Basic Research—Technology
Comparison of Different Dentin Pretreatment Protocols on the Bond Strength of Glass Fiber Post Using Self-etching Adhesive Frederico C. Martinho, DDS, MSc, PhD, Claudio Antonio Talge Carvalho, DDS, MSc, PhD, Luciane D. Oliveira, DDS, MSc, PhD, Ana J ulia Farias de Lacerda, DDS, MSc, Ana Cl audia Carvalho Xavier, DDS, MSc, Marina Gullo Augusto, DDS, MSc, Rayssa Ferreira Zanatta, DDS, MSc, and Cesar Rogerio Pucci, DDS, MSc, PhD Abstract Introduction: This study compared the influence of different irrigants with and without ultrasound or laser irradiation on the bond strength of glass fiber posts using a self-etching adhesive in a supplementary dentin pretreatment. Methods: Ninety bovine incisor roots were divided into 3 groups according to the irrigant tested: 2% chlorhexidine (CHX) (n = 30); 2.5% sodium hypochlorite (NaOCl) (n = 30), and saline solution (control) (n = 30). Each group was randomly divided into 3 subgroups according to the supplementary dentin pretreatment: ultrasound, Nd:YAG laser, and nonsupplemented (control). A self-etching adhesive system (Futurabond DC; VOCO GmbH, Cuxhaven, Germany) was used, and the glass fiber posts were cemented with dual-cure epoxy-based luting agent (Bifix QM, VOCO GmbH). All roots were sectioned transversely, and the push-out test was performed. Failure mode analysis was also evaluated. Results: Bond strength decreased significantly after the use of 2.5% NaOCl in all root thirds (P < .05). CHX showed no difference in the mean bond strength value compared with saline solution (P > .05). The supplementary dentin pretreatment using the Nd:YAG laser or ultrasound did not improve the bond strength values for both NaOCl and CHX (P > .05). Moreover, the apical third exhibited the lowest mean bond strength values (P < .05). Analysis indicated that the predominant failure mode was the mixed type. Conclusions: Regardless of the irrigant used, the supplementary dentin pretreatment with ultrasound or laser irradiation showed no improvement in bond strength. Also, the use of NaOCl decreased the bond strength of glass fiber posts using a self-etching adhesive system, whereas CHX preserved it. (J Endod 2014;-:1–5)
Key Words Chlorhexidine, endodontics, irrigants, lasers, sodium hypochlorite
A
tooth with large structural loss usually requires the use of an intraradicular post for improving the retention of additional restoration (1). Fiber posts have led to greater advantages compared with the traditional cast metal and core systems, especially regarding mechanical properties, such as high flexural strength and elasticity modulus, similar to those of dentin (1). This minimizes the transmission of stresses to the root walls, decreasing the possibility of fractures and improving the esthetic appearance with no risk of gingival discoloration or alteration of the root surface by corrosive products, especially at the anterior region (1). Composite luting cements are used to bond the fiber post to root canal dentin because they provide mechanical retention to dentin with a hybrid layer and mechanical and/or chemical bonding to the post (2). Studies have shown that self-etching adhesive, commonly used in dentin, is capable of promoting a favorable bond strength between composites and dentin structure (3, 4). The most common failure associated with fiber posts is their debonding at the adhesive resin-dentin interface caused by difficulties regarding dentin hybridization (2, 5). Studies have shown that dentin hybridization can be affected by modifications in the dentin substrate caused by irrigants (2, 6–15), obstruction of the dentin tubules during instrumentation, post space preparation (5, 8, 11, 16, 17), and type of adhesive system (5, 18), including the limited action of light-curing units that can be achieved even in deep canals (19). Although sodium hypochlorite (NaOCl) is the most commonly used irrigant in endodontics (10, 12, 15, 20), it interferes with the organic/inorganic constituents of the dentin (10, 12, 15), which is of concern regarding the adhesion of luting agents (10, 15). On the other hand, chlorhexidine (CHX) is an alternative irrigant (2, 6, 9, 21, 22) that does not seem to interfere with the collagen present in the organic matrix of root dentin (9), thus maintaining the quality of the dentin substrate (2, 6, 9, 13, 14). It has been determined that ultrasound (23) and laser techniques (24) contribute to both disinfection and elimination of residual tissue (23, 24), and it has been argued whether they can contribute to bond strength (25–29) by altering the dentin layer (4, 5, 16, 17, 30, 31). In fact, controversies exist regarding whether
From the Department of Restorative Dentistry, Endodontic Division, S~ao Jose dos Campos Dental School, State University of S~ao Paulo, S~ao Paulo, Brazil. Address requests for reprints to Dr Frederico C. Martinho, Endodontic Division, Department of Restorative Dentistry, S~ao Jose dos Campos Dental School –State University of S~ao Paulo -UNESP, Eng Francisco Jose Longo, 777, S~ao Jose dos Campos, S~ao Paulo, Brazil, CEP 12245-000. E-mail address: Frederico.martinho@fosjc. unesp.br 0099-2399/$ - see front matter Copyright ª 2014 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2014.07.018
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Basic Research—Technology supplementary dentin pretreatment using either ultrasound or Nd:YAG lasers can improve bond strength. This study compared the influence of different irrigants with and without ultrasound or laser irradiation on the bond strength of glass fiber posts using a self-etching adhesive system in a supplementary dentin pretreatment.
Materials and Methods Specimen Preparation Ninety freshly extracted bovine incisors with anatomically similar root segments and fully developed roots were selected. Teeth were stored in 0.02% thymol solution and prepared within 1 month of extraction. Each tooth was decoronated below the cementoenamel junction perpendicularly to the longitudinal axis by using a slow-speed, water-cooled diamond saw (90 mm; Microdont, S~ao Paulo, SP, Brazil) at low rotation. The roots were cut in a uniform length of 16 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). All root canals were prepared by 1 trained operator. Pulp tissue and predentin were removed, and the root canals were enlarged up to #80 file size (Dentsply Maillefer, Ballaigues, Switzerland). The apical end (1 mm) was left unprepared to prevent apical extrusion of both solutions and luting cement. Roots were rinsed with 5 mL saline solution to remove the remaining debris, dried with paper points, and filled with gutta-percha (Dentsply Ind E Com Ltd, Petropolis, RJ, Brazil) by lateral condensation and Sealer 26 (Dentsply DeTrey, Konstanz, Germany). The specimens were kept at 37 C and relative humidity for 7 days for full cement setting. Roots were embedded vertically with acrylic resin (Jet; S~ao Paulo, SP, Brazil) using a prosthetic liner to ensure orientation in the long axis of the root. After this procedure, the filling material was removed from the root canal by using drills until leaving a remnant of 3 mm in the apex before the use of the fiberglass post system (White Post DC4; FGM, Joinville, SC, Brazil). The specimens were divided into 3 groups according to the irrigant solution: saline solution (n = 30), 2% CHX (n = 30), and 2.5% NaOCl (n = 30). Each group was randomly divided into 3 subgroups according to the supplementary dentin pretreatment: ultrasound, Nd:YAG laser, and nonsupplemented (control). The canals were irrigated with 5 mL of the irrigant solution according to the irrigants tested. For the laser subgroups, the Nd:YAG laser handset (300-D Laser; American Dental Technologies, Corpus Christi, TX) was used in the pulsed mode and high power. Irradiation was set to 100-mJ energy, a repetition rate (frequency) of 15 Hz, and a maximum power of 1.5 W. For guidance of the laser light, a helium-neon laser was used at low intensity (with a wavelength of 632.8 nm). The delivery system used an optical fiber of 0.32 mm in diameter, which was kept in contact with the tissue. The laser application was performed by introducing the optical fiber into the total length of the root canal apex to the cervical region, reaching the entire length of the root canal, for 5–7 seconds. This procedure was repeated 4 times, giving a total time of about 20 seconds at a rate of 2 mm/s. For the ultrasound subgroups, the ultrasonic device used was the CVDent 1000 (Clorovale, S~ao Jose dos Campos, SP, Brazil), with TOS-E2 tips running all root canal walls during 15 seconds, totaling 10 laps around them, with 10% of power. The canals were dried with paper points. Then, a dual-curing selfetch adhesive system (Futurabond DC; VOCO GmbH, Cuxhaven, Germany) was actively applied with a microbrush for 20 seconds, and the solvent was dispersed with air for 5 seconds. According to the manufacturer’s recommendation, the adhesive layer was not polymerized. 2
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The dual-cured radiopaque resin-based adhesive luting system (Bifix QM, VOCO GmbH) was applied by using the root canal tip of the double syringe. The cement was injected into the root from the apical end toward the entire length of the root canal, with the fiberglass post (White Post DC4, FGM) placed on the canal to ensure only a slight excess. Before luting, the fiberglass posts were cleaned with alcohol for disinfection and silanized with a silane coupling agent (Prosil, FGM). The post was held in place with firm pressure for 5–10 seconds and cured for 40 seconds by placing the light guide onto it. The specimens were kept at 37 C and relative humidity for 7 days.
Push-out Test For the bond strength test, the roots were horizontally sectioned into 3 slices of 2.0 0.1 mm in thickness by using a slow-speed saw (LabCut 1010; EXTEC-ERIOS, S~ao Paulo, SP, Brazil) with a 4 0.12 ½–inch diamond blade (EXTEC-ERIOS) under continuous water cooling. Each slice represented 1 of the root thirds: cervical, middle, and apical. The first slice of 1 mm in thickness was discarded to avoid imperfections on the adhesive interface specially caused by the oxygen presence. The other slices represented each 1 of the root thirds: cervical, middle, and apical. The exact thickness of each slice was measured with a digital caliper to an accuracy of 0.01 mm. The diameter and perimeter of the canal, in both sides of the slice, were measured for calculation of the adhesive area by using the following formula of area for the frustum of a cone: A = p(R + r)O(R r)2 + h2, where p is the constant 3.14, R is the larger radius, r the lower radius, and h the thickness of the dental slice. The push-out test was performed using a universal testing machine (DI-1000; EMIC, Curitiba, PR, Brazil) at a crosshead speed of 1.0 mm/min and a load cell of 50 kgF. Each specimen was carefully positioned over a rigid basis, with the apical face facing the punch tip with the diameter corresponding with the diameter with the set post/cement. The push-out bond strength of each specimen (MPa) was calculated as the force (N) of failure divided by the adhesive area (mm2). The means and standard deviations of bond strength were calculated, and data were analyzed by using 3-way analysis of variance followed by the post hoc Tukey test (P < .05). Failure Mode Pattern After the push-out test, the slices were analyzed with a stereomicroscope (50) to verify the failure mode, which was divided as follows: adhesive between resin cement and post, adhesive between resin cement and dentin, mixed with resin cement covering less than 50% of the post, mixed with resin cement covering more than 50% of the post, and cohesive in dentin. Illustrative pictures of the failure patterns are shown in Figure 1A–D.
Results The mean and standard deviation values of the push-out test, showing the bond strength for each group, are shown in Table 1. A significant bond strength decrease was found after the use of 2.5% NaOCl in all root thirds (P < .05). CHX showed no difference in the mean bond strength value compared with saline solution (P > .05). The supplementary dentin pretreatment using either the Nd:YAG laser or ultrasound did not improve the bond strength values regarding both NaOCl and CHX (P > .05). Moreover, the apical third exhibited the lowest mean bond strength values (P < .05). Analysis indicated that the predominant failure mode was the mixed type. However, the control group showed more mixed failures with resin cement covering less than 50% of the post, and the groups with supplementary treatments had predominance of the mixed failure with more than 50% of cement covering JOE — Volume -, Number -, - 2014
Basic Research—Technology
Figure 1. Scanning electron microscopic illustrative images of failure mode pattern: (A) adhesive failure between resin cement and dentin (100 magnification), (B) interface of dentin marked in A with 500 magnification, (C) mixed failure with resin cement covering less than 50% of the post (arrow shows cement in dentin interface) (100 magnification), and (D) interface of cement/dentin marked in C with 500 magnification.
the post. No cohesive failures were identified in dentin. The distribution of failure patterns among the groups tested is shown in Figure 2.
in post bond cementation, showing no significant difference compared with saline solution. According to Moreira et al (9), CHX does not interfere with the collagen present in the organic matrix of root dentin as it maintains the quality of the dentin substrate. Typically, results showed that the use of CHX had no negative effect on the push-out bond strength in post bond cementation (2, 6, 7, 13, 14). Moreover, previous studies have shown that CHX improves the longevity of the composite adhesive bonded to dentin by inhibiting matrix metalloproteinase in the hybrid layer, which are collagen-degrading enzymes (32). Considering the implication of irrigants on the dentin substrate, in particular, NaOCl (the most frequently used one), and the limited enamel and denting etching provided by self-etching systems along with the ability of ultrasound and the Nd:YAG laser in yielding a cleaner dentin surface and modifying the dentin layer, the present study hypothesized whether supplementary dentin pretreatment with such devices would improve the bond strength of glass fiber posts using a selfetching adhesive associated with NaOCl or CHX. Regarding the supplementary dentin pretreatment, the chemical vapor deposition (CVD) ultrasound burs were shown to be an option
Discussion The data obtained in the present study revealed that regardless of the irrigant used (NaOCl or CHX), the supplementary dentin pretreatment with ultrasound or laser irradiation showed no improvement in bond strength. Also, the use of NaOCl decreased the bond strength of glass fiber posts using a self-etching adhesive system, whereas CHX preserved it. Moreover, the failure analysis indicated that the predominant failure mode was the mixed type. Our findings are in agreement with previous studies showing that NaOCl (the most commonly used irrigant) (7, 8, 10, 12, 13, 15, 20) decreases the bond strength of glass fiber posts cemented with a composite luting agent. This causes degeneration of the dentin because of dissolution of collagen by breaking down the bonds between carbon atoms, thus disorganizing the protein primary structure (10, 15). On the other hand, CHX did not affect negatively the push-out bond strength
TABLE 1. Mean Bond Strength (MPa) and Standard Deviation from Different Root Canal Preparation Cervical third SSL
CHX
Medium third NaOCl
SSL
CHX
Apical third NaOCl
SSL
CHX
NaOCl
EF 9.4 (3.0) Aa 8.7 (3.6) Aa 6.1 (1.5) Ab 7.4 (2.9) Aa 8.1 (2.6) Aa 6.0 (0.8) Ab 6.2 (3.3) Aa* 7.6 (2.0) Aa* 4.9 (2.9) Ab* US 7.8 (2.8) ABa 9.9 (2.6) ABa 5.6 (2.5) ABb 6.9 (3.8) ABa 8.7 (2.4) ABa 5.2 (1.8) ABb 4.3 (1.1) ABa* 6.1 (1.9) ABa* 4.2 (1.3) ABb* La 7.9 (1.7) Ba 6.2 (2.4) Ba 5.1 (1.3) Bb 7.0 (1.5) Ba 7.7 (2.3) Ba 4.9 (1.9) Bb 7.1 (2.5) Ba* 6.4 (2.1) Ba* 5.1 (1.5) Bb* CHX, chlorhexidine; EF, endodontic file; La, laser; NaOCl, sodium hypochlorite; SSL, saline solution; US, ultrasound. Uppercase letters show difference between the lines, and lowercase letters shows difference between the columns (all P < .05). *Difference between root third (all P < .05).
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Figure 2. Failure mode distribution among groups tested, indicating that the predominant failure mode was the mixed type (green and red). No cohesive failures in dentin were found. Acd, adhesive between resin cement and dentin; Acp, adhesive between resin cement and post; C, control group; Coh, cohesive in dentin; CLX, chlorhexidine solution; La, laser group; M50%, mixed with resin cement covering more than 50% of the post; NAOCl, sodium hypochlorite; SS, saline solution; US, ultrasound group.
for the cleaning of root canals and they did not interfere with bond strength values. Ultrasound has gained ground in dentistry by presenting good efficiency in root canal irrigation, such as chemical disinfection, debris cleaning, and smear layer removal (23, 31, 33). Its efficiency on root dentin is assigned to the improvement in the fabrication of burs that present a diamond covered by CVD (34) and new designs, thus allowing its use inside the root canal (35). The CVD diamond burs are produced in a reactor in which methane and hydrogen gases are mixed, resulting in a unique layer of artificial diamonds without space for substrate grains (a molybdenum rod). This technique allows the diamond to have sufficient adherence on the metallic rod to support the vibration of the ultrasound (36). The smear layer removal increases the penetration of the adhesive, providing better values of bond strength (37). The Nd:YAG laser was tested as a supplementary dentin pretreatment to improve bond strength. Although it has been shown that the dentin structure can be changed according to the Nd:YAG laser energy used, causing the dentinal tubules to be sealed and the formation of fungiform projections that aid in the mechanical adhesion of the dentin (38) and thus possibly improving the bond strength, the present study showed lower bond strength values. Additionally, Nagase et al (39) showed that the use of the Nd:YAG laser negatively affects the post retention force. It might be argued that the use of the Nd:YAG laser before adhesive application might have caused the melting of the dentin, consequently sealing the dentin tubules and affecting the formation of resin tags for a proper smear layer (16, 30). Regarding post cementation, the adhesive systems are also of concern, with different generations of adhesive systems being presented in the literature (40). Particularly, the self-etching adhesive system used in this study is characterized by acid etching, primer, and adhesive stages occurring at the same time. Such an adhesive system modifies the smear layer, which is essential for the formation of a quality hybrid layer. It has been reported that a self-etching adhesive system is capable of performing etching of the dentin (3). The epoxy-based resin cement used (Bifix QM) is a dual-cure luting agent, which requires the previous use of an adhesive system. The lower values found in the apical region are usually reported in the literature; thus, they are associated with the difficulties in the adhesion protocol, such as the many steps for dentin hybridization and the type of resin cement used (6, 40–42). Also, there is always a risk of the presence of gutta-percha and endodontic cement waste, which weakens the adhesion (43). The lack of light fully reaching 4
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the interior of the root canals is also a factor that influences the bond strength of fiberglass posts because this affects the proper cure of the resin cements (44, 45). Fracture analysis showed a predominance of mixed fractures with less than 50% of cement around the post for the control groups. For ultrasound and laser groups, the adhesive failures between resin cement and dentin and mixed failures with more than 50% of cement around the post summed more than 50% of the failures types, indicating that the interface between resin cement and dentin was compromised. Overall, the present study has revealed that regardless of the irrigant used, the supplementary dentin pretreatment with ultrasound or laser irradiation showed no improvement in bond strength. Also, the use of NaOCl decreased the bond strength of glass fiber posts using a self-etching adhesive system, whereas CHX preserved it.
Acknowledgments Supported by the Brazilian agencies S~ao Paulo Research Foundation (grant no. 2012/19536-5), FAPERJ (grant no. E-26/110.429/ 2014), Conselho Nacional de Desenvolvimento Cientıfico e Tecnologico (grant no. 23038.009469/2012-24), and Coordenac¸~ao de Aperfeic¸oamento de Pessoal de Nıvel Superior. The authors deny any conflicts of interest related to this study.
References 1. Schwartz RS, Robbins JW. Post placement and restoration of endodontically treated teeth: a literature review. J Endod 2004;30:289–301. 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 composite to the root canal. J Endod 2011;37:678–83. 3. Aziz TM, Anwar MN, El-Askary FS. Push-out bond strength of fiber posts to root canal dentin using a one-step self-etching adhesive: the effect of solvent removal and light-curing methods. J Adhes Dent 2014;16:79–86. 4. Oliveira SS, Pugach MK, Hilton JF, et al. The influence of the dentin smear layer on adhesion: a self-etching primer vs. a total-etch system. Dent Mater 2003;19:758–67. 5. Pashley DH. Smear layer: physiological considerations. Oper Dent Suppl 1984;3: 13–29. 6. Cecchin D, Giacomin M, Farina AP, et al. Effect of chlorhexidine and ethanol on push-out bond strength of fiber posts under cyclic loading. J Adhes Dent 2014; 16:87–92. 7. 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.
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Basic Research—Technology 8. Ari H, Erdemir A, Belli S. Evaluation of the effect of endodontic irrigation solutions on the microhardness and the roughness of root canal dentin. J Endod 2004;30: 792–5. 9. 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. 10. Moreira DM, de Andrade Feitosa JP, Line SR, Zaia AA. Effects of reducing agents on birefringence dentin collagen after use of different endodontic auxiliary chemical substances. J Endod 2011;37:1406–11. 11. Gu XH, Mao CY, Kern M. Effect of different irrigation on smear layer removal after post space preparation. J Endod 2009;35:583–6. 12. 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. 13. Lindblad RM, Lassila LV, Salo V, et al. Effect of chlorhexidine on initial adhesion of fiber-reinforced post to root canal. J Dent 2010;38:796–801. 14. Leitune VC, Collares FM, Werner Samuel SM. Influence of chlorhexidine application at longitudinal push-out bond strength of fiber posts. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2010;110:e77–81. 15. Morris MD, Lee KW, Agee KA, et al. Effects of sodium hypochlorite and RC-prep on bond strengths of resin cement to endodontic surfaces. J Endod 2001;27: 753–7. 16. Takeda FH, Harashima T, Kimura Y, Matsumoto K. A comparative study of the removal of smear layer by three endodontic irrigants and two types of laser. Int Endod J 1999;32:32–9. 17. Bowen RL, Eick JD, Henderson DA, Anderson DW. Smear layer: removal and bonding considerations. Oper Dent Suppl 1984;3:30–4. 18. Ermis RB, De Munck J, Cardoso MV, et al. Bond strength of self-etch adhesives to dentin prepared with three different diamond burs. Dent Mater 2008;24: 978–85. 19. Zorba YO, Erdemir A, Ahmetoglu F, Yoldas O. Effect of different light sources in combination with a light-transmitting post on the degree of conversion of resin composite at different depths of simulated root canals. Dent Traumatol 2011;27:195–8. 20. Zehnder M. Root canal irrigants. J Endod 2006;32:389–98. 21. 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. 22. Carrilho MR, Carvalho RM, Sousa EN, et al. Substantivity of chlorhexidine to human dentin. Dent Mater 2010;26:779–85. 23. Paiva SS, Siqueira JF Jr, Rocas IN, et al. Molecular microbiological evaluation of passive ultrasonic activation as a supplementary disinfecting step: a clinical study. J Endod 2013;39:190–4. 24. Cheng X, Guan S, Lu H, et al. Evaluation of the bactericidal effect of Nd:YAG, Er:YAG, Er,Cr:YSGG laser radiation, and antimicrobial photodynamic therapy (aPDT) in experimentally infected root canals. Lasers Surg Med 2012;44:824–31. 25. Borges AB, da Silva MA, Borges AL, et al. Microshear bond strength of self-etching bonding systems to ultrasound diamond bur-prepared dentin. J Adhes Dent 2011; 13:433–8. 26. da Silva MA, Di Nicolo R, Barcellos DC, et al. Influence of CVD diamond tips and Er:YAG laser irradiation on bonding of different adhesive systems to dentin. J Contemp Dent Pract 2013;14:14–20.
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27. Sousa-Neto MD, Silva Coelho FI, Marchesan MA, et al. Ex vivo study of the adhesion of an epoxy-based sealer to human dentine submitted to irradiation with Er : YAG and Nd : YAG lasers. Int Endod J 2005;38:866–70. 28. Tuncdemir AR, Yildirim C, Ozcan E, Polat S. The effect of a diode laser and traditional irrigants on the bond strength of self-adhesive cement. J Adv Prosthodont 2013;5:457–63. 29. Das M, Kumar GA, Ramesh S, et al. An in vitro evaluation of microtensile bond strength of resin-based sealer with dentin treated with diode and Nd:YAG laser. J Contemp Dent Pract 2013;14:183–7. 30. Brugnera A Jr, Zanin F, Barbin EL, et al. Effects of Er:YAG and Nd:YAG laser irradiation on radicular dentine permeability using different irrigating solutions. Lasers Surg Med 2003;33:256–9. 31. Niu LN, Luo XJ, Li GH, et al. Effects of different sonic activation protocols on debridement efficacy in teeth with single-rooted canals. J Dent 2014;42:1001–9. 32. Mazzoni A, Scaffa P, Carrilho M, et al. Effects of etch-and-rinse and self-etch adhesives on dentin MMP-2 and MMP-9. J Dent Res 2013;92:82–6. 33. van der Sluis LW, Versluis M, Wu MK, Wesselink PR. Passive ultrasonic irrigation of the root canal: a review of the literature. Int Endod J 2007;40:415–26. 34. Carvalho CA, Fagundes TC, Barata TJ, et al. The use of CVD diamond burs for ultraconservative cavity preparations: a report of two cases. J Esthet Restor Dent 2007;19: 19–28. discussion 9. 35. Yip HK, Samaranayake LP. Caries removal techniques and instrumentation: a review. Clin Oral Investig 1998;2:148–54. 36. de Vasconcellos BT, Thompson JY, de Paula Macedo MR, et al. Ultrasonic cavity preparation using CVD coated diamond bur: a case report. Eur J Dent 2013;7: 127–32. 37. Phrukkanon S, Burrow MF, Hartley PG, Tyas MJ. The influence of the modification of etched bovine dentin on bond strengths. Dent Mater 2000;16:255–65. 38. Goncalves SE, de Araujo MA, Damiao AJ. Dentin bond strength: influence of laser irradiation, acid etching, and hypermineralization. J Clin Laser Med Surg 1999; 17:77–85. 39. Nagase DY, de Freitas PM, Morimoto S, et al. Influence of laser irradiation on fiber post retention. Lasers Med Sci 2011;26:377–80. 40. Scotti N, Rota R, Scansetti M, et al. Fiber post adhesion to radicular dentin: the use of acid etching prior to a one-step self-etching adhesive. Quintessence Int 2012;43: 615–23. 41. Soares CJ, Valdivia AD, da Silva GR, et al. Longitudinal clinical evaluation of post systems: a literature review. Braz Dent J 2012;23:135–740. 42. Ozcan E, Cetin AR, Tuncdemir AR, Ulker M. The effect of luting cement thicknesses on the push-out bond strength of the fiber posts. Acta Odontol Scand 2013;71: 703–9. 43. Yoldas O, Alacam T. Microhardness of composites in simulated root canals cured with light transmitting posts and glass-fiber reinforced composite posts. J Endod 2005;31:104–6. 44. Radovic I, Corciolani G, Magni E, et al. Light transmission through fiber post: the effect on adhesion, elastic modulus and hardness of dual-cure resin cement. Dent Mater 2009;25:837–44. 45. Zorba YO, Erdemir A, Turkyilmaz A, Eldeniz AU. Effects of different curing units and luting agents on push-out bond strength of translucent posts. J Endod 2010;36: 1521–5.
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Comparison of Different Dentin Pretreatment Protocols on the Bond Strength of Glass Fiber Post Using Self-etching Adhesive Frederico C. Martinho, DDS, MSc, PhD, Claudio Antonio Talge Carvalho, DDS, MSc, PhD, Luciane D. Oliveira, DDS, MSc, PhD, Ana J ulia Farias de Lacerda, DDS, MSc, Ana Cl audia Carvalho Xavier, DDS, MSc, Marina Gullo Augusto, DDS, MSc, Rayssa Ferreira Zanatta, DDS, MSc, and Cesar Rogerio Pucci, DDS, MSc, PhD Abstract Introduction: This study compared the influence of different irrigants with and without ultrasound or laser irradiation on the bond strength of glass fiber posts using a self-etching adhesive in a supplementary dentin pretreatment. Methods: Ninety bovine incisor roots were divided into 3 groups according to the irrigant tested: 2% chlorhexidine (CHX) (n = 30); 2.5% sodium hypochlorite (NaOCl) (n = 30), and saline solution (control) (n = 30). Each group was randomly divided into 3 subgroups according to the supplementary dentin pretreatment: ultrasound, Nd:YAG laser, and nonsupplemented (control). A self-etching adhesive system (Futurabond DC; VOCO GmbH, Cuxhaven, Germany) was used, and the glass fiber posts were cemented with dual-cure epoxy-based luting agent (Bifix QM, VOCO GmbH). All roots were sectioned transversely, and the push-out test was performed. Failure mode analysis was also evaluated. Results: Bond strength decreased significantly after the use of 2.5% NaOCl in all root thirds (P < .05). CHX showed no difference in the mean bond strength value compared with saline solution (P > .05). The supplementary dentin pretreatment using the Nd:YAG laser or ultrasound did not improve the bond strength values for both NaOCl and CHX (P > .05). Moreover, the apical third exhibited the lowest mean bond strength values (P < .05). Analysis indicated that the predominant failure mode was the mixed type. Conclusions: Regardless of the irrigant used, the supplementary dentin pretreatment with ultrasound or laser irradiation showed no improvement in bond strength. Also, the use of NaOCl decreased the bond strength of glass fiber posts using a self-etching adhesive system, whereas CHX preserved it. (J Endod 2014;-:1–5)
Key Words Chlorhexidine, endodontics, irrigants, lasers, sodium hypochlorite
A
tooth with large structural loss usually requires the use of an intraradicular post for improving the retention of additional restoration (1). Fiber posts have led to greater advantages compared with the traditional cast metal and core systems, especially regarding mechanical properties, such as high flexural strength and elasticity modulus, similar to those of dentin (1). This minimizes the transmission of stresses to the root walls, decreasing the possibility of fractures and improving the esthetic appearance with no risk of gingival discoloration or alteration of the root surface by corrosive products, especially at the anterior region (1). Composite luting cements are used to bond the fiber post to root canal dentin because they provide mechanical retention to dentin with a hybrid layer and mechanical and/or chemical bonding to the post (2). Studies have shown that self-etching adhesive, commonly used in dentin, is capable of promoting a favorable bond strength between composites and dentin structure (3, 4). The most common failure associated with fiber posts is their debonding at the adhesive resin-dentin interface caused by difficulties regarding dentin hybridization (2, 5). Studies have shown that dentin hybridization can be affected by modifications in the dentin substrate caused by irrigants (2, 6–15), obstruction of the dentin tubules during instrumentation, post space preparation (5, 8, 11, 16, 17), and type of adhesive system (5, 18), including the limited action of light-curing units that can be achieved even in deep canals (19). Although sodium hypochlorite (NaOCl) is the most commonly used irrigant in endodontics (10, 12, 15, 20), it interferes with the organic/inorganic constituents of the dentin (10, 12, 15), which is of concern regarding the adhesion of luting agents (10, 15). On the other hand, chlorhexidine (CHX) is an alternative irrigant (2, 6, 9, 21, 22) that does not seem to interfere with the collagen present in the organic matrix of root dentin (9), thus maintaining the quality of the dentin substrate (2, 6, 9, 13, 14). It has been determined that ultrasound (23) and laser techniques (24) contribute to both disinfection and elimination of residual tissue (23, 24), and it has been argued whether they can contribute to bond strength (25–29) by altering the dentin layer (4, 5, 16, 17, 30, 31). In fact, controversies exist regarding whether
From the Department of Restorative Dentistry, Endodontic Division, S~ao Jose dos Campos Dental School, State University of S~ao Paulo, S~ao Paulo, Brazil. Address requests for reprints to Dr Frederico C. Martinho, Endodontic Division, Department of Restorative Dentistry, S~ao Jose dos Campos Dental School –State University of S~ao Paulo -UNESP, Eng Francisco Jose Longo, 777, S~ao Jose dos Campos, S~ao Paulo, Brazil, CEP 12245-000. E-mail address: Frederico.martinho@fosjc. unesp.br 0099-2399/$ - see front matter Copyright ª 2014 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2014.07.018
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Basic Research—Technology supplementary dentin pretreatment using either ultrasound or Nd:YAG lasers can improve bond strength. This study compared the influence of different irrigants with and without ultrasound or laser irradiation on the bond strength of glass fiber posts using a self-etching adhesive system in a supplementary dentin pretreatment.
Materials and Methods Specimen Preparation Ninety freshly extracted bovine incisors with anatomically similar root segments and fully developed roots were selected. Teeth were stored in 0.02% thymol solution and prepared within 1 month of extraction. Each tooth was decoronated below the cementoenamel junction perpendicularly to the longitudinal axis by using a slow-speed, water-cooled diamond saw (90 mm; Microdont, S~ao Paulo, SP, Brazil) at low rotation. The roots were cut in a uniform length of 16 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). All root canals were prepared by 1 trained operator. Pulp tissue and predentin were removed, and the root canals were enlarged up to #80 file size (Dentsply Maillefer, Ballaigues, Switzerland). The apical end (1 mm) was left unprepared to prevent apical extrusion of both solutions and luting cement. Roots were rinsed with 5 mL saline solution to remove the remaining debris, dried with paper points, and filled with gutta-percha (Dentsply Ind E Com Ltd, Petropolis, RJ, Brazil) by lateral condensation and Sealer 26 (Dentsply DeTrey, Konstanz, Germany). The specimens were kept at 37 C and relative humidity for 7 days for full cement setting. Roots were embedded vertically with acrylic resin (Jet; S~ao Paulo, SP, Brazil) using a prosthetic liner to ensure orientation in the long axis of the root. After this procedure, the filling material was removed from the root canal by using drills until leaving a remnant of 3 mm in the apex before the use of the fiberglass post system (White Post DC4; FGM, Joinville, SC, Brazil). The specimens were divided into 3 groups according to the irrigant solution: saline solution (n = 30), 2% CHX (n = 30), and 2.5% NaOCl (n = 30). Each group was randomly divided into 3 subgroups according to the supplementary dentin pretreatment: ultrasound, Nd:YAG laser, and nonsupplemented (control). The canals were irrigated with 5 mL of the irrigant solution according to the irrigants tested. For the laser subgroups, the Nd:YAG laser handset (300-D Laser; American Dental Technologies, Corpus Christi, TX) was used in the pulsed mode and high power. Irradiation was set to 100-mJ energy, a repetition rate (frequency) of 15 Hz, and a maximum power of 1.5 W. For guidance of the laser light, a helium-neon laser was used at low intensity (with a wavelength of 632.8 nm). The delivery system used an optical fiber of 0.32 mm in diameter, which was kept in contact with the tissue. The laser application was performed by introducing the optical fiber into the total length of the root canal apex to the cervical region, reaching the entire length of the root canal, for 5–7 seconds. This procedure was repeated 4 times, giving a total time of about 20 seconds at a rate of 2 mm/s. For the ultrasound subgroups, the ultrasonic device used was the CVDent 1000 (Clorovale, S~ao Jose dos Campos, SP, Brazil), with TOS-E2 tips running all root canal walls during 15 seconds, totaling 10 laps around them, with 10% of power. The canals were dried with paper points. Then, a dual-curing selfetch adhesive system (Futurabond DC; VOCO GmbH, Cuxhaven, Germany) was actively applied with a microbrush for 20 seconds, and the solvent was dispersed with air for 5 seconds. According to the manufacturer’s recommendation, the adhesive layer was not polymerized. 2
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The dual-cured radiopaque resin-based adhesive luting system (Bifix QM, VOCO GmbH) was applied by using the root canal tip of the double syringe. The cement was injected into the root from the apical end toward the entire length of the root canal, with the fiberglass post (White Post DC4, FGM) placed on the canal to ensure only a slight excess. Before luting, the fiberglass posts were cleaned with alcohol for disinfection and silanized with a silane coupling agent (Prosil, FGM). The post was held in place with firm pressure for 5–10 seconds and cured for 40 seconds by placing the light guide onto it. The specimens were kept at 37 C and relative humidity for 7 days.
Push-out Test For the bond strength test, the roots were horizontally sectioned into 3 slices of 2.0 0.1 mm in thickness by using a slow-speed saw (LabCut 1010; EXTEC-ERIOS, S~ao Paulo, SP, Brazil) with a 4 0.12 ½–inch diamond blade (EXTEC-ERIOS) under continuous water cooling. Each slice represented 1 of the root thirds: cervical, middle, and apical. The first slice of 1 mm in thickness was discarded to avoid imperfections on the adhesive interface specially caused by the oxygen presence. The other slices represented each 1 of the root thirds: cervical, middle, and apical. The exact thickness of each slice was measured with a digital caliper to an accuracy of 0.01 mm. The diameter and perimeter of the canal, in both sides of the slice, were measured for calculation of the adhesive area by using the following formula of area for the frustum of a cone: A = p(R + r)O(R r)2 + h2, where p is the constant 3.14, R is the larger radius, r the lower radius, and h the thickness of the dental slice. The push-out test was performed using a universal testing machine (DI-1000; EMIC, Curitiba, PR, Brazil) at a crosshead speed of 1.0 mm/min and a load cell of 50 kgF. Each specimen was carefully positioned over a rigid basis, with the apical face facing the punch tip with the diameter corresponding with the diameter with the set post/cement. The push-out bond strength of each specimen (MPa) was calculated as the force (N) of failure divided by the adhesive area (mm2). The means and standard deviations of bond strength were calculated, and data were analyzed by using 3-way analysis of variance followed by the post hoc Tukey test (P < .05). Failure Mode Pattern After the push-out test, the slices were analyzed with a stereomicroscope (50) to verify the failure mode, which was divided as follows: adhesive between resin cement and post, adhesive between resin cement and dentin, mixed with resin cement covering less than 50% of the post, mixed with resin cement covering more than 50% of the post, and cohesive in dentin. Illustrative pictures of the failure patterns are shown in Figure 1A–D.
Results The mean and standard deviation values of the push-out test, showing the bond strength for each group, are shown in Table 1. A significant bond strength decrease was found after the use of 2.5% NaOCl in all root thirds (P < .05). CHX showed no difference in the mean bond strength value compared with saline solution (P > .05). The supplementary dentin pretreatment using either the Nd:YAG laser or ultrasound did not improve the bond strength values regarding both NaOCl and CHX (P > .05). Moreover, the apical third exhibited the lowest mean bond strength values (P < .05). Analysis indicated that the predominant failure mode was the mixed type. However, the control group showed more mixed failures with resin cement covering less than 50% of the post, and the groups with supplementary treatments had predominance of the mixed failure with more than 50% of cement covering JOE — Volume -, Number -, - 2014
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Figure 1. Scanning electron microscopic illustrative images of failure mode pattern: (A) adhesive failure between resin cement and dentin (100 magnification), (B) interface of dentin marked in A with 500 magnification, (C) mixed failure with resin cement covering less than 50% of the post (arrow shows cement in dentin interface) (100 magnification), and (D) interface of cement/dentin marked in C with 500 magnification.
the post. No cohesive failures were identified in dentin. The distribution of failure patterns among the groups tested is shown in Figure 2.
in post bond cementation, showing no significant difference compared with saline solution. According to Moreira et al (9), CHX does not interfere with the collagen present in the organic matrix of root dentin as it maintains the quality of the dentin substrate. Typically, results showed that the use of CHX had no negative effect on the push-out bond strength in post bond cementation (2, 6, 7, 13, 14). Moreover, previous studies have shown that CHX improves the longevity of the composite adhesive bonded to dentin by inhibiting matrix metalloproteinase in the hybrid layer, which are collagen-degrading enzymes (32). Considering the implication of irrigants on the dentin substrate, in particular, NaOCl (the most frequently used one), and the limited enamel and denting etching provided by self-etching systems along with the ability of ultrasound and the Nd:YAG laser in yielding a cleaner dentin surface and modifying the dentin layer, the present study hypothesized whether supplementary dentin pretreatment with such devices would improve the bond strength of glass fiber posts using a selfetching adhesive associated with NaOCl or CHX. Regarding the supplementary dentin pretreatment, the chemical vapor deposition (CVD) ultrasound burs were shown to be an option
Discussion The data obtained in the present study revealed that regardless of the irrigant used (NaOCl or CHX), the supplementary dentin pretreatment with ultrasound or laser irradiation showed no improvement in bond strength. Also, the use of NaOCl decreased the bond strength of glass fiber posts using a self-etching adhesive system, whereas CHX preserved it. Moreover, the failure analysis indicated that the predominant failure mode was the mixed type. Our findings are in agreement with previous studies showing that NaOCl (the most commonly used irrigant) (7, 8, 10, 12, 13, 15, 20) decreases the bond strength of glass fiber posts cemented with a composite luting agent. This causes degeneration of the dentin because of dissolution of collagen by breaking down the bonds between carbon atoms, thus disorganizing the protein primary structure (10, 15). On the other hand, CHX did not affect negatively the push-out bond strength
TABLE 1. Mean Bond Strength (MPa) and Standard Deviation from Different Root Canal Preparation Cervical third SSL
CHX
Medium third NaOCl
SSL
CHX
Apical third NaOCl
SSL
CHX
NaOCl
EF 9.4 (3.0) Aa 8.7 (3.6) Aa 6.1 (1.5) Ab 7.4 (2.9) Aa 8.1 (2.6) Aa 6.0 (0.8) Ab 6.2 (3.3) Aa* 7.6 (2.0) Aa* 4.9 (2.9) Ab* US 7.8 (2.8) ABa 9.9 (2.6) ABa 5.6 (2.5) ABb 6.9 (3.8) ABa 8.7 (2.4) ABa 5.2 (1.8) ABb 4.3 (1.1) ABa* 6.1 (1.9) ABa* 4.2 (1.3) ABb* La 7.9 (1.7) Ba 6.2 (2.4) Ba 5.1 (1.3) Bb 7.0 (1.5) Ba 7.7 (2.3) Ba 4.9 (1.9) Bb 7.1 (2.5) Ba* 6.4 (2.1) Ba* 5.1 (1.5) Bb* CHX, chlorhexidine; EF, endodontic file; La, laser; NaOCl, sodium hypochlorite; SSL, saline solution; US, ultrasound. Uppercase letters show difference between the lines, and lowercase letters shows difference between the columns (all P < .05). *Difference between root third (all P < .05).
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Figure 2. Failure mode distribution among groups tested, indicating that the predominant failure mode was the mixed type (green and red). No cohesive failures in dentin were found. Acd, adhesive between resin cement and dentin; Acp, adhesive between resin cement and post; C, control group; Coh, cohesive in dentin; CLX, chlorhexidine solution; La, laser group; M50%, mixed with resin cement covering more than 50% of the post; NAOCl, sodium hypochlorite; SS, saline solution; US, ultrasound group.
for the cleaning of root canals and they did not interfere with bond strength values. Ultrasound has gained ground in dentistry by presenting good efficiency in root canal irrigation, such as chemical disinfection, debris cleaning, and smear layer removal (23, 31, 33). Its efficiency on root dentin is assigned to the improvement in the fabrication of burs that present a diamond covered by CVD (34) and new designs, thus allowing its use inside the root canal (35). The CVD diamond burs are produced in a reactor in which methane and hydrogen gases are mixed, resulting in a unique layer of artificial diamonds without space for substrate grains (a molybdenum rod). This technique allows the diamond to have sufficient adherence on the metallic rod to support the vibration of the ultrasound (36). The smear layer removal increases the penetration of the adhesive, providing better values of bond strength (37). The Nd:YAG laser was tested as a supplementary dentin pretreatment to improve bond strength. Although it has been shown that the dentin structure can be changed according to the Nd:YAG laser energy used, causing the dentinal tubules to be sealed and the formation of fungiform projections that aid in the mechanical adhesion of the dentin (38) and thus possibly improving the bond strength, the present study showed lower bond strength values. Additionally, Nagase et al (39) showed that the use of the Nd:YAG laser negatively affects the post retention force. It might be argued that the use of the Nd:YAG laser before adhesive application might have caused the melting of the dentin, consequently sealing the dentin tubules and affecting the formation of resin tags for a proper smear layer (16, 30). Regarding post cementation, the adhesive systems are also of concern, with different generations of adhesive systems being presented in the literature (40). Particularly, the self-etching adhesive system used in this study is characterized by acid etching, primer, and adhesive stages occurring at the same time. Such an adhesive system modifies the smear layer, which is essential for the formation of a quality hybrid layer. It has been reported that a self-etching adhesive system is capable of performing etching of the dentin (3). The epoxy-based resin cement used (Bifix QM) is a dual-cure luting agent, which requires the previous use of an adhesive system. The lower values found in the apical region are usually reported in the literature; thus, they are associated with the difficulties in the adhesion protocol, such as the many steps for dentin hybridization and the type of resin cement used (6, 40–42). Also, there is always a risk of the presence of gutta-percha and endodontic cement waste, which weakens the adhesion (43). The lack of light fully reaching 4
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the interior of the root canals is also a factor that influences the bond strength of fiberglass posts because this affects the proper cure of the resin cements (44, 45). Fracture analysis showed a predominance of mixed fractures with less than 50% of cement around the post for the control groups. For ultrasound and laser groups, the adhesive failures between resin cement and dentin and mixed failures with more than 50% of cement around the post summed more than 50% of the failures types, indicating that the interface between resin cement and dentin was compromised. Overall, the present study has revealed that regardless of the irrigant used, the supplementary dentin pretreatment with ultrasound or laser irradiation showed no improvement in bond strength. Also, the use of NaOCl decreased the bond strength of glass fiber posts using a self-etching adhesive system, whereas CHX preserved it.
Acknowledgments Supported by the Brazilian agencies S~ao Paulo Research Foundation (grant no. 2012/19536-5), FAPERJ (grant no. E-26/110.429/ 2014), Conselho Nacional de Desenvolvimento Cientıfico e Tecnologico (grant no. 23038.009469/2012-24), and Coordenac¸~ao de Aperfeic¸oamento de Pessoal de Nıvel Superior. The authors deny any conflicts of interest related to this study.
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