- Email: [email protected]
The Effect of Thermocycling on a Colored Glass Ionomer Intracoronal Barrier
Basic Research–Technology
The Effect of Thermocycling on a Colored Glass Ionomer Intracoronal Barrier Scott M. Maloney, DDS, MS, Scott B. McClanahan, DDS, MS, Gary G. Goodell, DDs, MS, MA Abstract The purpose of this study was to evaluate the effect of thermocycling on a colored glass ionomer intracoronal barrier used for the prevention of microleakage. Thirty single canal premolars were decoronated, standardized in length, instrumented, obturated, and randomly assigned to three groups. Group 1 received a 1 mm intracoronal barrier of Triage glass ionomer, group 2 received a 2 mm Triage barrier, and group 3 received no barrier. After incubation for sealer set, teeth were thermocycled. Microleakage was measured using the fluid transport model. Groups 1, 2, and 3 demonstrated 1.68 mm, 0.60 mm, and 23.24 mm of movement, respectively. Using ANOVA and Student-Neumann-Keuls, group 3 leaked significantly more (p ⬍ 0.05) than groups 1 and 2, with no difference between groups 1 and 2. A 1 or 2 mm intracoronal barrier of Triage significantly reduced coronal microleakage in thermocycled endodontically treated teeth.
The opinions or assertions expressed in this article are those of the authors and are not to be construed as official policy or position of the Department of the Navy, Department of Defense or the U.S. Government. Dr. Maloney is a former endodontic resident; Dr. Goodell is a staff endodontist; and Dr. McClanahan is the Chairman, Endodontics Department, Naval Postgraduate Dental School, Bethesda, MD. Address requests for reprints to Dr. McClanahan, 5419 Flint Tavern Place, Burke, VA 22015-2109; E-mail address: [email protected]. Copyright © 2005 by the American Association of Endodontists
526
Maloney et al.
C
oronal microleakage has been implicated in post-treatment disease. If the patient delays placement of a permanent restoration and the temporary seal breaks down, or if restorative materials and/or tooth structures are lost or fractured, bacteria may be reintroduced into the root canal system (1– 4). A temporary restoration is routinely used before the placement of the final restoration. Cavit requires a thickness of 3.5 mm (5) and has been shown to be effective against bacterial contamination for up to 3 weeks (6). In teeth that are severely broken down, this thickness may not be possible increasing the likelihood of loss of temporary seal. It has been suggested that temporary restorations be replaced after 3 months (3, 7). However, many other studies have shown that microleakage may occur much sooner. Contamination of the entire root canal system was shown to occur in unrestored teeth exposed to artificial saliva in as little as 3 days (1). Khayat et al. determined saliva contamination through to the apical foramen can occur within 4 days in nonrestored teeth (4). Bacterial models have been used to confirm contamination of 50% of filled canals within 19 or 42 days with Staphylococcus epidermidis or P. vulgaris, respectively (2). It seems prudent to place the permanent restoration as soon as possible after root canal therapy. Safavi et al. found successful results more often in teeth with permanent restorations compared to teeth with temporary restorations but the difference was not statistically significant (8). Ricucci et al. found a trend of periradicular lesions more often in the “open” group compared to the group with intact coronal restorations (9). Hommez et al. found that teeth restored with a base under the coronal filling had significantly less apical periodontitis than teeth without bases (10). When used in addition to an endodontic temporary, an intracoronal barrier provides a supplementary layer to protect the obturated canal. During a 90 day bacterial leakage study, it was shown that only 15% of Cavit and 35% of SuperEBA and IRM intraorifice barriers allowed leakage, which was significantly better than obturated, unsealed canals (11). A 1 mm liner of a resin-modified glass ionomer, Vitrebond, resulted in no bacterial contamination over 60 days (12). More recently, the use of dentin bonding agents has been advocated to help provide a better intracoronal seal. A 2 to 3 mm barrier of flowable composite used with a dentin-bonding agent was shown to provide a significantly better seal than IRM. This transparent material allowed visualization of the gutta-percha after placement, facilitating re-entry into the tooth (13–15). Another study using this material found no significant difference between placing 2 mm into the canal and covering the entire pulpal floor. An advantage of restricting intracoronal barrier placement to the canal space is no interference with any required dimension of the core (16). The ideal properties of an intraorifice barrier have been proposed by Wolcott et al. to include the following characteristics: (a) easily placed, (b) bonds to tooth structure, (c) seals against microleakage, (d) distinguishable from natural tooth structure, and (e) does not interfere with the final restoration (17). Many restorative materials, however, are tooth colored, increasing the possibility of perforation during restoration or reentry into the canals. Nontooth colored intraorifice barriers may decrease the risk of these iatrogenic mishaps. Triage, a new pink trial material from GC America, was judged to be the most visible through the access preparation (17). Numerous studies have shown that intracoronal barriers decrease coronal microleakage (11–18). However, none of these studies, which used glass ionomers or bonding agents, tested the materials by thermocycling (12–18). Thermocycling can cause bond weakening or failure, resulting in microleakage (19). The purpose of this
JOE — Volume 31, Number 7, July 2005
Basic Research–Technology study was to evaluate the effect of thermocycling on a colored glass ionomer intracoronal barrier used for the prevention of microleakage.
Methods and Materials Thirty extracted, single canal premolars were stored in 0.2% sodium azide (Sigma Chemical Co., St. Louis, MO). All teeth were examined by transillumination under ⫻6.4 magnification for fractures or defects, then decoronated to a standardized length of 18 mm. Working length was determined by visually placing a #15 file at the apex and subtracting 1 mm. The teeth were instrumented with a standard rotary technique in a crown down manner to a .04 taper master apical file size of #40. The canals were then irrigated with 3 ml of 17% EDTA (Roth International Ltd., Chicago, IL) followed by a 3-ml rinse with 5.25% NaOCl. Canals were dried with paper points and patency was reconfirmed with a #15 file. The teeth were obturated with gutta-percha and Roth 801 sealer (Roth International Ltd., Chicago, IL) using lateral compaction. The coronal aspect of the gutta-percha was removed with a System B Heat Source (Sybron Endo, Orange, CA) at 200°C and vertically compacted leaving a 4.5 mm canal space. Excess sealer was removed with cotton pellets soaked in 70% isopropyl alcohol using the dental microscope at ⫻6.4 magnification. All teeth were again examined for fractures or defects. They were then placed in 100% humidity at 37°C for 3 weeks to allow the sealer to set. The teeth were randomly divided into three equal groups of 10. Group 1 received 1 mm intracoronal barriers of Triage (GC America Inc., Alsip, IL), a colored, resin- modified glass ionomer. Group 2 received 2-mm intracoronal barriers. The Triage was mixed according to the manufacturer’s instructions and loaded into Centrix Accudose Needle Tubes (Centrix Inc., Shelton, PA). The Centrix tubes had previously been marked at a distance either 3 or 4 mm from the tip, which was used to control the placement of the barriers. They were placed randomly using an individual Triage capsule and Centrix Accudose Needle Tube for each tooth. Group 3 received no barriers and served as the positive control. All teeth were thermocycled 500 times (5°C/55°C) with a 60 s dwell time in a Willytec thermocycler (Thermo Haake, Germany). The teeth were again examined for fractures or defects. One tooth in the control group was cracked and was eliminated from the study. Holes were drilled in acrylic blocks (25 ⫻ 25 ⫻ 8 mm) such that blunt 18 gauge needles fit snugly extending 2 mm out one side and 12 mm out the other. The roots were attached to the blocks with cyanoacrylate so that the 2 mm needle extensions fit into the lumen of each canal. The teeth were sealed with two coats of nail polish on the entire surface except for the apical 2 mm. Two teeth were coated completely with nail polish and served as negative controls. Leakage was evaluated using a fluid transport model with 10 psi of pressure (Fig. 1). Each tooth was tested three times and the average of these results was calculated. Differences in fluid transport among groups were analyzed with a one-way ANOVA and the Student-NewmanKeuls test. The level of statistical significance was set at p ⬍ 0.05.
Results Figure 2 illustrates the fluid transport results. Group 1, 1 mm barriers, had a mean of 1.68 mm movement. Group 2, 2 mm barriers, had a mean of 0.60 mm movement. Group 3, the positive control group, with no barriers, showed a mean of 23.24 mm movement. Group 3 leaked significantly more than groups 1 and 2, and there was no significant difference between Groups 1 and 2. However, there was a trend for less fluid movement in group 2. Negative controls demonstrated no movement.
JOE — Volume 31, Number 7, July 2005
Figure 1. Schematic representation of the fluid transport system.
Figure 2. Fluid movement.
Discussion This study evaluated the effect of thermocycling on the intracoronal barrier, Triage. Thermocycling is a standard protocol in restorative literature when bonded materials are evaluated, simulating in vivo aging by subjecting them to cyclic exposures of hot and cold temperatures. In general, physical properties tend to decrease or remain unchanged following thermal stress (20). Resin composite restorative materials and adhesive systems are sensitive to thermocycling. Thermocycling stress may induce a significant amount of bond fatigue and microleakage at the tooth/restoration interface. Marginal leakage is believed to be the result of a difference in the coefficient of thermal expansion between the restorative material and the tooth (21). The internal environment of the tooth compared to that of a coronal restoration is certainly an area for further study. However, if the temporary or restoration has significant breakdown or loss, the barrier would be exposed to the temperature fluctuations of the oral environment. A major concern when placing a restorative material over a surface contaminated with eugenol is the potential for decreased bond strength or incomplete setting of the material. However, the presence of eugenol has been shown not to affect the ability of dentin bonding agents or resin-modified glass ionomers to provide an adequate seal (13, 22). Furthermore, the use of alcohol and 37% phosphoric acid gel have been shown to be effective in removing excess sealer before bonding (23). The fluid flow apparatus was designed similar to the model used by Galvan et al. (14) to allow direct visualization of the exterior surface of the tooth versus a system where the tooth is submerged in fluid. This
Thermocycling on a Glass Ionomer Intracoronal Barrier
527
Basic Research–Technology allowed verification that fluid movement was through the apex of the tooth and not the result of a crack or a failed seal at the tooth/plastic block interface. Fluid movement results that were viewed as outliers could be easily accepted or eliminated based on monitoring the leakage at the apex. In 2002, Friedman reviewed 14 endodontic studies that evaluated the prognosis of initial endodontic therapy. His review determined that 88 to 95% of the teeth were functional upon follow up (24). If a canal system becomes infected after initial root canal therapy and subsequently requires endodontic retreatment, the prognosis is greatly decreased. Allen et al. found the chances of healing after nonsurgical retreatment or endodontic surgery were 73% and 60%, respectively (25). It seems evident that the best prognosis is afforded the first time the tooth is treated. It is therefore crucial to protect the canal system from bacterial contamination once endodontic therapy is completed. The placement of an intracoronal barrier could potentially decrease the incidence of microleakage and subsequent canal contamination. The results of this study are consistent with the findings of previous authors who found that an intracoronal barrier significantly reduced microleakage. Triage satisfies the five criteria proposed by Wolcott et al. for an ideal intraorifice barrier (17). In addition, it was able to withstand the effects of thermocycling. It possesses an advantage over dentin bonding systems in that no additional steps are needed to etch the dentin or apply primer/bonding agents. If the restorative treatment plan is later modified to include a post space, the intracoronal barrier can be carefully removed with ultrasonics or a surgical length bur. When the restorative treatment plan is known to include a post, an intracanal barrier could be placed immediately over the gutta-percha while accounting for the required minimum dimension of remaining gutta-percha (26). The results of this study showed that teeth with thermocycled Triage intracoronal barriers leaked significantly less than teeth with no barriers. There was no significant difference between the 1- and 2-mm barriers; however, there was a trend towards less fluid movement when the thicker barrier was placed. A clinician may choose to place a thicker barrier as dictated by the restorative considerations.
References 1. Swanson K, Madison S. An evaluation of coronal microleakage in endodontically treated teeth. Part I. Time periods. J Endod 1987;13:56 –9. 2. Torabinejad M, Ung B, Kettering JD. In vitro bacterial penetration of coronally unsealed endodontically treated teeth. J Endod 1990;16:566 –9. 3. Magura ME, Kafrawy AH, Brown CE, Jr, Newton CW. Human saliva coronal microleakage in obturated root canals: an in vitro study. J Endod 1991;17:324 –31. 4. Khayat A, Lee SJ, Torabinejad M. Human saliva penetration of coronally unsealed obturated root canals. J Endod 1993;19:458 – 61.
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5. Webber RT, del Rio CE, Brady JM, Segall RO. Sealing quality of a temporary filling material. Oral Surg Oral Med Oral Pathol 1978;46:123–30. 6. Beach CW, Calhoun JC, Bramwell JD, Hutter JW, Miller GA. Clinical evaluation of bacterial leakage of endodontic temporary filling materials. J Endod 1996;22:459 – 62. 7. Begotka BA, Hartwell GR. The importance of the coronal seal following root canal treatment. Va Dent J 1996;73:8 –10. 8. Safavi KE, Dowden WE, Langeland K. Influence of delayed coronal permanent restoration on endodontic prognosis. Endod Dent Traumatol 1987;3:187–91. 9. Ricucci D, Grondahl K, Bergenholtz G. Periapical status of root-filled teeth exposed to the oral environment by loss of restoration or caries. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;90:354 –9. 10. Hommez GMG, Coppens CRM, De Moor RJG. Periapical health related to the quality of coronal restorations and root fillings. Int Endod J 2002;35:680 –9. 11. Pisano DM, DiFiore PM, McClanahan SB, Lautenschlager EP, Duncan JL. Intraorifice sealing of gutta-percha obturated root canals to prevent coronal microleakage. J Endod 1998;24:659 – 62. 12. Chailertvanitkul P, Saunders WP, Saunders EM, MacKenzie D. An evaluation of microbial coronal leakage in the restored pulp chamber of root-canal treated multirooted teeth. Int Endod J 1997;30:318 –22. 13. Wolanek GA, Loushine RJ, Weller RN, Kimbrough WF, Volkmann KR. In vitro bacterial penetration of endodontically treated teeth coronally sealed with a dentin bonding agent. J Endod 2001;27:354 –7. 14. Galvan RR, Jr., West LA, Liewehr FR, Pashley DH. Coronal microleakage of five materials used to create an intracoronal seal in endodontically treated teeth. J Endod 2002;28:59 – 61. 15. Belli S, Zhang Y, Pereira PN, Pashley DH. Adhesive sealing of the pulp chamber. J Endod 2001;27:521– 6. 16. Wells JD, Pashley DH, Loushine RJ, Weller RN, Kimbrough WF, Pereira PN. Intracoronal sealing ability of two dental cements. J Endod 2002;28:443–7. 17. Wolcott JF, Hicks ML, Himel VT. Evaluation of pigmented intraorifice barriers in endodontically treated teeth. J Endod 1999;25:589 –92. 18. Lawley GR, Schindler WG, Walker WA, 3rd, Kolodrubetz. Evaluation of ultrasonically placed MTA and fracture resistance with intra canal composite resin in a model of apexification. J Endod 2004;30:167–72. 19. Yap AU. Effects of storage, thermal and load cycling on a new reinforced glassionomer cement. J Oral Rehabil 1998;25:40 – 4. 20. Draughn RA. Effects of temperature on mechanical properties of composite dental restorative materials. J Biomed Mater Res 1981;15:489 –95. 21. Hakimeh S, Vaidyanathan J, Houpt ML, Vaidyanathan TK, Von Hagen S. Microleakage of compomer class V restorations: effect of load cycling, thermal cycling, and cavity shape differences. J Prosthet Dent 2000;83:194 –203. 22. Terata R, Nakashima K, Kubota M. Effect of temporary materials on bond strength of resin-modified glass-ionomer luting cements to teeth. Am J Dent 2000;13:209 –11. 23. Tjan AH, Nemetz H. Effect of eugenol-containing endodontic sealer on retention of prefabricated posts luted with adhesive composite resin cement. Quintessence Int 1992;23:839 – 44. 24. Friedman S. Prognosis of initial endodontic therapy. Endod Topics 2002;2:59 – 88. 25. Allen RK, Newton CW, Brown CE, Jr. A statistical analysis of surgical and nonsurgical endodontic retreatment cases. J Endod 1989;15:261– 6. 26. Mavec JC, Minah GE, Blundell RE, McClanahan SB. Influence of an intracanal glass ionomer barrier on coronal microleakage in post pre-prepared teeth [abstract]. J Endod 2003;29:297.
JOE — Volume 31, Number 7, July 2005
The Effect of Thermocycling on a Colored Glass Ionomer Intracoronal Barrier Scott M. Maloney, DDS, MS, Scott B. McClanahan, DDS, MS, Gary G. Goodell, DDs, MS, MA Abstract The purpose of this study was to evaluate the effect of thermocycling on a colored glass ionomer intracoronal barrier used for the prevention of microleakage. Thirty single canal premolars were decoronated, standardized in length, instrumented, obturated, and randomly assigned to three groups. Group 1 received a 1 mm intracoronal barrier of Triage glass ionomer, group 2 received a 2 mm Triage barrier, and group 3 received no barrier. After incubation for sealer set, teeth were thermocycled. Microleakage was measured using the fluid transport model. Groups 1, 2, and 3 demonstrated 1.68 mm, 0.60 mm, and 23.24 mm of movement, respectively. Using ANOVA and Student-Neumann-Keuls, group 3 leaked significantly more (p ⬍ 0.05) than groups 1 and 2, with no difference between groups 1 and 2. A 1 or 2 mm intracoronal barrier of Triage significantly reduced coronal microleakage in thermocycled endodontically treated teeth.
The opinions or assertions expressed in this article are those of the authors and are not to be construed as official policy or position of the Department of the Navy, Department of Defense or the U.S. Government. Dr. Maloney is a former endodontic resident; Dr. Goodell is a staff endodontist; and Dr. McClanahan is the Chairman, Endodontics Department, Naval Postgraduate Dental School, Bethesda, MD. Address requests for reprints to Dr. McClanahan, 5419 Flint Tavern Place, Burke, VA 22015-2109; E-mail address: [email protected]. Copyright © 2005 by the American Association of Endodontists
526
Maloney et al.
C
oronal microleakage has been implicated in post-treatment disease. If the patient delays placement of a permanent restoration and the temporary seal breaks down, or if restorative materials and/or tooth structures are lost or fractured, bacteria may be reintroduced into the root canal system (1– 4). A temporary restoration is routinely used before the placement of the final restoration. Cavit requires a thickness of 3.5 mm (5) and has been shown to be effective against bacterial contamination for up to 3 weeks (6). In teeth that are severely broken down, this thickness may not be possible increasing the likelihood of loss of temporary seal. It has been suggested that temporary restorations be replaced after 3 months (3, 7). However, many other studies have shown that microleakage may occur much sooner. Contamination of the entire root canal system was shown to occur in unrestored teeth exposed to artificial saliva in as little as 3 days (1). Khayat et al. determined saliva contamination through to the apical foramen can occur within 4 days in nonrestored teeth (4). Bacterial models have been used to confirm contamination of 50% of filled canals within 19 or 42 days with Staphylococcus epidermidis or P. vulgaris, respectively (2). It seems prudent to place the permanent restoration as soon as possible after root canal therapy. Safavi et al. found successful results more often in teeth with permanent restorations compared to teeth with temporary restorations but the difference was not statistically significant (8). Ricucci et al. found a trend of periradicular lesions more often in the “open” group compared to the group with intact coronal restorations (9). Hommez et al. found that teeth restored with a base under the coronal filling had significantly less apical periodontitis than teeth without bases (10). When used in addition to an endodontic temporary, an intracoronal barrier provides a supplementary layer to protect the obturated canal. During a 90 day bacterial leakage study, it was shown that only 15% of Cavit and 35% of SuperEBA and IRM intraorifice barriers allowed leakage, which was significantly better than obturated, unsealed canals (11). A 1 mm liner of a resin-modified glass ionomer, Vitrebond, resulted in no bacterial contamination over 60 days (12). More recently, the use of dentin bonding agents has been advocated to help provide a better intracoronal seal. A 2 to 3 mm barrier of flowable composite used with a dentin-bonding agent was shown to provide a significantly better seal than IRM. This transparent material allowed visualization of the gutta-percha after placement, facilitating re-entry into the tooth (13–15). Another study using this material found no significant difference between placing 2 mm into the canal and covering the entire pulpal floor. An advantage of restricting intracoronal barrier placement to the canal space is no interference with any required dimension of the core (16). The ideal properties of an intraorifice barrier have been proposed by Wolcott et al. to include the following characteristics: (a) easily placed, (b) bonds to tooth structure, (c) seals against microleakage, (d) distinguishable from natural tooth structure, and (e) does not interfere with the final restoration (17). Many restorative materials, however, are tooth colored, increasing the possibility of perforation during restoration or reentry into the canals. Nontooth colored intraorifice barriers may decrease the risk of these iatrogenic mishaps. Triage, a new pink trial material from GC America, was judged to be the most visible through the access preparation (17). Numerous studies have shown that intracoronal barriers decrease coronal microleakage (11–18). However, none of these studies, which used glass ionomers or bonding agents, tested the materials by thermocycling (12–18). Thermocycling can cause bond weakening or failure, resulting in microleakage (19). The purpose of this
JOE — Volume 31, Number 7, July 2005
Basic Research–Technology study was to evaluate the effect of thermocycling on a colored glass ionomer intracoronal barrier used for the prevention of microleakage.
Methods and Materials Thirty extracted, single canal premolars were stored in 0.2% sodium azide (Sigma Chemical Co., St. Louis, MO). All teeth were examined by transillumination under ⫻6.4 magnification for fractures or defects, then decoronated to a standardized length of 18 mm. Working length was determined by visually placing a #15 file at the apex and subtracting 1 mm. The teeth were instrumented with a standard rotary technique in a crown down manner to a .04 taper master apical file size of #40. The canals were then irrigated with 3 ml of 17% EDTA (Roth International Ltd., Chicago, IL) followed by a 3-ml rinse with 5.25% NaOCl. Canals were dried with paper points and patency was reconfirmed with a #15 file. The teeth were obturated with gutta-percha and Roth 801 sealer (Roth International Ltd., Chicago, IL) using lateral compaction. The coronal aspect of the gutta-percha was removed with a System B Heat Source (Sybron Endo, Orange, CA) at 200°C and vertically compacted leaving a 4.5 mm canal space. Excess sealer was removed with cotton pellets soaked in 70% isopropyl alcohol using the dental microscope at ⫻6.4 magnification. All teeth were again examined for fractures or defects. They were then placed in 100% humidity at 37°C for 3 weeks to allow the sealer to set. The teeth were randomly divided into three equal groups of 10. Group 1 received 1 mm intracoronal barriers of Triage (GC America Inc., Alsip, IL), a colored, resin- modified glass ionomer. Group 2 received 2-mm intracoronal barriers. The Triage was mixed according to the manufacturer’s instructions and loaded into Centrix Accudose Needle Tubes (Centrix Inc., Shelton, PA). The Centrix tubes had previously been marked at a distance either 3 or 4 mm from the tip, which was used to control the placement of the barriers. They were placed randomly using an individual Triage capsule and Centrix Accudose Needle Tube for each tooth. Group 3 received no barriers and served as the positive control. All teeth were thermocycled 500 times (5°C/55°C) with a 60 s dwell time in a Willytec thermocycler (Thermo Haake, Germany). The teeth were again examined for fractures or defects. One tooth in the control group was cracked and was eliminated from the study. Holes were drilled in acrylic blocks (25 ⫻ 25 ⫻ 8 mm) such that blunt 18 gauge needles fit snugly extending 2 mm out one side and 12 mm out the other. The roots were attached to the blocks with cyanoacrylate so that the 2 mm needle extensions fit into the lumen of each canal. The teeth were sealed with two coats of nail polish on the entire surface except for the apical 2 mm. Two teeth were coated completely with nail polish and served as negative controls. Leakage was evaluated using a fluid transport model with 10 psi of pressure (Fig. 1). Each tooth was tested three times and the average of these results was calculated. Differences in fluid transport among groups were analyzed with a one-way ANOVA and the Student-NewmanKeuls test. The level of statistical significance was set at p ⬍ 0.05.
Results Figure 2 illustrates the fluid transport results. Group 1, 1 mm barriers, had a mean of 1.68 mm movement. Group 2, 2 mm barriers, had a mean of 0.60 mm movement. Group 3, the positive control group, with no barriers, showed a mean of 23.24 mm movement. Group 3 leaked significantly more than groups 1 and 2, and there was no significant difference between Groups 1 and 2. However, there was a trend for less fluid movement in group 2. Negative controls demonstrated no movement.
JOE — Volume 31, Number 7, July 2005
Figure 1. Schematic representation of the fluid transport system.
Figure 2. Fluid movement.
Discussion This study evaluated the effect of thermocycling on the intracoronal barrier, Triage. Thermocycling is a standard protocol in restorative literature when bonded materials are evaluated, simulating in vivo aging by subjecting them to cyclic exposures of hot and cold temperatures. In general, physical properties tend to decrease or remain unchanged following thermal stress (20). Resin composite restorative materials and adhesive systems are sensitive to thermocycling. Thermocycling stress may induce a significant amount of bond fatigue and microleakage at the tooth/restoration interface. Marginal leakage is believed to be the result of a difference in the coefficient of thermal expansion between the restorative material and the tooth (21). The internal environment of the tooth compared to that of a coronal restoration is certainly an area for further study. However, if the temporary or restoration has significant breakdown or loss, the barrier would be exposed to the temperature fluctuations of the oral environment. A major concern when placing a restorative material over a surface contaminated with eugenol is the potential for decreased bond strength or incomplete setting of the material. However, the presence of eugenol has been shown not to affect the ability of dentin bonding agents or resin-modified glass ionomers to provide an adequate seal (13, 22). Furthermore, the use of alcohol and 37% phosphoric acid gel have been shown to be effective in removing excess sealer before bonding (23). The fluid flow apparatus was designed similar to the model used by Galvan et al. (14) to allow direct visualization of the exterior surface of the tooth versus a system where the tooth is submerged in fluid. This
Thermocycling on a Glass Ionomer Intracoronal Barrier
527
Basic Research–Technology allowed verification that fluid movement was through the apex of the tooth and not the result of a crack or a failed seal at the tooth/plastic block interface. Fluid movement results that were viewed as outliers could be easily accepted or eliminated based on monitoring the leakage at the apex. In 2002, Friedman reviewed 14 endodontic studies that evaluated the prognosis of initial endodontic therapy. His review determined that 88 to 95% of the teeth were functional upon follow up (24). If a canal system becomes infected after initial root canal therapy and subsequently requires endodontic retreatment, the prognosis is greatly decreased. Allen et al. found the chances of healing after nonsurgical retreatment or endodontic surgery were 73% and 60%, respectively (25). It seems evident that the best prognosis is afforded the first time the tooth is treated. It is therefore crucial to protect the canal system from bacterial contamination once endodontic therapy is completed. The placement of an intracoronal barrier could potentially decrease the incidence of microleakage and subsequent canal contamination. The results of this study are consistent with the findings of previous authors who found that an intracoronal barrier significantly reduced microleakage. Triage satisfies the five criteria proposed by Wolcott et al. for an ideal intraorifice barrier (17). In addition, it was able to withstand the effects of thermocycling. It possesses an advantage over dentin bonding systems in that no additional steps are needed to etch the dentin or apply primer/bonding agents. If the restorative treatment plan is later modified to include a post space, the intracoronal barrier can be carefully removed with ultrasonics or a surgical length bur. When the restorative treatment plan is known to include a post, an intracanal barrier could be placed immediately over the gutta-percha while accounting for the required minimum dimension of remaining gutta-percha (26). The results of this study showed that teeth with thermocycled Triage intracoronal barriers leaked significantly less than teeth with no barriers. There was no significant difference between the 1- and 2-mm barriers; however, there was a trend towards less fluid movement when the thicker barrier was placed. A clinician may choose to place a thicker barrier as dictated by the restorative considerations.
References 1. Swanson K, Madison S. An evaluation of coronal microleakage in endodontically treated teeth. Part I. Time periods. J Endod 1987;13:56 –9. 2. Torabinejad M, Ung B, Kettering JD. In vitro bacterial penetration of coronally unsealed endodontically treated teeth. J Endod 1990;16:566 –9. 3. Magura ME, Kafrawy AH, Brown CE, Jr, Newton CW. Human saliva coronal microleakage in obturated root canals: an in vitro study. J Endod 1991;17:324 –31. 4. Khayat A, Lee SJ, Torabinejad M. Human saliva penetration of coronally unsealed obturated root canals. J Endod 1993;19:458 – 61.
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JOE — Volume 31, Number 7, July 2005