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Mandibular molars with five canals: report of two cases
CLINICAL
REPORTS
Mandibular molars with five canals: report of two cases Richard G . Beatty, DDS, MS Keith Krell, DDS, MS V
A m andibular first and second molar fou n d to contain five root canals are described. Recent literature pertaining to unusual root canal m orphological structure is reviewed and a recommendation is made for a complete and thorough exam ination o f the chamber floor for even seemingly straightforward and sim ple nonsurgical endodontic cases.
onsurgical endodontic therapy is usually perform ed in teeth in which the general practitioner is able to identify and treat the anticipated 11umber of root canals. The number of root canals to be anticipated in any case is usu ally based on the data from root canal mor phological structure studies that have eval uated the frequency and distribution of root canals in hum an teeth. In 1929, Hess1 examined the root canal m orphological structure of m andibular molars. In that study, it was reported that 10% of the specimens had two root canals, 85% had three canals, and 5% had four canals with no distinction being made between first and second molars in regard to canal frequency. Later studies of m an dibular m olar root canal morphological structure departed from these statistics. Skidmore and Bjorndal2 studied plastic casts that were made from root canal sys tems of 45 m andibular first molars. Two root canals were present in 6.7% of the teeth, three root canals were present in 64.4% of the teeth, and four root canals were present in 28.9% of the teeth. Also, in departing from the results of Hess,1 Vande Voorde and others3 found that 31% of 318 consecutively treated m an d ib u lar first molars had four canals. Vertucci and W il
liams4 examined the root canal m orpho logical structure of 100 m andibular first molars. They reported that 60% of mesial roots had two canals at the apex and 40% had one. In the distal roots, 5% had two canals at the apex and 85% had one. In two mesial roots and in two distal roots, two canals joined and then separated.
Apart from the morphological studies, frequent case reports have shown unusual root canal anatom ic variations, many of which have been attributed to fusion,5-8 gem ination,9,10 or concrescence11 of tooth form. Additional root canals in teeth have also been frequently reported in teeth that clinically and/or radiographically appear
N
802 ■ JADA, Vol. 114, June 1987
Fig 1 ■ Preoperative ra d io g ra p h sh o w in g a seem-Fig 2 ■ W orking le n g th ra d io g ra p h w ith four in g ly n o rm a l m a n d ib u la r second m o la r w ith w hat
canals negotiated by endodontic files,
ap p ears to be n o rm al anatom y.
F ig 3 ■ P o stin stru m e n ta tio n ra d io g ra p h w ith all fin al apical in strum ents seated.
Fig 4 ■ M aster cone radiograph,
CLINICAL
Fig 5 ■ P osttreatm en t rad io g rap h .
norm al.12' 3 Ruiz-Badanelli14 reported a mandibular molar with five canals in which the mesial root had three canals and the distal root had two. Stroner and others15 reported a case in which a m andibular first molar had five root canals. T he tooth had two canals in the mesial root and three canals in two distal roots. T he distobuccal root had two canals and the distolingual root had a single canal. Beatty and Interian 16 reported a sim ilar case of a five-canal m andibular first molar. T h at case also had two mesial canals, two distobuccal canals, and one distolingual canal. Berihiaume17 reported a m andibular first molar with five canals, three of which were in the distal root. The third distal canal converged with the distolingual canal in the apical third and with the distobuccal canal in the coro nal third. Fabra-Campos18 examined 145 mandibular first molars and found that four of the teeth had five canals (2.7%). All four molars had three canals in the mesial root and the canals terminated in either two or three foramina. This report presents a m andibular first molar and a m andibular second molar, both of which have five root canals, and discusses the significance of finding such cases.
tio n al canal orifice in the m esial p o rtio n of the cham ber. All five canals were subsequently negotiated. E ndodontic K-type files were used to create the apical prep aratio n s in all canals and GatesG lidden d rills (size 2 a n d 3) were used to enlarge the orifices a n d coronal third of the canals. D ur ing in stru m e n tatio n , a ll ro o t canals were kept wet by freq u en t irrig a tio n w ith 5.25% sodium hypochlorite. All final apical instrum ents are show n in F igure 3. A t a second a p p o in tm en t all five root canals were obturated w ith a zinc oxideeugenol sealer a n d laterally condensed g u tta percha. F igure 4 show s a ll gutta-percha m aster cones seated in to the root canals. After o b tu ra tion, a cotton pellet a n d tem porary restoration were placed in to the cham ber a n d access o p en in g a n d a ra d io g ra p h was taken (Fig 5). T h e p a tie n t was referred for restoration of the tooth. Case 2 . A 44-year-old m ale was referred for non-
surgical en dodontic treatm ent of an asym ptom atic, badly broken-dow n m an d ib u lar rig h t first m olar (Fig 6). A diagnosis of a necrotic p u lp w ith chronic apical periodontitis was m ade and no a p p a re n t radiographic anom alies were seen. How ever, the m an d ib u lar rig h t second prem olar was seen to have a t least two canals and possibly three. T h e first m o la r was isolated a n d the re m a in in g caries removed. F our canals were in itially identified, and a “ stick” was seen in an u n u su a l position in the m esial root relative to the other two canals. A no. 15 K-type file was passed easily in to this orifice w ith o u t hem orrhage a n d subsequently a w ork
REPORTS
in g len g th ra d io g ra p h taken (Fig 7). O n com ple tion of the in itial debridem ent w ith a size 25 K-type file, G ates-G lidden nos. 3 and 4 drills were used to establish straight line access in all five canals (Fig 8). T h e canals were then p re pared usin g a step-back technique. T h e canal space was irrigated frequently w ith 2.5% sodium h ypochlorite delivered w ith a 27-gauge needle d u rin g the debridem ent a n d enlargem ent phases. C otton pellets were placed in the canals and a tem porary restoration placed. At the second a p p o in tm e n t, all canals were irrigated, dried, a n d filled w ith a zinc oxideeugenol sealer a n d laterally condensed g u tta percha. A cotton pellet w ith tem porary restora tion were then placed. A po sto b tu ratio n radio g ra p h was taken a n d the p a tie n t referred for im m ediate resto ratio n of this to o th a n d other teeth (Fig 9).
Discussion
Some morphological studies1,19 have not drawn a distinction between the numbers of root canals in m andibular first and second molars. Barker and others,20 how ever, found greater variation in the second molar as compared with the first molar. Vertucci21 studied the anatomy of 100 m an dibular first molars and 100 m andibular second molars and reported the frequency of canal type in mesial roots and in distal roots separately but did not tabulate the num ber of molars found to have four
Report of cases Case 1 . A 35-year-old female was referred for nonsurgical en dodontic treatm ent of the m an d ib u lar right second m olar. A lthough the radiog raphic o u tlin e of the roots (Fig 1) was not com pletely distinct, the tooth was ju d g ed at pre treatm ent to have two separate roots w ith norm al shape and size. T h e cham ber of the root canal system appeared clearly radiolucent; however, the root canals were n o t well defined, suggesting they could be calcified. An endodontic access p re p ara tio n was cut th ro u g h the occlusal surface of the tooth and three cham bers exposed. Initially, four canals were located (Fig 2). How ever, contin u ed explo ratio n of the cham ber floor disclosed one addi
F ig 8 ■ L o catio ns of th e five canal orifices (lin g u al
F ig 9 ■ P osttreatm ent o b tu ra tio n .
surface is isolated w ith the a id of a tem porary m aterial).
Beatty-Krell : MOLARS W ITH FIVE CANALS ■ 803
CLINICAL REPORTS
canals. However, the first molars had 15 distal roots with two canals at the apex whereas the second molars had five. This would seem to indicate (assuming mesial roots with two canals) that the first molars had a greater tendency for four root canals than did the second molars. Root canal morphological studies have shown practical information for the clini cian. However, the existence of fifth canals in mandibular molars has been largely ignored. This is, of course, because the results of studies are predicated on the characteristics of the particular teeth exam ined. These studies have made predictions as to the number of root canals that the practitioner could anticipate finding in nonsurgical endodontic cases. However, most morphological studies have exam ined only a limited number of teeth for any tooth type (often less than 100). Based on the nature of the random sampling per formed to obtain the teeth in those studies, the resultant estimates of frequency of root canals encountered in individual tooth types could be somewhat biased. This bias may be particularly noticeable in morpho logical patterns with small percentages of occurrence. Also, when morphological studies vary in percentages in their conclu sions or fail to recognize that teeth may often have additional canals, such statistics must not be judged as absolute. For example, the presentation of molar case reports with five root canals has been frequent. Some authors have presented sev eral cases in a single article.13,22,23 The fre quent presentation of such unusual cases by a few authors further suggests that the frequency of such cases in the general pop
804 ■ JADA, Vol. 114, June 1987
ulation could be greater than otherwise predicted in the morphological studies. Inasmuch as most root canal morpho logical studies have not recognized the pos sibility for fifth canals in mandibular molars, the practitioner, if approaching clinical cases with absolute confidence in those results, may have a false sense of security for case success in locating and treating only a predicted number of canals. However, as the common complexity and variability in root canal number and dis tribution has been shown, the practitioner should proceed with a complete examina tion of the interior of the tooth to exclude the possibility that any additional root canals exist.
--------------- J/OA --------------T h e a u th o rs th a n k J o h n T hee, senior d e ntal student, U niversity of F lo rida C ollege of D entistry, an d C lark Stanford, senior d e ntal student, U niversity of Iow a C ol lege o f D entistry.
D r. Beatty is a ssistant professor, d e partm ent of endodontics, J. H illis M iller H ealth Center, Box J-436, U niversity of F lorida C ollege of D entistry, G ainesville, FL 32610. Dr. Krell is associate professor, departm ent of endodontics, U niversity of Iow a College of Dentistry. Address requests for reprints to Dr. Beatty.
1. Hess, W. A natom y of the ro o t canals of the teeth of th e p e rm a n e n t d e n titio n , p a rt 1. New York, W illiam W ood a n d Co, 1925, p p 1-35. 2. Skidm ore, A.E., a n d B jorndal, A.M. R oot canal m o rp h o lo g y o f the h u m a n m a n d ib u la r first m olar. O ral S urg 32(5):778-784,1971. 3. V ande V oorde, H .E .; O dendahl, D.; a n d Davis, J. M o lar 4 th canals: freq u e n t cause of endodontic failure. Ill D ent J 44(12):779-786,1975. 4. Vertucci, F .J., an d W illiam s, R .G . R oot canal
anatom y of the m a n d ib u la r first m olar. J N J D ent Assoc 45:27-28, 1974. 5. Stabholz, A., a n d Friedm an, S. E ndodontic th er apy of a n u n u s u a l m ax illary p erm an en t first m olar. J E ndod 9(7):293-295, 1983. 6. Shteyer, A. F u sio n of a th ird m a n d ib u la r m olar w ith a d isto m o lar. O ral S urg 42(3):410, 1976. 7. H em m ig, S.B. T h ird a n d fo urth m o la r fusion. O ral S urg 48(6):572, 1979. 8. F ink, H .D ., an d V enokurs, P.C. Posterior fusion. O ral S urg 42(6):852, 1976. 9. R om e, W .J. E n d odontic therapy involving an u n u su al case of g em ination. J E ndod 10(11):546*548, 1984. 10. T agger, M. T o o th g e m ination treated by end odontic therapy. J E ndod 1(5): 181-184, 1975. 11. Levitas, T .C . G em ination, fusion, tw in n in g an d concrescence. ASDC J D ent C h ild 32(2):93-100,1965. 12. Beatty, R .G . A five-canal m axillary first m olar. J E ndod 10(4): 156-157,1984. 13. Cecic, P.L .; H artw ell, G.; a n d Bellizzi, R. T h e m u ltip le ro o t c an a l system in the m axillary first m olar: a case report. J E ndod 8(3):113-115, 1982. 14. R uiz-B adanelli, P. P rim er m o la r inferior con cinco conductos. In L asala, A., ed. Endodoncia, ed 3. Barcelona, Sal vat, 1979. 15. Stroner, W .F.; Rem eikis, N.A.; a n d C arr, G.B. M an d ib u lar first m o la r w ith three distal canals. O ral S urg 57(5):554*557, 1984. 16. Beatty, R .G ., a n d In terian , C.M. A m a n d ib u la r first m o la r w ith five canals: report of case. JADA 111(5):769-771, 1985. 17. B erthiaum e, J .T . Five canals in a low er first m olar. J M ich D ent Assoc 65(4-5):213-214, 1983. 18. Fabra-C am pos, H . U n u su al ro o t anatom y of m a n d ib u la r first m olars. J E ndod ll(12):568-572, 1985. 19. G reen, D. M orphology of the p u lp cavity of the p erm anent teeth. O ral S urg 8(7):743-759, 1955. 20. B arker, B. C ., a n d others. A natom y of ro o t canals: p erm a n e n t m a n d ib u la r m olars. A ust D ent J 19( 12):408413, 1974. 21. Vertucci, F. R oot canal anatom y of the h u m a n p erm an en t teeth. O ral S u rg 58(5):589-599, 1984. 22. M artinez-Berna, A., an d R uiz-B adanelli, P. M ax illary first m olars w ith six canals. J E ndod 9(9):375-381, 1983. 23. El Deeb, M .E. T h re e root canals in m an d ib u la r second prem olars: literature review a n d a case report. J E ndod 8(8):376-377, 1982.
REPORTS
Mandibular molars with five canals: report of two cases Richard G . Beatty, DDS, MS Keith Krell, DDS, MS V
A m andibular first and second molar fou n d to contain five root canals are described. Recent literature pertaining to unusual root canal m orphological structure is reviewed and a recommendation is made for a complete and thorough exam ination o f the chamber floor for even seemingly straightforward and sim ple nonsurgical endodontic cases.
onsurgical endodontic therapy is usually perform ed in teeth in which the general practitioner is able to identify and treat the anticipated 11umber of root canals. The number of root canals to be anticipated in any case is usu ally based on the data from root canal mor phological structure studies that have eval uated the frequency and distribution of root canals in hum an teeth. In 1929, Hess1 examined the root canal m orphological structure of m andibular molars. In that study, it was reported that 10% of the specimens had two root canals, 85% had three canals, and 5% had four canals with no distinction being made between first and second molars in regard to canal frequency. Later studies of m an dibular m olar root canal morphological structure departed from these statistics. Skidmore and Bjorndal2 studied plastic casts that were made from root canal sys tems of 45 m andibular first molars. Two root canals were present in 6.7% of the teeth, three root canals were present in 64.4% of the teeth, and four root canals were present in 28.9% of the teeth. Also, in departing from the results of Hess,1 Vande Voorde and others3 found that 31% of 318 consecutively treated m an d ib u lar first molars had four canals. Vertucci and W il
liams4 examined the root canal m orpho logical structure of 100 m andibular first molars. They reported that 60% of mesial roots had two canals at the apex and 40% had one. In the distal roots, 5% had two canals at the apex and 85% had one. In two mesial roots and in two distal roots, two canals joined and then separated.
Apart from the morphological studies, frequent case reports have shown unusual root canal anatom ic variations, many of which have been attributed to fusion,5-8 gem ination,9,10 or concrescence11 of tooth form. Additional root canals in teeth have also been frequently reported in teeth that clinically and/or radiographically appear
N
802 ■ JADA, Vol. 114, June 1987
Fig 1 ■ Preoperative ra d io g ra p h sh o w in g a seem-Fig 2 ■ W orking le n g th ra d io g ra p h w ith four in g ly n o rm a l m a n d ib u la r second m o la r w ith w hat
canals negotiated by endodontic files,
ap p ears to be n o rm al anatom y.
F ig 3 ■ P o stin stru m e n ta tio n ra d io g ra p h w ith all fin al apical in strum ents seated.
Fig 4 ■ M aster cone radiograph,
CLINICAL
Fig 5 ■ P osttreatm en t rad io g rap h .
norm al.12' 3 Ruiz-Badanelli14 reported a mandibular molar with five canals in which the mesial root had three canals and the distal root had two. Stroner and others15 reported a case in which a m andibular first molar had five root canals. T he tooth had two canals in the mesial root and three canals in two distal roots. T he distobuccal root had two canals and the distolingual root had a single canal. Beatty and Interian 16 reported a sim ilar case of a five-canal m andibular first molar. T h at case also had two mesial canals, two distobuccal canals, and one distolingual canal. Berihiaume17 reported a m andibular first molar with five canals, three of which were in the distal root. The third distal canal converged with the distolingual canal in the apical third and with the distobuccal canal in the coro nal third. Fabra-Campos18 examined 145 mandibular first molars and found that four of the teeth had five canals (2.7%). All four molars had three canals in the mesial root and the canals terminated in either two or three foramina. This report presents a m andibular first molar and a m andibular second molar, both of which have five root canals, and discusses the significance of finding such cases.
tio n al canal orifice in the m esial p o rtio n of the cham ber. All five canals were subsequently negotiated. E ndodontic K-type files were used to create the apical prep aratio n s in all canals and GatesG lidden d rills (size 2 a n d 3) were used to enlarge the orifices a n d coronal third of the canals. D ur ing in stru m e n tatio n , a ll ro o t canals were kept wet by freq u en t irrig a tio n w ith 5.25% sodium hypochlorite. All final apical instrum ents are show n in F igure 3. A t a second a p p o in tm en t all five root canals were obturated w ith a zinc oxideeugenol sealer a n d laterally condensed g u tta percha. F igure 4 show s a ll gutta-percha m aster cones seated in to the root canals. After o b tu ra tion, a cotton pellet a n d tem porary restoration were placed in to the cham ber a n d access o p en in g a n d a ra d io g ra p h was taken (Fig 5). T h e p a tie n t was referred for restoration of the tooth. Case 2 . A 44-year-old m ale was referred for non-
surgical en dodontic treatm ent of an asym ptom atic, badly broken-dow n m an d ib u lar rig h t first m olar (Fig 6). A diagnosis of a necrotic p u lp w ith chronic apical periodontitis was m ade and no a p p a re n t radiographic anom alies were seen. How ever, the m an d ib u lar rig h t second prem olar was seen to have a t least two canals and possibly three. T h e first m o la r was isolated a n d the re m a in in g caries removed. F our canals were in itially identified, and a “ stick” was seen in an u n u su a l position in the m esial root relative to the other two canals. A no. 15 K-type file was passed easily in to this orifice w ith o u t hem orrhage a n d subsequently a w ork
REPORTS
in g len g th ra d io g ra p h taken (Fig 7). O n com ple tion of the in itial debridem ent w ith a size 25 K-type file, G ates-G lidden nos. 3 and 4 drills were used to establish straight line access in all five canals (Fig 8). T h e canals were then p re pared usin g a step-back technique. T h e canal space was irrigated frequently w ith 2.5% sodium h ypochlorite delivered w ith a 27-gauge needle d u rin g the debridem ent a n d enlargem ent phases. C otton pellets were placed in the canals and a tem porary restoration placed. At the second a p p o in tm e n t, all canals were irrigated, dried, a n d filled w ith a zinc oxideeugenol sealer a n d laterally condensed g u tta percha. A cotton pellet w ith tem porary restora tion were then placed. A po sto b tu ratio n radio g ra p h was taken a n d the p a tie n t referred for im m ediate resto ratio n of this to o th a n d other teeth (Fig 9).
Discussion
Some morphological studies1,19 have not drawn a distinction between the numbers of root canals in m andibular first and second molars. Barker and others,20 how ever, found greater variation in the second molar as compared with the first molar. Vertucci21 studied the anatomy of 100 m an dibular first molars and 100 m andibular second molars and reported the frequency of canal type in mesial roots and in distal roots separately but did not tabulate the num ber of molars found to have four
Report of cases Case 1 . A 35-year-old female was referred for nonsurgical en dodontic treatm ent of the m an d ib u lar right second m olar. A lthough the radiog raphic o u tlin e of the roots (Fig 1) was not com pletely distinct, the tooth was ju d g ed at pre treatm ent to have two separate roots w ith norm al shape and size. T h e cham ber of the root canal system appeared clearly radiolucent; however, the root canals were n o t well defined, suggesting they could be calcified. An endodontic access p re p ara tio n was cut th ro u g h the occlusal surface of the tooth and three cham bers exposed. Initially, four canals were located (Fig 2). How ever, contin u ed explo ratio n of the cham ber floor disclosed one addi
F ig 8 ■ L o catio ns of th e five canal orifices (lin g u al
F ig 9 ■ P osttreatm ent o b tu ra tio n .
surface is isolated w ith the a id of a tem porary m aterial).
Beatty-Krell : MOLARS W ITH FIVE CANALS ■ 803
CLINICAL REPORTS
canals. However, the first molars had 15 distal roots with two canals at the apex whereas the second molars had five. This would seem to indicate (assuming mesial roots with two canals) that the first molars had a greater tendency for four root canals than did the second molars. Root canal morphological studies have shown practical information for the clini cian. However, the existence of fifth canals in mandibular molars has been largely ignored. This is, of course, because the results of studies are predicated on the characteristics of the particular teeth exam ined. These studies have made predictions as to the number of root canals that the practitioner could anticipate finding in nonsurgical endodontic cases. However, most morphological studies have exam ined only a limited number of teeth for any tooth type (often less than 100). Based on the nature of the random sampling per formed to obtain the teeth in those studies, the resultant estimates of frequency of root canals encountered in individual tooth types could be somewhat biased. This bias may be particularly noticeable in morpho logical patterns with small percentages of occurrence. Also, when morphological studies vary in percentages in their conclu sions or fail to recognize that teeth may often have additional canals, such statistics must not be judged as absolute. For example, the presentation of molar case reports with five root canals has been frequent. Some authors have presented sev eral cases in a single article.13,22,23 The fre quent presentation of such unusual cases by a few authors further suggests that the frequency of such cases in the general pop
804 ■ JADA, Vol. 114, June 1987
ulation could be greater than otherwise predicted in the morphological studies. Inasmuch as most root canal morpho logical studies have not recognized the pos sibility for fifth canals in mandibular molars, the practitioner, if approaching clinical cases with absolute confidence in those results, may have a false sense of security for case success in locating and treating only a predicted number of canals. However, as the common complexity and variability in root canal number and dis tribution has been shown, the practitioner should proceed with a complete examina tion of the interior of the tooth to exclude the possibility that any additional root canals exist.
--------------- J/OA --------------T h e a u th o rs th a n k J o h n T hee, senior d e ntal student, U niversity of F lo rida C ollege of D entistry, an d C lark Stanford, senior d e ntal student, U niversity of Iow a C ol lege o f D entistry.
D r. Beatty is a ssistant professor, d e partm ent of endodontics, J. H illis M iller H ealth Center, Box J-436, U niversity of F lorida C ollege of D entistry, G ainesville, FL 32610. Dr. Krell is associate professor, departm ent of endodontics, U niversity of Iow a College of Dentistry. Address requests for reprints to Dr. Beatty.
1. Hess, W. A natom y of the ro o t canals of the teeth of th e p e rm a n e n t d e n titio n , p a rt 1. New York, W illiam W ood a n d Co, 1925, p p 1-35. 2. Skidm ore, A.E., a n d B jorndal, A.M. R oot canal m o rp h o lo g y o f the h u m a n m a n d ib u la r first m olar. O ral S urg 32(5):778-784,1971. 3. V ande V oorde, H .E .; O dendahl, D.; a n d Davis, J. M o lar 4 th canals: freq u e n t cause of endodontic failure. Ill D ent J 44(12):779-786,1975. 4. Vertucci, F .J., an d W illiam s, R .G . R oot canal
anatom y of the m a n d ib u la r first m olar. J N J D ent Assoc 45:27-28, 1974. 5. Stabholz, A., a n d Friedm an, S. E ndodontic th er apy of a n u n u s u a l m ax illary p erm an en t first m olar. J E ndod 9(7):293-295, 1983. 6. Shteyer, A. F u sio n of a th ird m a n d ib u la r m olar w ith a d isto m o lar. O ral S urg 42(3):410, 1976. 7. H em m ig, S.B. T h ird a n d fo urth m o la r fusion. O ral S urg 48(6):572, 1979. 8. F ink, H .D ., an d V enokurs, P.C. Posterior fusion. O ral S urg 42(6):852, 1976. 9. R om e, W .J. E n d odontic therapy involving an u n u su al case of g em ination. J E ndod 10(11):546*548, 1984. 10. T agger, M. T o o th g e m ination treated by end odontic therapy. J E ndod 1(5): 181-184, 1975. 11. Levitas, T .C . G em ination, fusion, tw in n in g an d concrescence. ASDC J D ent C h ild 32(2):93-100,1965. 12. Beatty, R .G . A five-canal m axillary first m olar. J E ndod 10(4): 156-157,1984. 13. Cecic, P.L .; H artw ell, G.; a n d Bellizzi, R. T h e m u ltip le ro o t c an a l system in the m axillary first m olar: a case report. J E ndod 8(3):113-115, 1982. 14. R uiz-B adanelli, P. P rim er m o la r inferior con cinco conductos. In L asala, A., ed. Endodoncia, ed 3. Barcelona, Sal vat, 1979. 15. Stroner, W .F.; Rem eikis, N.A.; a n d C arr, G.B. M an d ib u lar first m o la r w ith three distal canals. O ral S urg 57(5):554*557, 1984. 16. Beatty, R .G ., a n d In terian , C.M. A m a n d ib u la r first m o la r w ith five canals: report of case. JADA 111(5):769-771, 1985. 17. B erthiaum e, J .T . Five canals in a low er first m olar. J M ich D ent Assoc 65(4-5):213-214, 1983. 18. Fabra-C am pos, H . U n u su al ro o t anatom y of m a n d ib u la r first m olars. J E ndod ll(12):568-572, 1985. 19. G reen, D. M orphology of the p u lp cavity of the p erm anent teeth. O ral S urg 8(7):743-759, 1955. 20. B arker, B. C ., a n d others. A natom y of ro o t canals: p erm a n e n t m a n d ib u la r m olars. A ust D ent J 19( 12):408413, 1974. 21. Vertucci, F. R oot canal anatom y of the h u m a n p erm an en t teeth. O ral S u rg 58(5):589-599, 1984. 22. M artinez-Berna, A., an d R uiz-B adanelli, P. M ax illary first m olars w ith six canals. J E ndod 9(9):375-381, 1983. 23. El Deeb, M .E. T h re e root canals in m an d ib u la r second prem olars: literature review a n d a case report. J E ndod 8(8):376-377, 1982.