endodontics Root canal anatomy of the human permanent teeth T he main objective of endodontic therapy is the

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1 endodontics Editor: MILTON SISKIN, D.D.S. College of Dentistry The University of Tennessee 847 Monroe Avenue Memphis, Tennessee Root canal anatomy of the human permanent teeth Frank J. Vertucci, D.iU.D.,* Gainesville, Fla. UNIVERSITY OF FLORIDA COLLEGE OF DENTISTRY Two thousand four hundred human permanent teeth were decalcified, injected with dye, and cleared in order to determine the number of root canals and their different types, the ramifications of the main root canals, the location of apical foramina and transverse anastomoses, and the frequency of apical deltas. (ORAL SURC. 58~ , 1984) T he main objective of endodontic therapy is the thorough mechanical and chemical cleansing of the entire pulp cavity and its complete obturation with an inert filling material. According to Seltzer and Bender, failures in treatment occur despite rigid adherence to this basic principle. Ingle2 lists the most frequent cause of endodontic failure as apical percolation and subsequent diffusion stasis into the canal. The main reasons for this failure are incomplete canal obturation, an untreated canal and inadvertent removal of a silver cone. A canal is often left untreated because the dentist fails to recognize its presence. The dentist must have a thorough knowledge of root canal morphology before he can successfully treat a tooth endodontically. In the literature, there is divergence of opinion as to the anatomy of the pulp cavities of the human permanent teeth.3-32 The incidence of two or more root canals in the mandibular first premolar, for example, has been reported to be as low as 2.7% and as high as 62.5%, whereas the incidence of two or more root canals in the mandibular second premolar has been reported to vary between % and 34.3%.3-1 The incidence of two canals at the apex of the maxillary second premolar has been reported to be as low as 4% and as high as 5%.6-13 *Associate Professor and Chairman, Department tics. of Endodon- These discrepancies are, in part, the result of the marked variations in anatomy that are present and, in part, the result of the very real difficulties that are always encountered when root canal morphology is studied. Because of the many dissimilarities in selection of material and classification of canal configurations, the results of most reports cannot be compared directly with one another. Because the literature is inconclusive, I decided to conduct a detailed investigation of the anatomy of the root canals of extracted human teeth. A standardized technique that involved examination of transparent specimens was used. METHODS AND MATERIALS For this investigation, 2,4 permanent teeth were obtained from various oral surgery practices. All teeth were obtained from adults. The age, sex, and race of the patients and the reasons for extraction were not recorded. Immediately after extraction, the teeth were fixed in 1% formalin and decalcified in 5% hydrochloric acid. On completion of this process, the teeth were washed in tap water and placed in a 5% solution of potassium hydroxide for 24 hours. The teeth were washed in tap water for 2 hours, and hematoxylin dye was injected into the pulp cavities with the use of a 25-gauge needle on a Luer-Lok plastic disposable syringe. Hematoxylin was used because of its ability to stain fresh pulp tissue, even 589

2 59 Vertucci Oral Surg. November, I984 Table I. Morphology of the maxillary permanent teeth Tooth Position of lateral canals No. of Canals with Root teeth lateral canals Cervical Middle Apical Furcation Central Lateral Canine First premolar Second premolar First molar Second molar Note: Figures represent percentage of the total I I IO Il MB f DB P MB 1 5 IO t DB IO P I.2 7. I 1 Table II. Morphology of the mandibular permanent teeth Tooth Central Lateral Canine First premolar Second premolar First molar Second molar Position of lateral canals No. of Canals with Root teeth lateral canals Cervical Middle Apical Furcation Mesial t 23 Distal IO Mesial t II Distal i Note: Figures represent percentage of total. Table III. Classification and percentage of root canals of the maxillary teeth Teeth No. We I Type II Type III Total with Type IV The V Type VI Type VII of I 2-l I-2-1 one canal 2 l-2 2-I-2 l teeth canal canals canals at apex canals canals canals canals Maxillary central Maxillary lateral Maxillary canine Maxillary first premolar* Maxillary second premolar Maxillary first molar MesiobuccalS Distobuccal Palatal Maxillary second molar Mesiobuccal Distobuccal Palatal I II 82 I8 1 1 I *Results published previously in Vertucci, F.J., and Gegauff, A.: Root canal morphology of the maxillary first premolar, J. Am. Dent. Asmc. 99:194, tresults published previously in Vertucci, F.J., Seelig, A., and Gillis, R.: Root canal morphology of the human maxillary second premolar, ORAL SIJRG. 58: 456, $Results published previously in Vertucci, F.J.: The endodontic significance of the mesiobuccal root of themaxillary first molar, Navy Med. 63: 29, 1974.

3 Volume 58 Number 5 Root canal anatomy of human permanent teeth 591 Transverse anastomosis between canals Position of transverse anastomosis Position of apical foramen Cervical Middle Apical Central Lateral Apical Deltas Note: Figures represent percentage of the total. Transverse anastomosis between canals Position of transverse anastomosis Position of apical foramen Cervical Middle Apical Central Lateral Apical Deltas IO Now Figures represent percentage of total. Total with Type VIII Total with two canals 3 three canals at apex canals at apex I in the smallest accessory canals, and because it can be removed from the external surface of the tooth, thereby allowing for a clearer specimen. The injected teeth were then dehydrated in successive solutions of 7%, 95%, and 1% alcohol for 5 hours each. The dehydration was necessary because the clearing agent is not miscible with water. Finally, the specimens were placed in clear liquid plastic casting resin* and were completely cleared within 24 hours. RESULTS The transparent specimens were examined under the dissecting microscope, and the number and type of root canals, the number and location of lateral canals and apical foramina, and the frequency of apical deltas were recorded. These data are summarized in Tables 1 and II. *Fibre-Glass Evercoat Co., Inc., Cincinnati, Ohio.

4 592 Vertucci Oral Surg. November, I984 Fig. 1. Maxillary anterior teeth. Top row, Maxillary canines. Middle row, Maxillary lateral incisors. Bottom row, Maxillary central incisors. Table IV. Classification and percentage of root canals of the mandibular teeth No. TYP I Type II Type III Total with Type IV Type V Type VI Type VII Of I-2-I one canal l-2 I Teeth terlh canal canals canals at apex canals canals canals canals Mandibular central incisor* Mandibular lateral incisor* Mandibular canine* Mandibular first premolar Mandibular second premolar? Mandibular first molar$ Mesial Distal Mandibular second molar Mesial Distal *Results published previously in Vertucci, F.J.: Root canal anatomy of the mandibular anterior teeth, J. Am. Dent. Assoc. 89:369, tresults published previously in Vertucci, F.J.: Root Canal Morphology of Mandibular Premolar Teeth, J. Am. Dent. Assoc. 97:47, $Re.sults published previously in Vertucci, F.J., and Williams, R.: Root canal anatomy of the mandibular first molar, J. N.J. Dent. Assoc , 1974

5 Volume 58 Number 5 Root canal anatomy of human permanent teeth 593 Fig. 2. A, Maxiilary first premolars, one canal at apex. Top row, Type II. Bottom row, Type I. B, Maxillary first premolars, two canals at apex. Top row, Type V. Bottom row, Type IV. C!, Maxillary first premolar, three canals at apex (Type VIII). Total with two canals at apex Type VIII 3 canals.5 Total with three canals at apex The root canal configurations present within the roots of human permanent teeth can be classified into eight types: Type I. A single canal extends from the pulp chamber to the apex. Type II. Two separate canals leave the pulp chamber and join short of the apex to form one canal. Type III. One canal leaves the pulp chamber, divides into two within the root, and then merges to exit as one canal. Type IV. Two separate and distinct canals extend from the pulp chamber to the apex. Type V. One canal leaves the pulp chamber and divides short of the apex into two separate and distinct canals with separate apical foramina.

6 594 Vertucci Oral Surg. November, 1984 Fig. 3. A, Maxillary second premolars, one canal at apex. Top row, Type I. Middle row, Type II. Bottom row, Type III. B, Maxillary second premolars, two canals at apex. Top row, Type IV. Middle row, Type V. Bottom row left, Type VI. Bottom row right, Type VII. C, Maxillary second premolar, three canals at apex (Type VIII). Fig. 4. Mesiobuccal root of maxillary first molars. Left, Type I. Middle, Type II. Right, Type IV. Type VI. Two separate canals leave the pulp chamber, merge in the body of the root, and redivide short of the apex to exit as two distinct canals. Type VII. One canal leaves the pulp chamber, divides and then rejoins within the body of the root, and tinally redivides into two distinct canals short of the apex. Type VIII. Three separate and distinct canals extend from the pulp chamber to the apex. The percentages of human permanent teeth with these canal configurations are presented in Tables III and IV. The anatomic variations present in each tooth are illustrated in Figs. 1 to IO. The most variable root canal anatomy was found in the maxillary second premolar. DlSCUSSlON During the past 1 years, there have been many excellent studies of pulp morphology. Upon comparing the findings of these studies with those of the

7 Volume 58 Number 5 Root canal anatomy of human permanent teeth 595 Fig. 5. Mesiobuccal root of maxillary second molars. Left, Type I. Middle, Type II. Right, Type IV. B I( : * B Fig. 6. Mandibular anterior teeth. Top row, Mandibular central incisors. A, Type I. B, Type II. C, Type III. D, Type IV. Middle row, Mandibular lateral incisors. A, Type I. B, Type II. C, Type III. D, Type IV. Bottom row, Mandibular canines. A, Type I. B, Type II. C, Type III. D, Type IV.

8 596 Vertucci Oral SW&. November, 1984 Fig. 7. A, Mandibular first premolars. Top row, Type I. Second row, Type III. Third row, Type IV. Bottom TOW, Type V. B, Mandibular first premolar, three canals at apex (Type VIII), Fig. 8. Mandibular second premolars. Top row, Type I. Bottom row, Type V.

9 Volume 58 Number 5 Root canal anatomy of human permanent teeth 597 Fig. 9. Mandibular first molars. Top row, Mesial root. A, Type I. B. Type II. C, Type IV. D, Type V. E, Type VI. F, Type VIII. Bottom row, Distal root. A, Type I. B, Type II. C, Type IV. D, Type V. E, Type VI. Fig. 1. Mandibular second molars. Top row, Mesial root. A, Type I. B, Type II. C. Type IV. D. Type V. Bottom row, Distal root. A, Type I. B, Type II. C, Type IV. D, Type V.

10 598 Vertucci Oral Surg. November. I984 Fig. 11. Root canal on direct periapical exposure (arrow) shows sudden narrowing; at this point canal divides into two parts as shown by radiographic view of buccolingual aspect and by transparent specimen. (D, Direct periapical exposure; B-L, buccolingual aspect; TS, transparent specimen.) present investigation, one finds that the results reported by Okumura,* who also used transparent specimens, and Pineda and Kuttler,l who employed a radiographic evaluative technique, come closest to the findings reported here. It appears that the use of an intact root of a specimen rendered transparent by decalcification and radiographic examination enables the investigator to view more clearly all of the ramifications of the root canal system. The clearing technique has considerable value in the study of root canal anatomy, for it gives a three-dimensional view of the pulp cavity in relation to the exterior of the tooth.33 In addition, it is not necessary to enter the specimens with instruments; thus, the original form and relationship of the canals are maintained. The technique used in the present study differs from other clearing techniques mainly in the nature of the clearing process; a liquid casting resin was used rather than an agent such as xylene. Slowey34 states that the root canal anatomy of each tooth has certain commonly occurring characteristics as well as numerous atypical ones that can be road maps to successful endodontics. The expected root canal anatomy dictates the location of the initial entry of access, it dictates the size of the first files used, and it contributes to a rational approach to solving the problems that arise during therapy. Therefore, a thorough knowledge of the root canal anatomy from access to obturation is essential to give the highest possible chance for success. The first consideration the dentist must have in performing endodontic therapy involves the anatomy of the tooth itself. Prior to beginning the access preparation, he should study radiographs from several different angles. If, on the direct periapical exposure, he notices that a root canal shows a sudden narrowing or even disappears, it means that at this point the canal divides into two parts which either remain separate (Type V) or merge (Type II) before reaching the apex (Fig. 11). Having the information observed from the radiographs and knowing what combinations of internal anatomy are possible, the dentist should be able to determine what type of canal configuration is present. This information, gained prior to initiation of therapy, will greatly facilitate subsequent treatment. Failure to find and fill a canal has been demonstrated to be a causative factor in the failure of endodontic therapy. 35 It is of utmost importance that all canals be located and treated during the course of nonsurgical endodontic therapy. An examination of the floor of the pulp chamber offers clues to the type of canal configuration present. When there is only one canal, it is usually located rather easily in the center of the access preparation. If only one orifice is found, and it is not in the center of the tooth, it is probable that another canal is present and the operator should search for it on the opposite side. Radiographs from various angles, some with a file in place, may be helpful. The relationship of the two canal orifices to each other is also significant. The closer the orifices are to each other, the greater are the chances that the two canals join at some point within the body of the root. Teeth with canal bifurcations in the middle or apical third may present problems in treatment. Although one of the two canals, the one most continuous with the large main passage, is usually amenable to adequate enlarging and filling procedures, the preparation and filling of the other canal is often extremely difficult. The presence of an unfilled canal may explain some of the endodontic failures associated with teeth, even though radiographically and clinically the canal system seems to be obturated. When either pain or periapical breakdown is seen after apparently effective nonsurgical endodontic

11 Volume 58 Number 5 therapy, the possible presence of an additional canal should be considered before the tooth is condemned or surgery is scheduled. If an apical root resection and reverse filling procedure becomes necessary, a complication may result. Surgery may cause a single apical foramen to become two separate foramina. Results will be poor if a search for the second canal is not routinely made during the surgical procedure. An awareness that eight possible canal configurations occur and that complications from a surgical endodontic procedure can arise should increase the rate of successful endodontic therapy. SUMMARY AND CONCLUSIONS Two thousand four hundred human permanent teeth were decalcified, injected with dye, cleared, and studied. The following data were obtained: the number of root canals and their different types, the ramifications of the main root canals, the location of apical foramina and transverse anastomoses, and the frequency of apical deltas. The findings are summarized in four tables, which have been prepared as a practical aid for the dentist. An accurate knowledge of the morphology of the pulp cavity is essential before an endodontic procedure can be approached rationally. The frequency with which root canals unite should be considered during enlargement and filling procedures. The dentist also should be aware of the possible existence of bifurcated and double canals if root canal therapy should unexpectedly fail. A knowledge of these variations will assist the dentist in reaching conclusions when diagnosing and treating endodontic cases. REFERENCES Seltzer S, Bender IB: Cognitive dissonance in endodontics. ORAL SURG 2: 55, Ingle JI: Endodontics, ed. 2, Philadelphia, 1965, Lea & Febiger, p. 43. Amos ER: Incidence of bifurcated root canals in mandibular bicuspids. J Am Dent Assoc 5: 7, Green D: Double canals in single roots. ORAL SURG 35: 689, Zillich R, Dowson J: Root canal morphology of mandibular first and second premolars. ORAL SURG 36: 738, Hess W: Anatomy of the root canals of the teeth of the permanent dentition, Part I, New York, 1925, William Wood & Company, pp Barrett MT: The internal anatomy of the teeth with special reference to the pulp with its branches. Dent Cosmos 67: 581, Okumura T: Anatomy of the root canals, Tram Seventh Int Dent Congress 1: 17, Mueller AH: Anatomy of the root canals of the incisors, cuspids and bicuspids of the permanent teeth. J Am Dent Assoc 2: 1361, Root canal anatomy of human permanent teeth Pineda F, Kuttler Y: Mesiodistal and buccolingual roentgenographic investigation of 7,275 root canals. ORAL SURG 33: 11, I. Vertucci FJ: Root canal morphology of mandibular premolar. J Am Dent Assoc 97: 47, Green D: Morphology of the endodontic system, New York, 1969, David Green, pp Vertucci FJ, Seelig A, Gillis R: Root canal morphology of the human maxillary second premolar. ORAL SURG 58: 456, Skillen WG: Morphology of root canals. J Am Dent Assoc 19: 719, Mueller AH: Morphology of root canals. J Am Dent Assoc 23: 1698, Green D: Morphology of the pulp cavity of the permanent teeth. ORAL SURG S: 743, Rankine-Wilson RW, Henry P: The bifurcated root canal in lower anterior teeth. J Am Dent Assoc 7: 1162, Vertucci FJ: Root canal anatomy of the mandibular anterior teeth, J Am Dent Assoc 89: 369, Carns EJ, Skidmore AE: Configurations and deviations of root canals of maxillary first premolars. ORAL SURG 36: 88, Vertucci FJ, Gegauff A: Root canal morphology of the maxillary first premolar. J Am Dent Assoc 99: 194, Weine FS, Healey HJ, Gerstein H, Evanson L: Canal configuration in the mesiobuccal root of the maxillary first molar and its endodontic significance. ORAL SURG 28: 419, Darnelles P: Consideracoes anatomicas sobre a conformacao interna da raiz mesiovestibular do primeiro molar superior permanente. Rev Gaucha Odontol 7: 35, Vertucci FJ: The endodontic significance of the mesiobuccal root of the maxillary first molar. Navy Med 63: 29, Skidmore AE, Bjorndal AM: Root canal morphology of the human mandibular first molar. ORAL SURG 32: 778, Vertucci FJ, Williams R: Root canal anatomy of the mandibular first molar. J N J Dent Assoc 45: 27-28, Cooke HG, Cox FL: C-shaped canal configurations in mandibular molars. J Am Dent Assoc 99: 832, Seidberg BH, Altman M, Guttuso J, Suson M: Frequency of two mesiobuccal root canals in maxillary permanent first molars. J Am Dent Assoc 87: 852, Pomeranz HH, Fishelberg G: The secondary mesiobuccal canal of maxillary molars. J Am Dent Assoc 88: 119, Altman M, Guttuso J, Seidberg BH, Langeland K: Apical root canal anatomy of human maxillary central incisors. ORAL SURG 3: , Green D: A stereomicroscopic study of the root apices of 4 maxillary and mandibular anterior teeth. ORAL SURG 9: , Nosonowitz DM, Brenner MR: The major canals of the mesiobuccal root of the maxillary first and second molars. NY J Dent 43: 12, Harris WE: Unusual root canal anatomy in a maxillary molar. J Endod 6: 573, Barker BCW, Lockett BC, Parsons KC: The demonstrations of root canal anatomy. Aust Dent J 14: 37-41, Slowey RR: Root canal anatomy, road map to successful endodontics. Dent Clin North Am 23: 555, Stewart GG: Evaluation of endodontics results. Dent Clin North Am 11: 711, Reprinf requests fo: Dr. Frank J. Vertucci Department of Endodontics University og Florida College of Dentistry Gainesville, FL 3261