Intricate internal anatomy of teeth and its clinical significance in endodontics - A review

Transcription

1 Review Article Intricate internal anatomy of teeth and its clinical significance in endodontics - A review A.P. Tikku * # W. Pragya Pandey ** # Ivy Shukla*** ABSTRACT Beyond the simple perception is often the intricate internal tooth anatomy and a complex root canal system. Root canal treatment has transformed remarkably since the hollow tube theory was postulated in Research into the morphology of the pulp has revealed that the dental pulp takes many intricate shapes and configurations before reaching the tooth apex. The prospect of the treatment depends on accurate diagnosis followed by location, cleaning and shaping and finally obturation of the root canal system. As a professional, one should be aware of all the probable nooks and crannies of the complex root canal, its protean permutations and combinations, to render the finest possible treatment. As is the case with any other treatment, endodontic therapy; if performed in the properly delineated and precise manner spells more than 99% success rate. This review article attempts to bring out the possible nuances of the complex root canal system and various methods of reckoning with these significantly essential details. Keywords: Intricate, internal, tooth anatomy, complex, root canal system Introduction Dental professionals conventionally have referred to the main/large passage lying at the core of the tooth as the pulp space and all effort was made to ensure debridement from that area only.. Factually, as we know now the root canal is a complex system of finely tuned and synchronized small tributaries running all through the length and breadth of the tooth dentine. Hence, it becomes imperative for a clinician to fully understand this system. Seasoned clinicians very aptly say - what we cannot see, we cannot negotiate and what we cannot negotiate we fail to prepare! A good obturation is possible only after meticulous cleaning and shaping which eventually and ultimately depends on the clinician s knowledge and ability to comprehend, visualize, perceive and prepare the root canal system. From the early work of Hess and Zurcher [1] to the contemporary studies regarding the anatomic complexities of the root canal system, it has been well established that the root with a graceful tapering canal and a single apical foramen is an exception rather than the rule. Investigators have very commonly encountered bifurcating canals, multiple foramina, fins, deltas, loops, cudle-sacs, inter-canal links, C-shaped canals and accessory canals in most teeth. The student and the clinician must approach the tooth presuming, that these Aberrations occur so often that they must be considered normal anatomy * Professor, ** Reader, ***Private Practice, # Dept. of Conservative Dentistry & Endodontics, King George s Medical University, Lucknow, India, Chandra Dental College and Hospital, Barabanki, India, Lucknow, India. 160

2 A.P TIKKU, W. PRAGYA PANDEY, IVY SHUKLA Anatomy of the pulp-chamber floor A thorough investigation of the sulcus, coronal clefts, restorations, tooth angulation, cusp position, occlusion, and contacts is mandatory before access is begun. Before tooth entry the clinician must visualize the expected location of the coronal pulp chamber and canal orifice position. Past literature describing pulp-chamber anatomy has been very general and undefined in determining the location and number of root canal orifice. Krasner and Henry 2 in 2004 studied the pulp chamber of 500 extracted teeth and their consistent observation regarding the pulp chamber anatomy in all teeth led to the formulation of new laws, forming guidelines for locating the pulp chamber and root canal orifice. If specific, consistent landmarks exist and are quantifiable, assessable and reproducible then surely the task of locating orifices becomes easier, systematic and much more certain. This is especially beneficial in challenging cases like heavily restored teeth, carious broken down teeth, malposed teeth, teeth with calcified canals and teeth gouged from previous access openings, where locating orifices becomes an onerous task. The anatomic laws/patterns observed 2 are categorized into two groups: 1) Relationships of the pulp-chamber to the clinical crown. 2) Relationships of the root canal orifice on the pulpchamber floor. 1) Relationships of the pulp chamber to the clinical crown: Law of Centrality: the floor of the pulp chamber is always located in the center of the tooth at the level of the CEJ (cemento-enameljunction).(figure-1) Law of Concentricity: The walls of the pulp chamber are always concentric to the external surface of the tooth at the level of the CEJ. Law of the CEJ: The CEJ is the most consistent, repeatable landmark for locating the position of the pulp-chamber. Figure-1: Cross-section of mandibular molar, showing equality of distance of the pulp chamber walls from the external root surfaces (arrows). 2) Relationships of the root canal orifice on the pulp chamber floor: Law of symmetry 1: except for maxillary molars, the orifices of the canals are equidistant from a line drawn in a mesial-distal direction through the pulp chamber floor.(figure-2) Law of symmetry 2: except for the maxillary molars, the orifices of the canals lie on a line perpendicular to a line drawn in a mesial-distal direction across the center of the floor of the pulp chamber.(figure-2) Law of Color Change: the color of the pulpchamber floor is always darker than the walls. Law of orifice location 1: the orifices of the root canals are always located at the junction of the walls and the floor. Law of orifice location 2: the orifices of the root canals are located at the angles in the floorwall junction. 161

3 INTRICATE INTERNAL ANATOMY OF TEETH AND ITS CLINICAL SIGNIFICANCE IN ENDODONTICS - A REVIEW Law of orifice location 3: the orifices of the root canals are located at the terminus of the root developmental fusion lines.(figure-2) canal; four canals joining into two; four canals extending from orifice to the apex and five canals joining into four at the apex. Figure-3: Classification showing Vertucci root canal system. Figure-2: Cross-section of mandibular molar showing: Equidistance of orifices (AB=AC) from the mesiodistal line (M-N); Orifices perpendicular to the mesiodistal line (M-N); Orifices located at the terminus of Developmental root fusion lines (D). Even the most proficient clinician cannot always prophesize the exact site and number of root canals present in any tooth before the beginning of the treatment. Even if a small part of the canal is left unclean, it significantly jeopardizes the success of the treatment. With the formulation of these anatomic laws, the practitioners can now locate the site and number of root canals present, with greater predictability and much more ease. Classification of the root canal system There are multitude pathways connecting the root canal orifice and the apex of the tooth running through the root dentine. Weine 3 categorized the root canal system in any root into four basic types. Vertucci et al. 4 categorized the root canal system into a more complex eight configurations (Figure-3). Interestingly the only tooth to demonstrate all eight configurations is the maxillary second premolar. 4 Gulabivala et al. 5 examined mandibular molars in a Burmese population and found additional canal configurations. These include three canals joining into one or two canals; two canals separating into three canals; two canals joining, re-dividing into two and terminating as one Over the past two decade there have been a plethora of published in-vitro studies and case reports depicting a variety of canal configurations. It was seen that gender, race and ethnic origin all play a role in determining the canal morphology and hence should be considered during the preoperative evaluation stage of the root canal therapy 6. Divisions of the canals may not be obvious, especially if they are fine. A tell-tale feature is the narrowing of canal when they divide. The sudden radiographic disappearance of a canal might indicate a dividing canal. Simple tubular (Types I, IV and VIII) canals may be cleaned satisfactorily by mechanical preparation alone. Preparation of such canals could probably be effectively achieved using nickel-titanium rotary instruments, but they have a tendency to break in certain clinical situations. This includes (i) broad canal with abrupt apical curve (ii) wide canal suddenly becoming narrow. In these situations the nickel-titanium rotary instruments should be preceded by hand files to avoid buckling and instrument separation 7. Branched canal configurations and inter-canal ramifications may render complete debridement of canal systems difficult. The use of sodium hypochlorite, preferably agitated by ultrasonic may help to clean the uninstrumented parts of the root canal system 8. The obturation of simple tubular or tapered canals may 162

4 A.P TIKKU, W. PRAGYA PANDEY, IVY SHUKLA be achieved satisfactorily with cold lateral condensation of gutta-percha points. However, irregular canals or those with complex ramifications are more satisfactorily obturated using the thermoplasticized gutta-percha techniques 9. Isthmus An isthmus is defined as a ribbon shaped intercanal connection 10 or transverse anastomosis or a corridor 11 between two root canals encompassing dental pulp and pulp related tissue. An isthmus can be observed between any two root canals within the same root. As the isthmus houses the dental pulp, it might serve as a potential site for bacterial growth and thus, making complete debridement of this area indispensible. Whenever two or more root canals are present, an isthmus should be suspected and all attempts should be made in detecting and debriding it. Classification of the isthmus: Isthmus classification was described by Hsu & Kim et al. 12 (Figure-4) Type I - is two or three canals with no notable communication. Type II - is two canals that possess a definite connection between the two main canals. Type III- is three canals that possess a definite connection between them. Type IV- is when the canals extend into the isthmus area. Type V- is the true connection or corridor throughout the section. Type I Type II Type III Type IV Type V Figure-4: Classification of Isthmus. The implication of an isthmus was taken into consideration first in 1971; however, it was in 1983 that Cambruzzi and Marshall 13 first reported this significant finding in molar surgery. The tissue left over in the isthmus can serve as a nidus for recurrent infections and lead to failures of orthograde endodontic treatment and endodontic surgery. The incidence of isthmus at different level section of the root were seen and reported by several authors 10,11,13,14,15,16. It was found to be 16% in maxillary premolar at 1mm resection level, 52% in maxillary premolar at 6mm resection level, 32% in mandibular premolar at 2mm resection level, 40% in mandibular premolar at 3mm resection level, nearly 50% at 4 mm resection level in mesiobuccal root of maxillary first molar and 15% in the distal roots of mandibular molar at 3mm resection level.the highest incidence was reported in the mesial root of the mandibular first molar, which was 80% at 4 mm resection level. Identification, debridement and filling of the isthmus is essential but challenging. Cambruzzi and Marshall 17 recommended the use of methylene blue dye to visualize the isthmus on a resected root surface. The conventional way of cleaning this anatomic complexity with the use of full strength sodium hypochlorite and mechanical instrumentation was found to be limited in its action 18. However the introduction of surgical operating microscope and ultrasonic has taken endodontic procedures to another level of sophistication 19,20. Under the high magnification of microscope, anatomic structures like isthmi, fins, deltas, accessory canals, C-shaped canals and apical micro-fractures can easily be identified. The ultrasonic tips can be used to prepare the isthmus and subsequently fill the preparation with a suitable 163

5 INTRICATE INTERNAL ANATOMY OF TEETH AND ITS CLINICAL SIGNIFICANCE IN ENDODONTICS - A REVIEW material 21. The introduction of micro-ultrasonic has greatly increased the endodontic success rates. C-shaped canal Cooks and Cox 22 first discovered the C-shaped anomaly in mandibular second and third molars in The presence of a C-shaped canal prevents effective cleaning, shaping and obturation during a root canal therapy. There are two common possible outcomes for the C-shaped mandibular molar (1) those that exhibit a single, ribbon like, C-shaped canal from orifice to apex and (2) those with three distinct canals below the C-shaped orifice, the more common form 23. The C-shaped canal has been observed in mandibular first premolars, mandibular first, second and third molars, maxillary first molars and maxillary second molars. Newton et al. 24 illustrated C-shape canal configuration in maxillary first molars. Yang et al. described C-shaped canal in mandibular molars as a ribbon shaped canal that includes the mesiobuccal and distal canals, and sometimes the mesiolingual. 25 (Figure-5). Melton and colleagues 26 discovered this phenomenon in maxillary second molars where the C-shape joins the distobuccal root with the palatal root. The occurrence of a C-shaped canal and its improper negotiation can lead to failure in endodontic therapy and hence should be gingerly examined. Figure-5: Cross-section of a mandibular molar showing a C-shaped canal. A: mesiolingual canal, B: ribbon shape C-shaped canal including the mesiobuccal and distal canals. Radiographic appearance of a C-shaped root in mandibular second molars may be diverse, depending on the exact nature and orientation of the root. It may present as a single fused root or as two distinct roots with a communication, the latter of which may not be very obvious at first glance. Haddad et al. 27 considered them to form a typical radiographic image revealing fusion, root proximity, large distal canal or the blurred image of a third canal in the middle of two roots. The canal orifice may present with a C-shape, but not always, and when it does, it is no guarantee that it continues spicily as a single canal. Fused roots and C-shaped roots may present with narrow root grooves that predispose to localized periodontal disease, which may, in fact be the first diagnostic indication of such anatomical variance. Moreover it must be kept in mind that very little dentin separates the external surface from the C-shaped canal system, increasing the probability of stripping or lateral perforation during endodontic and restorative procedures. AbouRass et al. 28 described an anti-curvature filing technique in which the bulkier root structure was filed away from the curvature and the thinner danger zone. An evaluation of the actual thickness of canal walls in C-shaped roots should identify which walls are in danger zones for anti-curvature filing. Studies have been designed to evaluate the cross-sectional morphology of C-shaped canals and to identify the location and measure the minimum widths (MWs) of buccal and lingual walls. 29 Canal curvatures A straight root canal extending the entire length of the root is uncommon The curvature may be a gradual curvature of the entire canal, a sharp curvature of the canal near the apex, or a gradual curvature of the canal with a straight apical ending. 164

6 A.P TIKKU, W. PRAGYA PANDEY, IVY SHUKLA Double curvatures in the form of S may also occur. Success in negotiating a narrow curved canal depends on the degree of curvature, the size and constriction of the root canal, the size and flexibility of the endodontic instrument and most important, the skill of the operator. Only few studies have actually measured the canal curvature. Canal curvature can be measured either by Berbert&Nishiyamas 30 method or by Schneiders 31 method. The most common method used to describe canal curvature was published by Schneider. According to the Schneiders method, considering both the angle of curvature together with the radius of the curve is supposedly the exact method of describing the canal curvature. Whereas the angle of curvature is independent of the radius, a more abrupt curve of the canal corresponds to a smaller radius of curvature. It is quite challenging to enlarge a canal with a great angle in degree and an abrupt short curve without any transportation regardless of whether rotary nickel-titanium or stainless steel hand instruments are used. Angle of curvature: A straight line (a) was drawn along the silver point, size 08(introduced into the canal prior to instrumentation) in the coronal straight portion of the canal; this line was parallel to the long axis of the canal. The point where the canal deviated from this line to begin the canal curvature was marked as point M. A second line (b) was drawn to intersect the apical foramen (point N) with the point where the canal began to leave the long axis (Point M), The angle of curvature(á) is formed by lines a and b 31.(Figure-6) Radius of curvature: The line (S) between the points M and N is the chord of the hypothetical circle that defines the curved part of the canal.(figure-6) The curved part of the canal between the points M and N is the circular arc of the hypothetical circle, which is specified by its radius (r). The radius is calculated on the basis of the measured length of the chord (S) between points M and N 31.The chord (S) was measured by using the computer program. Henceforth the radius can be calculated using the following formula:- Radius of curvature (r) = 2 sin S Figure-6: Angle of Curvature ( ) The preparation of curved canals is challenging and has an increased likelihood for iatrogenic damage. To avoid any procedural errors the clinicians generally tend to under prepare these canals. The key to dealing with severely curved canals is to pre-curve the instrument prior to instrumentation and try to negotiate the entire root canal length at the first attempt, using push-pull movements rather than twisting movements until a more straightened guide path is created before any attempt is made of taking rotary files around these abrupt curves. Such procedures significantly reduce the chances of ledge formation. 165

7 Horizontal shapes and dimension of root canal The horizontal dimension of the root canal system is not only more complicated than the vertical dimension (working length) but is also more difficult to investigate, because the horizontal dimension varies greatly at each vertical level of the canal. Very few clinical attempts and studies have been done to determine the working width of the canal and hence it is very aptly referred to as the Forgotten Dimension.Enlarging of the canal during root canal treatment is known to all but how large is large enough is a question that still needs serious attention. Ideally during root canal preparation the instruments and the techniques used should always conform to and retain the original shape of the canal to maximize the cleaning and minimize unnecessary weakening of the tooth structure 32. Current descriptions of the horizontal dimensions (cross-sections) of the root canal 32 : 1)Round: Max IWW** equals Min IWW* 2)Oval : Max IWW is greater than Min IWW (Up to two times more) 3)Longoval : Max IWW is two or more times greater than Min IWW(up to 4 times more) 4)Flattened: Max IWW is four or more times greater than Min IWW. 5)Irregular: Cannot be defined by 1-4. * Minimum Initial working width. ** Maximum Initial working width. In a relatively round canal, the lesser and the greater initial horizontal dimensions are approximately the same. In an oval, long-oval, or flat canal, the maximal initial horizontal dimensions (Max IWW) may be several times larger than the minimal initial dimension (Min IWW) at different INTRICATE INTERNAL ANATOMY OF TEETH AND ITS CLINICAL SIGNIFICANCE IN ENDODONTICS - A REVIEW levels of the canal. In a maxillary cuspid, Min IWW at working length (Min IWW0) may be the same as Max IWW at working length (Max IWW0). But 12 mm short of working length, Max IWW 12 is probably three to four times larger than Min IWW In long oval /flat canals reaming action may lead to in-complete debridement of the root canal system. Circumferential filing can better conform to the outline of the horizontal dimension of the root canals at different levels of the canal. Comprehending the concepts of working width can reduce the underestimation of the minimum initial working width at working length (Min IWW0) and consequently incomplete cleaning of the root canal system 32. The dogma of enlarging the canal three sizes larger than the first file that binds to the apex might not be applicable in all the cases. Apical anatomy The anatomy of the root apex was first described by Kutler 33. Anatomic and histologic features that constitute the root apex (Figure-7) are apical constriction (minor apical foramen), cementodentinaljunction (CDJ) and apical foramen (major apical foramen). Apical limit of canal instrumentation and obturation is the apical constriction which is not only the narrowest part of canal but a morphologic landmark that can help to improve the apical seal when the canal is obturated 34. CDJ the point where cementum meets dentine, is where the pulp tissue ends and the periodontal tissue begins. From the apical constriction the canal widens as it exits the roots at the apical foramen or major diameter. The space in between the major and minor foramen is funnel shaped. (Figure-7) 166

8 Figure-7: Morphology of the root apex. Dummer et al. 35 classified (Figure-8) the apical constriction into four main types: (A) Traditional single constriction (B) Tapering constriction (C) Multiconstricted (D) Parallel constriction which need to be analyzed, to prevent under and over preparation. Failure to accurately determine the working length may lead to perforation through the apical constriction, together with overfilling, overextension, incomplete debridement or short fillings. All these procedural errors will increase the incidence of postoperative pain and failure of the root canal treatment. Thus the focus should be to accurately measure the working length maintaining it throughout the entire procedure and avoiding extravagant apical enlargement, transportation, zipping, ledging and perforation of the apical foramen. Figure-8: Types of Apical Constriction Few tips to see the unseen: A.P TIKKU, W. PRAGYA PANDEY, IVY SHUKLA 1. When the radiograph shows that the root canal shadow suddenly stops in the radicular region it can safely be assumed that it has bifurcated or trifurcated into finer diameter tributaries at that point. To confirm this dichotomy a second radiograph may be exposed from a mesial angulation of 10 to 30 degrees. This diagnostic clue as pointed out by Slowey, 36 called the Fast Break, is usually seen in maxillary first premolars. 2. Whenever the outline of the root is unclear, has an unusual contour, or strays in any way from the expected radiographic appearance, one should suspect an additional root canal It is imperative that radiographs should be taken, from minimum two angulations before attempting endodontic treatment. Angled views of teeth can better reveal the anatomic variances. Mesial angulation technique is used for identifying two canals wherein the lingual root always appears mesially on the film (SLOB rule same lingual opposite buccal) The radiograph also gives several clues to anatomic aberration: lateral radiolucency indicates the presence of lateral or accessory canals, an abrupt ending of a large canal signifies a bifurcation, a knob like image indicates an apex that curves towards or away from the X-ay beam (Bull s eye), multiple vertical lines indicates thin root which may be hourglass shaped in cross section, hence susceptible to strip or lateral perforations If an extra dark line is apparent in the coronal third of the root, running parallel to the test file in the radiograph, particularly in the coronal part of the root, one should suspect a second canal. This is especially helpful in detecting the fourth 167

9 INTRICATE INTERNAL ANATOMY OF TEETH AND ITS CLINICAL SIGNIFICANCE IN ENDODONTICS - A REVIEW canal in the mesiobuccal root of the maxillary first molars and in the distal roots of the mandibular first molars Knowledge of normal root curvatures may be quite helpful in interpretation of the radiographs. For example, palatal roots of permanent maxillary molars often have sharp apical curvatures towards the buccal. 7. Ethnicity has a significant influence on aberrant anatomy. Radix Entomolaris, an extra distal root in a mandibular molar, is often seen in Oriental and Eskimo population 38. Similarly C-shaped anatomy is seen more commonly in Chinese, Korean and Indian population 39, The endodontic pathfinder inserted into the orifice openings will reveal the direction that the canal takes in leaving the pulp chamber. 9. Tactile perception with a hand instrument can identify curvatures, obstructions, root divisions, and additional canal orifices including apical constrictions. 10. Fiberoptic transillumination can reveal calcifications, orifice locations, abfractions and fracture lines. Radiography is needed, first as an aid to the diagnosis, then periodically during treatment. Surgical operating microscopes, magnifying optical loupes, endodontic endoscopes help us to further search and find the normal structures, variations and components of unprepared as well as prepared root canal morphology. Unfortunately radiographs provide only two dimensional blueprint of the actual three dimensional pulp anatomy. It is the third dimension that the clinician must visualize to achieve success in Endodontic treatment. Conclusion It would be quite erroneous to refer to this complex system simply as the Root Canal - because it actually is a very complex system of finely tuned small tributaries running through the entire length and breadth of the tooth. It is crucial to be aware and admire the various complexities of the spaces we are expected to clean and fill. Since during endodontic treatment we cannot see much inside the area we work, we must keep in mind the various laid down guidelines and laws to comprehend and perceive the unseen complexities and details to efficiently clean, shape and obturate the root canal to ensure an acceptable endodontic success rate. References : 1. Hess W, Zurcher E. The Anatomy of Root Canals of the teeth of the Permanent and Deciduous dentitions.1925;newyork:william Wood & Co. 2. Krasner P, Rankow HJ. Anatomy of the pulp chamber floor. J Endod 2004;30: Weine FS. Endodontic Therapy, 5 th edn. St.Louis:Mosby- Yearbook Inc.,1996: Vertucci FJ, Seelig A, Gilles R. Root canal morphology of the human maxillary second premolar. Oral Surg Oral Med Oral Pathol Oral RadiolEndod 1974;38: Gulabivala K, Aung TH, Alavi A, Mg Y-L. Root and canal morphology of Burmese mandibular molars. IntEndod J 2001;34: Vertucci FJ. Root canal morphology and its relationship to endodontic procedures. Endod Top 2005;10: Ruddle C. Cleaning and shaping the root canal system. In: Cohen S, Burns RC, eds. Pathway of the pulp. 8th ed. St. Louis: Mosby,2002: Iqbal MK. Nonsurgical ultrasonic endodontic instruments. Dent Clin N Am 2004;48: Kratchman SI. Obturation of the root canal system. Dent Clin N Am 2004;48: 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:

10 A.P TIKKU, W. PRAGYA PANDEY, IVY SHUKLA 11. Green D: Double canals in single roots. Oral Surg 1973;35: Hsu Y, Kim S. The resected root surface: the issue of canal isthmuses. Dent Clin N Am 1997:3: CambruzziJV, Marshall FJ: Molar endodontic Surgery J Can Dent Assoc.1983;1: Vertucci FJ: Root canal anatomy of the human permanent teeth. Oral Surg 1984;58: Pineda F, Kuttler Y: Mesiodistal and buccolingualroentgenographic investigation of 7,275 root canals. Oral Surg1972;33: Skidmore AE, Bjornal AM: Root morphology of the human mandibular first molar.oral Surg 1971;32: Cambruzzi JV, Marshall FJ, PappinJB.Methylene blue dye. An aid to endodontic surgery. Endo Report 1985;11: Senia ES, Marshall FJ, Rosen S: The solvent action of sodium hypochlorite on pulp tissue of extracted teeth. Oral Surg1971;31: Carr GB: Microscopes in endodontics. J Calif Dent Assoc1992;11: Engle TK, Steiman HR: Preliminary investigation of ultrasonics root end preparation.j Endod1995;21: Rubinstein R. The anatomy of the surgical operating microscope and operating position.dent Clin of N Am 1997;41: Cooke HG, Cox FL: C-shaped canal configuration in mandibular molars. J Am Dent Assoc 1979;99: Cohen S, Burns R: Pathways of the Pulp, ed 6 th.st Louis, Mosby Year Book, Newton CW, McDonald S. A C-shaped canal configuration in a maxillary first molar. J Endod 1984;10: Yang ZP, Yang SF, Lin YC, Shay JC, Chi CY. C-shaped root canals in mandibular second molars in a Chinese population.endod Dent Traumatol 1988;4: Melton DC, Krell KV, Fuller MW: Anatomical and histological features of C-shaped canals in mandibular second molars. J Endodon1991;17: Haddad GY, Nehme WB, Ounsi HF. Diagnosis, classification and frequency of C-shaped canals in mandibular second molars in the Lebanese population. J Endod1999;25: Abou-Rass M, Frank AL, Glick DH. The anticurvature filing method to prepare the curved root canal. J Am Dent Assoc 1980;101: Chai WL, Thong YL: Cross-sectional Morphology and Minimum canal widths in C-shaped roots of Mandibular Molars J Endod2004;30: Berbert A, Nishiyama CK. Curvaturasradiculares:uma nova metodologiapara a mensuracado e localizacao. Rev GauchaOdontol 1994;42(6): Schneider SW. A comparison of canal preparations in straight and curved root canals. Oral Surg Oral Med Oral Pathol1971;32: Jou YT, Karabucak B, Levin J, Donald Liu. Endodontic working width: current concepts and techniques. Dent Clin North Am2004;48: Kutler Y. Microscopic investigation of root apexes. J Am Dent Assoc 1955;50: Riccuci, Langeland. Apical limit of root canal instrumentation and obturation, part 2. A histologic study. IntEndodJ1998;31: Dummer PM, McGinn JH, Rees DG. The position and topography of the apical canal constriction and apical foramen. IntEndod J1984;17: Slowey RR. Radiographic aids in the detection of extra root canals. Oral Surg 1974;37: Georig AC, Neaverth EJ. A simplified look at the buccal object rule in endodontics. J Endod1987;13: Demoor, Deroose, Calberson. The radix entomolaris in mandibular first molars an endodontic challenge. IntEndod J 2004 Nov;37(11): Nallapati S. Three canal mandibular first and second premolars: a treatment approach. J Endod 2005;31(6): Trope M, Elfenbein L, Tronstad L. Mandibular premolars with more than one root canal in different race groups. J Endod 1986;12(8):