Although authors have stated that the use of burs can lead to perforations, no specific evidence has been presented (1, 15). If burs do increase the incidence of perforations, their use should be discouraged. The ideal would be to develop techniques which would increase the efficiency of locating the canal without increasing the chance of perforation. The purposes of this study were: (a) reconfirm the actual incidence of a ML canal in both first and second maxillary molars; (b) determine whether the careful use of a bur to remove the dentinal overgrowth and follow the subpulpal groove apically in the floor of the chamber would increase the incidence of locating ML canals; (c) report if the careful use of burs increases the incidence of perforations; (d) determine the positional relationship of the ML canal to the MB canal when orientated to the entire tooth; (e) determine the relationship of the MB and ML canals to the mesial and distal surface of the root; and (f) develop a more complete classification of the canals' configurations.
The anatomy of the mesiobuccal (MB) root of 51 maxillary first and 32 maxillary second molars was studied. Initially, an attempt was made to locate all canals using a standard access and hand instruments. A bur was next used carefully to locate any additional second mesiobuccal (mesiolingual (ML)) canals. Finally, after crown removal, the teeth were reduced horizontally in 1-mm increments and examined by microscope. A second ML canal was located in the coronal half of 95.2% of the roots: by hand instruments in 54.2%; bur in 31.3%; and microscope in 9.6%. There were no root perforations when the bur was used as described. The ML canal orifice averaged 1.82 mm lingual to the MB canal orifice. The difference in incidence of ML canals between the first and second molars was not statistically significant. The canal systems were type 1, 4.8%; type 2, 49.4%, and type 3, 45.8%.
Weine (1) has stated that the frequent failure of endodontic treatment of the maxillary first permanent molar is likely due to the failure to locate and fill the second mesiobuccal (mesiolingual (ML)) canal. This second canal in the mesiobuccal (MB) root has been observed at least since 1925 and 1927 when Hess (2) and Okumura (3) discussed it. However, it was not until 1969 that its significance appeared to be recognized by Weine et al.(4). Since then, its incidence has been reported and discussed by several authors (5-l 5). According to Weine et al. (4), the MB and ML canals generally either join 1 to 4 m m from the apex and exit with a common foramen (type 2), or remain separate and exit through two foramen (type 3). Obviously, before the practitioner can clean, shape, and obturate the ML canal, it must be located. This has proved to be a difficult in vivo procedure for many dental practitioners (8). Hartwell and Bellizzi (11) demonstrated this when they reported treating a second canal in only 18% of 538 maxillary first molars and 9.6% of 176 second molars. However, Neaverth et al. (12) located and treated a much higher percentage, 77.2% (176 of 228), in maxillary first molars.
MATERIALS AND M E T H O D S Fifty-one first molars and 32 second molars were collected and stored in 10% formalin. A standard access was made in each molar and an attempt was made to locate the MS and ML canals utilizing only an endodontic explorer (group 1). Next, new long-shank endodontic round burs were used sequentially (# 8 - 6 - 4 - 2 ) to open the subpulpal groove to locate the ML canal. Dentin was removed carefully at the expense
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of the mesial wall away from the trifurcation area, moving the entire access mesially and apically. The burs were used until the M L canal was located (group 2) or until the subpulpal groove and discolored dentin, appearing to be a calcified canal, was reduced 2 to 3 m m below the pulpal floor. Once a ML canal was located, fine instruments were placed in the MB and M L canals and 35-mm photographs taken (Fig. 1). Radiographs were made of each tooth with files in place. Each tooth was mounted in clear orthodontic resin with the mesial of the MB root perpendicular to the horizontal plane as shown in Fig. 2a. Using a rotating sandpaper disk on a polisher/grinder (Buehler Ltd., Evanston, IL), the crown o f each tooth was removed perpendicular to the long axis of the MB root down to the floor of the chamber (Fig. 2b). Two dots were placed with indelible ink on the superior surface of the base of the acrylic block below the apex of the MB root (Fig. 2a). The dots were placed on a line (B) parallel to a line (A) connecting the center of the lingual (L) canal with a point equidistant between the MB and distobuccal (DB) canals (Fig. 3a). The dots and flat acrylic base allowed the resin block to be reoriented in precisely the same position during measurements using a measuring microscope (Nikon Microscope; Nikon, Inc., Garden City, NY). Evaluation and measurement of the anatomy was then done as the tooth was reduced in 1-mm increments (Fig. 3b). The presence or absence of the M L canal was recorded (Fig. 4), resulting in groups 3 and 4 (Table 1). Ten measurements were made as shown in Fig. 3a (xl-8; yl-2). They gave dentin thickness, mesial and distal of each canal, canal diameters,
and distance between the MB and ML canals. The measurements also allowed evaluation of the movement of the ML canal in respect to the MB canal at each level. RESULTS Table 1 shows that 95.2% of the MB roots of both the first (96.1%) and second (93.7%) maxillary molars had two canals in the coronal half o f the root. The difference between first and second molars was not statistically significance. Fiftyfour percent were located by normal access preparation. Thirty-one percent were located with careful use o f a bur. The microscope revealed M L canals in 8 of the remaining 12 teeth. Only four MB roots (4.8%) did not demonstrate a second canal in the coronal half of the root. Two of the four did manifest a definite M L canal in the apical 3 to 4 m m of the root (type 1A, Fig. 5b).Pearson's chi-square evaluation showed no significance relative to numbers of M L canals located by use of a bur between the first and second molars (p < 0.12). However, for both molars the use of a bur was significant in locating a ML canal at a p < 0.01 incidence. One tooth, a maxillary first molar, had a second M L canal, or three canals, in the MB root (Fig. 3b). The root contained
'
a
FIG 1. Six of the maxillary molars in the study showing characteristic broad configuration of MB root. Note fused DB and L roots of tooth in center bottom row, a second molar.
MB ROOT
2-~- .~
FIG 2. a, Diagram of side view of tooth embedded in acrylic base. Reference dots below apex level allowing reorientation of block during total sectioning of tooth. Perpendicular line (PL) placed on MB root to orientate to acrylic base. b, Cut through chamber of maxillary molar showing lip of dentin over ML canal (arrow).
Vol. 16, No. 7, July 1990
Canal Anatomy in MB Roots
a
At
313
tB I
MB ROOT
X;
x4X3 i.
o|
ROOT
L
(
ROOT .D
i I ACRYLIC BASE
REFERENCE DOTS
J
FIG 3, a, Diagram of occlusal view of section with crown and portion of roots removed. Apices of roots embedded in acrylic base. Reference lines (,4 and B) used to establish reference dots which allowed precise reorientation of acrylic base and tooth to microscope after each section was removed, b, Photograph of sectioned specimen of only tooth in the study that had a second ML canal. Note two orientation dots countersunk below apices of tooth.
a type 3 canal system, and all measurements used were from the buccal and lingual canals. Figure 5 shows the 10 variations observed of the three basic root canal configurations and Table 2 shows the incidence of their occurrence. Pearson's chi-square test showed no significance (p < 0.36) in difference in the incidence of type 2 or 3 canal systems in the MB root of first or second molars. Table 3 shows the average canal separation at each level where two canals were-observed in roots with either the type 2 or 3 canal configurations. The first evidence of an orifice of the ML canal was an average distance of 1.82 m m lingual to the orifice of the MB canal (Table 3). It originated slightly distal to the MB but as it progressed apically it moved immediately mesiolingually relative to the MB canal. At approximately level six, the M L area of the root moved distal in respect to the MB area of the root. In cases where the canal was located without extensive use of the bur, there was often evidence of the dentinal growth over the area where the ML canal orifice was located (Fig. 2b). Table 4 shows the average thickness of dentin mesial and distal to each canal at each level and the average diameter of the canal at each level. Each measurement, except for the area of dentinal growth over the M L orifice, was significantly smaller for the M L area of the root compared with the MB area of the root. There were no cases where the dentin mesial or distal to the M L canal was less than 0.5-mm thick in any sections at the levels where the burs were used. No perforations were identified. Apical to this area of bur use, there were sections of the canal that microscopically appeared to be completely occluded (type 2B and 3B roots) (Fig. 4a). Finally, one or more additional "accessory canals" were observed in the final one or two levels of nine additional MB roots.
DISCUSSION In this investigation, two patent canals could be demonstrated from the chamber to the apical area, exiting via either one or two foramina, in 71.1% (types 2, 2C, 2D, and 3) of the MB roots. Additionally, remnants of canals, or partial canals, were located clinically in an additional 14.4% o f the roots and microscopically in an additional 12%. In some of these roots the point where the canal turned either buccally or lingually was apparently so acute that it was lost during sectioning, resulting in the type 2A and 3A canal configurations. The type 2B and 3B roots appeared to have ML canals that were occluded by calcifications (Fig. 4a) for an extensive portion of their length. This occurred in seven cases or 8.9% of all M L canals. It appeared that the occlusal portion o f these canals was the space created by the bur following the discolored calcified "dot." This was followed by an additional 2 to 3 m m o f calcified canal. The apical portion of the canal was the only truly patent portion of these canals. In two of the type 1 roots, canals were observed only in the apical third (type 1A). Weine (1) has referred to these as type IV canal configurations. However, in this study they were also seen to occur in type 2 canal configurations (type 2D). Therefore, it was decided to consider both as variations of the three basic canal configurations. These apical second canals could have been only accessory canals. However, definite accessory canals, shorter and not necessarily lingual to the MB canal, were seen in nine (10.8%) additional MB roots. One of these accessory canals was present in the apical two sections o f one of the two MB roots with only one primary canal (type 1). The high incidence of two canals in the coronal half o f the MB root strongly supports the hypothesis that two canals are
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FiG 4. a, Photomicrograph of section through roots (level 5) showing remnant of canal between MB and ML canals of maxillary first molar. Note calcified remnant of ML canal (arrow). b, Higher magnification of another mesial root at level with both M B and ML canals patent. TABLE 1. Mesiolingual canals located by each technique
MesiolingualCanals Located Tooth First molars Second molars Total
51 32 83
Group 1
Group 2
Group 3
Group 4
No Bur
Bur
Microscope
1 Canal
3 (5.9%) 5 (15.6%) 8 (9.6%)
2* (3.9%) 2* (6.3%) 4 (4.8%)
31 (60.8%) 15 (29.4%) 14 (43.8%) 11 (34.4%) 45 (54.2%) 26 (31.3%)
* Onecanalin eachgroupwas of the type 1A, or had a secondmajorapicalcanal.
normal in this root in fully developed teeth. This hypothesis also is supported by the basic oblong, "bean-shaped," configuration of the root (Fig. 1). Evaluation of the photomicrographs of the MB roots in this study suggests a developmental pattern. Originally a ribbon bean-shaped canal which conforms to the external anatomy develops within the root. During maturation, the isthmus area between the MB and ML areas closes, leaving a larger MB canal and a smaller ML canal (Fig. 4b). It is proposed that this is the manner in which two canals form in all bean-shaped roots. It is feasible that one or more of the four teeth with only one canal in the MB root became pulpally involved and was extracted prior to final closure of the isthmus.
This investigation found a very low incidence of type 1 canal systems compared with previous studies. One reason could be that this sample of teeth was skewed. However, two other reasons appear more likely. First, the use of the bur and microscope helped identify the highly calcified ML canals which could have been easily missed in previous in vitro studies. Second, previous in vitro studies may have included more pulpally involved teeth from very young patients. It may be that a decrease in caries incidence and an increase in endodontic treatment have significantly reduced the incidence of molars from young patients. Pineda and Kuttler (5) found 48.5% of their maxillary molar cases demonstrated two apical foramen. This study's finding of 51.8% closely approximates their finding. Obviously, with present clinical techniques the second apical foramina of the type IA, 2D, and 3B roots would most likely not be located in present in vivo studies. The authors feel that a combination of factors is responsible for the difficulties encountered in locating the ML canal. First, the ML canal is the smallest canal during normal development (Table 4 and Fig. 4b). Second, during normal development, the ML area of the MB root first moves slightly mesially and lingually (Fig. 3a). This mesial position of the ML canal has been well diagrammed previously (12, 16). Third, these molars often become pulpally involved due to mesial caries. This means that, prior to endodontic therapy, the area most adjacent to this canal experiences the greatest chronic irritation due to caries, deep restorations, leakage, and so forth, prior to the irreversible pulpitis. These irritants could stimulate irritational dentin formation, whether the "dentinal growth" of Acosta and Trugeda (10), pulp stones in the chamber, or the other canal calcifications which appear to add to the difficulty in locating the canal. The MB, DB, and L canals in each tooth were located after standard access preparation and use of an endodontic explorer in the floor of the chamber. These canals were all patent to the apex. However, only 45 of 79 ML canals (60.0%) were located without additional use of a cutting instrument within the pulp chamber, and only 26 of the 34 remaining canals observed were located with use of the bur. Almost 10% (9.6%) of the ML canals were occluded occlusally to such a degree that they were not located even with use of a bur. This study supports the finding of Neaverth et al.(12) that with careful access and opening of the canals, a significant additional number of ML canals can be located. In fact, under ideal in vitro conditions, 90.2% of first molars and 78.2% of second molars had a locatable ML canal. The most important step in successfully locating the ML canal is to establish excellent access to the entire pulp chamber. After the chamber is well cleansed and the three main canals located, the growth needs to be removed so the mesiocentral area of the chamber can be well visualized. This study indicates that at this point, about 50 to 60% of the teeth should contain a ML canal easily entered by an instrument. However, most of the remaining ML roots will contain partially calcified ML canals. Careless search with burs to locate these canals may lead to perforations. However, an indication of their presence is usually noted as a discolored dot area about 1.8 m m lingual to the MB canal. Clinically, it appears that the greatest danger lies in a trifurcation perforation. This occurs when the orifice is lo-
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Canal Anatomy in MB Roots
315
Type 1A
Type 1
b
Type 2
Type 2A
Type 28
Type3
Type 2C
d
Type3A
Type 3B
Type 2D
f
FIG 5. a, Radiographs of one of each type 1 canal configurations observed. Tooth on left had no second canal (type 1) and tooth on the right had a second canal in apical third to fourth levels (type 1A). b, Diagram of type 1 canals, c, Radiographs of five type 2 canal configurations observed: top left, ML canal unites with MB canal at midroot (type 2); top middle, microscopically ML canal appeared to turn toward MB canal but actual point of contact apparently was in area sectioned (type 2A); top right, occlusally, canal appeared to be created by bur following calcified canal. Microscope showed continued calcification in midroot area, but patent apically (Fig. 4a) (type 2B); bottom left, ML canal unites with MB in apical area (type 2C); bottom right, using radiograph only would classify as type 3, but microscope showed canals united in midroot (type 2D). d, Diagram of type 2 canals, e, Radiographs of three type 3 canal configurations observed: top left, two canals from chamber to apex (type 3); top right, canal appeared to turn and exit to lingual about midroot level (type 3A); bottom, occlusally, canal appeared to be created by bur following calcified canal, continued calcificed in midroot area, but patent in apical area (type 3B). f, Diagram of type 3 canals.
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three, four, and six, it had diameters of 0.511, 0.391, and 0.334 mm. A #2 round bur with a diameter of 0.92 m m could not have reached this level (17). The ML canal in this root at the fifth level was 0.246 m m in diameter. With the technique described, ML canals were located in vitro 85% of the time. In each case, use of the described technique resulted in the "heart" rhomboidal shaped access preparation described by Neaverth et al. (12). Three other points can be made re 1ative to the anatomical variations of the M L canal observed in this study. First, as indicated by the standard deviations in Table 3 for the initial three to four levels, the M L canal was generally 1 to 3 m m lingual to the MB canal in both type 2 and 3 canal systems. It was rare for the canals to be over 3 m m apart. Second, in this sample of teeth there were no cases of two lingual canals. Third, while there were cases of fusion between the DB and L roots (Fig. 1) (18), there were no cases of second molars with only two canals (1).
cated beneath the dentinal growth but the dentist does not recognize the initial ML movement of the canal as it progresses apically. In this case, using the bur directly at the initial orifice opening may allow the bur to cut into the floor of the chamber and result in a trifurcation perforation. As described, initially the canal apical to the dentinal growth moves mesiolingually (4, 9). If the dot is followed indiscriminately to the mesial by the bur, the position at which it stops moving to the mesial can be missed, resulting in a mesial surface perforation. However, if the whole mesial wall occlusal to the dot is planed to the mesial as the bur opens the canal apically, the turning of the calcified canal can be observed and followed. In all of the measurements through the first levels, there were no perforations and only one canal with dentin thinner than 0.5 mm. In this canal the dentin was thinner on both the mesial and distal of a MB canal at the fifth level. It appeared to be an area of internal resorption, since, at this level, the canal had a diameter of 1.284 m m whereas at levels
CONCLUSIONS
TABLE 2. Number of teeth in each mesial root configuration Root Type
No. %
1
1A
2
2A
2B
2C
2 2.4
2 2.4
22 26.5
7 8.4
1 1.2
2 2.4
Totals* 4.8
2D
3
9 26 10.8 31.3
49.4
3A
3B
6 7.2
6 7.2
This study demonstrated that the normal anatomy of both the first and second maxillary molars is two canals in the MB root. Careful use of a bur increased the incidence in locating the ML canal, in vitro, from 54.2 to 85.5%.This study also showed that the careful use of a bur in the floor of the chamber should not lead to an increase in perforations. Relative to a plane bisecting the lingual canal and a point midway between the MB and DB roots, the M L canal orifice is initially slightly distal of the MB canal orifice but moves immediately mesiolingually relative to the MB canal. Then, at about the midroot level, the ML canal moves, relative to the MB canal, buccodistally i r a type 2 canal system is present and distally if a type 3 canal system is present. Both the MB and M L canals have thicker dentin on the mesial than on the distal and the MB canal is consistently larger than the M L canal. Microscopically, there were 10 primary variations of the three basic root canal systems. Microscopic evaluation also revealed only 4.8% of the roots as a true type 1 canal system, 49.4%, type 2, and 45.8%, type 3.
45.8
* Total percentage of each type of root.
TABLE 3. Mean distance at each level between centers of MB and ML canals (in millimeters) for type 2 and 3 roots Level Root Type 1 2
3
2
3
4
5
6
7
8
9
mm 1 . 8 0 1.85 1.99 1.78 1.47 1.07 1,01 0.74 1.03 SD 0.69 0.82 0.72 0.71 0.61 0 . 5 9 0.51 0.54 0.62 No.* 41 41 41 41 39 27 20 19 11t mm 1 . 8 4 1.88 1.96 1.82 1.83 1.72 1.75 1.48 0.74 SD 0.85 0.94 0.79 0.76 0.64 0.64 0.51 0.99 0.45 No.* 38 38 38 33 30 28 29 26 5
* Number of roots with two canals available at each level. t Relates to type 2D's (apical second canal).
TABLE 4. Mean thickness of dentin (mesial and distal) of each canal and mean diameters of each canal* Level
Wall mesial to MB canal Wall mesial to ML canal Diametert MB canal Diameter? ML canal Wall distal to MB canal Wall distal to ML canal
mm SD mm SD mm SD mm SD mm SD mm SD
1
2
3
4
5
6
7
8
9
2.30 0.33 2.4610.41 0.68 0.55 0.38 0.25 --w
2.08 0.35 2.07 0.37 0.61 0.25 0.35 0.11
1.76 0.25 1.57 0.32 0.52 0.18 0.44 0.08 1.50 0.28 1.11 0.26
1.52 0.20 1.27 0.20 0.44 0.09 0.30 0.09 1.40 0.38 1.21 0.28
1.39 0.28 1.21 0.22 0.45 0.21 0.25 0.08 1.28 0.31 1.13 0.28
1.37 0.26 1.1 8 0.30 0.39 0.07 0.25 0.10 1.33 0.31 1.15 0.32
1.33 0,31 1,11 0,33 0,37 0,03 0,25 0,16 1,35 0,34 1,12 0.30
1.20 0.34 1.17 0.36 0.31 0.08 0.20 0.07 1.23 0.25 1.13 0.45
1.13 0.39 0.95 0.35 0.26 0.08 0.15 0.05 1.06 0.38 0.94 0.40
* Comparison was made in all measurements between type 2 and type 3 canals. There were no significant differences at the p < 0.05 level. t Area of remnant of dentinal growth over first location of orifice of ML canal. 1: Measurements used in occlusal three levels only from canals where no bur was used to locate canals. w Dentin trifurcation area,
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Canal Anatomy in MB Roots
The authors wish to thank Dr. Patrice D. Primack and Dr. Jerome C. Donnelly for their help in classifying each tooth, Mrs. Mary Scovill for her assistance in preparation of the manuscript, Dr. Richard Guerin for helping design the study, and Dr. Lewis Lorton for helping with the statistical analysis. The opinions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense. Dr. Kulild, a Colonel, US Army Dental Corps, is presently assistant director, Endodontic Residency Program, Ft. Gordon, GA. Dr. Peters, a Colonel, US Army Dental Corps, is commander, US Army DENTAC, Ft. Gordon, and former director, Endodontic Residency Program, US Army Institute of Dental Research, Walter Reed Army Medical Center, Washington, DC.
References 1. Weine FS. Endodontic therapy. St. Louis: CV Mosby, 1982:210-35. 2. Hess W. The anatomy of the root canals of the teeth of permanent dentition. London: John Bale, Sons & Danielsson Ltd., 1925. 3. Okumura T. Anatomy of the root canals. J Am Dent Assoc 1927;14:6326. 4. Weine FS, Healey NJ, Gerstein H, Evanson L, Canal configuration in the mesiobuccal root of the maxillary first molar and its endodontic significance. Oral Surg 1969;28:419-25. 5. Pineda F, Kuttler Y. Mesiodistal and buccolingual roentgenographic investigation of 7,275 root canals. Oral Surg 1972;33:101-10.
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6. Pineda F. Roentgenographic investigation of the mesiobuccal root of the maxillary first molar, Oral Surg 1973;36:253-60. 7. Green D. Double canals in single roots. Oral Surg 1973;35:689-96. 8. Seidberg BH, Altman M, Guttuso J, Suson M. Frequency of two mesiobuccal root canals in maxillary permanent first molars. J Am Dent Assoc 1973;87:852-6. 9. Pomeranz H, Fishelberg G. The secondary mesiobuccal canal of maxillary molars. J Am Dent Assoc 1974;88:119-24. 10. Acosta Vigouroux SA, Trugeda Bossans SA. Anatomy of the pulp chamber floor of the permanent maxillary first molar. J Endodon 1978;4:2149. 11. Hartwell G, Bettizzi R. Clinical investigation of in vivo endodonticatly treated mandibular and maxillary molars. J Endodon 1982;12:555-7. 12. Neaverth EJ, Kotler LM, Kaltenback RF. Clinical investigation (in vivo) of endodontically treated maxillary first molars. J Endedon 1987; 13:506-12. 13. Nosonowitz DM, Brenner MR. The major canals of the mesiobuccal root of the maxillary 1st and 2nd molars. NY J Dent 1973;43:1215. 14. Slowey RR. Root canal anatomy road map to successful endedontics. Dent Clin North Am 1979;23:555-73. 15. Sampeck BS. Instruments of endedontics: their manufacture, use, and abuse. Dent Clin North Am 1967;579-601. 16. Bower RC. Furcation morphology relative to periodontal treatment: furcation root surface anatomy. J Peddonto11979;50:366-74. 17. Kessler JR, Peters DD, Lorton L. Comparison of the relative risk of molar root perforation using various endodontic instrumentation techniques. J Endodon 1983;9:439-47. 18. Cecic P, Hartwell G, Bellizzi R. The multiple root canal system in the maxillary first molar: a case report. J Endodon 1982;8:113-5.
