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The significance of locating and filling the canal isthmus in multiple root canal systems. A scanning electron microscopy study of the mesiobuccal root of maxillary first permanent molars
Pergamon Plh S0968-4328(98)00063-2
MicHm Vol. 29, No. 4, pp. 261 265, 1998 ~g?)1998 Elsevier Science Ltd All righls reserved. Printed in Great Britain 0968-4328/98 $19.(X)+0.00
The Significance of Locating and Filling the Canal Isthmus in Multiple Root Canal Systems. A Scanning Electron Microscopy Study of the Mesiobuccal Root of Maxillary First Permanent Molars D O N A L D C. Y U t , A L P H O N S U S TAM+ and M I N G H. CHEN$ tDentisto,/Pharmacy Building, University of Alberta, Edmonton. Alberto, Canada T6G 2N8 +~Surgical-Medical Research Institute. Universi~' of Alberta, Edmonton, Alberta, Canada T6G 2N8 (Received 9 June 1997: accepted 19 September 1997)
Abstract--The mesiobuccal (MB) roots of 50 randomly selected maxillary first permanent molars were examined to evaluate the different configurations of canal isthmus and their incidences. Sections of the roots at 3, 4 and 5 mm from the apex were prepared, acid etched, washed and dried. The apical side of each section was sputter coated with gold, examined by a Hitachi S-2500 scanning electron m!croscope and photographed. 36% of the mesiobuccalroots had one canal, whereas 64% had two canals. In the roots with two canals 31.25% contained either a complete isthmus, or accessory canals between the two main canals. 31.25% showed partial isthmus formation. The significanceof the different configurationsis discussed. Our present findings indicate that the mesiobuccal roots of maxillary first permanent molars exhibit complex anatomy. Prudentjudgement is essential in the canal isthmus preparation so that operators must provide meticulous skill and care to the patients. © 1998 Elsevier Science Ltd. All rights reserved. Key words: scanning electron microscopy canal isthmus, accessory canal, mesiobuccal root. maxillary first permanent molar.
INTRODUCTION
molar apicoectomies respectively. However, a recent 20 year retrospective study which reviewed the results of four In the past periradicular endodontic surgery was less fre- practitioners suggested a failure rate approaching 50% quently performed. This is due to the fact that nonsurgical (Frank et al., 1992). procedures are easier to manage and the successful results It has been suggested that most surgical failures were due are relatively predictable. Indeed, nonsurgical treatment still to lack of seal of the resected root (Carr, 1992). This lack of is and always will be the preferred choice. However, as the seal could be caused by failure to properly prepare the isthdemand of saving teeth has increased, more failing nonsurmus area of posterior teeth. A 30.1% incidence of canal isthmus in the mesiobuccal root of the maxil!ary first pergically treated teeth are now subject to surgery. In surgery, manent molar has been reported (Cambruzzi and Marshall, the instruments, equipment, knowledge and case management have improved vastly in the last few years. More and 1983). Recently a 100% incidence of a complete or partial more surgical endodontic procedures are expected from canal isthmus was reported, these were detected about 4 mm both endodontists and general practitioners, especially from the root apex of mesiobuccal roots of a sample of 50 when surgical operating microscopes with high power illu- maxillary first permanent molars using transverse serial sections stained with methylene blue dye and viiewed with a mination and magnification are now readily available and surgical operating microscope at 32 × magnification (Weller financially affordable. Numerous studies of the long-term results of apical sur- et al., 1995). We believe the root canal system of the mesiobuccal root gery have been reported (Gutmann and Harrison, 1991). The of maxillary first permanent molar is very complex, and that success rate of endodontic surgery in the literature ranges the viewing of the sections with surgical operating microfrom 25% to over 90%. A success rate of 44.1% was reported in 136 roots in premolar and molar teeth (Fried- scopes at 32 × magnification does not necessarily reveal all mann et al., 1991). The observation period varied from 6 the fine details of the apical root canal anatomy. In addition, months to 8 years. Complete healing was found in 65% of the reflection of high intensity surgical light may give illusion of root canal aberration. To study the intricate root 424 recall cases (Rapp et al., 1991). Other authors have found 72% of 46 apicoectomised molars to be successful canal system, we propose to investigate the m o r p h o l o g y (Altonen and Mattila, 1976). Similar results were reported of root sections using a scanning electron microscope at high magnification. in 25 (Persson, 1982) and 70 (Ioannides and Borstlap, 1983) The purpose of this study is to evaluate the significance of locating and filling the canal isthmus in the mesiobuccal *Corresponding author. 261
262
D.C. Yu et al.
roots of maxillary first permanent molars using scanning electron microscopy.
M A T E R I A L S AND M E T H O D S Fifty human maxillary left and right first permanent molars were randomly selected and stored in a thymol solution. The sex, age and race of the patients from which these teeth were obtained were unknown. The teeth were identified using the criteria outlined by (Sicher and Dubral, 1975) and (Kraus et al., 1969). Using an ultra thin diamond disk (Horico Diaflex, Pfingst, Germany) the mesiobuccal root of the maxillary first permanent molars, were sectioned at 3, 4 and 5 mm away from the root apex perpendicular to the long axis of the root. This closely resembles the actual level of sectioning in endodontic surgery. The 3 sections of the same tooth were acid etched (Ultra-etch, Ultradent Products Inc., USA) for one minute to remove the smear layer and then washed in distilled water. These sections were then placed in a small vial and dehydrated in a series of 50-100% ethanol solutions for 10 minutes each. The specimens were then subjected to critical point drying (Critical Point Dryer, Seevac Inc. Florida, U.S.A.). After critical point drying, the root sections were mounted on a labelled stub, and sputter coated with gold (Sputter Coater, Model S/50 B, Edwards, England). Only the apical sides were coated and evaluated. All sections were scanned by a Hitachi S-2500 scanning electron microscope and photographed to determine the number of root canals present and the presence or absence of an isthmus. The canal configurations were then classified. The data were tabulated.
RESULTS The results are listed in Tables 1-3. One canal was present in 36% of the cases and two canals were found in 64% of all the roots examined (Table 1). Different canal configurations were found among different meisobuccal roots in the 3 - 5 mm region as measured from the root apex Table I. Number of canals in the mesiobuccal root of maxillary first permanent molar Number of canals 1 2 Total
Number of cases
%
18 32 50
36 64 100
(Figs 1-6). However, in the same root, we found that the sections at 3, 4 and 5 mm levels showed no significant differences in canal configuration. Accessory canals show as smaller openings located in the neighbourhood of the main canals. Between the two main canals, usually one is larger than the other, an isthmus may connect or intercommunicate them totally or partially at the particular level of section. The incidences of different canal configurations were summarised in Tables 2 and 3. In our present scanning electron microscopy study, 36% of the meisobuccal roots had one canal and 64% had two canals (Table 1). There are six types of canal configuration in the meisobuccal roots (Figs 1-6) found in this study. Table 2 shows the incidences of each type of the canal configuration. In the group with two canals, the following classification of canal configurations and incidences were found (Table 3): (1) Two separated canals - - 37.5% (Fig. 2). (2) Two separated canals with one or more accessory canals in between - - 12.5% (Fig. 3). (3) Two Canals with one showing partial isthmus formation - - 31.25% (Fig. 4). (4) Two canals joined by an isthmus - - 12.5% (Fig. 5). (5) Two canals joined by an isthmus and one or more accessory canals within the isthmus - - 6.25% (Fig. 6).
DISCUSSION In this study, the incidence of a complete isthmus between two canals in sections 3 - 5 mm from the apex was found to be 12.5%. This is similar to the results of previous authors (Weller et al., 1995). We found 6.25% of mesiobuccal roots had one or more accessory canals within the isthmus joining meisobuccal 1 (MB 1) and mesiobuccal2 (MB 2) canals (Figs 7 and 8). The presence of this accessory canal should not be ignored. With high magnification, dentinal tubules are shown in the accessory canal (Fig. 8). The objective of surgical endodontic procedures is to place an effective reverse filling at the terminus of the resected root and to clean and shape the entire terminus (Figs 7 and 8). 12.5% of the mesiobuccal roots in this study had one or more definite accessory canals when the MBI and MB2 canals were not joined by an isthmus (Fig. 9). Any opening on the resected root surface acts as a portal of exit or foramen and may contain necrotic debris or organic substrates capable of supporting the growth of microorganisms. Judicious cleaning and shaping of this accessory canal and a definite seal, equivalent to a nonsurgical
Table 2. Canal configuration incidences in the mesiobuccal roots of maxillary first permanent molars Canal configuration One canal Two separated canals Two separated canals and one or more accessory canals in between Two canals with one showing partial isthmus formation Two canals joined by an isthmus Two canals joined by an isthmus with accessory canals within the isthmus Total
Number of cases
%
18 12 4 10 4 2 50
36 24 8 20 8 4 100
Canal Isthmus Incidences and Configurations
263
Table 3. Incidence of an isthmus or accessory canals in sections with two canals Canal configuration Two separated canals Two separated canals and one or more accessory canals in between Two canals with one showing partial isthmus formation Two canals joined by an isthmus Two canals joined by an isthmus and or more accessory canals within the isthmus Total
0
Fig. 1. One canal.
Fig. 2. Two separated canals.
Fig. 3. Two separated canals and one or more accessory canals inbetween.
Fig. 4. Two canals with one showing partial isthmus formation.
Iil
Fig. 5. Two canals joined by and isthmus in mesiobuccal root.
Number of cases
%
12 4 10 4 2 32
37.5 12.5 31.25 12.5 6.25 100
endodontic procedure, is desirable. An omission of this accessory canal opening will lead to eventual failure of endodontic surgery. The preparation o f the resected root surface to receive a reverse filling must incorporate the isthmus and any accessory canal opening between the MB~ and MB2 canals. In this study, we found the incidence amounted to 31.25% (categories 2, 4 and 5). This is similar to the 30.1% previously reported (Cambruzzi and Marshall, 1983), but much lower than the 100% incidence of a complete of partial canal isthmus as reported recently (Weller et al., 1995). The operating microscope of high light intensity may give illusion of more root canal aberrations. The concept o f partial isthmus formation is difficult to articulate. 31.25% of the MB roots in this study had two canals with one canal showing an extension towards the other canal (Fig. 10). The cross-section of !his canal is similar to a c o m m a shape. This tail extension of the canal may come about in several ways. Firstly, it may be part of the fin or loop of the root canal anatomy. Secondly, it may be that the section is made at the point where one canal starts to twist and turn to merge with a second canal. Thirdly, it may be an 'actual' partial isthmus formationi such that a complete isthmus will be formed elsewhere irl the root. In our examination of these sections at the level 3~5 mm from the root apex, we found that the partial isthmuses remained as partial isthmuses. This leads us to believe that not every partial isthmus formation will become a complete isthmus elsewhere in the MB root. Based on our current findings, we propose the following classification of the MB root of maxillary first permanent molars: T y p e I. One main canal; if an accessory canali is present, a suffix is added to indicate the number, e.g. Type I-A, I-B and I-C signify one main canal plus 1, 2, or 3 accessory canals. T y p e II. Two main canals, i.e. MBI and MB2; if an accessory canal is present, a suffix is added to indicate the number (see above), e.g. Type II-D signifies two canals plus 4 accessory canals.
Fig. 6. Two canals joined by an isthmus and one or more accessory canals within the isthmus.
264
D.C. Yu et al,
Type III. Two main canals plus partial isthmus formation; if an accessory canals is present, a suffix is added to indicate the number (see above). Type IV. Two main canals joined by a complete isthmus; if an accessory canal is present, a suffix is added to indicate the number (see above). This classification is universal and specifies both the configuration of the mesiobuccal canal and number of accessory canals present. The variation of success rate may be due to the factors such as radiographic interpretation, untreated root canal systems, operator skill, the complexity of the surgical procedure and the use of high power illumination and magnification. One of the keys to success is to know the details of the apical root canal anatomy. The isthmus must be obturated by reverse filling to ensure periapical healing. Our present findings using scanning electron microscopy indicates that the MB roots of the maxillary first permanent molars exhibit complex anatomy, and that no two root canal systems are exactly alike. We believe this study using the
scanning electron microscope is important because it allows us to examine the root sections of common surgical sites in fine detail. At the present time surgical operating microscopes cannot study the root sections at such high magnification. It is common knowledge that scanning electron microscopy is best used to study the surface topography and its use allows us to reveal the intricate cross-sectional anatomy of the mesiobuccal root of the maxillary first permanent molar. To prevent vexing complications for both the clinician and patient, it behoves the clinician to be completely familiar with the possible variety of root canal anatomy of a planned surgical site. Prudent judgement is essential before attempting a new procedure, including the incorporation of the area between the MB1 and MB2 canals during reverse filling cavity preparation. The most predictable treatment outcomes will occur when the experienced clinician has accurate knowledge of the root canal anatomy to guide both nonsurgical and surgical endodontic therapy, impeccable patient care.
Fig. 7. Representative sample of a section with two main canals joined by an isthmus and a accessory canal (arrow) within the isthmus.
Fig. 9. Representative sample of a section with two main canals and one accessory canal (arrow) in between.
Fig. 8. Higher magnification of the accessory canal from Fig. 7.
Fig. 10. Representative sample of a section with partial isthmus formation (arrow).
Canal Isthmus Incidences and Configurations
REFERENCES Altonen M., Mattila K., 1976. Follow up study of apicoectomised molars. Int. J. Oral Surg., $, 33-40. Cambruzzi T. V., Marshall F. J., 1983. Molar endodontics surgery. J. Canada Dent Assn., 1, 61-66. Carr G., 1992. Advanced techniques and visual enhancement for endodontic surgery. Endodon. Rep., 7 (1), 6-9. Frank A., Click D., Paterson S., Wiene F., 1992. Long term evaluation of surgically placed amalgam fillings. J. Endodon., 18, 391-398. Friedmann S., Lustmann T., Shaharabany V., 1991. Treatment results of apical surgery in premolar and molar teeth. J. Endodon., 17, 30-33. Gutmann, J. and Harrison, J. (1991) Surgical Endodontics. Blackwell Scientific Publications, Boston.
265
Ioannides C., Borstlap W., 1983. A Apicoectomy of molars: a clinical and radiographic study. Int. J. Oral Surg., 12, 73-79. Kraus, B. S., Jordan, R. E. and Abrams, L. (1969) Dental Anatomy and Occlusion. The Williams and Wilkins Company, Baltimore, pp. 74115. Persson G., 1982. Periapical surgery of molars. Int. Z Oral Surg.. 11, 96100. Rapp E., Brown C., Nawton C., 1991. An analysis of success and Iailure of apicoectomies. J. Endodon., 17, 508-512. Sicher, H. and Dubral, E. L. (1975) In OralAnatomy, ed C. V. Mosby, 6th edn. St. Louis. Weller R. N., Niemczyk S. P., Kim S., 1995. Incidence and position of canal isthmus part 1. Mesiobuccat root of the maxillary first molar. J. Endodon., 7, 380-383
MicHm Vol. 29, No. 4, pp. 261 265, 1998 ~g?)1998 Elsevier Science Ltd All righls reserved. Printed in Great Britain 0968-4328/98 $19.(X)+0.00
The Significance of Locating and Filling the Canal Isthmus in Multiple Root Canal Systems. A Scanning Electron Microscopy Study of the Mesiobuccal Root of Maxillary First Permanent Molars D O N A L D C. Y U t , A L P H O N S U S TAM+ and M I N G H. CHEN$ tDentisto,/Pharmacy Building, University of Alberta, Edmonton. Alberto, Canada T6G 2N8 +~Surgical-Medical Research Institute. Universi~' of Alberta, Edmonton, Alberta, Canada T6G 2N8 (Received 9 June 1997: accepted 19 September 1997)
Abstract--The mesiobuccal (MB) roots of 50 randomly selected maxillary first permanent molars were examined to evaluate the different configurations of canal isthmus and their incidences. Sections of the roots at 3, 4 and 5 mm from the apex were prepared, acid etched, washed and dried. The apical side of each section was sputter coated with gold, examined by a Hitachi S-2500 scanning electron m!croscope and photographed. 36% of the mesiobuccalroots had one canal, whereas 64% had two canals. In the roots with two canals 31.25% contained either a complete isthmus, or accessory canals between the two main canals. 31.25% showed partial isthmus formation. The significanceof the different configurationsis discussed. Our present findings indicate that the mesiobuccal roots of maxillary first permanent molars exhibit complex anatomy. Prudentjudgement is essential in the canal isthmus preparation so that operators must provide meticulous skill and care to the patients. © 1998 Elsevier Science Ltd. All rights reserved. Key words: scanning electron microscopy canal isthmus, accessory canal, mesiobuccal root. maxillary first permanent molar.
INTRODUCTION
molar apicoectomies respectively. However, a recent 20 year retrospective study which reviewed the results of four In the past periradicular endodontic surgery was less fre- practitioners suggested a failure rate approaching 50% quently performed. This is due to the fact that nonsurgical (Frank et al., 1992). procedures are easier to manage and the successful results It has been suggested that most surgical failures were due are relatively predictable. Indeed, nonsurgical treatment still to lack of seal of the resected root (Carr, 1992). This lack of is and always will be the preferred choice. However, as the seal could be caused by failure to properly prepare the isthdemand of saving teeth has increased, more failing nonsurmus area of posterior teeth. A 30.1% incidence of canal isthmus in the mesiobuccal root of the maxil!ary first pergically treated teeth are now subject to surgery. In surgery, manent molar has been reported (Cambruzzi and Marshall, the instruments, equipment, knowledge and case management have improved vastly in the last few years. More and 1983). Recently a 100% incidence of a complete or partial more surgical endodontic procedures are expected from canal isthmus was reported, these were detected about 4 mm both endodontists and general practitioners, especially from the root apex of mesiobuccal roots of a sample of 50 when surgical operating microscopes with high power illu- maxillary first permanent molars using transverse serial sections stained with methylene blue dye and viiewed with a mination and magnification are now readily available and surgical operating microscope at 32 × magnification (Weller financially affordable. Numerous studies of the long-term results of apical sur- et al., 1995). We believe the root canal system of the mesiobuccal root gery have been reported (Gutmann and Harrison, 1991). The of maxillary first permanent molar is very complex, and that success rate of endodontic surgery in the literature ranges the viewing of the sections with surgical operating microfrom 25% to over 90%. A success rate of 44.1% was reported in 136 roots in premolar and molar teeth (Fried- scopes at 32 × magnification does not necessarily reveal all mann et al., 1991). The observation period varied from 6 the fine details of the apical root canal anatomy. In addition, months to 8 years. Complete healing was found in 65% of the reflection of high intensity surgical light may give illusion of root canal aberration. To study the intricate root 424 recall cases (Rapp et al., 1991). Other authors have found 72% of 46 apicoectomised molars to be successful canal system, we propose to investigate the m o r p h o l o g y (Altonen and Mattila, 1976). Similar results were reported of root sections using a scanning electron microscope at high magnification. in 25 (Persson, 1982) and 70 (Ioannides and Borstlap, 1983) The purpose of this study is to evaluate the significance of locating and filling the canal isthmus in the mesiobuccal *Corresponding author. 261
262
D.C. Yu et al.
roots of maxillary first permanent molars using scanning electron microscopy.
M A T E R I A L S AND M E T H O D S Fifty human maxillary left and right first permanent molars were randomly selected and stored in a thymol solution. The sex, age and race of the patients from which these teeth were obtained were unknown. The teeth were identified using the criteria outlined by (Sicher and Dubral, 1975) and (Kraus et al., 1969). Using an ultra thin diamond disk (Horico Diaflex, Pfingst, Germany) the mesiobuccal root of the maxillary first permanent molars, were sectioned at 3, 4 and 5 mm away from the root apex perpendicular to the long axis of the root. This closely resembles the actual level of sectioning in endodontic surgery. The 3 sections of the same tooth were acid etched (Ultra-etch, Ultradent Products Inc., USA) for one minute to remove the smear layer and then washed in distilled water. These sections were then placed in a small vial and dehydrated in a series of 50-100% ethanol solutions for 10 minutes each. The specimens were then subjected to critical point drying (Critical Point Dryer, Seevac Inc. Florida, U.S.A.). After critical point drying, the root sections were mounted on a labelled stub, and sputter coated with gold (Sputter Coater, Model S/50 B, Edwards, England). Only the apical sides were coated and evaluated. All sections were scanned by a Hitachi S-2500 scanning electron microscope and photographed to determine the number of root canals present and the presence or absence of an isthmus. The canal configurations were then classified. The data were tabulated.
RESULTS The results are listed in Tables 1-3. One canal was present in 36% of the cases and two canals were found in 64% of all the roots examined (Table 1). Different canal configurations were found among different meisobuccal roots in the 3 - 5 mm region as measured from the root apex Table I. Number of canals in the mesiobuccal root of maxillary first permanent molar Number of canals 1 2 Total
Number of cases
%
18 32 50
36 64 100
(Figs 1-6). However, in the same root, we found that the sections at 3, 4 and 5 mm levels showed no significant differences in canal configuration. Accessory canals show as smaller openings located in the neighbourhood of the main canals. Between the two main canals, usually one is larger than the other, an isthmus may connect or intercommunicate them totally or partially at the particular level of section. The incidences of different canal configurations were summarised in Tables 2 and 3. In our present scanning electron microscopy study, 36% of the meisobuccal roots had one canal and 64% had two canals (Table 1). There are six types of canal configuration in the meisobuccal roots (Figs 1-6) found in this study. Table 2 shows the incidences of each type of the canal configuration. In the group with two canals, the following classification of canal configurations and incidences were found (Table 3): (1) Two separated canals - - 37.5% (Fig. 2). (2) Two separated canals with one or more accessory canals in between - - 12.5% (Fig. 3). (3) Two Canals with one showing partial isthmus formation - - 31.25% (Fig. 4). (4) Two canals joined by an isthmus - - 12.5% (Fig. 5). (5) Two canals joined by an isthmus and one or more accessory canals within the isthmus - - 6.25% (Fig. 6).
DISCUSSION In this study, the incidence of a complete isthmus between two canals in sections 3 - 5 mm from the apex was found to be 12.5%. This is similar to the results of previous authors (Weller et al., 1995). We found 6.25% of mesiobuccal roots had one or more accessory canals within the isthmus joining meisobuccal 1 (MB 1) and mesiobuccal2 (MB 2) canals (Figs 7 and 8). The presence of this accessory canal should not be ignored. With high magnification, dentinal tubules are shown in the accessory canal (Fig. 8). The objective of surgical endodontic procedures is to place an effective reverse filling at the terminus of the resected root and to clean and shape the entire terminus (Figs 7 and 8). 12.5% of the mesiobuccal roots in this study had one or more definite accessory canals when the MBI and MB2 canals were not joined by an isthmus (Fig. 9). Any opening on the resected root surface acts as a portal of exit or foramen and may contain necrotic debris or organic substrates capable of supporting the growth of microorganisms. Judicious cleaning and shaping of this accessory canal and a definite seal, equivalent to a nonsurgical
Table 2. Canal configuration incidences in the mesiobuccal roots of maxillary first permanent molars Canal configuration One canal Two separated canals Two separated canals and one or more accessory canals in between Two canals with one showing partial isthmus formation Two canals joined by an isthmus Two canals joined by an isthmus with accessory canals within the isthmus Total
Number of cases
%
18 12 4 10 4 2 50
36 24 8 20 8 4 100
Canal Isthmus Incidences and Configurations
263
Table 3. Incidence of an isthmus or accessory canals in sections with two canals Canal configuration Two separated canals Two separated canals and one or more accessory canals in between Two canals with one showing partial isthmus formation Two canals joined by an isthmus Two canals joined by an isthmus and or more accessory canals within the isthmus Total
0
Fig. 1. One canal.
Fig. 2. Two separated canals.
Fig. 3. Two separated canals and one or more accessory canals inbetween.
Fig. 4. Two canals with one showing partial isthmus formation.
Iil
Fig. 5. Two canals joined by and isthmus in mesiobuccal root.
Number of cases
%
12 4 10 4 2 32
37.5 12.5 31.25 12.5 6.25 100
endodontic procedure, is desirable. An omission of this accessory canal opening will lead to eventual failure of endodontic surgery. The preparation o f the resected root surface to receive a reverse filling must incorporate the isthmus and any accessory canal opening between the MB~ and MB2 canals. In this study, we found the incidence amounted to 31.25% (categories 2, 4 and 5). This is similar to the 30.1% previously reported (Cambruzzi and Marshall, 1983), but much lower than the 100% incidence of a complete of partial canal isthmus as reported recently (Weller et al., 1995). The operating microscope of high light intensity may give illusion of more root canal aberrations. The concept o f partial isthmus formation is difficult to articulate. 31.25% of the MB roots in this study had two canals with one canal showing an extension towards the other canal (Fig. 10). The cross-section of !his canal is similar to a c o m m a shape. This tail extension of the canal may come about in several ways. Firstly, it may be part of the fin or loop of the root canal anatomy. Secondly, it may be that the section is made at the point where one canal starts to twist and turn to merge with a second canal. Thirdly, it may be an 'actual' partial isthmus formationi such that a complete isthmus will be formed elsewhere irl the root. In our examination of these sections at the level 3~5 mm from the root apex, we found that the partial isthmuses remained as partial isthmuses. This leads us to believe that not every partial isthmus formation will become a complete isthmus elsewhere in the MB root. Based on our current findings, we propose the following classification of the MB root of maxillary first permanent molars: T y p e I. One main canal; if an accessory canali is present, a suffix is added to indicate the number, e.g. Type I-A, I-B and I-C signify one main canal plus 1, 2, or 3 accessory canals. T y p e II. Two main canals, i.e. MBI and MB2; if an accessory canal is present, a suffix is added to indicate the number (see above), e.g. Type II-D signifies two canals plus 4 accessory canals.
Fig. 6. Two canals joined by an isthmus and one or more accessory canals within the isthmus.
264
D.C. Yu et al,
Type III. Two main canals plus partial isthmus formation; if an accessory canals is present, a suffix is added to indicate the number (see above). Type IV. Two main canals joined by a complete isthmus; if an accessory canal is present, a suffix is added to indicate the number (see above). This classification is universal and specifies both the configuration of the mesiobuccal canal and number of accessory canals present. The variation of success rate may be due to the factors such as radiographic interpretation, untreated root canal systems, operator skill, the complexity of the surgical procedure and the use of high power illumination and magnification. One of the keys to success is to know the details of the apical root canal anatomy. The isthmus must be obturated by reverse filling to ensure periapical healing. Our present findings using scanning electron microscopy indicates that the MB roots of the maxillary first permanent molars exhibit complex anatomy, and that no two root canal systems are exactly alike. We believe this study using the
scanning electron microscope is important because it allows us to examine the root sections of common surgical sites in fine detail. At the present time surgical operating microscopes cannot study the root sections at such high magnification. It is common knowledge that scanning electron microscopy is best used to study the surface topography and its use allows us to reveal the intricate cross-sectional anatomy of the mesiobuccal root of the maxillary first permanent molar. To prevent vexing complications for both the clinician and patient, it behoves the clinician to be completely familiar with the possible variety of root canal anatomy of a planned surgical site. Prudent judgement is essential before attempting a new procedure, including the incorporation of the area between the MB1 and MB2 canals during reverse filling cavity preparation. The most predictable treatment outcomes will occur when the experienced clinician has accurate knowledge of the root canal anatomy to guide both nonsurgical and surgical endodontic therapy, impeccable patient care.
Fig. 7. Representative sample of a section with two main canals joined by an isthmus and a accessory canal (arrow) within the isthmus.
Fig. 9. Representative sample of a section with two main canals and one accessory canal (arrow) in between.
Fig. 8. Higher magnification of the accessory canal from Fig. 7.
Fig. 10. Representative sample of a section with partial isthmus formation (arrow).
Canal Isthmus Incidences and Configurations
REFERENCES Altonen M., Mattila K., 1976. Follow up study of apicoectomised molars. Int. J. Oral Surg., $, 33-40. Cambruzzi T. V., Marshall F. J., 1983. Molar endodontics surgery. J. Canada Dent Assn., 1, 61-66. Carr G., 1992. Advanced techniques and visual enhancement for endodontic surgery. Endodon. Rep., 7 (1), 6-9. Frank A., Click D., Paterson S., Wiene F., 1992. Long term evaluation of surgically placed amalgam fillings. J. Endodon., 18, 391-398. Friedmann S., Lustmann T., Shaharabany V., 1991. Treatment results of apical surgery in premolar and molar teeth. J. Endodon., 17, 30-33. Gutmann, J. and Harrison, J. (1991) Surgical Endodontics. Blackwell Scientific Publications, Boston.
265
Ioannides C., Borstlap W., 1983. A Apicoectomy of molars: a clinical and radiographic study. Int. J. Oral Surg., 12, 73-79. Kraus, B. S., Jordan, R. E. and Abrams, L. (1969) Dental Anatomy and Occlusion. The Williams and Wilkins Company, Baltimore, pp. 74115. Persson G., 1982. Periapical surgery of molars. Int. Z Oral Surg.. 11, 96100. Rapp E., Brown C., Nawton C., 1991. An analysis of success and Iailure of apicoectomies. J. Endodon., 17, 508-512. Sicher, H. and Dubral, E. L. (1975) In OralAnatomy, ed C. V. Mosby, 6th edn. St. Louis. Weller R. N., Niemczyk S. P., Kim S., 1995. Incidence and position of canal isthmus part 1. Mesiobuccat root of the maxillary first molar. J. Endodon., 7, 380-383