- Email: [email protected]
The Operating Microscope Enhances Detection and Negotiation of Accessory Mesial Canals in Mandibular Molars
Clinical Research
The Operating Microscope Enhances Detection and Negotiation of Accessory Mesial Canals in Mandibular Molars Meric Karapinar-Kazandag, DDS, PHD,* Bettina R. Basrani, DDS, PhD,† and Shimon Friedman, DMD† Abstract Introduction: Detection and negotiation of accessory mesial canals in mandibular molars was investigated with the aid of magnifying loupes or the operating microscope. Methods: First and second mandibular molars (n = 96) were mounted in mannequins. Three independent investigators (endodontists) prepared access cavities using 4.5 loupes, attempting to detect and negotiate accessory mesial canals with ultrasonic instruments. If detection or negotiation was unsuccessful, the procedure was continued using the microscope. The location of accessory mesial canals was mapped in relation to the main mesial canals, and their pathway shown with inserted files. The mesial roots were cross-sectioned at three levels to inspect for nonnegotiated accessory mesial canals. Results: With the microscope, the number of detected accessory mesial canals increased from 8 (16%) to 9 (18%) in first molars and from 8 (16%) to 11 (22%) in second molars. Negotiated accessory mesial canals increased from 6 (12%) to 7 (14%) and from 5 (10%) to 9 (18%) in the first and second molars, respectively. All 20 detected accessory mesial canals were located in the mesial subpulpal groove, closer to the mesiolingual canal (45%), in the middle (30%), or closer to the mesiobuccal canal (25%). All negotiated accessory mesial canals merged with one of the main two canals. Cross-sections of the roots confirmed that no accessory canals were present in addition to those negotiated. Conclusions: Within the limitations of this study, more accessory canals were detected and negotiated when using the microscope compared with loupes. This improvement was more pronounced in second molars than in first molars. All negotiated accessory canals merged with either one of the main mesial canals. (J Endod 2010;36:1289–1294)
Key Words Accessory canals, magnifying loupes, mandibular molars, operating microscope
T
he recent influx of current technologies intended for endodontic treatment has been focused largely on improving the quality of treatment. The primary example of this trend has been the introduction to endodontics of the operating microscope, widely accepted as a beneficial aid in improving clinicians’ ability to detect root canals (1, 2), particularly in teeth in which accessory canals are present. Several investigations have supported the advantage of the microscope over the use of no magnification (3–9). When compared with magnifying loupes, the microscope was either comparable (9) or superior (7). For the test model, researchers have used the frequently present but often elusive accessory canal in the mesiobuccal (MB) root of maxillary molars (4, 6–10). According to Gorduysus et al (6), clinicians did not detect more accessory canals in maxillary molars with the aid of the microscope, but their ability to negotiate the canals improved by over 10% when compared with no magnification. One of the teeth with a complex root canal system is the mandibular molar, as shown in the early work of Hess and Zurcher (11) and in subsequent investigations (5, 12–25). The mesial root in mandibular molars is commonly considered to have two canals (11–13) with an isthmus in between (14, 16, 21, 24, 26–28). Within this system, the presence of an accessory mesial canal has been identified with a prevalence ranging from 0% to 17% (5, 12–22, 24, 25) (Table 1). The discrepancy between the studies has been attributed to ethnicity (29), age (28, 30), and sex (23). Although the location of the accessory mesial canal orifice has been reported closer to the mesiolingual (ML) canal (5), its pathway converges with either the ML(15) canal or the MB canal (17, 18). When explored with the aid of the operating microscope, an accessory mesial canal was detected in 17% of first molars and under 5% of second molars compared with 0% when no magnification was used (5). Apart from the prevalence, the ability to negotiate the detected accessory mesial canals, including the troughing depth required to enable negotiation, has not been well characterized. The primary purpose of this study was to assess the ability to detect and negotiate the accessory mesial canals in mandibular first and second molars, with the aid of magnifying loupes and the microscope. The secondary goal was to characterize the detected canals with regard to prevalence, location, negotiability, and pathway.
Methods This study methodology was modeled after a previous study on maxillary molars (6). Mandibular first and second molars were collected from oral surgery clinics in Istanbul, Turkey, and exposed on periapical radiographs in the buccolingual direction. After exclusion of molars with previous endodontic treatment, a deficient coronal
From the *Department of Endodontics Faculty of Dentistry, Yeditepe University, Istanbul, Turkey; and †Discipline of Endodontics, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada. Address requests for reprints to Dr Meric Karapinar-Kazandag, Yeditepe University, Faculty of Dentistry, Department of Endodontics, Bagdat cad No:238 34728, Goztepe/Istanbul/Turkey. E-mail address: [email protected]. 0099-2399/$0 - see front matter Copyright ª 2010 American Association of Endodontists. doi:10.1016/j.joen.2010.04.005
JOE — Volume 36, Number 8, August 2010
Accessory Mesial Canals in Mandibular Molars
1289
Clinical Research TABLE 1. Summary of Studies on the Prevalence of Accessory Mesial Canals in Mandibular Molars Number of molars (n)
Mesial accessory canals (%n)
Study
Methodology
First
Second
First
Second
Skidmore & Bjorndal, 1971 Pineda & Kuttler, 1972 Pomeranz et al, 1981 Martinez-Berna, 1983 Vertucci, 1984 Fabra-Campos, 1985 Fabra-Campos, 1989 Goel, 1991 Caliskan et al, 1995 de Carvalho & Zuolo, 2000 Gulabivala et al, 2001 Gulabivala et al, 2002 Sert & Bayirli, 2004 Ahmed et al, 2007 Navarro et al, 2007
Plastic casts Radiography Clinical Clinical Clearing Clinical Clinical Clinical Clearing Extracted teeth Clearing Clearing Clearing Clearing Micro-CT Scanning electron microscope
45 300 61 1,418 100 145 760 60 100 93 139 118 200 100 27 25
40 300 39 944 100 0 0 0 100 111 134 60 200 100 0 0
0 0 11.4 1.3 1 2.7 2.6 15 3.4 17.2 7.1 5.9 1.5 4 14.8 12
0 0 12.8 0.2 0 — — — 1.9 4.5 0 1.7 0 0 — —
structure nonamenable to conventional endodontic access cavity preparation, aberrant anatomy, calcified canals, fused roots, single roots, and C-shaped canals, 48 first and 48 second molars were selected for the study. They were stored in 0.1% thymol solution until used. The teeth were embedded in dentaforms and mounted in mannequins to simulate clinical conditions as best as possible. Conventional endodontic access cavities were completed in all teeth with the aid of 4.5 magnification loupes. Each of the first and second molars groups was randomly divided into three subgroups (n = 18). Three endodontists were assigned a subgroup of first and second molars each. Working independently, they set out to explore the mesial root canals in an attempt to detect accessory mesial canals using a standardized sequence as follows. In the first stage, only loupes were used for magnification. The access cavity was refined with ultrasonic tips (Buc 1 and Buc 3; Sybron
Endo, Orange, CA) to remove any dentin overhanging the mesial canal orifices and the isthmus. The mesial subpulpal groove was explored with sharp endodontic explorers (DG 16; Hu-Friedy, Chicago, IL, and Stewart probe; Premier Dental Products, Norristown, PA), and the number of canal orifices detected was recorded. Attempts were then made to negotiate detected accessory mesial canals with size 06 Ktype hand files (Dentsply Maillefer, Balleigue, Switzerland). When negotiation was unsuccessful, the isthmus was troughed apically with the ultrasonic tips to pursue the accessory canal deeper into the root while repeating negotiation attempts. Irrigation with 1% NaOCl and a Stropko air irrigator (Sybron Endo) were used intermittently to optimize visibility. Troughing was continued apically until (1) the accessory mesial canal was negotiated, (2) it was considered too risky to continue troughing further apically, (3) the accessory mesial canal was no longer detectable, or (4) a perforation occurred.
Figure 1. (A-C) Radiographs of mandibular molars exposed from the mesial direction (the distal roots were resected) showing the pathway of the accessory mesial canals. Files were inserted into the MB, ML, and accessory canals. (D) The depth of dentin removal while troughing to negotiate the accessory canal using the pulp chamber floor as a reference.
1290
Karapinar-Kazandag et al.
JOE — Volume 36, Number 8, August 2010
Clinical Research In the second stage, the teeth in which no accessory mesial canal was detected and those in which a detected accessory mesial canal could not be negotiated were submitted to further investigation aided with the microscope (Protege, Global Surgical Corp, St Louis, MO). Under the microscope, further dentin was selectively removed along the subpulpal groove with the ultrasonic tips while repeating negotiation attempts. Again, the results were recorded in the same four categories defined previously. In the third stage, a K-type file was negotiated into each of the mesial canals as far apically as possible. The teeth were removed from the dentaforms and then exposed on periapical radiographs from the mesial direction to show the pathways of the mesial canals (Fig. 1). In the fourth stage, the files were removed, and 1% sodium hypochlorite was left in the pulp chambers for 24 hours in order to remove any soft-tissue remnants. The chambers were dried and subsequently photographed with the aid of a stereomicroscope (Nikon, Tokyo, Japan). The number of teeth having 1, 2 (Fig. 2A), or 3 (Fig. 2B and C) canals or an open isthmus (Fig. 2D) was recorded. The location of the accessory mesial canals orifices in the photographs was mapped with the aid of Spot Software (Diagnostic Instruments, Sterling Heights, MI).
At the fifth stage, the distal roots of the teeth were resected, and radiographs of the teeth were exposed from the mesial aspect. These radiographs were digitized (Sony Cyber-shot, DSC-W80, Tokyo, Japan), and the depth of dentin removal was measured with Spot Software using the pulp chamber floor as reference (Fig. 1D). Finally, the mesial roots of all 96 molars were sectioned at three levels: 1 mm, 4 mm, and 8 mm from the apex. The sectioned surfaces at each level were examined under the operating microscope at 30 magnification to detect additional accessory mesial canals beyond those detected during the experimental procedure and to trace the pathway of detected accessory mesial canals relative to the main canals.
Results Tables 2 and 3 summarize the results of the investigation in the 96 first and second mandibular molars, regarding the effect of magnification aids on detection and negotiation of accessory mesial canals, the location and pathways of the accessory canals and the depth of troughing required to negotiate or rule out the presence of the accessory canals.
Figure 2. Photographs and a schematic representation of the subpulpal groove observed in mandibular molars with (A) two canals, (B and C) three canals, and (D) an open isthmus.
JOE — Volume 36, Number 8, August 2010
Accessory Mesial Canals in Mandibular Molars
1291
Clinical Research TABLE 2. Numbers and Proportion of Detected and Negotiated Accessory Mesial Canals in Mandibular Molars First molars (n = 48) Magnification aid
Second molars (n = 48)
Total (n = 96)
Detected
Negotiated
Detected
Negotiated
Detected
Negotiated
8 (16) 9 (18)
6 (12) 7 (14)
8 (16) 11 (22)
5 (10) 9 (18)
16 (16) 20 (20)
11 (11) 16 (16)
Loupes (%) Microscope (%)
Loupes were used first as the magnification aid followed by the use of the operating microscope for teeth where the previous attempts were unsuccessful.
Effect of Magnification Aids The total number of accessory mesial canals detected and negotiated was 4% higher in the second molars than in the first molars (Table 2). In both tooth types, the use of the microscope improved the results achieved with the loupes. The total number of detected and negotiated accessory mesial canals increased from 16% to 20% and from 11% to 16%, respectively, with 4 of 20 accessory mesial canals (20%) detected but not negotiated. Location of Accessory Mesial Canal Orifices All 20 accessory mesial canals were located in the mesial subpulpal groove. The distribution pattern along the groove was rather similar in the first and second molars, with the highest proportion of accessory mesial canals (45%) located closer to the ML canals, 30% located in the middle between the MB and ML canals, and 25% located closer to the MB canals (Table 3). The mean distance between the MB and ML canals in the first and second molars was 3.2 0.8 mm and 2.8 0.9 mm, respectively. When the accessory mesial canals were closer to either the ML or MB canals, their distance from the closest main canal was greater in the first molars (1.0-1.3 mm) than in the second molars (0.8-0.9 mm) (Table 3). Pathways of Negotiated Accessory Mesial Canals All 16 negotiated accessory mesial canals were confluent with the main canals, with none terminating in an independent apical foramen (Table 3). The pathways of the accessory mesial canals differed between the first and second molars. In the first molars, the majority (42%) merged with the MB canals, whereas in the second molars 55% merged with the ML canals. Cross-sections of the roots revealed only the negotiated accessory mesial canals at the 8-mm level, suggesting that all accessory mesial canals present were successfully negotiated. None of
the negotiated accessory mesial canals were observed at 4 mm from the apex.
Depth of Troughs Required The mean depth of dentin removed in order to negotiate or rule out the presence of accessory mesial canals in the first and second molars was 1.1 1.4 mm and 0.7 0.6 mm, respectively (Table 3).
Discussion One of the challenges facing clinicians when performing endodontic treatment in molars is the complexity of the root canal systems. Although the high-prevalence accessory mesiobuccal canals in maxillary molars have been well characterized (4, 6–10), the lower-prevalence accessory mesial canals in mandibular molars (12–14, 20–24) are not well recognized by clinicians. The accessory mesial canals invariably originate within the subpulpal groove or isthmus connecting the two main canals (14, 16, 21, 24, 26–28), making their detection very challenging. This study was undertaken to assess the potential to facilitate the detection and negotiation of accessory mesial canals in mandibular molars with the aid of the operating microscope. Teeth were mounted in dentaforms to simulate clinical conditions (6, 8). The detection of accessory mesial canals without magnification aids, which was assessed in several previous studies (5, 6, 8, 9), was not attempted because currently magnification is considered indispensable when performing endodontic treatment (1, 29). Thus, 4.5 loupes were used first to enhance magnification, followed by the use of the operating microscope (up to 30 power) to assess its potential advantage. The access cavities were refined with ultrasonic tips to allow accurate, controlled removal of dentin along the mesial subpulpal groove in search for accessory mesial canal orifices. The mesial dentinal protuberance was removed to afford a direct view of
TABLE 3. Characteristics of Detected and Negotiated Accessory Mesial Canals (AMCs) in Mandibular Molars First molars
Second molars
Location (%) Closer to MB Closer to ML At middle
Observation
n = 9 detected 2 (22) 4 (44) 3 (33)
n = 11 detected 3 (27) 5 (45) 3 (27)
n = 20 detected 5 (25) 9 (45) 6 (30)
Total
Distance (mm) MB to ML AMC to MB* AMC to ML*
3.21 0.76 1.00 0.28 1.30 0.14
2.80 0.90 0.87 0.39 0.81 0.58
Mean 3.00 0.90 Mean 0.93 0.32 Mean 0.95 0.53
Pathway (%) Merged with MB Merged with ML Merged with both
n = 7 negotiated 3 (42) 2 (29) 2 (29)
n = 9 negotiated 3 (33) 5 (55) 1(11)
n = 16 negotiated 6 (38) 7 (43) 3 (19)
Depth† (mm)
1.10 1.14
0.66 0.57
0.93 0.94
AMC, accessory mesial canals; MB, mesiobuccal; ML, mesiolingual. Location and pathway are related to the main canals in the mesial root, the MB, and the ML. *Teeth where the AMC was closest to either main canal. † Relative to the pulp chamber floor.
1292
Karapinar-Kazandag et al.
JOE — Volume 36, Number 8, August 2010
Clinical Research the line angle between the mesial wall and the pulp chamber floor (17).The investigators were three endodontists with varying levels of experience to eliminate the individual’s skill as a dominant variable. Accessory mesial canals were characterized for proportion of successful detection (5) and negotiation (14), location and depth of the orifices (6), and pathway (18). The findings were confirmed for accuracy by radiographic examination (31) and cross-sectioning of the mesial roots (7, 8, 32). With the aid of the microscope, the number of detected accessory mesial canals increased by 4% overall in all teeth, with a greater improvement in the second molars (6%) than in the first molars (2%). When the use of the microscope was compared with no magnification in a previous study (5), the number of detected accessory mesial canals increased by 17% in first molars and by almost 5% in second molars. Also, in maxillary molars, the microscope facilitated the detection of MB2 canals (4, 6, 8, 9). Our ability to negotiate accessory mesial canals with the aid of loupes in 12% and 10% of first and second molars, respectively, was similar to that reported previously without any magnification (14). Importantly, the final microscope-aided negotiation of accessory mesial canals in 14% of the first molars matched the 14.8% observed by computerized tomography (25), which is the ultimate method for investigating root canal morphology. Also, as suggested earlier, crosssections through the roots confirmed that no additional accessory mesial canals were present beyond the negotiated ones. The greater benefit of the microscope in the second molar was again apparent, with the 8% increase in negotiated accessory mesial canals, compared with the 2% increase in the first molars. The second molars have been reported to have accessory mesial canals less frequently (5, 16, 20–24) and an isthmus more frequently (21, 22) than the first molars. However, our combined use of microendodontic instruments (4) and the microscope facilitated exploration of the isthmuses (33), resulting in additional accessory mesial canals negotiated in the second molars. Pomeranz et al (14) classified the accessory mesial canals into three categories: (1) ‘‘fin,’’ allowing free instrument movement between the main and accessory canals (we did not consider such fins as accessory mesial canals); (2) ‘‘independent,’’ having a separate orifice and apical terminus, which is known to be rare (5, 12–25) and was not observed in our sample; and (3) ‘‘confluent,’’ having a separate orifice but merging more apically with the MB or ML canals as in all accessory mesial canals observed in our sample (15, 17, 18). Although also relating detected and negotiated accessory mesial canals to this classification, we aimed primarily to map the location of accessory mesial canals in relation to the main mesial canals (MB and ML). The main purpose of such mapping was to provide clinicians with a navigation guide for detection of accessory mesial canals, such as previously reported for maxillary molars (6). All of the accessory mesial canals were located in the mesial subpulpal groove (5, 25, 33). In about 45% of both the first and second molars, the accessory mesial canals were detected closer to the ML canals, which is in agreement with previous reports (5). The mean distance from the ML orifice was longer in the first molars (1.3 mm) than in the second molars (0.8 mm), reflecting the larger buccal-lingual dimension of the pulp chamber in the former. Thus, clinicians should specifically search for accessory mesial canals starting from the ML canal orifice and progress systematically along the subpulpal groove towards the MB canal. Frequently, there was the need to explore the mesial subpulpal groove by troughing in the apical direction to allow negotiation of a detected accessory mesial canal with an endodontic instrument. The mean depth of the troughs in the first molars reached 1.1 mm compared with
JOE — Volume 36, Number 8, August 2010
approximately 0.7 mm in the second molars. Although in several teeth the troughs were as deep as 2.2 mm, we found them less deep than what is occasionally required in maxillary molars when accessory MB canals are negotiated (6). In the maxillary molars, the accessory MB canals depart the chamber at a sharp mesial inclination and then bend again distally, which makes their negotiation challenging (6); the deeper trough helps eliminate the first angled portion of the canal, allowing insertion of instruments beyond the bend (6). In the mandibular molars, once the mesial dentinal protuberance is eliminated, the accessory mesial canals are not strongly inclined mesially, and they do not bend distally after departing the chamber. Thus, a shallow trough is sufficient to allow insertion of instruments into the accessory mesial canals. All the negotiated accessory mesial canals in this study were confluent with one of the main mesial canals, but the confluence pattern differed between the first and second molars. In the former, the accessory mesial canals frequently crossed the midline and merged with the MB canals (17, 18), whereas in the latter they more frequently merged with the ML canals (15). The cross-sections through the roots confirmed that all negotiated accessory mesial canals were no longer observed at 4 mm from the apex, having blended with either the isthmus or one of the main canals. This finding supported the argument that the accessory mesial canals are not additional canals but rather an access into the isthmus between the main canals (33). The isthmus is a characteristic feature of the mesial roots of mandibular molars found in 17% to 83% of first molars, most frequently at the level of 3 to 6 mm from the apical foramen (26–28). It has been defined as a lateral interconnection (13), transverse anastomosis (12, 16), or intercanal communication (32, 21). It can be complete, forming a continuous connection between the main canals, or partial, forming an incomplete or narrow communication with one or more patent openings (32). Despite current advances in irrigation delivery, disinfection of the isthmus is an elusive goal (34, 35). The accessory mesial canals, when negotiated and shaped, comprise a pathway into the isthmus (33), which may provide access for irrigation solutions and root filling materials. This appears to be the main clinical significance of detecting and attempting to negotiate accessory mesial canals in the mandibular molars. In conclusion, within its limitations, this study suggested that use of the operating microscope enhanced both the detection and negotiation of accessory mesial canals in the mandibular first and second molars beyond what could be achieved with the aid of loupes. This benefit was more pronounced in the second molars than in the first molars, resulting in an 8% increase in the number of negotiated accessory canals. Not all detected accessory canals could be negotiated. Although accessory canals were negotiated in as many as 14% of first molars and 18% of second molars, all of these canals merged with either one of the main mesial canals. The importance of negotiating the accessory mesial canals in mandibular molars is in the access it provides for irrigation solutions and filling materials into the otherwise inaccessible isthmus.
References 1. Kersten DD, Mines P, Sweet M. Use of the microscope in endodontics: results of a questionnaire. J Endod 2008;34:804–7. 2. Lee M, Winkler J, Hartwell G, et al. Current trends in endodontic practice: emergency treatments and technological armamentarium. J Endod 2009;35:35–9. 3. Saunders WP, Saunders EM. Conventional endodontics and the operating microscope. Dent Clin North Am 1997;41:415–28. 4. Stropko JJ. Canal morphology of maxillary molars: clinical observations of canal configurations. J Endod 1999;25:446–50. 5. de Carvalho MC, Zuolo ML. Orifice locating with a microscope. J Endod 2000;26: 532–4.
Accessory Mesial Canals in Mandibular Molars
1293
Clinical Research 6. Gorduysus MO, Gorduysus M, Friedman S. Operating microscope improves negotiation of second mesiobuccal canals in maxillary molars. J Endod 2001;27:683–6. 7. Schwarze T, Baethge C, Stecher T, et al. Identification of second canals in the mesiobuccal root of maxillary first and second molars using magnifying loupes or an operating microscope. Aust Endod J 2002;28:57–60. 8. Baldassari-Cruz LA, Lilly JP, Rivera EM. The influence of dental operating microscope in locating the mesiolingual canal orifice. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002;93:190–4. 9. Buhrley LJ, Barrows MJ, BeGole EA, et al. Effect of magnification on locating the MB2 canal in maxillary molars. J Endod 2002;28:324–7. 10. Sempira HN, Hartwell GR. Frequency of second mesiobuccal canals in maxillary molars as determined by use of an operating microscope: a clinical study. J Endod 2000;26:673–4. 11. Hess W, Zurcher E. The anatomy of the root canals of the teeth of the permanent and deciduous dentitions. New York: William Wood & Co; 1925. 12. Skidmore AE, Bjorndal AM. Root canal morphology of the human mandibular first molar. Oral Surg Oral Med Oral Pathol 1971;32:778–84. 13. Pineda F, Kuttler Y. Mesiodistal and buccolingual roentgenographic investigation of 7,275 root canals. Oral Surg Oral Med Oral Pathol 1972;33:101–10. 14. Pomeranz HH, Eidelman DL, Goldberg MG. Treatment considerations of the middle mesial canal of mandibular first and second molars. J Endod 1981;7:565–8. 15. Martinez-Berna A, Badanelli P. Investigacion clinica de molars inferiors con cinco conductos. Boletin de Informacion Dental 1983;43:27–41. 16. Vertucci FJ. Root canal anatomy of the human permanent teeth. Oral Surg Oral Med Oral Pathol 1984;58:589–99. 17. Fabra-Campos H. Unusual root anatomy of mandibular first molars. J Endod 1985; 11:568–72. 18. Fabra-Campos H. Three canals in the mesial root of mandibular first permanent molars: a clinical study. Int Endod J 1989;22:39–43. 19. Goel N, Gill K, Taneja J. Study of root canals configuration in mandibular first permanent molar. J Indian Soc Pedod Prev Dent 1991;8:12–4. 20. Caliskan MK, Pehlivan Y, Sepetcioglu F, et al. Root canal morphology of human permanent teeth in a Turkish population. J Endod 1995;21:200–4. 21. Gulabivala K, Aung TH, Alavi A, et al. Root and canal morphology of Burmese mandibular molars. Int Endod J 2001;34:359–70.
1294
Karapinar-Kazandag et al.
22. Gulabivala K, Opasanon A, Ng YL, et al. Root and canal morphology of Thai mandibular molars. Int Endod J 2002;35:56–62. 23. Sert S, Bayirli GS. Evaluation of the root canal configurations of the mandibular and maxillary permanent teeth by gender in the Turkish population. J Endod 2004;30: 391–8. 24. Ahmed HA, Abu-bakr NH, Yahia NA, et al. Root and canal morphology of permanent mandibular molars in a Sudanese population. Int Endod J 2007;40:766–71. 25. Navarro LF, Luzi A, Garcia AA, et al. Third canal in the mesial root of permanent mandibular first molars: review of the literature and presentation of 3 clinical reports and 2 in vitro studies. Med Oral Patol Oral Cir Bucal 2007; 12:E605–9. 26. Mannocci F, Peru M, Sherriff M, et al. The isthmuses of the mesial root of mandibular molars: a micro-computed tomographic study. Int Endod J 2005; 38:558–63. 27. von Arx T. Frequency and type of canal isthmuses in first molars detected by endoscopic inspection during periradicular surgery. Int Endod J 2005;38:160–8. 28. Gu L, Wei X, Ling J, et al. A microcomputed tomographic study of canal isthmuses in the mesial root of mandibular first molars in a Chinese population. J Endod 2009; 35:353–6. 29. Vertucci F. Root canal morphology and its relationship to endodontic procedures. Endod Topics 2005;10:3–29. 30. Peiris HR, Pitakotuwage TN, Takahashi M, et al. Root canal morphology of mandibular permanent molars at different ages. Int Endod J 2008;41:828–35. 31. Kulild JC, Peters DD. Incidence and configuration of canal systems in the mesiobuccal root of maxillary first and second molars. J Endod 1990;16:311–7. 32. Weller RN, Niemczyk SP, Kim S. Incidence and position of the canal isthmus. Part 1. Mesiobuccal root of the maxillary first molar. J Endod 1995;21:380–3. 33. Mortman RE, Ahn S. Mandibular first molars with three mesial canals. Gen Dent 2003;51:549–51. 34. Burleson A, Nusstein J, Reader A, et al. The in vivo evaluation of hand/rotary/ultrasound instrumentation in necrotic, human mandibular molars. J Endod 2007;33: 782–7. 35. Carr GB, Schwartz RS, Schaudinn C, et al. Ultrastructural examination of failed molar retreatment with secondary apical periodontitis: an examination of endodontic biofilms in an endodontic retreatment failure. J Endod 2009;35:1303–9.
JOE — Volume 36, Number 8, August 2010
The Operating Microscope Enhances Detection and Negotiation of Accessory Mesial Canals in Mandibular Molars Meric Karapinar-Kazandag, DDS, PHD,* Bettina R. Basrani, DDS, PhD,† and Shimon Friedman, DMD† Abstract Introduction: Detection and negotiation of accessory mesial canals in mandibular molars was investigated with the aid of magnifying loupes or the operating microscope. Methods: First and second mandibular molars (n = 96) were mounted in mannequins. Three independent investigators (endodontists) prepared access cavities using 4.5 loupes, attempting to detect and negotiate accessory mesial canals with ultrasonic instruments. If detection or negotiation was unsuccessful, the procedure was continued using the microscope. The location of accessory mesial canals was mapped in relation to the main mesial canals, and their pathway shown with inserted files. The mesial roots were cross-sectioned at three levels to inspect for nonnegotiated accessory mesial canals. Results: With the microscope, the number of detected accessory mesial canals increased from 8 (16%) to 9 (18%) in first molars and from 8 (16%) to 11 (22%) in second molars. Negotiated accessory mesial canals increased from 6 (12%) to 7 (14%) and from 5 (10%) to 9 (18%) in the first and second molars, respectively. All 20 detected accessory mesial canals were located in the mesial subpulpal groove, closer to the mesiolingual canal (45%), in the middle (30%), or closer to the mesiobuccal canal (25%). All negotiated accessory mesial canals merged with one of the main two canals. Cross-sections of the roots confirmed that no accessory canals were present in addition to those negotiated. Conclusions: Within the limitations of this study, more accessory canals were detected and negotiated when using the microscope compared with loupes. This improvement was more pronounced in second molars than in first molars. All negotiated accessory canals merged with either one of the main mesial canals. (J Endod 2010;36:1289–1294)
Key Words Accessory canals, magnifying loupes, mandibular molars, operating microscope
T
he recent influx of current technologies intended for endodontic treatment has been focused largely on improving the quality of treatment. The primary example of this trend has been the introduction to endodontics of the operating microscope, widely accepted as a beneficial aid in improving clinicians’ ability to detect root canals (1, 2), particularly in teeth in which accessory canals are present. Several investigations have supported the advantage of the microscope over the use of no magnification (3–9). When compared with magnifying loupes, the microscope was either comparable (9) or superior (7). For the test model, researchers have used the frequently present but often elusive accessory canal in the mesiobuccal (MB) root of maxillary molars (4, 6–10). According to Gorduysus et al (6), clinicians did not detect more accessory canals in maxillary molars with the aid of the microscope, but their ability to negotiate the canals improved by over 10% when compared with no magnification. One of the teeth with a complex root canal system is the mandibular molar, as shown in the early work of Hess and Zurcher (11) and in subsequent investigations (5, 12–25). The mesial root in mandibular molars is commonly considered to have two canals (11–13) with an isthmus in between (14, 16, 21, 24, 26–28). Within this system, the presence of an accessory mesial canal has been identified with a prevalence ranging from 0% to 17% (5, 12–22, 24, 25) (Table 1). The discrepancy between the studies has been attributed to ethnicity (29), age (28, 30), and sex (23). Although the location of the accessory mesial canal orifice has been reported closer to the mesiolingual (ML) canal (5), its pathway converges with either the ML(15) canal or the MB canal (17, 18). When explored with the aid of the operating microscope, an accessory mesial canal was detected in 17% of first molars and under 5% of second molars compared with 0% when no magnification was used (5). Apart from the prevalence, the ability to negotiate the detected accessory mesial canals, including the troughing depth required to enable negotiation, has not been well characterized. The primary purpose of this study was to assess the ability to detect and negotiate the accessory mesial canals in mandibular first and second molars, with the aid of magnifying loupes and the microscope. The secondary goal was to characterize the detected canals with regard to prevalence, location, negotiability, and pathway.
Methods This study methodology was modeled after a previous study on maxillary molars (6). Mandibular first and second molars were collected from oral surgery clinics in Istanbul, Turkey, and exposed on periapical radiographs in the buccolingual direction. After exclusion of molars with previous endodontic treatment, a deficient coronal
From the *Department of Endodontics Faculty of Dentistry, Yeditepe University, Istanbul, Turkey; and †Discipline of Endodontics, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada. Address requests for reprints to Dr Meric Karapinar-Kazandag, Yeditepe University, Faculty of Dentistry, Department of Endodontics, Bagdat cad No:238 34728, Goztepe/Istanbul/Turkey. E-mail address: [email protected]. 0099-2399/$0 - see front matter Copyright ª 2010 American Association of Endodontists. doi:10.1016/j.joen.2010.04.005
JOE — Volume 36, Number 8, August 2010
Accessory Mesial Canals in Mandibular Molars
1289
Clinical Research TABLE 1. Summary of Studies on the Prevalence of Accessory Mesial Canals in Mandibular Molars Number of molars (n)
Mesial accessory canals (%n)
Study
Methodology
First
Second
First
Second
Skidmore & Bjorndal, 1971 Pineda & Kuttler, 1972 Pomeranz et al, 1981 Martinez-Berna, 1983 Vertucci, 1984 Fabra-Campos, 1985 Fabra-Campos, 1989 Goel, 1991 Caliskan et al, 1995 de Carvalho & Zuolo, 2000 Gulabivala et al, 2001 Gulabivala et al, 2002 Sert & Bayirli, 2004 Ahmed et al, 2007 Navarro et al, 2007
Plastic casts Radiography Clinical Clinical Clearing Clinical Clinical Clinical Clearing Extracted teeth Clearing Clearing Clearing Clearing Micro-CT Scanning electron microscope
45 300 61 1,418 100 145 760 60 100 93 139 118 200 100 27 25
40 300 39 944 100 0 0 0 100 111 134 60 200 100 0 0
0 0 11.4 1.3 1 2.7 2.6 15 3.4 17.2 7.1 5.9 1.5 4 14.8 12
0 0 12.8 0.2 0 — — — 1.9 4.5 0 1.7 0 0 — —
structure nonamenable to conventional endodontic access cavity preparation, aberrant anatomy, calcified canals, fused roots, single roots, and C-shaped canals, 48 first and 48 second molars were selected for the study. They were stored in 0.1% thymol solution until used. The teeth were embedded in dentaforms and mounted in mannequins to simulate clinical conditions as best as possible. Conventional endodontic access cavities were completed in all teeth with the aid of 4.5 magnification loupes. Each of the first and second molars groups was randomly divided into three subgroups (n = 18). Three endodontists were assigned a subgroup of first and second molars each. Working independently, they set out to explore the mesial root canals in an attempt to detect accessory mesial canals using a standardized sequence as follows. In the first stage, only loupes were used for magnification. The access cavity was refined with ultrasonic tips (Buc 1 and Buc 3; Sybron
Endo, Orange, CA) to remove any dentin overhanging the mesial canal orifices and the isthmus. The mesial subpulpal groove was explored with sharp endodontic explorers (DG 16; Hu-Friedy, Chicago, IL, and Stewart probe; Premier Dental Products, Norristown, PA), and the number of canal orifices detected was recorded. Attempts were then made to negotiate detected accessory mesial canals with size 06 Ktype hand files (Dentsply Maillefer, Balleigue, Switzerland). When negotiation was unsuccessful, the isthmus was troughed apically with the ultrasonic tips to pursue the accessory canal deeper into the root while repeating negotiation attempts. Irrigation with 1% NaOCl and a Stropko air irrigator (Sybron Endo) were used intermittently to optimize visibility. Troughing was continued apically until (1) the accessory mesial canal was negotiated, (2) it was considered too risky to continue troughing further apically, (3) the accessory mesial canal was no longer detectable, or (4) a perforation occurred.
Figure 1. (A-C) Radiographs of mandibular molars exposed from the mesial direction (the distal roots were resected) showing the pathway of the accessory mesial canals. Files were inserted into the MB, ML, and accessory canals. (D) The depth of dentin removal while troughing to negotiate the accessory canal using the pulp chamber floor as a reference.
1290
Karapinar-Kazandag et al.
JOE — Volume 36, Number 8, August 2010
Clinical Research In the second stage, the teeth in which no accessory mesial canal was detected and those in which a detected accessory mesial canal could not be negotiated were submitted to further investigation aided with the microscope (Protege, Global Surgical Corp, St Louis, MO). Under the microscope, further dentin was selectively removed along the subpulpal groove with the ultrasonic tips while repeating negotiation attempts. Again, the results were recorded in the same four categories defined previously. In the third stage, a K-type file was negotiated into each of the mesial canals as far apically as possible. The teeth were removed from the dentaforms and then exposed on periapical radiographs from the mesial direction to show the pathways of the mesial canals (Fig. 1). In the fourth stage, the files were removed, and 1% sodium hypochlorite was left in the pulp chambers for 24 hours in order to remove any soft-tissue remnants. The chambers were dried and subsequently photographed with the aid of a stereomicroscope (Nikon, Tokyo, Japan). The number of teeth having 1, 2 (Fig. 2A), or 3 (Fig. 2B and C) canals or an open isthmus (Fig. 2D) was recorded. The location of the accessory mesial canals orifices in the photographs was mapped with the aid of Spot Software (Diagnostic Instruments, Sterling Heights, MI).
At the fifth stage, the distal roots of the teeth were resected, and radiographs of the teeth were exposed from the mesial aspect. These radiographs were digitized (Sony Cyber-shot, DSC-W80, Tokyo, Japan), and the depth of dentin removal was measured with Spot Software using the pulp chamber floor as reference (Fig. 1D). Finally, the mesial roots of all 96 molars were sectioned at three levels: 1 mm, 4 mm, and 8 mm from the apex. The sectioned surfaces at each level were examined under the operating microscope at 30 magnification to detect additional accessory mesial canals beyond those detected during the experimental procedure and to trace the pathway of detected accessory mesial canals relative to the main canals.
Results Tables 2 and 3 summarize the results of the investigation in the 96 first and second mandibular molars, regarding the effect of magnification aids on detection and negotiation of accessory mesial canals, the location and pathways of the accessory canals and the depth of troughing required to negotiate or rule out the presence of the accessory canals.
Figure 2. Photographs and a schematic representation of the subpulpal groove observed in mandibular molars with (A) two canals, (B and C) three canals, and (D) an open isthmus.
JOE — Volume 36, Number 8, August 2010
Accessory Mesial Canals in Mandibular Molars
1291
Clinical Research TABLE 2. Numbers and Proportion of Detected and Negotiated Accessory Mesial Canals in Mandibular Molars First molars (n = 48) Magnification aid
Second molars (n = 48)
Total (n = 96)
Detected
Negotiated
Detected
Negotiated
Detected
Negotiated
8 (16) 9 (18)
6 (12) 7 (14)
8 (16) 11 (22)
5 (10) 9 (18)
16 (16) 20 (20)
11 (11) 16 (16)
Loupes (%) Microscope (%)
Loupes were used first as the magnification aid followed by the use of the operating microscope for teeth where the previous attempts were unsuccessful.
Effect of Magnification Aids The total number of accessory mesial canals detected and negotiated was 4% higher in the second molars than in the first molars (Table 2). In both tooth types, the use of the microscope improved the results achieved with the loupes. The total number of detected and negotiated accessory mesial canals increased from 16% to 20% and from 11% to 16%, respectively, with 4 of 20 accessory mesial canals (20%) detected but not negotiated. Location of Accessory Mesial Canal Orifices All 20 accessory mesial canals were located in the mesial subpulpal groove. The distribution pattern along the groove was rather similar in the first and second molars, with the highest proportion of accessory mesial canals (45%) located closer to the ML canals, 30% located in the middle between the MB and ML canals, and 25% located closer to the MB canals (Table 3). The mean distance between the MB and ML canals in the first and second molars was 3.2 0.8 mm and 2.8 0.9 mm, respectively. When the accessory mesial canals were closer to either the ML or MB canals, their distance from the closest main canal was greater in the first molars (1.0-1.3 mm) than in the second molars (0.8-0.9 mm) (Table 3). Pathways of Negotiated Accessory Mesial Canals All 16 negotiated accessory mesial canals were confluent with the main canals, with none terminating in an independent apical foramen (Table 3). The pathways of the accessory mesial canals differed between the first and second molars. In the first molars, the majority (42%) merged with the MB canals, whereas in the second molars 55% merged with the ML canals. Cross-sections of the roots revealed only the negotiated accessory mesial canals at the 8-mm level, suggesting that all accessory mesial canals present were successfully negotiated. None of
the negotiated accessory mesial canals were observed at 4 mm from the apex.
Depth of Troughs Required The mean depth of dentin removed in order to negotiate or rule out the presence of accessory mesial canals in the first and second molars was 1.1 1.4 mm and 0.7 0.6 mm, respectively (Table 3).
Discussion One of the challenges facing clinicians when performing endodontic treatment in molars is the complexity of the root canal systems. Although the high-prevalence accessory mesiobuccal canals in maxillary molars have been well characterized (4, 6–10), the lower-prevalence accessory mesial canals in mandibular molars (12–14, 20–24) are not well recognized by clinicians. The accessory mesial canals invariably originate within the subpulpal groove or isthmus connecting the two main canals (14, 16, 21, 24, 26–28), making their detection very challenging. This study was undertaken to assess the potential to facilitate the detection and negotiation of accessory mesial canals in mandibular molars with the aid of the operating microscope. Teeth were mounted in dentaforms to simulate clinical conditions (6, 8). The detection of accessory mesial canals without magnification aids, which was assessed in several previous studies (5, 6, 8, 9), was not attempted because currently magnification is considered indispensable when performing endodontic treatment (1, 29). Thus, 4.5 loupes were used first to enhance magnification, followed by the use of the operating microscope (up to 30 power) to assess its potential advantage. The access cavities were refined with ultrasonic tips to allow accurate, controlled removal of dentin along the mesial subpulpal groove in search for accessory mesial canal orifices. The mesial dentinal protuberance was removed to afford a direct view of
TABLE 3. Characteristics of Detected and Negotiated Accessory Mesial Canals (AMCs) in Mandibular Molars First molars
Second molars
Location (%) Closer to MB Closer to ML At middle
Observation
n = 9 detected 2 (22) 4 (44) 3 (33)
n = 11 detected 3 (27) 5 (45) 3 (27)
n = 20 detected 5 (25) 9 (45) 6 (30)
Total
Distance (mm) MB to ML AMC to MB* AMC to ML*
3.21 0.76 1.00 0.28 1.30 0.14
2.80 0.90 0.87 0.39 0.81 0.58
Mean 3.00 0.90 Mean 0.93 0.32 Mean 0.95 0.53
Pathway (%) Merged with MB Merged with ML Merged with both
n = 7 negotiated 3 (42) 2 (29) 2 (29)
n = 9 negotiated 3 (33) 5 (55) 1(11)
n = 16 negotiated 6 (38) 7 (43) 3 (19)
Depth† (mm)
1.10 1.14
0.66 0.57
0.93 0.94
AMC, accessory mesial canals; MB, mesiobuccal; ML, mesiolingual. Location and pathway are related to the main canals in the mesial root, the MB, and the ML. *Teeth where the AMC was closest to either main canal. † Relative to the pulp chamber floor.
1292
Karapinar-Kazandag et al.
JOE — Volume 36, Number 8, August 2010
Clinical Research the line angle between the mesial wall and the pulp chamber floor (17).The investigators were three endodontists with varying levels of experience to eliminate the individual’s skill as a dominant variable. Accessory mesial canals were characterized for proportion of successful detection (5) and negotiation (14), location and depth of the orifices (6), and pathway (18). The findings were confirmed for accuracy by radiographic examination (31) and cross-sectioning of the mesial roots (7, 8, 32). With the aid of the microscope, the number of detected accessory mesial canals increased by 4% overall in all teeth, with a greater improvement in the second molars (6%) than in the first molars (2%). When the use of the microscope was compared with no magnification in a previous study (5), the number of detected accessory mesial canals increased by 17% in first molars and by almost 5% in second molars. Also, in maxillary molars, the microscope facilitated the detection of MB2 canals (4, 6, 8, 9). Our ability to negotiate accessory mesial canals with the aid of loupes in 12% and 10% of first and second molars, respectively, was similar to that reported previously without any magnification (14). Importantly, the final microscope-aided negotiation of accessory mesial canals in 14% of the first molars matched the 14.8% observed by computerized tomography (25), which is the ultimate method for investigating root canal morphology. Also, as suggested earlier, crosssections through the roots confirmed that no additional accessory mesial canals were present beyond the negotiated ones. The greater benefit of the microscope in the second molar was again apparent, with the 8% increase in negotiated accessory mesial canals, compared with the 2% increase in the first molars. The second molars have been reported to have accessory mesial canals less frequently (5, 16, 20–24) and an isthmus more frequently (21, 22) than the first molars. However, our combined use of microendodontic instruments (4) and the microscope facilitated exploration of the isthmuses (33), resulting in additional accessory mesial canals negotiated in the second molars. Pomeranz et al (14) classified the accessory mesial canals into three categories: (1) ‘‘fin,’’ allowing free instrument movement between the main and accessory canals (we did not consider such fins as accessory mesial canals); (2) ‘‘independent,’’ having a separate orifice and apical terminus, which is known to be rare (5, 12–25) and was not observed in our sample; and (3) ‘‘confluent,’’ having a separate orifice but merging more apically with the MB or ML canals as in all accessory mesial canals observed in our sample (15, 17, 18). Although also relating detected and negotiated accessory mesial canals to this classification, we aimed primarily to map the location of accessory mesial canals in relation to the main mesial canals (MB and ML). The main purpose of such mapping was to provide clinicians with a navigation guide for detection of accessory mesial canals, such as previously reported for maxillary molars (6). All of the accessory mesial canals were located in the mesial subpulpal groove (5, 25, 33). In about 45% of both the first and second molars, the accessory mesial canals were detected closer to the ML canals, which is in agreement with previous reports (5). The mean distance from the ML orifice was longer in the first molars (1.3 mm) than in the second molars (0.8 mm), reflecting the larger buccal-lingual dimension of the pulp chamber in the former. Thus, clinicians should specifically search for accessory mesial canals starting from the ML canal orifice and progress systematically along the subpulpal groove towards the MB canal. Frequently, there was the need to explore the mesial subpulpal groove by troughing in the apical direction to allow negotiation of a detected accessory mesial canal with an endodontic instrument. The mean depth of the troughs in the first molars reached 1.1 mm compared with
JOE — Volume 36, Number 8, August 2010
approximately 0.7 mm in the second molars. Although in several teeth the troughs were as deep as 2.2 mm, we found them less deep than what is occasionally required in maxillary molars when accessory MB canals are negotiated (6). In the maxillary molars, the accessory MB canals depart the chamber at a sharp mesial inclination and then bend again distally, which makes their negotiation challenging (6); the deeper trough helps eliminate the first angled portion of the canal, allowing insertion of instruments beyond the bend (6). In the mandibular molars, once the mesial dentinal protuberance is eliminated, the accessory mesial canals are not strongly inclined mesially, and they do not bend distally after departing the chamber. Thus, a shallow trough is sufficient to allow insertion of instruments into the accessory mesial canals. All the negotiated accessory mesial canals in this study were confluent with one of the main mesial canals, but the confluence pattern differed between the first and second molars. In the former, the accessory mesial canals frequently crossed the midline and merged with the MB canals (17, 18), whereas in the latter they more frequently merged with the ML canals (15). The cross-sections through the roots confirmed that all negotiated accessory mesial canals were no longer observed at 4 mm from the apex, having blended with either the isthmus or one of the main canals. This finding supported the argument that the accessory mesial canals are not additional canals but rather an access into the isthmus between the main canals (33). The isthmus is a characteristic feature of the mesial roots of mandibular molars found in 17% to 83% of first molars, most frequently at the level of 3 to 6 mm from the apical foramen (26–28). It has been defined as a lateral interconnection (13), transverse anastomosis (12, 16), or intercanal communication (32, 21). It can be complete, forming a continuous connection between the main canals, or partial, forming an incomplete or narrow communication with one or more patent openings (32). Despite current advances in irrigation delivery, disinfection of the isthmus is an elusive goal (34, 35). The accessory mesial canals, when negotiated and shaped, comprise a pathway into the isthmus (33), which may provide access for irrigation solutions and root filling materials. This appears to be the main clinical significance of detecting and attempting to negotiate accessory mesial canals in the mandibular molars. In conclusion, within its limitations, this study suggested that use of the operating microscope enhanced both the detection and negotiation of accessory mesial canals in the mandibular first and second molars beyond what could be achieved with the aid of loupes. This benefit was more pronounced in the second molars than in the first molars, resulting in an 8% increase in the number of negotiated accessory canals. Not all detected accessory canals could be negotiated. Although accessory canals were negotiated in as many as 14% of first molars and 18% of second molars, all of these canals merged with either one of the main mesial canals. The importance of negotiating the accessory mesial canals in mandibular molars is in the access it provides for irrigation solutions and filling materials into the otherwise inaccessible isthmus.
References 1. Kersten DD, Mines P, Sweet M. Use of the microscope in endodontics: results of a questionnaire. J Endod 2008;34:804–7. 2. Lee M, Winkler J, Hartwell G, et al. Current trends in endodontic practice: emergency treatments and technological armamentarium. J Endod 2009;35:35–9. 3. Saunders WP, Saunders EM. Conventional endodontics and the operating microscope. Dent Clin North Am 1997;41:415–28. 4. Stropko JJ. Canal morphology of maxillary molars: clinical observations of canal configurations. J Endod 1999;25:446–50. 5. de Carvalho MC, Zuolo ML. Orifice locating with a microscope. J Endod 2000;26: 532–4.
Accessory Mesial Canals in Mandibular Molars
1293
Clinical Research 6. Gorduysus MO, Gorduysus M, Friedman S. Operating microscope improves negotiation of second mesiobuccal canals in maxillary molars. J Endod 2001;27:683–6. 7. Schwarze T, Baethge C, Stecher T, et al. Identification of second canals in the mesiobuccal root of maxillary first and second molars using magnifying loupes or an operating microscope. Aust Endod J 2002;28:57–60. 8. Baldassari-Cruz LA, Lilly JP, Rivera EM. The influence of dental operating microscope in locating the mesiolingual canal orifice. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002;93:190–4. 9. Buhrley LJ, Barrows MJ, BeGole EA, et al. Effect of magnification on locating the MB2 canal in maxillary molars. J Endod 2002;28:324–7. 10. Sempira HN, Hartwell GR. Frequency of second mesiobuccal canals in maxillary molars as determined by use of an operating microscope: a clinical study. J Endod 2000;26:673–4. 11. Hess W, Zurcher E. The anatomy of the root canals of the teeth of the permanent and deciduous dentitions. New York: William Wood & Co; 1925. 12. Skidmore AE, Bjorndal AM. Root canal morphology of the human mandibular first molar. Oral Surg Oral Med Oral Pathol 1971;32:778–84. 13. Pineda F, Kuttler Y. Mesiodistal and buccolingual roentgenographic investigation of 7,275 root canals. Oral Surg Oral Med Oral Pathol 1972;33:101–10. 14. Pomeranz HH, Eidelman DL, Goldberg MG. Treatment considerations of the middle mesial canal of mandibular first and second molars. J Endod 1981;7:565–8. 15. Martinez-Berna A, Badanelli P. Investigacion clinica de molars inferiors con cinco conductos. Boletin de Informacion Dental 1983;43:27–41. 16. Vertucci FJ. Root canal anatomy of the human permanent teeth. Oral Surg Oral Med Oral Pathol 1984;58:589–99. 17. Fabra-Campos H. Unusual root anatomy of mandibular first molars. J Endod 1985; 11:568–72. 18. Fabra-Campos H. Three canals in the mesial root of mandibular first permanent molars: a clinical study. Int Endod J 1989;22:39–43. 19. Goel N, Gill K, Taneja J. Study of root canals configuration in mandibular first permanent molar. J Indian Soc Pedod Prev Dent 1991;8:12–4. 20. Caliskan MK, Pehlivan Y, Sepetcioglu F, et al. Root canal morphology of human permanent teeth in a Turkish population. J Endod 1995;21:200–4. 21. Gulabivala K, Aung TH, Alavi A, et al. Root and canal morphology of Burmese mandibular molars. Int Endod J 2001;34:359–70.
1294
Karapinar-Kazandag et al.
22. Gulabivala K, Opasanon A, Ng YL, et al. Root and canal morphology of Thai mandibular molars. Int Endod J 2002;35:56–62. 23. Sert S, Bayirli GS. Evaluation of the root canal configurations of the mandibular and maxillary permanent teeth by gender in the Turkish population. J Endod 2004;30: 391–8. 24. Ahmed HA, Abu-bakr NH, Yahia NA, et al. Root and canal morphology of permanent mandibular molars in a Sudanese population. Int Endod J 2007;40:766–71. 25. Navarro LF, Luzi A, Garcia AA, et al. Third canal in the mesial root of permanent mandibular first molars: review of the literature and presentation of 3 clinical reports and 2 in vitro studies. Med Oral Patol Oral Cir Bucal 2007; 12:E605–9. 26. Mannocci F, Peru M, Sherriff M, et al. The isthmuses of the mesial root of mandibular molars: a micro-computed tomographic study. Int Endod J 2005; 38:558–63. 27. von Arx T. Frequency and type of canal isthmuses in first molars detected by endoscopic inspection during periradicular surgery. Int Endod J 2005;38:160–8. 28. Gu L, Wei X, Ling J, et al. A microcomputed tomographic study of canal isthmuses in the mesial root of mandibular first molars in a Chinese population. J Endod 2009; 35:353–6. 29. Vertucci F. Root canal morphology and its relationship to endodontic procedures. Endod Topics 2005;10:3–29. 30. Peiris HR, Pitakotuwage TN, Takahashi M, et al. Root canal morphology of mandibular permanent molars at different ages. Int Endod J 2008;41:828–35. 31. Kulild JC, Peters DD. Incidence and configuration of canal systems in the mesiobuccal root of maxillary first and second molars. J Endod 1990;16:311–7. 32. Weller RN, Niemczyk SP, Kim S. Incidence and position of the canal isthmus. Part 1. Mesiobuccal root of the maxillary first molar. J Endod 1995;21:380–3. 33. Mortman RE, Ahn S. Mandibular first molars with three mesial canals. Gen Dent 2003;51:549–51. 34. Burleson A, Nusstein J, Reader A, et al. The in vivo evaluation of hand/rotary/ultrasound instrumentation in necrotic, human mandibular molars. J Endod 2007;33: 782–7. 35. Carr GB, Schwartz RS, Schaudinn C, et al. Ultrastructural examination of failed molar retreatment with secondary apical periodontitis: an examination of endodontic biofilms in an endodontic retreatment failure. J Endod 2009;35:1303–9.
JOE — Volume 36, Number 8, August 2010