0099-2399/91/1708-0384/$03.00/0 JOURNAL OF ENDODONTICS Copyright 9 1991 by The American Association of Endodontists
Printed in U.S.A. VOL. 17, NO. 8, AUGUST1991
Anatomical and Histological Features of C-Shaped Canals in Mandibular Second Molars Darlene C. Melton, DDS, Keith V. Krell, DDS, MS, MA, and Michel W. Fuller, DDS, MS
The mandibular second molar has many root canal variations. This investigation used two evaluation methods to examine the canal morphology of mandibular second molars having C-shaped canals. Fifteen extracted mandibular second molars with a conical root and C-shaped canal orifice were separated into two groups. A polyester cast resin technique allowed three-dimensional visualization of the root canal system in eight teeth; the remaining seven molars were prepared for histological examination in cross-section in the coronal, middle, and apical thirds for study under the light microscope. The results illustrated that C-shaped canals in mandibular second molars can vary in number and shape along the length of the root with the result that debridement, obturation, and restoration in this group may be unusually difficult.
and distal roots. Radiographic detection of root fusion is difficult, making clinical recognition of the C-shaped canal unlikely until access to the chamber. When negotiating the C-shaped canal, instruments may both clinically and radiographically be centered and therefore appear to be exiting the furcation, thus adding to the confusion and troublesome task of determining whether a perforation has occurred. Although the reported incidence of the C-shaped canal in the mandibular second molar is 2.7 to 8% (7, 9), the criteria for its recognition, particularly clinically, are ambiguous. Once recognized, the C-shaped canal is a challenge with respect to debridement and obturation, especially since it is unclear whether the C-shaped orifice found on the floor of the pulp chamber (Fig. 1) actually continues to the apical third of the root. To data, there has been no morphological or histological examinations of the C-shaped canal in the mandibular second molar. The purpose of this study was to use two different methods of evaluation to study this specific canal variation as to (a) the number of canal(s) along the length of the root and (b) the overall canal morphology, especially in the apical third of the root canal system.
Inherent to cleaning, shaping, and obturation of the root canal system is a thorough knowledge of canal morphology. Recognition of unusual canal configurations and variations are paramount, since it has been established that the root with a single tapering canal and apical foramen is the exception rather than the rule (1). Of particular interest is the canal configuration of the mandibular second molar. Although this tooth has a great deal of variation in canal morphology, some authors speak in general rather than in specific terms concerning its internal anatomy. Some studies oversimplified their findings by suggesting that the root canal system of the mandibular second molar is merely a reflection of the canal morphology of the mandibular first molar (2-4). Conversely, more recent studies reported more variation in canal configuration than that found in the mandibular first molar (5-7). These discrepancies are most likely attributable to the differing techniques used to determine root canal anatomy and to the combined sampiing of mandibular first and second molars in early studies. Anecdotal descriptions and case reports of one type of canal variant, the C-shaped canal of the mandibular second molar, can be found in the literature (7-9). The root configuration of molars having this canal shape may be represented by fusion of either the facial or lingual aspect of the mesial
MATERIALS AND METHODS Fifteen extracted mandibular second molars with conical roots and a C-shaped canal orifice were obtained from patients 18 to 40 yr old. Reasons for extraction included one or more of the following: caries, "cracked tooth," or perforation during endodontic access opening. These 15 teeth were randomly placed into one of two groups for evaluation.
Group 1 Eight teeth were stored in a solution of thymol and distilled water until time of manipulation. The pulps were extirpated with fine broaches and the teeth were placed into a fresh solution of 3% hydrogen peroxide daily for a period of 24 days to dissolve out remaining pulp remnants. Polyester resin cast replicas of the pulp space were then formed according to the technique developed by Skidmore and Bjorndal (10). After 24 h, the tooth structure was dissolved in 35% nitric acid for 10 days, leaving only the resin casts of the pulp space. These casts were washed in water and allowed to bench dry for 10 days.
384
Vol. 17, No. 8, August 1991
C-Shaped Canal Mandibular Molar
385
The casts were examined under the stereomicroscope with special attention paid to canal numbers and relationships, and areas of possible anastomoses within the confines of the root.
of the roots studied were fused with a convex surface opposite this radicular groove.
Group 2
The majority of the eight resin case replicas of the root canal system showed broad, fan-shaped communications from the coronal to the apical third of the canal (Fig. 4). Seven casts demonstrated narrow, transverse anastomoses communicating along the length of the root. Only one cast was C shaped in the coronal third which divided into two distinct, separate canals in the middle and apical thirds.
Seven mandibular second molars (five of which were accessed and instrumented) were demineralized in 10% formic acid-formic citrate, washed in tap water, and cross-sectioned into equal lengths at the coronal (below the cementoenamel junction), middle, and apical levels of the root. The specimens were dehydrated, cleared, and mounted in paraffin. A 4-~m section was taken from each level and stained with hematoxylin and eosin. Each section contained a complete crosssection of the pulp. The sections were examined using light microscopy.
Evaluation Criteria for Cross-Sections The canal configurations were assessed and assigned to one of three categories (Fig. 2): 1. Category I (the continuous C-shaped canal) was any C canal outline without any separation. 2. Category II the ("semicolon" (;) shaped canal) referred to those canal configurations in which dentin separated one distinct canal from a buccal or lingual C-shaped canal in the same section. 3. Category III simply had two or more discrete and separate canals. RESULTS Utilizing the two evaluation techniques from both groups, the internal pulp canal morphology was seen to reflect the external root surface configuration. All of the roots of these mandibular second molars displayed an occluso-apical groove which represented the line of fusion between mesial and distal roots (Fig. 3). Eight of the teeth had this groove present on the buccal surface and seven had it on the lingual surface. All
FIG 1. C-shaped canal orifice on the chamber floor of a mandibular second molar.
Group I
Group 2 The canal morphology of the teeth examined histologically resembled the gross findings of the resin casts. Table 1 groups the number of sections found in each of the three categories of canal configurations. It is evident that the mandibular second molar with a C-shaped canal orifice has many variations in pulp canal morphology. In four teeth, the canal(s) changed shape from the coronal aspect of the roots as compared with the apical aspect of the root. For example, a continuous C-shaped canal (Category I) would change to a semicolon (;) configuration (Category 1I) in the midroot and then become a continuous C shape in the apical third of the root or vice versa. Only two of seven teeth demonstrated a continuous C-shaped canal in the coronal, middle, and apical sections of the root. One of seven teeth exhibited separate canals in the middle and apical thirds of the root. Those five teeth with some canal preparation showed large areas ofpulpal remnants and debris remaining within the middle and apical thirds of the root canal system. DISCUSSION Morphological descriptions and histological assessment of the C-shaped canal configuration in the mandibular second molar are lacking. This study used two techniques, each with advantages and disadvantages, to qualitatively evaluate this type of canal configuration. Byusing the resin casts, the threedimensional, complete complexity of the root canal morphology was readily apparent. Examining the histological sections, it was apparent that variations both in the number and location of the canal(s) occur as the canal(s) courses from the coronal to the apical third. Obviously, there are limitations to both techniques used. There is a possibility of the resin not flowing into all canal ramifications or the resin might tear in thin areas. However, such occurrences would tend to make the incidence of reproducing continuous C-shaped canals or isthmuses in resin even lower. It could 'be argued that more histological sections at different levels would give additional details as to morphology. However, for this study, serial sections were not deemed essential, since the sections were intended to be only representative of the three different levels and used in conjunction with the resin casts to develop a further understanding of the canal morphology. Additionally, the sections did demonstrate that the canal morphology changed along the length of the root and that a C-shaped canal configuration did occur even
386
Melton et al.
Journal of Endodontics
FIG 2. Photomicrographs of cross-sections at the mid or apical root level illustrating examples of categories used to classify canal type when viewing histological specimens. A, Category 1: continuous C-shaped canal. B, Category It: "semicolon"-shaped canal. C, Category 111:discrete, separate canals (hematoxylin and eosin; original magnification •
9
,
=
'
=
:::::)
o: 9
'
.
,
....
~ ~
, ,
~
i . . . . 9. ". . . .
i
ii.
.. ?
F
,,,
=,
..... .....
: .....
: ....... : .............
"
, . . . . . .
= '
~
FIG 4. Broad, fan-shaped communication representative of those seen in seven of eight cast models of the mandibular second molars. All canals had continuous C-shaped configuration at least at the floor of the chamber.
TABLE 1, Classification of canal type
Category 1 : continuous C shaped Category 2: semicolonshaped canal Category 3: separate, discrete canals
o
FLG 3. Mandibular molar having a fused, conically shaped root with a buccal groove oriented occluso-apically.
Coronal Section
Middle Section
Apical Section
n = 4
n= 2
n = 4
n= 2
n = 4
n = 2
n= 1
n= 1
n = 1
in the apical third of the root similar to the resin casts, At any rate, it is unclear as to the clinical implications of changing from a C-shaped canal to that of a semicolon C) or vice versa.
Vol. 17, No. 8, August 1991
FIG 5. Symmetrical, circular areas on photomicrograph indicate areas of instrumentation at the midroot level. Clearly, debris and pulp tissue remain in the continuous C-shaped canal (hematoxylin and eosin; original magnification x25).
The most striking features of the teeth examined histologically was the amount of debris and uninstrumented canal space in accessed and instrumented teeth, particularly in the middle and apical thirds of the root length (Fig. 5). The wide fins and small surface area of these canals preclude complete debridement using traditional hand instrumentation techniques. In addition, most teeth examined changed canal configuration along the length of the root making full debridement and preparation even more difficult. Perhaps alternative canal cleaning techniques, such as those which use ultrasonics, would be more effective. Martin et al. (11) and others (12, 13) have advocated ultrasonics to increase the removal of debris in inaccessible areas of the root canal system. However, Langeland et al. (14) reported that ultrasonic instrumentation failed to show the same degree of cleanliness as hand instrumentation in small, curved root canals. Furthermore, Reynolds et al. (15) compare ultrasonic devices to a step-back hand instrumentation technique in moderately curved canals. The step-back technique planed a greater percentage of canal walls than did any of the ultrasonic devices. On the other hand, an increased volume of irrigant and deeper penetration with small instruments using sonics or ultrasonics may allow for more cleansibility in broad or narrow fan-shaped areas of the C-shaped canal (16, 17).
C-Shaped Canal Mandibular Molar
387
FIG 6. Photomicrograph of the midroot showing that very little dentin separates the external surface from the root canal system, thereby increasing the possibility of a stripping perforation during endodontic or restorative treatment. A, canal wall; B, external root surface (hematoxylin and eosin; original magnification x30).
Restoration of these mandibular second molars may also be compromised due to the relatively small amount of dentin between the external surface of the root and the internal canal system. Interestingly, in some histological sections, less than 1 mm of dentin separated the canal(s) from the outside surface of the tooth (Fig. 6). Should prefabricated posts or cast posts be used, the risk of creating a stripping perforation increases. From the results of this study, it appears that possible perforation coupled with the high incidence of undebrided and unobturated canal space may explain some of the clinical failures associated with these teeth. Cautious optimism would seem most appropriate when prognosticating the success of root canal treatment of a mandibular second molar with a Cshaped orifice. CONCLUSIONS Combining the observations from the resin casts and the histology, the following conclusions were drawn: 1. There were variations in canal morphology between different teeth. 2. Variations were seen within an individual root; canal shapes frequently changed at different levels.
388
Melton et al.
Journal of Endodontics
3. The continuous C-shaped canal morphology could be demonstrated even in the apical third of the root. 4. These canal variations are clinically important when considering debfidement, obturation, restoration, and possibly prognosis of mandibular second molars having a C-shaped canal configuration. Dr. Melton is a former graduate student, Department of Endodontics, University of Iowa College of Dentistry and is presently in private practice limited to endodontics in Ann Arbor, MI. Dr. Krell is a clinical associate professor and former graduate director, Department of Endodontics, University of Iowa College of Dentistry, Iowa City. IA and is in private practice limited to endodontics in Des Moines, IA. Dr. Fuller is also a former graduate student, Department of Endodontics, University of Iowa College of Dentistry and is now in private practice limited to endodontics in Cedar Rapids, IA. Address requests for reprints to Dr. Keith V. Krell, 534 42nd Street, Des Moines, Iowa 50312.
References 1. Abou-Rass M, Frank L, Glick DH. The anticurvature method to prepare the curved root canal. J Am Dent Assoc 1980;101:792. 2. Hess W. The anatomy of the root canals of the teeth of the permanent dentition, Part I. New York: William Wood & Co., 1925:35-44. 3. Barrett MT. The internal anatomy of the teeth with special reference to the pulp with its branches. Dent Cosmos 1925;67:581-92. 4. Green D. Morphology of the pulp cavity of the permanent teeth. Oral Surg 1955;8:743-59.
5. Barker BC, Parsons KC, Mills PR, Williams GL. Anatomy of root canals. III. permanent mandibular molars. Aust Dent J 1974;19:408-13. 6. Vertucci FJ. Root canal anatomy of the human permanent teeth. Oral Surg 1984;58:589-99. 7. Weine FS, Pasiewicz RA, Rice RT. Canal configuration of the mandibular second molar using a clinically oriented in vitro method. J Endodon 1988;14:207-13. 8. Weine FS. Endodontic therapy. 3rd ed., St. Louis: CV Mosby, 1982; 245-9. 9. Cooke HG, Cox FL. C-shaped canal configurations in mandibular molars. J Am Dent Assoc 1979;99:836-9. 10. Skidmore AE, Bjorndal AM. Root canal morphology of the human mandibular first molar. Oral Surg 1971 ;32:119-241. 11. Martin H, Cunningham WT, Norris JP, Cotton WR. Ultrasonic vs. hand filing of dentin: a quantitative study. Oral Surg 1980;49:79-84. 12. Cunningham W, Martin H, Forest WR. Evaluation of root canal debridement by the endosonic ultrasonic synergistic system. Oral Surg 1982;53: 401-4. 13. Miserendino LJ, Miserendino CA, Moser JB, Heuer MA, Osetek EM. Cutting efficiency of endodontic instruments. Part II1. Comparison of sonic and ultrasonic instrument systems. J Endodon 1988;14:24-30. 14. Langeland K, Liao K, Pascon EA. Work-saving devices in endodontics: efficacy of sonic and ultrasonic techniques. J Endodon 1985;11:499-510. 15. Reynolds MA, Madison S, Walton RE, Krell KV, Rittman BR. An in vitro histological comparison of the step-back, sonic and ultrasonic instrumentation techniques in small, curved root canals. J Endodon 1987;13:307-14. 16. Teplitsky PE, Chanail BL, Mack G, Machnee CH. Endodontic irrigation-a comparison of endosonic and syringe delivery systems. Int Endod J 1987;20:233-41. 17. Krell KV, Johnson RJ, Madison S. Irrigation patterns during ultrasonic canal instrumentation. Part I. K-type files. J Endodon 1988;14:65-8.
Printed in U.S.A. VOL. 17, NO. 8, AUGUST1991
Anatomical and Histological Features of C-Shaped Canals in Mandibular Second Molars Darlene C. Melton, DDS, Keith V. Krell, DDS, MS, MA, and Michel W. Fuller, DDS, MS
The mandibular second molar has many root canal variations. This investigation used two evaluation methods to examine the canal morphology of mandibular second molars having C-shaped canals. Fifteen extracted mandibular second molars with a conical root and C-shaped canal orifice were separated into two groups. A polyester cast resin technique allowed three-dimensional visualization of the root canal system in eight teeth; the remaining seven molars were prepared for histological examination in cross-section in the coronal, middle, and apical thirds for study under the light microscope. The results illustrated that C-shaped canals in mandibular second molars can vary in number and shape along the length of the root with the result that debridement, obturation, and restoration in this group may be unusually difficult.
and distal roots. Radiographic detection of root fusion is difficult, making clinical recognition of the C-shaped canal unlikely until access to the chamber. When negotiating the C-shaped canal, instruments may both clinically and radiographically be centered and therefore appear to be exiting the furcation, thus adding to the confusion and troublesome task of determining whether a perforation has occurred. Although the reported incidence of the C-shaped canal in the mandibular second molar is 2.7 to 8% (7, 9), the criteria for its recognition, particularly clinically, are ambiguous. Once recognized, the C-shaped canal is a challenge with respect to debridement and obturation, especially since it is unclear whether the C-shaped orifice found on the floor of the pulp chamber (Fig. 1) actually continues to the apical third of the root. To data, there has been no morphological or histological examinations of the C-shaped canal in the mandibular second molar. The purpose of this study was to use two different methods of evaluation to study this specific canal variation as to (a) the number of canal(s) along the length of the root and (b) the overall canal morphology, especially in the apical third of the root canal system.
Inherent to cleaning, shaping, and obturation of the root canal system is a thorough knowledge of canal morphology. Recognition of unusual canal configurations and variations are paramount, since it has been established that the root with a single tapering canal and apical foramen is the exception rather than the rule (1). Of particular interest is the canal configuration of the mandibular second molar. Although this tooth has a great deal of variation in canal morphology, some authors speak in general rather than in specific terms concerning its internal anatomy. Some studies oversimplified their findings by suggesting that the root canal system of the mandibular second molar is merely a reflection of the canal morphology of the mandibular first molar (2-4). Conversely, more recent studies reported more variation in canal configuration than that found in the mandibular first molar (5-7). These discrepancies are most likely attributable to the differing techniques used to determine root canal anatomy and to the combined sampiing of mandibular first and second molars in early studies. Anecdotal descriptions and case reports of one type of canal variant, the C-shaped canal of the mandibular second molar, can be found in the literature (7-9). The root configuration of molars having this canal shape may be represented by fusion of either the facial or lingual aspect of the mesial
MATERIALS AND METHODS Fifteen extracted mandibular second molars with conical roots and a C-shaped canal orifice were obtained from patients 18 to 40 yr old. Reasons for extraction included one or more of the following: caries, "cracked tooth," or perforation during endodontic access opening. These 15 teeth were randomly placed into one of two groups for evaluation.
Group 1 Eight teeth were stored in a solution of thymol and distilled water until time of manipulation. The pulps were extirpated with fine broaches and the teeth were placed into a fresh solution of 3% hydrogen peroxide daily for a period of 24 days to dissolve out remaining pulp remnants. Polyester resin cast replicas of the pulp space were then formed according to the technique developed by Skidmore and Bjorndal (10). After 24 h, the tooth structure was dissolved in 35% nitric acid for 10 days, leaving only the resin casts of the pulp space. These casts were washed in water and allowed to bench dry for 10 days.
384
Vol. 17, No. 8, August 1991
C-Shaped Canal Mandibular Molar
385
The casts were examined under the stereomicroscope with special attention paid to canal numbers and relationships, and areas of possible anastomoses within the confines of the root.
of the roots studied were fused with a convex surface opposite this radicular groove.
Group 2
The majority of the eight resin case replicas of the root canal system showed broad, fan-shaped communications from the coronal to the apical third of the canal (Fig. 4). Seven casts demonstrated narrow, transverse anastomoses communicating along the length of the root. Only one cast was C shaped in the coronal third which divided into two distinct, separate canals in the middle and apical thirds.
Seven mandibular second molars (five of which were accessed and instrumented) were demineralized in 10% formic acid-formic citrate, washed in tap water, and cross-sectioned into equal lengths at the coronal (below the cementoenamel junction), middle, and apical levels of the root. The specimens were dehydrated, cleared, and mounted in paraffin. A 4-~m section was taken from each level and stained with hematoxylin and eosin. Each section contained a complete crosssection of the pulp. The sections were examined using light microscopy.
Evaluation Criteria for Cross-Sections The canal configurations were assessed and assigned to one of three categories (Fig. 2): 1. Category I (the continuous C-shaped canal) was any C canal outline without any separation. 2. Category II the ("semicolon" (;) shaped canal) referred to those canal configurations in which dentin separated one distinct canal from a buccal or lingual C-shaped canal in the same section. 3. Category III simply had two or more discrete and separate canals. RESULTS Utilizing the two evaluation techniques from both groups, the internal pulp canal morphology was seen to reflect the external root surface configuration. All of the roots of these mandibular second molars displayed an occluso-apical groove which represented the line of fusion between mesial and distal roots (Fig. 3). Eight of the teeth had this groove present on the buccal surface and seven had it on the lingual surface. All
FIG 1. C-shaped canal orifice on the chamber floor of a mandibular second molar.
Group I
Group 2 The canal morphology of the teeth examined histologically resembled the gross findings of the resin casts. Table 1 groups the number of sections found in each of the three categories of canal configurations. It is evident that the mandibular second molar with a C-shaped canal orifice has many variations in pulp canal morphology. In four teeth, the canal(s) changed shape from the coronal aspect of the roots as compared with the apical aspect of the root. For example, a continuous C-shaped canal (Category I) would change to a semicolon (;) configuration (Category 1I) in the midroot and then become a continuous C shape in the apical third of the root or vice versa. Only two of seven teeth demonstrated a continuous C-shaped canal in the coronal, middle, and apical sections of the root. One of seven teeth exhibited separate canals in the middle and apical thirds of the root. Those five teeth with some canal preparation showed large areas ofpulpal remnants and debris remaining within the middle and apical thirds of the root canal system. DISCUSSION Morphological descriptions and histological assessment of the C-shaped canal configuration in the mandibular second molar are lacking. This study used two techniques, each with advantages and disadvantages, to qualitatively evaluate this type of canal configuration. Byusing the resin casts, the threedimensional, complete complexity of the root canal morphology was readily apparent. Examining the histological sections, it was apparent that variations both in the number and location of the canal(s) occur as the canal(s) courses from the coronal to the apical third. Obviously, there are limitations to both techniques used. There is a possibility of the resin not flowing into all canal ramifications or the resin might tear in thin areas. However, such occurrences would tend to make the incidence of reproducing continuous C-shaped canals or isthmuses in resin even lower. It could 'be argued that more histological sections at different levels would give additional details as to morphology. However, for this study, serial sections were not deemed essential, since the sections were intended to be only representative of the three different levels and used in conjunction with the resin casts to develop a further understanding of the canal morphology. Additionally, the sections did demonstrate that the canal morphology changed along the length of the root and that a C-shaped canal configuration did occur even
386
Melton et al.
Journal of Endodontics
FIG 2. Photomicrographs of cross-sections at the mid or apical root level illustrating examples of categories used to classify canal type when viewing histological specimens. A, Category 1: continuous C-shaped canal. B, Category It: "semicolon"-shaped canal. C, Category 111:discrete, separate canals (hematoxylin and eosin; original magnification •
9
,
=
'
=
:::::)
o: 9
'
.
,
....
~ ~
, ,
~
i . . . . 9. ". . . .
i
ii.
.. ?
F
,,,
=,
..... .....
: .....
: ....... : .............
"
, . . . . . .
= '
~
FIG 4. Broad, fan-shaped communication representative of those seen in seven of eight cast models of the mandibular second molars. All canals had continuous C-shaped configuration at least at the floor of the chamber.
TABLE 1, Classification of canal type
Category 1 : continuous C shaped Category 2: semicolonshaped canal Category 3: separate, discrete canals
o
FLG 3. Mandibular molar having a fused, conically shaped root with a buccal groove oriented occluso-apically.
Coronal Section
Middle Section
Apical Section
n = 4
n= 2
n = 4
n= 2
n = 4
n = 2
n= 1
n= 1
n = 1
in the apical third of the root similar to the resin casts, At any rate, it is unclear as to the clinical implications of changing from a C-shaped canal to that of a semicolon C) or vice versa.
Vol. 17, No. 8, August 1991
FIG 5. Symmetrical, circular areas on photomicrograph indicate areas of instrumentation at the midroot level. Clearly, debris and pulp tissue remain in the continuous C-shaped canal (hematoxylin and eosin; original magnification x25).
The most striking features of the teeth examined histologically was the amount of debris and uninstrumented canal space in accessed and instrumented teeth, particularly in the middle and apical thirds of the root length (Fig. 5). The wide fins and small surface area of these canals preclude complete debridement using traditional hand instrumentation techniques. In addition, most teeth examined changed canal configuration along the length of the root making full debridement and preparation even more difficult. Perhaps alternative canal cleaning techniques, such as those which use ultrasonics, would be more effective. Martin et al. (11) and others (12, 13) have advocated ultrasonics to increase the removal of debris in inaccessible areas of the root canal system. However, Langeland et al. (14) reported that ultrasonic instrumentation failed to show the same degree of cleanliness as hand instrumentation in small, curved root canals. Furthermore, Reynolds et al. (15) compare ultrasonic devices to a step-back hand instrumentation technique in moderately curved canals. The step-back technique planed a greater percentage of canal walls than did any of the ultrasonic devices. On the other hand, an increased volume of irrigant and deeper penetration with small instruments using sonics or ultrasonics may allow for more cleansibility in broad or narrow fan-shaped areas of the C-shaped canal (16, 17).
C-Shaped Canal Mandibular Molar
387
FIG 6. Photomicrograph of the midroot showing that very little dentin separates the external surface from the root canal system, thereby increasing the possibility of a stripping perforation during endodontic or restorative treatment. A, canal wall; B, external root surface (hematoxylin and eosin; original magnification x30).
Restoration of these mandibular second molars may also be compromised due to the relatively small amount of dentin between the external surface of the root and the internal canal system. Interestingly, in some histological sections, less than 1 mm of dentin separated the canal(s) from the outside surface of the tooth (Fig. 6). Should prefabricated posts or cast posts be used, the risk of creating a stripping perforation increases. From the results of this study, it appears that possible perforation coupled with the high incidence of undebrided and unobturated canal space may explain some of the clinical failures associated with these teeth. Cautious optimism would seem most appropriate when prognosticating the success of root canal treatment of a mandibular second molar with a Cshaped orifice. CONCLUSIONS Combining the observations from the resin casts and the histology, the following conclusions were drawn: 1. There were variations in canal morphology between different teeth. 2. Variations were seen within an individual root; canal shapes frequently changed at different levels.
388
Melton et al.
Journal of Endodontics
3. The continuous C-shaped canal morphology could be demonstrated even in the apical third of the root. 4. These canal variations are clinically important when considering debfidement, obturation, restoration, and possibly prognosis of mandibular second molars having a C-shaped canal configuration. Dr. Melton is a former graduate student, Department of Endodontics, University of Iowa College of Dentistry and is presently in private practice limited to endodontics in Ann Arbor, MI. Dr. Krell is a clinical associate professor and former graduate director, Department of Endodontics, University of Iowa College of Dentistry, Iowa City. IA and is in private practice limited to endodontics in Des Moines, IA. Dr. Fuller is also a former graduate student, Department of Endodontics, University of Iowa College of Dentistry and is now in private practice limited to endodontics in Cedar Rapids, IA. Address requests for reprints to Dr. Keith V. Krell, 534 42nd Street, Des Moines, Iowa 50312.
References 1. Abou-Rass M, Frank L, Glick DH. The anticurvature method to prepare the curved root canal. J Am Dent Assoc 1980;101:792. 2. Hess W. The anatomy of the root canals of the teeth of the permanent dentition, Part I. New York: William Wood & Co., 1925:35-44. 3. Barrett MT. The internal anatomy of the teeth with special reference to the pulp with its branches. Dent Cosmos 1925;67:581-92. 4. Green D. Morphology of the pulp cavity of the permanent teeth. Oral Surg 1955;8:743-59.
5. Barker BC, Parsons KC, Mills PR, Williams GL. Anatomy of root canals. III. permanent mandibular molars. Aust Dent J 1974;19:408-13. 6. Vertucci FJ. Root canal anatomy of the human permanent teeth. Oral Surg 1984;58:589-99. 7. Weine FS, Pasiewicz RA, Rice RT. Canal configuration of the mandibular second molar using a clinically oriented in vitro method. J Endodon 1988;14:207-13. 8. Weine FS. Endodontic therapy. 3rd ed., St. Louis: CV Mosby, 1982; 245-9. 9. Cooke HG, Cox FL. C-shaped canal configurations in mandibular molars. J Am Dent Assoc 1979;99:836-9. 10. Skidmore AE, Bjorndal AM. Root canal morphology of the human mandibular first molar. Oral Surg 1971 ;32:119-241. 11. Martin H, Cunningham WT, Norris JP, Cotton WR. Ultrasonic vs. hand filing of dentin: a quantitative study. Oral Surg 1980;49:79-84. 12. Cunningham W, Martin H, Forest WR. Evaluation of root canal debridement by the endosonic ultrasonic synergistic system. Oral Surg 1982;53: 401-4. 13. Miserendino LJ, Miserendino CA, Moser JB, Heuer MA, Osetek EM. Cutting efficiency of endodontic instruments. Part II1. Comparison of sonic and ultrasonic instrument systems. J Endodon 1988;14:24-30. 14. Langeland K, Liao K, Pascon EA. Work-saving devices in endodontics: efficacy of sonic and ultrasonic techniques. J Endodon 1985;11:499-510. 15. Reynolds MA, Madison S, Walton RE, Krell KV, Rittman BR. An in vitro histological comparison of the step-back, sonic and ultrasonic instrumentation techniques in small, curved root canals. J Endodon 1987;13:307-14. 16. Teplitsky PE, Chanail BL, Mack G, Machnee CH. Endodontic irrigation-a comparison of endosonic and syringe delivery systems. Int Endod J 1987;20:233-41. 17. Krell KV, Johnson RJ, Madison S. Irrigation patterns during ultrasonic canal instrumentation. Part I. K-type files. J Endodon 1988;14:65-8.
