- Email: [email protected]
Influence of Chlorhexidine Application Time on the Bond Strength between Fiber Posts and Dentin
Basic Research—Technology
Influence of Chlorhexidine Application Time on the Bond Strength between Fiber Posts and Dentin Doglas Cecchin, PhD,* Ana Paula Farina, PhD,* Mateus Giacomin, DDS,* unior, PhD,* Cristina de Mattos Pimenta Vidal, PhD,† Bruno Carlini-J and Caio Cezar Randi Ferraz, PhD‡ Abstract Introduction: The aim of this study was to investigate the effects of chlorhexidine (CHX) application time on the bond strength and durability of the adhesion of fiber posts relined with resin composite to the root dentin. Methods: Eighty bovine incisor roots were divided into 4 groups after root preparation: control group (irrigation with physiological solution) and experimental groups, CHX for 30 seconds, CHX for 60 seconds, and CHX for 120 seconds. Fiber posts relined with resin composite were cemented with RelyX ARC. The Scotchbond Multi-Purpose total-etching adhesive system was used in half of the samples of each group, and the Clearfil SE Bond self-etching adhesive system was used in the other half. The samples were randomly divided into 2 subgroups, 24 hours of storage and 12 months of storage. All roots were sectioned transversely, and push-out tests were performed. Bond strength means were analyzed by analysis of variance and Tukey test (a = 0.05). Failure mode was determined by examining specimen’s surfaces under scanning electron microscope, and its distribution was evaluated by using c2 test (a = 0.05). Results: CHX pretreatment resulted in homogeneous bond strength values at 24 hours and 12 months of storage, irrespective of the CHX application time and adhesive system (P < .05). A significant bond strength decrease was noticed after 12 months of storage when irrigation was performed with physiological solution in the control groups (P > .05). Significant differences were observed for fracture patterns (P < .001). Conclusion: The use of CHX pretreatment could preserve the bond strength of the fiber post relined with resin composite to root dentin for 12 months, irrespective of the CHX application time and adhesive system used. (J Endod 2014;-:1–4)
Key Words Application time, bond strength, chlorhexidine, durability, fiber post, root canal
F
iber-reinforced posts have been widely used for the restoration of endodontically treated teeth. Because of the similarity in elastic behavior between fiber posts and the residual root dentin, root fracture rarely occurs in these restorations (1). To improve the retention of the composite core to post and tooth, prefabricated fiber posts are cemented with adhesives and composite resin luting cements (2, 3). However, adhesion between resin and dentin is considered to be a weak point in luting a fiber post (4). Current studies have indicated that the loss of integrity of resin-dentin bonds over time is likely to be due to the degradation of denuded collagen fibrils exposed to incompletely infiltrated hybrid layers (5, 6). This is attributed to an endogenous proteolytic mechanism involving the activity of matrix metalloproteinases (MMPs) (7) found in the coronal (8–10) and radicular dentin (11, 12). Furthermore, recent studies revealed that cysteine cathepsins are also present in dentin, which may also contribute to the breakdown of the exposed collagen in dentin hybrid layers and caries progression (13, 14). Chlorhexidine digluconate (CHX) has been proposed as an irrigant in endodontic treatment because of its antimicrobial activity (15), substantivity (16), and also because it does not affect the bond strength of resin composite restorations (17) and root canal sealers to the dentin (18). According to Moreira et al (19), CHX does not promote morphologic structure alterations in the dentin organic matrix of root dentin; thus, it maintains the quality of the dentin substrate for later obturation or restoration of the tooth with resin-based materials. Moreover, some studies have shown that CHX has beneficial effects on the preservation of resin-dentin bonds by inhibiting the proteolytic activity of MMPs in the hybrid layer (2, 3, 20–22) and that CHX can also inhibit the activity of dentin cysteine cathepsins (23). Both in vitro and in vivo studies have shown that CHX applied to demineralized dentin postpones the resin-dentin degradation of adhesive interfaces, when compared with interfaces to which no CHX is applied (2, 3, 20–22). Despite these advantages, the use of CHX demands more chair time during the adhesive procedure, and this contrasts with the clinician’s needs for simplification. Therefore, the aim of this study was to investigate the effects of CHX application time on the bond strength and durability of the adhesion of the fiber post relined with resin composite to the root dentin by using a total-etching and a self-etching adhesive system. The tested null hypothesis was that irrespective of the application time, CHX could not prevent the bond strength reduction of fiber posts to root dentin after 12 months of water storage.
From the *Department of Restorative Dentistry, College of Dentistry, University of Passo Fundo, Passo Fundo, Rio Grande do Sul, Brazil; †Department of Restorative Dentistry, College of Dentistry, University of Illinois at Chicago, Chicago, Illinois; and ‡Department of Restorative Dentistry, Piracicaba Dental School, State University of Campinas, Piracicaba, S~ao Paulo, Brazil. Address requests for reprints to Dr Doglas Cecchin, Universidade de Passo Fundo, Campus I, Faculdade de Odontologia, BR 285, Km 171, Bairro S~ao Jose, Caixa Postal 611, 99052-900, Passo Fundo, Rio Grande do Sul, Brazil. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2014 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2014.08.019
JOE — Volume -, Number -, - 2014
Chlorhexidine Treatment for Adhesive Durability
1
Basic Research—Technology Materials and Methods Specimen Preparation Eighty freshly extracted bovine incisors with anatomically similar root segments and fully developed apices were selected. Each tooth was decoronated below the cementoenamel junction perpendicular to the longitudinal axis. The roots were cut to a uniform length of 14 mm from the apical end. The apices of the teeth were sealed with a temporary filling material (Cavit W; Premier Dental Produtos, Rio de Janeiro, RJ, Brazil). Pulp tissue and the predentin were removed, and the root canals were enlarged by using #6 Largo burs (Maillefer, Ballaigues, Switzerland) and a #130 file (Maillefer). The apical end (1 mm) was left unprepared to prevent the apical extrusion of solutions and luting cement. Roots were rinsed with 5 mL physiological saline solution (NaCl) to remove remaining debris, and the roots were divided as follows: control group, no treatment; and experimental groups: the root canals were completely filled with 2% CHX for 30 seconds, 60 seconds, or 120 seconds. All roots were dried with paper points, and fiberglass posts relined with resin composite were cemented as described below. The Scotchbond Multi-Purpose (SBMP) total-etching adhesive system was used in half of the samples of each group, and the Clearfil SE Bond (CB) self-etching adhesive system was used in the other half. Intracanal Restoration with Composite Resin The intracanal restoration was done by using fiberglass posts no. 3 (Angelus, Londrina, PR, Brazil) relined with composite resin (B 0.5, Z250; 3M ESPE, St Paul, MN). Initially, the adhesive systems were applied into the canals according to manufacturer’s instructions. CHX was applied after 37% phosphoric acid etching and before primer application when SBMP was used. In the case of CB, CHX was applied before primer application. Both adhesive systems were light-cured for 40 seconds by using a halogen light-curing unit operated at 600 mW/cm2 (Optilux; Demetron Res Corp, Danbury, CT). Then, the walls were lubricated with a water-soluble gel (Natrosol; Drogal Pharmacy, Piracicaba, SP, Brazil). The posts were cleaned with 37% phosphoric acid for 5 seconds, washed, and dried with an air/water syringe. Next, they were silanized twice, waiting 60 seconds after each application. SBMP or CB adhesives were applied to the post surface and immediately polymerized for 20 seconds on each side. The fiber post was covered with resin composite and inserted into the canal, and resin was polymerized for 20 seconds. After removing the post, polymerization was completed outside the root canal for more than 40 seconds (2, 3, 23). After copious rinsing to remove the lubricant gel from the root canal, the root canals were dried with absorbent paper points. One additional drop of the respective adhesive system was applied onto the root canal surface, and the excess was removed with absorbent paper points before light polymerization for 40 seconds. The dual-polymerizing resin luting material Rely X ARC (3M ESPE) was mixed and injected into the prepared root canal with a Centrix
syringe (Shelton, CT) by using an appropriate needle (20-gauge). Subsequently, the fiber post relined with resin composite was covered with cement and seated inside the root canal and kept under finger pressure for 20 seconds, with the excess cement removed. The cement was lightpolymerized for 30 seconds on each surface (buccal, palatal, mesial, and distal), resulting in a 2-minute light polymerization cycle. Specimens of each group were randomly divided into 2 subgroups according to their storage, 24 hours of water storage and 12 months storage in water, which was renewed every 15 days.
Push-out Test: Specimen Preparation, Post Dislodgment, and Failure Pattern Analysis Each root was cut horizontally with a slow-speed, water-cooled diamond saw (Isomet 2000; Buehler Ltd, Lake Bluff, IL) to produce 2 slices approximately 1 mm thick. Seven slices were obtained from each root canal. The first slice was excluded. Thus, 6 slices were considered from each root canal (n = 30). The push-out test was performed by applying a load at 0.5 mm/min to the apex in the direction of the crown until the fiber post relined segment was dislodged from the root slice. Care was also taken to ensure that the contact between the punch tip and the fiber post section occurred over the most extended area possible to avoid notching effect of the punch tip on the fiber post’s surface. The bonding area was calculated as previously described (2, 3), and the bond strength values were expressed in megapascals (MPa). The fractured specimens were sputter-coated with gold in a Denton Vacuum Desk II Sputtering device (Denton Vacuum, Cherry Hill, NJ) and observed by scanning electron microscopy (JSM–5600LV; JEOL Ltd, Tokyo, Japan) to classify the failure pattern into 5 types (2, 3): (1) adhesive between the fiber post and resin cement (no cement visible around the post); (2) mixed, with resin cement covering 0%–50% of the post’s diameter; (3) mixed, with resin cement covering 50%–100% of the post’s surface; (4) adhesive between resin cement and root canal (post enveloped by resin cement); and (5) cohesive in dentin. Bond strength data were analyzed by using analysis of variance and Tukey test for post hoc comparisons (a = 0.05). The distribution of failure patterns was evaluated by c2 test (a = 0.05).
Results The means and standard deviations are presented in Table 1. The statistical analysis revealed significant differences among the groups (P < .05). Immediate groups showed similar bond strength values with or without CHX pretreatment (P > .05). After 12 months of storage, a significant decrease in the control group was observed (P < .05), whereas the use of CHX preserved the bond strength in the groups stored in water for 12 months (P < .05), irrespective of the CHX application time and adhesive system. A significant difference in predominant failure mode between groups was revealed by the c2 test (P < .001). The mixed failure types 2, 3, and 4 were the predominant failures in all groups (Fig. 1). When
TABLE 1. Bond Strength Means (MPa) and the Respective Standard Deviations Obtained in Each Experimental Condition SBMP
CB
Groups
Immediate
12 mo of storage
Immediate
12 mo of storage
NaCl (control) CHX for 30 s CHX for 60 s CHX for 120 s
5.92 1.79aA 5.89 1.37aA 6.39 1.44aA 6.29 1.42aA
4.38 1.34bB 5.76 1.31aA 6.02 1.38aA 6.06 1.55aA
6.38 0.98aA 5.66 0.47aA 6.00 1.41aA 6.01 1.54aA
4.15 1.15bB 5.41 1.16aA 5.80 1.53aA 5.81 1.09aA
Comparisons are only valid within each adhesive system. Means followed by different uppercase letters in same row and lowercase letters in same column are significantly different at 5% level.
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Cecchin et al.
JOE — Volume -, Number -, - 2014
Basic Research—Technology
Figure 1. Failure mode distribution in the experimental groups.
CHX was applied, a decrease in adhesive failures between resin cement and root canal was observed after 12 months of storage for CB, with an increase in mixed failures. For SBMP, CHX application promoted more homogeneity in failure distribution after 12 months of storage.
Discussion Coronal restoration quality is an important factor in the success of endodontically treated teeth (24). Therefore, bonding of the post to the root dentin should aim to achieve gap-free interfaces, which is indicative of coronal seal and adequate retention (25). The results of this study showed that CHX used as pretreatment in the root dentin does not interfere with the immediate bond strength of fiber posts relined with resin composite in any of the adhesive systems used, which is supported by previous studies (2, 3). However, there was a significant decrease in the bond strength values in the control after 12 months of storage, as indicated by the degradation of the adhesive-dentin bonds over time. On the other hand, irrespective of the application time, CHX kept the bond strength in the long-term evaluation, thereby preserving the durability of adhesive-dentin bonds. Therefore, the null hypothesis was rejected. The present study confirms previous findings that resin-dentin interfaces bonded with total-etching or self-etching adhesives can degrade over time (2, 3, 5, 20–22). These findings suggest that deterioration of the resin-dentin bonds occurred mainly as a result of intrinsic factors, possibly because of activation of endogenous proteolytic enzymes such as MMPs (20–22) and cysteine cathepsins, as recently speculated (14, 26). However, the higher bond strength observed after 12 months of storage with CHX pretreatment compared with control can be explained by the CHX-related improvement in the long-term stability of hybrid layer integrity and bond strength that is based on MMPs’ inhibition (2, 3, 20–22). Carrilho et al (21) demonstrated in vivo a protective effect of CHX application against the degradation of the coronal adhesive interface that lasted for up to 14 months after the establishment of resin-dentin bonds. Although the presence of cysteine cathepsins was recently demonstrated in coronal dentin (14), these enzymes are thought to have an important role in collagen degradation (14). The effect of CHX in preserving the bond strength values may be due to inhibition of dentinal cysteine cathepsins also (26). In addition, it should be mentioned that CHX has an antimicrobial effect (15) and could interfere with collagen degradation promoted by proteolytic enzymes produced by bacteria (27). Moreover, less reduction in bond strength was observed irrespective of the application time, so one may suggest that CHX is likely to bind to collagen fibrils at a very fast rate, and JOE — Volume -, Number -, - 2014
thus even short periods of time such as 30 seconds seem to be sufficient to guarantee such binding. The long-term action of CHX can also be explained by its confinement to the adhesive interface because its removal by the dentinal fluid outflow is likely minimized by the formation of resin tags that obliterate the tubules. The adhesive monomers that envelop the collagen fibrils treated with CHX, as well as the presence of an adhesive layer on the hybrid layer, can also contribute to the preservation of CHX at the interface and prolong its inhibitory action (20, 21). Substantivity of CHX, or its ability to be retained in dentin matrices (16), could be another reason why CHX-treated dentin may form more stable hybrid layers. Previous studies investigated the effects of CHX treatment associated or not with ethanol. The ethanol wet-bonding technique and CHX in combination or not preserved the bond strength of the selfetching adhesive system (2); on the other hand, they did not preserve the bond strength of a total-etch adhesive system (3). Similar results were reported by Manso et al (28), which showed that the combined use of ethanol/1% CHX diacetate did not stabilize bond strengths after 15 months by using 2 total-etching adhesive systems. Dentin degradation caused by endogenous enzymes after 12 months of storage is reinforced by these findings. Regarding the fracture analysis, it should be emphasized that the predominant types of failure in all groups were adhesive and mixed, implying homogeneity in failure distribution. The decrease in adhesive failures indicates superior quality of the bond when CHX was applied before the use of CB. This suggests that the bond between the resin cement and root canal dentin was less affected than in the groups with no pretreatment with CHX.
Conclusion Despite the limitations of the present study, the use of CHX pretreatment could preserve the bond strength of the fiber post relined with resin composite to root dentin for 12 months, irrespective of CHX application time (30, 60, or 120 seconds) and of the adhesive system used.
Acknowledgments The authors thank Angelus for donating the fiber post and FAPERGS Foundation-Brazil for financial support through grant 2010/00100-7. The authors deny conflicts of interest related to this study. Chlorhexidine Treatment for Adhesive Durability
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Basic Research—Technology References 1. Zhou L, Wang Q. Comparison of fracture resistance between cast posts and fiber posts: a meta-analysis of literature. J Endod 2013;39:11–5. 2. Cecchin D, de Almeida JF, Gomes BP, et al. Effect of chlorhexidine and ethanol on the durability of the adhesion of the fiber post relined with resin. J Endod 2011;37:678–83. 3. Cecchin D, de Almeida JF, Gomes BP, et al. Influence of chlorhexidine and ethanol on the bond strength and durability of the adhesion of the fiber posts to root dentin using a total etching adhesive system. J Endod 2011;37:1310–5. 4. Ari H, Yasar E, Belli S. Effects of NaOCl on bond strengths of resin cements to root canal dentin. J Endod 2003;29:248–51. 5. Hashimoto M, Ohno H, Sano H, et al. In vitro degradation of resin-dentin bonds analyzed by microtensile test, scanning and transmission electron microscopy. Biomaterials 2003;24:3795–803. 6. Wang Y, Spencer P. Hybridization efficiency of the adhesive/dentin interface in wet bonding. J Dent Res 2003;85:141–5. 7. Pashley DH, Tay FR, Yiu C, et al. Collagen degradation by host-derived enzymes during aging. J Dent Res 2004;83:216–21. 8. Martin-De Las Heras S, Valenzuela A, Overall CM. The matrix metalloproteinase gelatinase A in human dentine. Arch Oral Biol 2000;45:757–65. 9. Mazzoni A, Mannello F, Tay FR, et al. Zymographic analysis and characterization of MMP-2 and -9 forms in human sound dentin. J Dent Res 2007;86:436–40. 10. Sulkala M, Tervahartiala T, Sorsa T, et al. Matrix metalloproteinase-8 (MMP-8) is the major collagenase in human dentin. Arch Oral Biol 2007;52:121–7. 11. Santos J, Carrilho M, Tervahartiala T, et al. Determination of matrix metalloproteinases in human radicular dentin. J Endod 2009;35:686–9. 12. Osorio R, Yamauti M, Sauro S, et al. Experimental resin cements containing bioactive fillers reduce matrix metalloproteinase-mediated dentin collagen degradation. J Endod 2012;38:1227–32. 13. Tersariol IL, Geraldeli S, Minciotti CL, et al. Cysteine cathepsins in human dentinpulp complex. J Endod 2010;36:475–8.
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14. Nascimento FD, Minciotti CL, Geraldeli S, et al. Cysteine cathepsins in human carious dentin. J Dent Res 2011;90:506–11. 15. Ferraz CC, Gomes BP, Zaia AA, et al. In vitro assessment of the antimicrobial action and the mechanical ability of chlorhexidine gel as an endodontic irrigant. J Endod 2001;27:452–5. 16. Souza M, Cecchin D, Farina AP, et al. Evaluation of chlorhexidine substantivity on human dentin: a chemical analysis. J Endod 2012;38:1249–52. 17. Santos JN, Carrilho MR, De Goes MF, et al. Effect of chemical irrigants on the bond strength of a self-etching adhesive to pulp chamber dentin. J Endod 2006;32:1088–90. 18. Prado M, Sim~ao RA, Gomes BP. Effect of different irrigation protocols on resin sealer bond strength to dentin. J Endod 2013;39:689–92. 19. Moreira DM, Almeida JF, Ferraz CC, et al. Structural analysis of bovine root dentin after use of different endodontics auxiliary chemical substances. J Endod 2009;35:1023–7. 20. Carrilho MR, Carvalho RM, de Goes MF, et al. Chlorhexidine preserves dentin bond in vitro. J Dent Res 2007;86:90–4. 21. Carrilho MR, Geraldeli S, Tay F, et al. In vivo preservation of the hybrid layer by chlorhexidine. J Dent Res 2007;86:529–33. 22. Breschi L, Mazzoni A, Nato F, et al. Chlorhexidine stabilizes the adhesive interface: a 2-year in vitro study. Dent Mater 2010;26:320–5. 23. Iglesia-Puig MA, Arellano-Cabornero A. Fiber-reinforced post and core adapted to a previous metal ceramic crown. J Prosthet Dent 2004;91:191–4. 24. Hoen MM, Pink FE. Contemporary endodontic retreatments: an analysis based on clinical treatment findings. J Endod 2002;28:834–6. 25. Schwartz RS, Robbins JW. Post placement and restoration of endodontically treated teeth: a literature review. J Endod 2004;30:289–301. 26. Scaffa PM, Vidal CM, Barros N, et al. Chlorhexidine inhibits the activity of dental cysteine cathepsins. J Dent Res 2012;91:420–5. 27. Ferrari M, Mason PN, Goracci C, et al. Collagen degradation in endodontically treated teeth after clinical function. J Dent Res 2004;83:414–9. 28. Manso AP, Grande RH, Bedran-Russo AK, et al. Can 1% chlorhexidine diacetate and ethanol stabilize resin-dentin bonds? Dent Mater 2014;30:735–41.
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Influence of Chlorhexidine Application Time on the Bond Strength between Fiber Posts and Dentin Doglas Cecchin, PhD,* Ana Paula Farina, PhD,* Mateus Giacomin, DDS,* unior, PhD,* Cristina de Mattos Pimenta Vidal, PhD,† Bruno Carlini-J and Caio Cezar Randi Ferraz, PhD‡ Abstract Introduction: The aim of this study was to investigate the effects of chlorhexidine (CHX) application time on the bond strength and durability of the adhesion of fiber posts relined with resin composite to the root dentin. Methods: Eighty bovine incisor roots were divided into 4 groups after root preparation: control group (irrigation with physiological solution) and experimental groups, CHX for 30 seconds, CHX for 60 seconds, and CHX for 120 seconds. Fiber posts relined with resin composite were cemented with RelyX ARC. The Scotchbond Multi-Purpose total-etching adhesive system was used in half of the samples of each group, and the Clearfil SE Bond self-etching adhesive system was used in the other half. The samples were randomly divided into 2 subgroups, 24 hours of storage and 12 months of storage. All roots were sectioned transversely, and push-out tests were performed. Bond strength means were analyzed by analysis of variance and Tukey test (a = 0.05). Failure mode was determined by examining specimen’s surfaces under scanning electron microscope, and its distribution was evaluated by using c2 test (a = 0.05). Results: CHX pretreatment resulted in homogeneous bond strength values at 24 hours and 12 months of storage, irrespective of the CHX application time and adhesive system (P < .05). A significant bond strength decrease was noticed after 12 months of storage when irrigation was performed with physiological solution in the control groups (P > .05). Significant differences were observed for fracture patterns (P < .001). Conclusion: The use of CHX pretreatment could preserve the bond strength of the fiber post relined with resin composite to root dentin for 12 months, irrespective of the CHX application time and adhesive system used. (J Endod 2014;-:1–4)
Key Words Application time, bond strength, chlorhexidine, durability, fiber post, root canal
F
iber-reinforced posts have been widely used for the restoration of endodontically treated teeth. Because of the similarity in elastic behavior between fiber posts and the residual root dentin, root fracture rarely occurs in these restorations (1). To improve the retention of the composite core to post and tooth, prefabricated fiber posts are cemented with adhesives and composite resin luting cements (2, 3). However, adhesion between resin and dentin is considered to be a weak point in luting a fiber post (4). Current studies have indicated that the loss of integrity of resin-dentin bonds over time is likely to be due to the degradation of denuded collagen fibrils exposed to incompletely infiltrated hybrid layers (5, 6). This is attributed to an endogenous proteolytic mechanism involving the activity of matrix metalloproteinases (MMPs) (7) found in the coronal (8–10) and radicular dentin (11, 12). Furthermore, recent studies revealed that cysteine cathepsins are also present in dentin, which may also contribute to the breakdown of the exposed collagen in dentin hybrid layers and caries progression (13, 14). Chlorhexidine digluconate (CHX) has been proposed as an irrigant in endodontic treatment because of its antimicrobial activity (15), substantivity (16), and also because it does not affect the bond strength of resin composite restorations (17) and root canal sealers to the dentin (18). According to Moreira et al (19), CHX does not promote morphologic structure alterations in the dentin organic matrix of root dentin; thus, it maintains the quality of the dentin substrate for later obturation or restoration of the tooth with resin-based materials. Moreover, some studies have shown that CHX has beneficial effects on the preservation of resin-dentin bonds by inhibiting the proteolytic activity of MMPs in the hybrid layer (2, 3, 20–22) and that CHX can also inhibit the activity of dentin cysteine cathepsins (23). Both in vitro and in vivo studies have shown that CHX applied to demineralized dentin postpones the resin-dentin degradation of adhesive interfaces, when compared with interfaces to which no CHX is applied (2, 3, 20–22). Despite these advantages, the use of CHX demands more chair time during the adhesive procedure, and this contrasts with the clinician’s needs for simplification. Therefore, the aim of this study was to investigate the effects of CHX application time on the bond strength and durability of the adhesion of the fiber post relined with resin composite to the root dentin by using a total-etching and a self-etching adhesive system. The tested null hypothesis was that irrespective of the application time, CHX could not prevent the bond strength reduction of fiber posts to root dentin after 12 months of water storage.
From the *Department of Restorative Dentistry, College of Dentistry, University of Passo Fundo, Passo Fundo, Rio Grande do Sul, Brazil; †Department of Restorative Dentistry, College of Dentistry, University of Illinois at Chicago, Chicago, Illinois; and ‡Department of Restorative Dentistry, Piracicaba Dental School, State University of Campinas, Piracicaba, S~ao Paulo, Brazil. Address requests for reprints to Dr Doglas Cecchin, Universidade de Passo Fundo, Campus I, Faculdade de Odontologia, BR 285, Km 171, Bairro S~ao Jose, Caixa Postal 611, 99052-900, Passo Fundo, Rio Grande do Sul, Brazil. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2014 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2014.08.019
JOE — Volume -, Number -, - 2014
Chlorhexidine Treatment for Adhesive Durability
1
Basic Research—Technology Materials and Methods Specimen Preparation Eighty freshly extracted bovine incisors with anatomically similar root segments and fully developed apices were selected. Each tooth was decoronated below the cementoenamel junction perpendicular to the longitudinal axis. The roots were cut to a uniform length of 14 mm from the apical end. The apices of the teeth were sealed with a temporary filling material (Cavit W; Premier Dental Produtos, Rio de Janeiro, RJ, Brazil). Pulp tissue and the predentin were removed, and the root canals were enlarged by using #6 Largo burs (Maillefer, Ballaigues, Switzerland) and a #130 file (Maillefer). The apical end (1 mm) was left unprepared to prevent the apical extrusion of solutions and luting cement. Roots were rinsed with 5 mL physiological saline solution (NaCl) to remove remaining debris, and the roots were divided as follows: control group, no treatment; and experimental groups: the root canals were completely filled with 2% CHX for 30 seconds, 60 seconds, or 120 seconds. All roots were dried with paper points, and fiberglass posts relined with resin composite were cemented as described below. The Scotchbond Multi-Purpose (SBMP) total-etching adhesive system was used in half of the samples of each group, and the Clearfil SE Bond (CB) self-etching adhesive system was used in the other half. Intracanal Restoration with Composite Resin The intracanal restoration was done by using fiberglass posts no. 3 (Angelus, Londrina, PR, Brazil) relined with composite resin (B 0.5, Z250; 3M ESPE, St Paul, MN). Initially, the adhesive systems were applied into the canals according to manufacturer’s instructions. CHX was applied after 37% phosphoric acid etching and before primer application when SBMP was used. In the case of CB, CHX was applied before primer application. Both adhesive systems were light-cured for 40 seconds by using a halogen light-curing unit operated at 600 mW/cm2 (Optilux; Demetron Res Corp, Danbury, CT). Then, the walls were lubricated with a water-soluble gel (Natrosol; Drogal Pharmacy, Piracicaba, SP, Brazil). The posts were cleaned with 37% phosphoric acid for 5 seconds, washed, and dried with an air/water syringe. Next, they were silanized twice, waiting 60 seconds after each application. SBMP or CB adhesives were applied to the post surface and immediately polymerized for 20 seconds on each side. The fiber post was covered with resin composite and inserted into the canal, and resin was polymerized for 20 seconds. After removing the post, polymerization was completed outside the root canal for more than 40 seconds (2, 3, 23). After copious rinsing to remove the lubricant gel from the root canal, the root canals were dried with absorbent paper points. One additional drop of the respective adhesive system was applied onto the root canal surface, and the excess was removed with absorbent paper points before light polymerization for 40 seconds. The dual-polymerizing resin luting material Rely X ARC (3M ESPE) was mixed and injected into the prepared root canal with a Centrix
syringe (Shelton, CT) by using an appropriate needle (20-gauge). Subsequently, the fiber post relined with resin composite was covered with cement and seated inside the root canal and kept under finger pressure for 20 seconds, with the excess cement removed. The cement was lightpolymerized for 30 seconds on each surface (buccal, palatal, mesial, and distal), resulting in a 2-minute light polymerization cycle. Specimens of each group were randomly divided into 2 subgroups according to their storage, 24 hours of water storage and 12 months storage in water, which was renewed every 15 days.
Push-out Test: Specimen Preparation, Post Dislodgment, and Failure Pattern Analysis Each root was cut horizontally with a slow-speed, water-cooled diamond saw (Isomet 2000; Buehler Ltd, Lake Bluff, IL) to produce 2 slices approximately 1 mm thick. Seven slices were obtained from each root canal. The first slice was excluded. Thus, 6 slices were considered from each root canal (n = 30). The push-out test was performed by applying a load at 0.5 mm/min to the apex in the direction of the crown until the fiber post relined segment was dislodged from the root slice. Care was also taken to ensure that the contact between the punch tip and the fiber post section occurred over the most extended area possible to avoid notching effect of the punch tip on the fiber post’s surface. The bonding area was calculated as previously described (2, 3), and the bond strength values were expressed in megapascals (MPa). The fractured specimens were sputter-coated with gold in a Denton Vacuum Desk II Sputtering device (Denton Vacuum, Cherry Hill, NJ) and observed by scanning electron microscopy (JSM–5600LV; JEOL Ltd, Tokyo, Japan) to classify the failure pattern into 5 types (2, 3): (1) adhesive between the fiber post and resin cement (no cement visible around the post); (2) mixed, with resin cement covering 0%–50% of the post’s diameter; (3) mixed, with resin cement covering 50%–100% of the post’s surface; (4) adhesive between resin cement and root canal (post enveloped by resin cement); and (5) cohesive in dentin. Bond strength data were analyzed by using analysis of variance and Tukey test for post hoc comparisons (a = 0.05). The distribution of failure patterns was evaluated by c2 test (a = 0.05).
Results The means and standard deviations are presented in Table 1. The statistical analysis revealed significant differences among the groups (P < .05). Immediate groups showed similar bond strength values with or without CHX pretreatment (P > .05). After 12 months of storage, a significant decrease in the control group was observed (P < .05), whereas the use of CHX preserved the bond strength in the groups stored in water for 12 months (P < .05), irrespective of the CHX application time and adhesive system. A significant difference in predominant failure mode between groups was revealed by the c2 test (P < .001). The mixed failure types 2, 3, and 4 were the predominant failures in all groups (Fig. 1). When
TABLE 1. Bond Strength Means (MPa) and the Respective Standard Deviations Obtained in Each Experimental Condition SBMP
CB
Groups
Immediate
12 mo of storage
Immediate
12 mo of storage
NaCl (control) CHX for 30 s CHX for 60 s CHX for 120 s
5.92 1.79aA 5.89 1.37aA 6.39 1.44aA 6.29 1.42aA
4.38 1.34bB 5.76 1.31aA 6.02 1.38aA 6.06 1.55aA
6.38 0.98aA 5.66 0.47aA 6.00 1.41aA 6.01 1.54aA
4.15 1.15bB 5.41 1.16aA 5.80 1.53aA 5.81 1.09aA
Comparisons are only valid within each adhesive system. Means followed by different uppercase letters in same row and lowercase letters in same column are significantly different at 5% level.
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Basic Research—Technology
Figure 1. Failure mode distribution in the experimental groups.
CHX was applied, a decrease in adhesive failures between resin cement and root canal was observed after 12 months of storage for CB, with an increase in mixed failures. For SBMP, CHX application promoted more homogeneity in failure distribution after 12 months of storage.
Discussion Coronal restoration quality is an important factor in the success of endodontically treated teeth (24). Therefore, bonding of the post to the root dentin should aim to achieve gap-free interfaces, which is indicative of coronal seal and adequate retention (25). The results of this study showed that CHX used as pretreatment in the root dentin does not interfere with the immediate bond strength of fiber posts relined with resin composite in any of the adhesive systems used, which is supported by previous studies (2, 3). However, there was a significant decrease in the bond strength values in the control after 12 months of storage, as indicated by the degradation of the adhesive-dentin bonds over time. On the other hand, irrespective of the application time, CHX kept the bond strength in the long-term evaluation, thereby preserving the durability of adhesive-dentin bonds. Therefore, the null hypothesis was rejected. The present study confirms previous findings that resin-dentin interfaces bonded with total-etching or self-etching adhesives can degrade over time (2, 3, 5, 20–22). These findings suggest that deterioration of the resin-dentin bonds occurred mainly as a result of intrinsic factors, possibly because of activation of endogenous proteolytic enzymes such as MMPs (20–22) and cysteine cathepsins, as recently speculated (14, 26). However, the higher bond strength observed after 12 months of storage with CHX pretreatment compared with control can be explained by the CHX-related improvement in the long-term stability of hybrid layer integrity and bond strength that is based on MMPs’ inhibition (2, 3, 20–22). Carrilho et al (21) demonstrated in vivo a protective effect of CHX application against the degradation of the coronal adhesive interface that lasted for up to 14 months after the establishment of resin-dentin bonds. Although the presence of cysteine cathepsins was recently demonstrated in coronal dentin (14), these enzymes are thought to have an important role in collagen degradation (14). The effect of CHX in preserving the bond strength values may be due to inhibition of dentinal cysteine cathepsins also (26). In addition, it should be mentioned that CHX has an antimicrobial effect (15) and could interfere with collagen degradation promoted by proteolytic enzymes produced by bacteria (27). Moreover, less reduction in bond strength was observed irrespective of the application time, so one may suggest that CHX is likely to bind to collagen fibrils at a very fast rate, and JOE — Volume -, Number -, - 2014
thus even short periods of time such as 30 seconds seem to be sufficient to guarantee such binding. The long-term action of CHX can also be explained by its confinement to the adhesive interface because its removal by the dentinal fluid outflow is likely minimized by the formation of resin tags that obliterate the tubules. The adhesive monomers that envelop the collagen fibrils treated with CHX, as well as the presence of an adhesive layer on the hybrid layer, can also contribute to the preservation of CHX at the interface and prolong its inhibitory action (20, 21). Substantivity of CHX, or its ability to be retained in dentin matrices (16), could be another reason why CHX-treated dentin may form more stable hybrid layers. Previous studies investigated the effects of CHX treatment associated or not with ethanol. The ethanol wet-bonding technique and CHX in combination or not preserved the bond strength of the selfetching adhesive system (2); on the other hand, they did not preserve the bond strength of a total-etch adhesive system (3). Similar results were reported by Manso et al (28), which showed that the combined use of ethanol/1% CHX diacetate did not stabilize bond strengths after 15 months by using 2 total-etching adhesive systems. Dentin degradation caused by endogenous enzymes after 12 months of storage is reinforced by these findings. Regarding the fracture analysis, it should be emphasized that the predominant types of failure in all groups were adhesive and mixed, implying homogeneity in failure distribution. The decrease in adhesive failures indicates superior quality of the bond when CHX was applied before the use of CB. This suggests that the bond between the resin cement and root canal dentin was less affected than in the groups with no pretreatment with CHX.
Conclusion Despite the limitations of the present study, the use of CHX pretreatment could preserve the bond strength of the fiber post relined with resin composite to root dentin for 12 months, irrespective of CHX application time (30, 60, or 120 seconds) and of the adhesive system used.
Acknowledgments The authors thank Angelus for donating the fiber post and FAPERGS Foundation-Brazil for financial support through grant 2010/00100-7. The authors deny conflicts of interest related to this study. Chlorhexidine Treatment for Adhesive Durability
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