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Effect of masticatory cycles on apical leakage of obturated teeth
0099-2399/98/2405-0322503.00/0 Printed in U.S.A.
JOURNALOF ENDODONTICS
MOL.24, NO. 5, MAY 1998
Copyright © 1998 by The American Association of Endodontists
SCIENTIFIC ARTICLES Effect of Masticatory Cycles on Apical Leakage of Obturated Teeth Samir Esber, DDS, Jean-Yves Blum, DDS, Jean-Christophe Chazel, DDS, and Eric Parahy, PhD
ment or years later. Early failures may be attributed to procedural errors or to chemical and physical properties of the filling materials. Failure after an extended period of function is more common and is the result of many environmental factors. One of these is the cyclic mechanical loading to which restorations are subjected during chewing movements. Huysmans et al. (11) studied the failure behavior of post and core restored teeth when subjected to cyclic mechanical loading. They concluded that, for increased clinical relevance of in vitro tests, fatigue tests are to be preferred, comprising > 105 cycles. A positive correlation was found between traumatic occlusion and periodontal disease. The occlusal forces producing tooth mobility may accelerate attachment loss in progressive periodontitis (12). Qvist (13) demonstrated the effect of mastication on marginal adaptation of composite restorations in the oral environment. The aim of this study was to determine in vitro the effect of masticatory cycles on the quality of apical sealing.
This study investigated the effect of apical leakage due to masticatory cycles on root canal treatment. Twenty upper maxillary molars were first obturated using the warm vertical compaction technique. Four maxillary casts were then built, with each holding four of the sample molars. The molars were embedded in resin with the roots separated from the resin by means of a light silicon. The four remaining teeth served as controls and were not submitted to occlusal forces. A mechanical device to simulate masticatory cycles subjected the teeth to 0.5 • 106 cycles (group A), 106 cycles (group B), 2.106 cycles (group C), and 3.106 cycles (group D); the control was group E. The roots were placed in 2% methylene blue dye solution for 72 h and then sectioned longitudinally so that dye penetration could be measured. The mean values of dye penetration were: 3.70 --- 0.69 mm, group A; 5.00 +__1.14 mm, group B; 6.00 -+ 1.01 mm, group C; 7.23 _+ 0.66 mm, group D; and 2.74 __. 0.75 mm, group E. The value of dye penetration increased in correlation with the number of masticatory cycles. This in vitro study suggests the significant effect of masticatory loads on apical leakage.
M A T E R I A L S AND M E T H O D S A device was adapted to simulate masticatory cycles (14). The basic apparatus was a Quick Perfect simulator (Fig. 1). The frame supported an electrical engine moving an eccentric camshaft on its upper posterior part. This acted on a lever arm that rotated around the upper middle axis of the frame, moving in turn the upper arm
The goals for consistently successful endodontic treatment are (i) total obliteration of the canal space and (ii) perfect sealing of the apical foramen at the dentin-cementum junction, and of the accessory canals at locations other than the root apex with an inert, dimensionally stable, and biologically compatible material (1). Numerous methods have been used to investigate the sealing ability of various endodontic clinical techniques and materials. These include the radionuclide detection technique (2), bacterial penetration (3), scanning electron microscopy (4), and electrochemical techniques (5). The most common method to study the quality of apical seal is dye penetration (6-10). Failure of root canal treatment may occur soon after the treat-
FIG 1. Front view of the masticatory device.
322
Vol. 24, No. 5, May 1998
Masticatory Cycles and Apical Leakage
323
TABLE1. Values of mean dye penetration for groups corresponding to the number of cycles Groups E No. of roots No. of cycles Mean dye penetration (rnm) SD
12 0 2, 74 0, 7537
A 12 0.5.108 3, 70 0, 6907
B
C
D
12 108 5, 00 1, 1481
12 2.106 6, 00 1, 0198
12 3.108 7, 23 0, 6624
Note the 0 cycles of control group E.
of the joint through a spring enclosed in a tube. An adjustable pin allowed only openings and closings. A weight positioned on the upper arm of the simulator was able to fix the mastication forces from 10 to 60 kg (14). On its lower part, the semiadjustable joint was secured by screws. Experimental casts were mounted on the simulator, and the entire assembly was set in a container to receive continuous irrigation by means of a pump. A thermobath kept the water at a constant 37°C temperature.
7 6
E
5
==
4 3 2
Protocol Twenty extracted upper maxillary molars were used in this study. Teeth with resorptive defects, caries, or cracks were excluded. Sample teeth were stored in Ringer's solution containing 0.2% sodium azide (pH 7.09) at room temperature before the study. The maxillary molars were prepared by the serial preparation described by Schilder (15). Working lengths were determined to l mm short of the radiographic apex. Canals were enlarged with a #25 file to ensure patency and provide a standardized apical preparation. A solution of 5.25% sodium hypochlorite was used between each instrumental step. After preparation, the canal was dried with sterile paper points. Teeth were obturated by warm vertical compaction (15) using Mynol gutta-percha points (Block Drug Corp., Jersey City, N J) and Sealite regular (Pierre Rolland, Paris, France). The coronal cavity was obturated with Ketac silver (ESPE, Seefeld, Germany). The maxillary molars were randomly assigned to 1 of 5 groups: A.(n = 4 ) , B (n = 4 ) , C ( n = 4 ) , D ( n = 4 ) , o r E ( n = 4). The upper and lower casts were composed of freshly extracted teeth. The teeth were embedded in resin, and all roots were separated from resin by means of a light silicon (Coltex, Pierre Rolland, France). Casts were positioned on the upper and lower arms of the masticatory device by means of Snow White no. 2 stone piaster. An equilibration was performed on each pair of casts. In occlusion, all upper molars had at least four occlusion points with mandibular molars. During experimentation, a 1.6-inch rubber dam was inserted between the upper and lower casts. The occlusion force was fixed at 30 kg by a weight placed on the upper arm of the simulator. The system moved in opening and closing motions at a rate of 77 cycles/rain and was irrigated by 37°C water. By randomization, one pair of casts was stopped at 500,000 cycles (group A), another at 1 million cycles (group B), another at 2 million cycles (group C), and one at 3 million cycles (group D). The teeth of group E were not subjected to masticatory cycles. At the end of each cycle, the four teeth of groups A, B, C, and D were separated from the cast. The external surfaces (except the apical foramen) of the roots were then painted with two coats of nail polish and one layer of sticky wax; each coat was allowed to dry between applications.
1 0
E: 0
A: 0.5 B: I C: 2 Masticatory cyles (million)
D: 3
FIG 2. Mean dye leakage of all groups. All of the roots of the sample teeth were placed in a 2% methylene blue dye solution (0.062 M) prepared by mixing 2 g of methylene blue powder (mol. wt. 319.9, Sigma Chemical Co., St. Louis, MO) with 100 ml of a standardized buffer solution (Labover, Montpellier, France) of pH 7 for 72 h. The roots were grooved longitudinally with a #699 L high-speed bur on the facial and lingual surfaces. Apical leakage was measured from the most apical part of the root to the most coronal penetration of the dye, to the nearest 0.1 mm, using a dissecting microscope at X7. All leakage results are given in millimeters. All measurements were performed blindly by one investigator.
RESULTS Mean leakage values were calculated and are presented in Table 1 and Fig. 2. For each group, the leakage between the different roots of the teeth was not significantly different (p > 0.05). They varied from 2.74 mm _+ 0.75 for the control group E to 7.23 + 0.66 mm for group D. The analysis of variance (Table 2) of all groups subjected to masticatory cycles (groups A - D ) showed that all were significantly different (p < 0.05) from group E. The differences were also significant between groups A and B, groups B and C, and groups C and D.
DISCUSSION A modified device (14) was used to simulate the masticatory loads exerted on canal filling materials (Fig. 1). Analysis of the masticatory cycles showed that apical leakage was correlated with the number of cycles. A significant difference appeared between 500,000, 1 million, 2 million, and 3 million cycles.
324
Journal of Endodontics
Esber et ah TABLE 2. Statistical analysis (general linear models of SAS) between different groups Groups E&A
E&B
E&C
E&D
A&B
B&C
C&D
0.0092
0.0001
0.0001
0.0001
0.0007
0.0071
0.0011
In agreement with the findings of Lundeen and Gibbs (16), the value of the masticatory loads during this experiment was fixed at 30 kg. Due to its design, the device reproduced only the opening and closing movements around the hinge axis. All of the excurcive and protrusive movements were omitted. However, according to Lundeen and Gibbs (16), the greatest masticatory forces occur at the end of closure. In terms of the experimental conditions, this part of the masticatory cycle was thus effectively reproduced by the device. During pre-experiment trials, the occlusion contacts between the teeth embedded in resin induced too many fractures during the masticatory cycles. A periodontal ligament was reproduced and joined to a light silicon, resulting in an elastic component that prevented further fractures and may have more closely reproduced the clinical reality. Spangberg et al. (7) reported that entrapped air can inhibit the penetration of dye between filling materials and dentinal walls when using passive dye penetration. Masters et al. (6), however, compared apical dye leakage with and without vacuum, and reported that the use of vacuum, unnatural forces, may not be necessary for dye leakage studies in filled root canals. Based on these latter results, the present study was conducted without a vacuum condition for the sample teeth. As recommended by Smith and Steiman (9), the leakage was measured using methylene blue dye because (i) it does not stain the dentin and (ii) the most coronal limit of the leakage is easily detected. Ahlberg et al. (10) compared the apical leakage shown by methylene blue and India ink in root-filled teeth and found that methylene blue has a lower molecular weight and penetrates more deeply into root canal fillings than India ink, which has a larger particle size and thus results in very high leakage values. The use of methylene blue in passive dye penetration thus seems to be the most accurate method for leakage investigation. Dalat and Spangberg (8) demonstrated that, with the most respected obturation methods and using a sealer with excellent physical properties, traceable microlumina--representing fluid penetration--will always occur. In agreement with this finding, group E, which was not subjected to masticatory loads, showed evidence of dye penetration. The other groups all presented an increase in the depth of dye penetration as a function of the number of masticatory cycles. As reported by Marciano et al. (3), fluid penetration and bacterial penetration can be associated. This phenomenon, fluid penetration, can explain why the masticatory factor induces an increase in the percentage of endodontic failure at long term. In the study by Blum et al. (14), the mean dye penetration showed an increase with the number of masticatory cycles, with a breakpoint at 2 million cycles. In the present study, only one linear function was observed. It should be noted that their protocol differed from the present protocol on one specific point: the palatal roots of all molars were not directly subjected to occlusal forces, whereas in this study the roots of all molars, although separated from resin by means of a light silicon, were directly subjected to the forces. This may explain why the present results showed greater values than those of Blum et al. Similarly, Qvist (13)
studied the effect of mastication on the marginal adaptation of class V composite restorations. His in vivo study compared two groups of teeth with and without occlusal forces. In the oral environment, after the equivalent of 4 months of masticatory function, results showed that functional mastication has a major influence on the marginal adaptation of composite restorations, even when not directly subjected to masticatory wear. Kawamura (17) reported that the number of daily occlusive mastication cycles varied from 500 to 1,000. According to these mean values, group A represented 1.36 yr; group B, 2.73 yr; group C, 5.47 yr; and group D, 8.21 yr. As previously stated, the leakage phenomena thus increased significantly with the number of masticatory cycles over a period of 8 yr. In a recent study, Smith et al. (18) found a success rate for nonsurgical endodontics of 84% over an observation period of 5 yr. After analyzing several of the factors that influenced this success rate, they concluded that canal debridement and obturation within 2 mm of the apex results in the highest success rate, although endodontically treated teeth will continue to fail at --2% per year. The effect of occlusion forces on the root-filled teeth in this study may indicate the reason for this failure rate. This in vitro study demonstrates the significant effect of occlusal loads on the apical seal. A linear function was observed between the number of masticatory cycles and the leakage measured by passive dye penetration. We thank Catherine Stott Carmeni and Dr. Paul Yramini for technical assistance. Drs. Esber, Blum, Chazel, and Parahy are affiliated with the Dental School of Montpellier, University of Montpellier, Montpellier, France. Address requests for reprints to Dr. Samir Esber, 149, rue Faventines, 26000 Valence, France.
References 1. Nguyen N. Obturation of the root canal system. In: Cohen S, Burns R, eds. Pathways of the pulp. 5th ed. St. Louis: CV Mosby, 1991. 2. Canalda-Sahli C, Brau-Aguade E, Sentis-Vilalta J, Aguade-Bruix S. The apical seal of root canal sealing cements using a radionuclide detection technique. Int Ended J 1992;25:250-6. 3. Marciano J, Michailesco P, Nardoux M. Le scellement apical: realit~ ou fiction. Etude in vitro par colonisation bact~rienne. Rev Franc Ended 1986;5: 33-47. 4. Lugassy AA, Yee F. Root canal obturation with gutta-percha: a scanning electron microscopic comparison of vertical compaction and automated thermatic condensation. J Endodon 1982;8:120-5. 5. Mattison GD, von Fraunhofer JA. Electrochemical microleakage study of endodontic sealer cements. Oral Surg Oral Med Oral Pathol 1983;55:402-7. 6. Masters J, Higa R, Torabinejad M. Effects of vacuuming on dye penetration patterns in root canals and glass tubes. J Endodon 1995;21:332-4. 7. Spangberg LSW, Acierno TG, Cha BY. Influence of entrapped air on the accuracy of leakage studies using dye penetration methods. J Endodon 1989;15:548-51. 8. Dalat DM, Spangberg LSW. Comparison of apical leakage in root canals obturated with various gutta-percha techniques using a dye vacuum tracing method. J Endodon 1994;20:315-9. 9. Smith MA, Steiman HR. An in vitro evaluation of microleakage of two new and two old root canal sealers. J Endodon 1994;20:18-21. 10. Ahlberg KMF, Assavanop P, Tay WM. A comparison of the apical dye penetration patterns shown by methylene blue and India ink in root-filled teeth. Int Ended J 1995;28:30-4. 11. Huysmans M-CDNJM, Peters MCRB, Van der varst PGT, Plasschaert
Vol. 24, No. 5, May 1998 AJM. Failure behaviour of fatigue-tested post and cores. Int Endod J 1993; 26:294-300. 12. Svanberg GK, King GJ, Gibbs CH. Occlusal considerations in periodontology. Periodontology 2000 1995;9:106-17. 13. Qvist V. The effect of mastication on marginal adaptation of composite restorationsin vivo. J Dent Res 1983;62:904-6. 14. Blum J-Y, Esber S, Parahy E, Franquin J-C. Effect of masticatory cycles on tooth structural changes: repercussions on leakage of retrofilled amalgam.J Endod 1997;23:605-9.
Masticatory Cycles and Apical Leakage
325
15. Schilder H. Filling root canals in three dimensions. Dent Clin North Am 1967;11:723-44. 16. Lundeen HC, Gibbs CH. Advances in occlusion: postgraduate dental Handbook. Boston: John Wright, PSG Inc., 1982. 17. Kawamura Y. Physiological concepts of occlusion. Acta Odontol Stomato11973;102:363-411. 18. Smith CS, Setchell DJ, Harty FJ. Factors influencing the success of conventional root canal therapy--a five-year retrospective study. Int Endod J 1993;26:32t -33.
The Way It Was Close observation of television commercials for analgesics might lead a person to conclude two things--the penchant for subtle half-truths, exaggeration, and misdirection did not die with snake-oil salesmen and the stakes, i.e., dollar volume of analgesic sales, must be enormous. Subtlety was not always de rigueur with pain-killer purveyors. A highly successful nostrum in the 1890s was called Cuforhedake Brane Fude. You laugh, but it sold more than 2 million bottles at 25¢ a bottle and made its compounder a millionaire. In fact it was of some value since it contained acetanilide, which though an effective analgesic is little used today because of its potential toxicity. In a way it is hard to understand how it competed with rival concoctions of that time, which were usually primarily laudanum, an alcoholic solution of opium. Must have been the catchy name that did it.
Zachariah Yeomans
JOURNALOF ENDODONTICS
MOL.24, NO. 5, MAY 1998
Copyright © 1998 by The American Association of Endodontists
SCIENTIFIC ARTICLES Effect of Masticatory Cycles on Apical Leakage of Obturated Teeth Samir Esber, DDS, Jean-Yves Blum, DDS, Jean-Christophe Chazel, DDS, and Eric Parahy, PhD
ment or years later. Early failures may be attributed to procedural errors or to chemical and physical properties of the filling materials. Failure after an extended period of function is more common and is the result of many environmental factors. One of these is the cyclic mechanical loading to which restorations are subjected during chewing movements. Huysmans et al. (11) studied the failure behavior of post and core restored teeth when subjected to cyclic mechanical loading. They concluded that, for increased clinical relevance of in vitro tests, fatigue tests are to be preferred, comprising > 105 cycles. A positive correlation was found between traumatic occlusion and periodontal disease. The occlusal forces producing tooth mobility may accelerate attachment loss in progressive periodontitis (12). Qvist (13) demonstrated the effect of mastication on marginal adaptation of composite restorations in the oral environment. The aim of this study was to determine in vitro the effect of masticatory cycles on the quality of apical sealing.
This study investigated the effect of apical leakage due to masticatory cycles on root canal treatment. Twenty upper maxillary molars were first obturated using the warm vertical compaction technique. Four maxillary casts were then built, with each holding four of the sample molars. The molars were embedded in resin with the roots separated from the resin by means of a light silicon. The four remaining teeth served as controls and were not submitted to occlusal forces. A mechanical device to simulate masticatory cycles subjected the teeth to 0.5 • 106 cycles (group A), 106 cycles (group B), 2.106 cycles (group C), and 3.106 cycles (group D); the control was group E. The roots were placed in 2% methylene blue dye solution for 72 h and then sectioned longitudinally so that dye penetration could be measured. The mean values of dye penetration were: 3.70 --- 0.69 mm, group A; 5.00 +__1.14 mm, group B; 6.00 -+ 1.01 mm, group C; 7.23 _+ 0.66 mm, group D; and 2.74 __. 0.75 mm, group E. The value of dye penetration increased in correlation with the number of masticatory cycles. This in vitro study suggests the significant effect of masticatory loads on apical leakage.
M A T E R I A L S AND M E T H O D S A device was adapted to simulate masticatory cycles (14). The basic apparatus was a Quick Perfect simulator (Fig. 1). The frame supported an electrical engine moving an eccentric camshaft on its upper posterior part. This acted on a lever arm that rotated around the upper middle axis of the frame, moving in turn the upper arm
The goals for consistently successful endodontic treatment are (i) total obliteration of the canal space and (ii) perfect sealing of the apical foramen at the dentin-cementum junction, and of the accessory canals at locations other than the root apex with an inert, dimensionally stable, and biologically compatible material (1). Numerous methods have been used to investigate the sealing ability of various endodontic clinical techniques and materials. These include the radionuclide detection technique (2), bacterial penetration (3), scanning electron microscopy (4), and electrochemical techniques (5). The most common method to study the quality of apical seal is dye penetration (6-10). Failure of root canal treatment may occur soon after the treat-
FIG 1. Front view of the masticatory device.
322
Vol. 24, No. 5, May 1998
Masticatory Cycles and Apical Leakage
323
TABLE1. Values of mean dye penetration for groups corresponding to the number of cycles Groups E No. of roots No. of cycles Mean dye penetration (rnm) SD
12 0 2, 74 0, 7537
A 12 0.5.108 3, 70 0, 6907
B
C
D
12 108 5, 00 1, 1481
12 2.106 6, 00 1, 0198
12 3.108 7, 23 0, 6624
Note the 0 cycles of control group E.
of the joint through a spring enclosed in a tube. An adjustable pin allowed only openings and closings. A weight positioned on the upper arm of the simulator was able to fix the mastication forces from 10 to 60 kg (14). On its lower part, the semiadjustable joint was secured by screws. Experimental casts were mounted on the simulator, and the entire assembly was set in a container to receive continuous irrigation by means of a pump. A thermobath kept the water at a constant 37°C temperature.
7 6
E
5
==
4 3 2
Protocol Twenty extracted upper maxillary molars were used in this study. Teeth with resorptive defects, caries, or cracks were excluded. Sample teeth were stored in Ringer's solution containing 0.2% sodium azide (pH 7.09) at room temperature before the study. The maxillary molars were prepared by the serial preparation described by Schilder (15). Working lengths were determined to l mm short of the radiographic apex. Canals were enlarged with a #25 file to ensure patency and provide a standardized apical preparation. A solution of 5.25% sodium hypochlorite was used between each instrumental step. After preparation, the canal was dried with sterile paper points. Teeth were obturated by warm vertical compaction (15) using Mynol gutta-percha points (Block Drug Corp., Jersey City, N J) and Sealite regular (Pierre Rolland, Paris, France). The coronal cavity was obturated with Ketac silver (ESPE, Seefeld, Germany). The maxillary molars were randomly assigned to 1 of 5 groups: A.(n = 4 ) , B (n = 4 ) , C ( n = 4 ) , D ( n = 4 ) , o r E ( n = 4). The upper and lower casts were composed of freshly extracted teeth. The teeth were embedded in resin, and all roots were separated from resin by means of a light silicon (Coltex, Pierre Rolland, France). Casts were positioned on the upper and lower arms of the masticatory device by means of Snow White no. 2 stone piaster. An equilibration was performed on each pair of casts. In occlusion, all upper molars had at least four occlusion points with mandibular molars. During experimentation, a 1.6-inch rubber dam was inserted between the upper and lower casts. The occlusion force was fixed at 30 kg by a weight placed on the upper arm of the simulator. The system moved in opening and closing motions at a rate of 77 cycles/rain and was irrigated by 37°C water. By randomization, one pair of casts was stopped at 500,000 cycles (group A), another at 1 million cycles (group B), another at 2 million cycles (group C), and one at 3 million cycles (group D). The teeth of group E were not subjected to masticatory cycles. At the end of each cycle, the four teeth of groups A, B, C, and D were separated from the cast. The external surfaces (except the apical foramen) of the roots were then painted with two coats of nail polish and one layer of sticky wax; each coat was allowed to dry between applications.
1 0
E: 0
A: 0.5 B: I C: 2 Masticatory cyles (million)
D: 3
FIG 2. Mean dye leakage of all groups. All of the roots of the sample teeth were placed in a 2% methylene blue dye solution (0.062 M) prepared by mixing 2 g of methylene blue powder (mol. wt. 319.9, Sigma Chemical Co., St. Louis, MO) with 100 ml of a standardized buffer solution (Labover, Montpellier, France) of pH 7 for 72 h. The roots were grooved longitudinally with a #699 L high-speed bur on the facial and lingual surfaces. Apical leakage was measured from the most apical part of the root to the most coronal penetration of the dye, to the nearest 0.1 mm, using a dissecting microscope at X7. All leakage results are given in millimeters. All measurements were performed blindly by one investigator.
RESULTS Mean leakage values were calculated and are presented in Table 1 and Fig. 2. For each group, the leakage between the different roots of the teeth was not significantly different (p > 0.05). They varied from 2.74 mm _+ 0.75 for the control group E to 7.23 + 0.66 mm for group D. The analysis of variance (Table 2) of all groups subjected to masticatory cycles (groups A - D ) showed that all were significantly different (p < 0.05) from group E. The differences were also significant between groups A and B, groups B and C, and groups C and D.
DISCUSSION A modified device (14) was used to simulate the masticatory loads exerted on canal filling materials (Fig. 1). Analysis of the masticatory cycles showed that apical leakage was correlated with the number of cycles. A significant difference appeared between 500,000, 1 million, 2 million, and 3 million cycles.
324
Journal of Endodontics
Esber et ah TABLE 2. Statistical analysis (general linear models of SAS) between different groups Groups E&A
E&B
E&C
E&D
A&B
B&C
C&D
0.0092
0.0001
0.0001
0.0001
0.0007
0.0071
0.0011
In agreement with the findings of Lundeen and Gibbs (16), the value of the masticatory loads during this experiment was fixed at 30 kg. Due to its design, the device reproduced only the opening and closing movements around the hinge axis. All of the excurcive and protrusive movements were omitted. However, according to Lundeen and Gibbs (16), the greatest masticatory forces occur at the end of closure. In terms of the experimental conditions, this part of the masticatory cycle was thus effectively reproduced by the device. During pre-experiment trials, the occlusion contacts between the teeth embedded in resin induced too many fractures during the masticatory cycles. A periodontal ligament was reproduced and joined to a light silicon, resulting in an elastic component that prevented further fractures and may have more closely reproduced the clinical reality. Spangberg et al. (7) reported that entrapped air can inhibit the penetration of dye between filling materials and dentinal walls when using passive dye penetration. Masters et al. (6), however, compared apical dye leakage with and without vacuum, and reported that the use of vacuum, unnatural forces, may not be necessary for dye leakage studies in filled root canals. Based on these latter results, the present study was conducted without a vacuum condition for the sample teeth. As recommended by Smith and Steiman (9), the leakage was measured using methylene blue dye because (i) it does not stain the dentin and (ii) the most coronal limit of the leakage is easily detected. Ahlberg et al. (10) compared the apical leakage shown by methylene blue and India ink in root-filled teeth and found that methylene blue has a lower molecular weight and penetrates more deeply into root canal fillings than India ink, which has a larger particle size and thus results in very high leakage values. The use of methylene blue in passive dye penetration thus seems to be the most accurate method for leakage investigation. Dalat and Spangberg (8) demonstrated that, with the most respected obturation methods and using a sealer with excellent physical properties, traceable microlumina--representing fluid penetration--will always occur. In agreement with this finding, group E, which was not subjected to masticatory loads, showed evidence of dye penetration. The other groups all presented an increase in the depth of dye penetration as a function of the number of masticatory cycles. As reported by Marciano et al. (3), fluid penetration and bacterial penetration can be associated. This phenomenon, fluid penetration, can explain why the masticatory factor induces an increase in the percentage of endodontic failure at long term. In the study by Blum et al. (14), the mean dye penetration showed an increase with the number of masticatory cycles, with a breakpoint at 2 million cycles. In the present study, only one linear function was observed. It should be noted that their protocol differed from the present protocol on one specific point: the palatal roots of all molars were not directly subjected to occlusal forces, whereas in this study the roots of all molars, although separated from resin by means of a light silicon, were directly subjected to the forces. This may explain why the present results showed greater values than those of Blum et al. Similarly, Qvist (13)
studied the effect of mastication on the marginal adaptation of class V composite restorations. His in vivo study compared two groups of teeth with and without occlusal forces. In the oral environment, after the equivalent of 4 months of masticatory function, results showed that functional mastication has a major influence on the marginal adaptation of composite restorations, even when not directly subjected to masticatory wear. Kawamura (17) reported that the number of daily occlusive mastication cycles varied from 500 to 1,000. According to these mean values, group A represented 1.36 yr; group B, 2.73 yr; group C, 5.47 yr; and group D, 8.21 yr. As previously stated, the leakage phenomena thus increased significantly with the number of masticatory cycles over a period of 8 yr. In a recent study, Smith et al. (18) found a success rate for nonsurgical endodontics of 84% over an observation period of 5 yr. After analyzing several of the factors that influenced this success rate, they concluded that canal debridement and obturation within 2 mm of the apex results in the highest success rate, although endodontically treated teeth will continue to fail at --2% per year. The effect of occlusion forces on the root-filled teeth in this study may indicate the reason for this failure rate. This in vitro study demonstrates the significant effect of occlusal loads on the apical seal. A linear function was observed between the number of masticatory cycles and the leakage measured by passive dye penetration. We thank Catherine Stott Carmeni and Dr. Paul Yramini for technical assistance. Drs. Esber, Blum, Chazel, and Parahy are affiliated with the Dental School of Montpellier, University of Montpellier, Montpellier, France. Address requests for reprints to Dr. Samir Esber, 149, rue Faventines, 26000 Valence, France.
References 1. Nguyen N. Obturation of the root canal system. In: Cohen S, Burns R, eds. Pathways of the pulp. 5th ed. St. Louis: CV Mosby, 1991. 2. Canalda-Sahli C, Brau-Aguade E, Sentis-Vilalta J, Aguade-Bruix S. The apical seal of root canal sealing cements using a radionuclide detection technique. Int Ended J 1992;25:250-6. 3. Marciano J, Michailesco P, Nardoux M. Le scellement apical: realit~ ou fiction. Etude in vitro par colonisation bact~rienne. Rev Franc Ended 1986;5: 33-47. 4. Lugassy AA, Yee F. Root canal obturation with gutta-percha: a scanning electron microscopic comparison of vertical compaction and automated thermatic condensation. J Endodon 1982;8:120-5. 5. Mattison GD, von Fraunhofer JA. Electrochemical microleakage study of endodontic sealer cements. Oral Surg Oral Med Oral Pathol 1983;55:402-7. 6. Masters J, Higa R, Torabinejad M. Effects of vacuuming on dye penetration patterns in root canals and glass tubes. J Endodon 1995;21:332-4. 7. Spangberg LSW, Acierno TG, Cha BY. Influence of entrapped air on the accuracy of leakage studies using dye penetration methods. J Endodon 1989;15:548-51. 8. Dalat DM, Spangberg LSW. Comparison of apical leakage in root canals obturated with various gutta-percha techniques using a dye vacuum tracing method. J Endodon 1994;20:315-9. 9. Smith MA, Steiman HR. An in vitro evaluation of microleakage of two new and two old root canal sealers. J Endodon 1994;20:18-21. 10. Ahlberg KMF, Assavanop P, Tay WM. A comparison of the apical dye penetration patterns shown by methylene blue and India ink in root-filled teeth. Int Ended J 1995;28:30-4. 11. Huysmans M-CDNJM, Peters MCRB, Van der varst PGT, Plasschaert
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The Way It Was Close observation of television commercials for analgesics might lead a person to conclude two things--the penchant for subtle half-truths, exaggeration, and misdirection did not die with snake-oil salesmen and the stakes, i.e., dollar volume of analgesic sales, must be enormous. Subtlety was not always de rigueur with pain-killer purveyors. A highly successful nostrum in the 1890s was called Cuforhedake Brane Fude. You laugh, but it sold more than 2 million bottles at 25¢ a bottle and made its compounder a millionaire. In fact it was of some value since it contained acetanilide, which though an effective analgesic is little used today because of its potential toxicity. In a way it is hard to understand how it competed with rival concoctions of that time, which were usually primarily laudanum, an alcoholic solution of opium. Must have been the catchy name that did it.
Zachariah Yeomans