- Email: [email protected]
Ethanol application protocols and microtensile dentin bond strength of hydrophobic adhesive
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H O S T E D BY
ScienceDirect Tanta Dental Journal 11 (2014) 206e212 www.elsevier.com/locate/tdj
Ethanol application protocols and microtensile dentin bond strength of hydrophobic adhesive M.K. Ayar Department of Restorative Dentistry, Faculty of Dentistry, Karadeniz Technical University, Trabzon, Turkey Received 19 October 2014; revised 15 November 2014; accepted 17 November 2014 Available online 16 December 2014
Abstract Purpose: Available knowledge on whether complicated and time-consuming ethanol application protocols are required for effective bonds between hydrophobic resin adhesive and dentin is inconclusive. Therefore, aim of this study is to evaluate effects of different ethanol application protocols on microtensile bond strength of hydrophobic adhesive to bovine dentin. Materials and methods: Bovine incisors were randomly divided into four groups (n ¼ 3). Standardized dentin cavities were acidetched with 37% H3PO4 and rinsed with water. Single Bond 2 applied to dentin with water-wet bonding was used as a control group. The rest groups had their dentine surface dehydrated according to different ethanol application protocols: Group 1 (Full-ChemicalDehydration-Protocol) ¼ 50%, 70%, 80%, 95% and 3 100%, 30 s for each ethanol application; Group 2 (Simplified-ChemicalDehydration-Protocol I) ¼ 100% ethanol applied for 60 s at one step and Group 3 (Simplified-Chemical-Dehydration-Protocol II) ¼ 100% ethanol applied for only 20 s at one step, respectively. After ethanol applications, a primer (50% HelioBond þ 50% absolute ethanol) was used, followed by the neat HelioBond application. Resin composite build-ups were then done. Results: Group 1 showed higher bond strength (27.46 ± 8.10). Group 1 showed bond strength statistically similar to Group 2 (22.75 ± 8.02) and Group 3 (25.16 ± 7.23) and statistically different to control group (34.06 ± 5.8). Conclusion: Results indicated that different ethanol application protocols may not affect bond strength of hydrophobic adhesive to dentin. However, slight statistical difference existed between control and full chemical dehydration protocol. © 2014, Hosting by Elsevier B.V. on behalf of the Faculty of Dentistry, Tanta University.
Keywords: Ethanol-wet bonding; Bovine dentin; Microtensile bond strength test; Hydrophobic adhesive
1. Introduction The use of increasing concentrations of hydrophilic monomers in current dentin adhesives raises a concern on if such adhesives have become too hydrophilic [1]. Combination of hydrophilic resin monomers with
E-mail addresses: [email protected], [email protected]. Peer review under the responsibility of the Faculty of Dentistry, Tanta University.
adhesive resins results in increases water sorption, and decreases in mechanical properties of these resin adhesives [2]. Therefore, the use of hydrophobic resins for dentin bonding would avoid these problems and increase durability of resin-dentin bonding in theory [3]. Recently, a new concept of wet bonding which is called ethanol-wet bonding was introduced to dental research community [4]. The ultimate aim of this concept is that providing dentin bonding techniques for increasing resin-dentin bond durability through (i)
http://dx.doi.org/10.1016/j.tdj.2014.11.003 1687-8574/© 2014, Hosting by Elsevier B.V. on behalf of the Faculty of Dentistry, Tanta University.
M.K. Ayar / Tanta Dental Journal 11 (2014) 206e212
improving quality of resultant dentin hybrid layer through efficient removal of residue water from interfibrillar spaces without causing significant collapse of collagen matrices by ethanol-dehydration, and (ii) rendering hydrophilic water-saturated dentin into hydrophobic ethanol-saturated dentin to coax applying more hydrophobic adhesive resin for dentin bonding [4e7,10]. According to ethanol wet bonding concept, water exists within interfibrillar spaces would be removed through an ethanol dehydration/saturation which is an individual application and an extra step [6]. As a result, improving resin e collagen ratio within hybrid layer would be achieved theoretically [8]. Although “ethanol-wet-bonding” looks promising [3,7,9e13], it involves an extra step of replacing residue water with ethanol application. Thus, more evidence is needed to justify this extra step [10]. However, it seems that there is no consensus regarding to how ethanol application for dehydration/saturation should be performed when ethanol-wet bonding would be used for dentin bonding under clinical conditions. Consequently, a vast of variability in ethanol application protocols in terms of concentration of ethanol used, number of application step and time of ethanol dehydration/saturation prior to application of hydrophobic adhesive to dentin exist in the literature. For instance, Nishitani et al., applied 100% ethanol for 15 s onto acidetched water-wet dentin surface to convert it to ethanolsaturated dentin surfaces prior to hydrophobic adhesive resin application [5]. Similarly, Sauro et al. [7], and Hosaka et al. [10], deployed ethanol dehydration protocol as a form of delivering 100% ethanol for 60 s in their studies, respectively. On another hand, Sadek et al., suggests that simplified ethanol dehydration techniques would not be efficient in water decontamination of dentin hybrid layer, thus yielding lower bond strengths [6]. Sadek et al., suggest using ethanol application protocol which is called “full chemical dehydration protocol” involves an application of series of increasing ethanol concentrations (50%, 70%, 80%, 95% and three times 100% ethanol for each 30 s, yielding total of 210 s) [6]. Despite that, all aforementioned researchers who were deployed simplified chemical dehydration protocols, achieved relatively high dentin bond strengths with hydrophobic adhesives. Therefore, it seems that a discrepancy regarding to ethanol application protocols of ethanol-wet bonding concept exists in the literature. Consequently, in the present study, effects of three different ethanol application protocols on microtensile bond strength of hydrophobic adhesive to bovine dentin was determined. The null
207
hypothesis tested was that there are no differences among the microtensile bond strengths of the hydrophobic dentin adhesive deployed using three different ethanol application protocols and those obtained from commercially available hydrophilic etch-and-rinse adhesives. 2. Materials and methods 2.1. Study design
Twelve bovine incisors from 2- to 3-yr-old animals were used in the present study. All labial surfaces were ground and flattened under water with a 180 grit SiC paper. On each surface, one standardized cavity was prepared to 8 mm width, 8 mm height and 2 mm depth by means of coarse cylindrical diamond burs.1 Prepared teeth were randomly divided into four groups (N ¼ 3) as following: Group 1 (Full Chemical Dehydration Protocol): Each acid-etched, wet dentin surface was treated with a series of increasing ethanol concentrations (50, 70, 80, 95, and 100% for three times for 30 s each) at seven steps. The ethanol/water mixture or absolute ethanol was dispensed from transfer pipettes to cover the entire dentin surface, replacing the 100% water or preceding ethanol solution that saturated the demineralized collagen matrix. This procedure was meticulously performed to ensure that the dentin surface was always immersed in a liquid phase by keeping it visibly moist prior to the application of subsequent solutions with higher ethanol concentration. Group 2 (Simplified Chemical Dehydration Protocol I): Each acid-etched, wet dentin surface was treated with absolute ethanol for 60 s at one step. Group 3 (Simplified Chemical Dehydration Protocol II): Each acid-etched, wet dentin surface was treated with only absolute ethanol for 15 s at one step. Group 4 (Conventional water-wet bonding technique þ Single Bond; Control): A commercially available hydrophilic etch-and-rinse adhesive (Single Bond 2) was applied to visibly moist, water-saturated demineralized dentin according to the manufacturers' instructions. 2.2. Hydrophobic adhesive
HelioBond2 which is a basically commercially available enamel bonding agent was used as a hydrophobic etch-and-rinse adhesive for dentin in the 1 2
Microdont, Sao Paulo, Brazil. Ivaclar, Vivadent, Schaan, Liechtenstein.
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Table 1 Chemical compositions of the materials used in the present study. HelioBond (Ivoclar, Vivadent, Schaan, Liechtenstein)Bis-GMA, TEGDMA, catalysts, stabilizers Single Bond 2 (3M ESPE, St Paul MN, USA) Dimethacrylates, HEMA, polyalkenoid acid copolymer, fillers, ethanol, water, photoinitiator Valux Plus (3M ESPE, St Paul MN, USA) TEDGMA, Bis-GMA, silane treated ceramic, 2-benzotriazolyl-4-methylphenol TEDGMA: Triethylene glycol dimethacrylate; Bis-BMA: Bisphenol A diglycidyl ether dimethacrylate; HEMA: Hydroxyethyl methacrylate.
Table 2 Immediate microtensile bond strength (mTBS) means and failure distributions. Groups
Details of ethanol application
mTBS (in MPa)
Group 1 (Full Chemical Dehydration Protocol)
50%, 70%, 80%, 95%, and 100% three times for 30 s each
Group 2 (Simplified Chemical Dehydration Protocol II)
100% ethanol for 60 s
Group 3 (Simplified Chemical Dehydration Protocol II)
100% ethanol for 20 s
Group 4 (Water-wet Bonding; Control)
e
27.46 ± 8.10a A>M>C 22.75 ± 8.02a A>M>C 25.16 ± 7.23a A>M>C 34.06 ± 5.8b A>M>C
Means (n ¼ 20) with the same superscript letters are not significantly different (p < 0.05). Failures were classed as adhesive (A), cohesive either in composite or in dentin (C) or mixed (M).
present study. This bonding agent composed of only hydrophobic monomers (50e100% Bis-GMA, 25e50% TEDGMA) (Table 1). Three-step hydrophobic etch-and-rinse adhesive system was designed based on HelioBond. 0.5 ml of absolute ethanol and 0.5 ml neat HelioBond were mixed in the glass tube to ensure miscibility of HelioBond in absolute ethanol by visually. Then, a primer which consists of 50/50 by vol% absolute ethanol and HelioBond was prepared. Two consecutive coats of the primer were used. The first coat was applied to the dentin with agitation for 15 s. A second application of primer was made, giving a total application time of 30 s. Excess solvent was evaporated with a gentle air stream for 10 s. After solvent evaporation, a coat of a neat HelioBond was applied, air-thinned, and light-cured for 20 s prior to composite placement. In each group, wet bonding techniques and adhesive applications were performed as described above, respectively. Light-curings were done with a 3M ELIPAR S10 LED light-curing unit3 with a power output of 1200 mW/cm2. Composite build-ups were constructed with Valux Plus3 in 5 1mm-thick increments. 2.3. Microtensile bond strength test
All bonded teeth were stored in tap water at 37 C for 24 h. Teeth were sectioned into 0.9 mm 0.9 mm dimensioned resin-dentin sticks using low speed 3
3M ESPE, St. Paul, MN, USA.
diamond saw according to non-trimming technique of microtensile bond strength test [14]. Obtained sticks from the same group were pooled, and twenty sticks were randomly selected to perform microtensile bond strength test. Sticks were fixed to test jig using cyanoacrylate, then stress to failure at cross-head speed of 0.5 mm/min using Bisco microtensile tester.4 Fractured sticks were examined using stereomicroscope and failure classed as adhesive, cohesive either in composite or in dentin or mixed. 2.4. Statistical analysis
Normality of distribution and equality of variances of bond strength data from all groups were checked by KolmogoroveSmirnov test and Levene tests, respectively. Since bond strength data were normal and exhibited equal variances, data were analyzed using one-way analysis of variance design and Tukey HSD test, with statistical significances set at p ¼ 0.05. 3. Results The microtensile bond strength test results for hydrophobic adhesive bonded using different ethanol application protocols and control group of one commercially available hydrophilic adhesive bonded using water-wet bonding technique are shown in Table 2 and Fig. 1. 4
Bisco, IL, USA.
M.K. Ayar / Tanta Dental Journal 11 (2014) 206e212
209
Fig. 1. Bond strength (Mean mTBS, in MPa) for different ethanol application protocol groups and control group. Bar connects results which were not significantly different from one another (ANOVA, Tukey, p ¼ 0.05, n ¼ 20).
The highest bond strength was recorded for group of hydrophilic adhesive bonded using water-wet bonding technique with significant difference from all other groups (p < 0.05). The lowest bond strength was recorded for group of hydrophobic adhesive bonded using simplified chemical dehydration protocol II. However, there was no significant difference among ethanol-wet bonding groups. The failure mode distribution of fractured specimens revealed that adhesive failures were dominant for all groups (Table 2). 4. Discussion The null hypothesis tested in the present study was that there were no differences among the microtensile bond strengths of the hydrophobic dentin adhesive deployed using three different ethanol-dehydration protocols and those obtained from commercially available hydrophilic etch-and-rinse adhesive. Findings indicated that null hypothesis should be partially rejected. All of tested ethanol-wet bonding techniques were not able to provide dentin bond strength for hydrophobic adhesive which is significantly similar to those of commercially available hydrophilic etch-andrinse adhesive deployed with water-wet bonding. However, it seems that different ethanol-dehydration
protocols did not affect bond strength of hydrophobic adhesive to dentin. Therefore, null hypothesis was partially rejected. According to ethanol-wet bonding concept, it is possible to deploy hydrophobic resin monomer blends for bonding to the dentin which is characteristically hydrophilic tissue [15]. To achieve this, replacement water within interfibrillar space of demineralized dentin matrices with ethanol by using ethanol application is mandatory [4]. This procedure renders hydrophilic water-saturated demineralized dentin matrices into more hydrophobic ethanol-saturated demineralized dentin matrices which are more favourably in terms of solubility of infiltrating resin monomers [4,10,16]. It should be noted that these conclusions are based on findings from macro model of hybrid layer [4]. Macro model of hybrid layer (200 mm-thick) is almost 40 times larger than clinical dentin hybrid layer. It had taken nearly 40 min to render macro model of water saturated demineralized dentin to ethanol-saturated demineralized dentin by application of absolute ethanol at one-step [4]. This ethanol application protocol is certainly inadequate to clinic application. If the direct proportion might exist between water replacement rate and dimensions of demineralized dentin matrices, it would be concluded
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that water replacement of clinical demineralized dentin matrices with ethanol might take one minute application of absolute ethanol. However, there is no evidence to support such direct proportion and available information about ethanol application protocols for ethanol-wet bonding in the literature exhibits great variations. For instance, Nishitani et al. [5] applied absolute ethanol onto watersaturated acid-etched dentin for 15 s at one step for deploying experimental hydrophobic resin blends. However, Sauro et al. [7] and Hosaka et al. [10] achieved ethanol-wet bonding substrates by covering water-saturated acid-etched dentin with absolute ethanol for 60 s, respectively. On the other side, long and more complicated ethanol application protocol called full chemical dehydration protocol was also proposed [6]. In the present study, it was found that, all of three different ethanol application protocols provide significantly similar microtensile bond strength for tested hydrophobic adhesive to those of each. Therefore, within limitations of the present study, it can be concluded that ethanol application for 20 s at one step with absolute ethanol was able to bond hydrophobic adhesive to dentin with relatively high initial microtensile bond strength, presenting the simplest way for clinic conditions. The presence of pulpal pressure simulation may play important role on water removal capacities of different ethanol-wet bonding techniques. Gregoire claimed that application of 100% ethanol twice for 10 s remove all excess and loosely bound water from acidetched dentin [17]. It should be noted that pulpal pressure had not simulated in that study. Similarly, Nishitani who applied 100% ethanol for 15 s onto acidetched water-wet dentin obtained comparable bond strength with hydrophobic adhesives when compared to hydrophilic adhesive deployed with water-wet bonding for dentin bonding when pulpal pressure had not simulated [5]. Conversely, Osorio who used an atomic force microscopy to assess the effects of different ethanol application protocols on collapse of dentin matrices claimed that application of 100% ethanol for 60 s might not able to remove water from dentin tubules and demineralized dentin matrices even in the absence of pulpal pressure simulation [18]. However, the findings of the present study support the notion that simplified ethanol wet bonding protocols is able to remove water as necessary to able to bond hydrophobic adhesive to dentin. Importance of pulpal fluid infiltration into acidetched dentin from dentin tubules and underlying sound intertubular dentin on bonding effectiveness of
hydrophobic adhesive deployed with ethanol wet bonding warrants further studies. Sauro claimed that clinical conditions such as lower water permeability of mature highly mineralized dentin than those of unerupted third molar teeth, and reduction of pulpal pressure when local anaesthesia is administered would be important [19]. Therefore, further studies should assess whether dentin substrate permeability might affect bond strength of hydrophobic adhesives to dentin with different ethanol application protocols under pulpal pressure simulation. Although simplest ethanol application protocol was able to bond hydrophobic adhesive to dentin with relatively high initial bond strength, Single Bond 2, a commercial hydrophilic adhesive, was deployed with water-wet bonding yielded significantly higher bond strength when compared to all of three ethanol wet bonding techniques. It should be bearing in mind that, drastic drops at dentin bond strengths of such hydrophilic adhesives after water-storages are well-known in the literature [20]. Therefore, further studies on effects of different ethanol application protocols on long-term bond strength of hydrophobic adhesive to dentin are guaranteed. It appears that vast of initial studies on ethanol-wet bonding deployed non-commercial experimental resin monomer blends, mostly hydrophobic monomers, for dentin bonding expectedly [4e6]. However, it seems that commercial hydrophilic dentin adhesive systems are being used more often in the recent ethanol-wet bonding studies [21e23]. Possibly, efforts to provide evident to constitute a sound clinic protocol for ethanol-wet bonding concept might drive this trend. Therefore, a commercial hydrophobic adhesive system (HelioBond) was used in the present study. HelioBond is a basically solvent-free resin-enamel bonding agent; consist of only hydrophobic resin monomers (50e100% Bis-GMA, 25e50% TEDGMA). It should be noted that HelioBond did not used according to manufacture instructions. To reduce influence of possibility that solubility parameters of neat HelioBond may be not match in favourable way with those of ethanol-saturated demineralized dentin matrices [15], ethanol solvented primer was formulated using neat HelioBond. So that, HelioBond was applied according to three-step etch-and-rinse rinse approach for ethanolwet bonding groups. Microtensile bond strength test, which uses specimens of smaller diameter than conventional tensile bond strength was, was selected as bond strength test in the present study in order to evaluate effects of test variables on bond strength values. The advantage of
M.K. Ayar / Tanta Dental Journal 11 (2014) 206e212
the use of microtensile bond strength test is that this test produces higher means from specimens of smaller diameter. This enables the microtensile bond strength test to be discriminative enough for detecting differences arising from treatment variables with the use of a smaller number of actual tooth specimens [24]. In the present study, bovine incisors were used as dentin bonding specimens. Bovine dentin is an accepted substitute for human dental hard tissue for bond strength studies [25]. In addition, the usage of bovine incisors provides the ready availability and increased homogeneity of the chemical composition of bovine teeth in comparison with human enamel [26]. 5. Conclusion Effects of different ethanol application protocols on initial bond strength of commercial hydrophobic adhesive to dentin were assessed in the present study. These protocols are (I) application of 100% ethanol for 60 s at one step, (II) application of 100% ethanol for 20 s at one step, and (III) full chemical dehydration protocols which involves application of a series of increasing ethanol concentrations (50, 70, 80, 95, and 100% for three times for 30 s each) at seven steps. Results indicated that even simplified ethanol wet bonding technique might able to bond hydrophobic adhesive to dentin with high bond strength. Therefore, results encourage to use simplest ethanol application protocol for ethanol-wet bonding technique for deploying hydrophobic adhesives for dentin bonding. However, further studies involve in vitro ageing regimes and pulp pressure simulation are guaranteed to reach more certain decisions. References [1] Tay FR, Pashley DH. Have dentin adhesives become too hydrophilic? J Can Dent Assoc 2003;69:726e32. [2] Breschi L, Mazzoni A, Ruggeri A, Cadenaro M, Di Lenarda R, De Stefano Dorigo E. Dental adhesion review: aging and stability of the bonded interface. Dent Mater 2008;24:90e101. [3] Sadek FT, Castellan CS, Braga BR, Mai S, Tjaderhane L, Pashley DH, et al. One-year stability of resin-dentin bonds created with a hydrophobic ethanol-wet bonding technique. Dent Mater 2010;26:380e6. [4] Pashley DH, Tay FR, Carvalho RM, Rueggeberg FA, Agee KA, Carrilho MA, et al. From dry bonding to water-wet bonding to ethanol-wet bonding. A review of the interactions between dentin matrix and solvated resins using a macromodel of the hybrid layer. Am J Dent 2007;20:7e20. [5] Nishitani Y, Yoshiyama M, Donnelly A, Agee K, Sword J, Tay FR, et al. Effects of resin hydrophilicity on dentin bond strength. J Dent Res 2006;85:1016e21.
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[6] Sadek FT, Pashley DH, Nishitani Y, Carrilho MR, Donnelly A, Ferrari M, et al. Application of hydrophobic resin adhesives to acid-etched dentin with an alternative wet bonding technique. J Biomed Mater Res A 2008;84:19e29. [7] Sauro S, Toledano M, Aguilera FS, Mannocci F, Pashley DH, Tay FR, et al. Resinedentin bonds to EDTA-treated vs. acidetched dentin using ethanol wet-bonding. Dent Mater 2010;26:368e79. [8] Pashley DH, Tay FR, Breschi L, Tj€aderhane L, Carvalho RM, Carrilho M, et al. State of the art etch-and-rinse adhesives. Dent Mater 2011;27:1e16. [9] Cadenaro M, Breschi L, Rueggeberg FA, Agee K, Di Lenarda R, Carrilho M, et al. Effect of adhesive hydrophilicity and curing time on the permeability of resins bonded to water vs. ethanol-saturated acid-etched dentin. Dent Mater 2009;25:39e47. [10] Hosaka K, Nishitani Y, Tagami J, Yoshiyama M, Brackett WW, Agee KA, et al. Durability of resin-dentin bonds to water- vs. ethanol-saturated dentin. J Dent Res 2009;88:146e51. [11] Sadek FT, Braga RR, Muench A, Liu Y, Pashley DH, Tay FR. Ethanol wet-bonding challenges current anti-degradation strategy. J Dent Res 2010;89:1499e504. [12] Sauro S, Toledano M, Aguilera FS, Mannocci F, Pashley DH, Tay FR, et al. Resin-dentin bonds to EDTA-treated vs. acidetched dentin using ethanol wet-bonding. Part II: effects of mechanical cycling load on microtensile bond strengths. Dent Mater 2011;27:563e72. [13] Sauro S, Watson TF, Mannocci F, Miyake K, Huffman BP, Tay FR, et al. Two-photon laser confocal microscopy of micropermeability of resin-dentin bonds made with water or ethanol wet bonding. J Biomed Mater Res B Appl Biomater 2009;90:327e37. [14] Pashley DH, Sano H, Ciucchi B, Yoshiyama M, Carvalho RM. Adhesion testing of dentin bonding agents: a review. Dent Mater 1995;11:117e25. [15] Tay FR, Pashley DH, Kapur RR, Carrilho MR, Hur YB, Garrett LV, et al. Bonding BisGMA to dentinea proof of concept for hydrophobic dentin bonding. J Dent Res 2007;86:1034e9. [16] Shin TP, Yao X, Huenergardt R, Walker MP, Wang Y. Morphological and chemical characterization of bonding hydrophobic adhesive to dentin using ethanol wet bonding technique. Dent Mater 2009;25:1050e7. [17] Gregoire G, Sharrock P, Delannee M, Delisle M-B. Depletion of water molecules during ethanol wet-bonding with etch and rinse dental adhesives. Mater Sci Eng C. 2013;33:21e7. [18] Osorio E, Toledano M, Aguilera F, Tay F, Osorio R. Ethanol wet-bonding technique sensitivity assessed by AFM. J Dent Res 2010;89:1264e9. [19] Sauro S, Watson TF, Mannocci F, Tay FR, Pashley DH. Prevention of water-contamination of ethanol-saturated dentin and hydrophobic hybrid layers. J Adhes Dent 2009;11:271. [20] De Munck J, Van Landuyt K, Peumans M, Poitevin A, Lambrechts P, Braem M, et al. A critical review of the durability of adhesion to tooth tissue: methods and results. J Dent Res 2005;84:118e32. [21] Simoes DM, Basting RT, Amaral FL, Turssi CP, Franca FM. Influence of chlorhexidine and/or ethanol treatment on bond strength of an etch-and-rinse adhesive to dentin: an in vitro and in situ study. Oper Dent 2014;39:64e71. [22] Guimar~aes LA, Almeida JCF, Wang L, D'Alpino PHP, Garcia FCP. Effectiveness of immediate bonding of etch-and-
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rinse adhesives to simplified ethanol-saturated dentin. Braz Oral Res 2012;26:177e82. [23] Mortazavi V, Samimi P, Rafizadeh M, Kazemi S. A randomized clinical trial evaluating the success rate of ethanol wet bonding technique and two adhesives. Dent Res J 2012;9:588e94. [24] Tay FR, Pashley DH, Yiu CK, Sanares AME, Wei SH. Factors contributing to the incompatibility between simplified-step
adhesives and chemically-cured or dual-cured composites. Part I. Single-step self-etching adhesive. J Adhes Dent 2003;5:27e40. [25] Nakamichi I, Iwaku M, Fusayama T. Bovine teeth as possible substitutes in the adhesion test. J Dent Res 1983;62:1076e81. [26] Zero D. In situ caries models. Adv Dent Res 1995;9:214e30.
H O S T E D BY
ScienceDirect Tanta Dental Journal 11 (2014) 206e212 www.elsevier.com/locate/tdj
Ethanol application protocols and microtensile dentin bond strength of hydrophobic adhesive M.K. Ayar Department of Restorative Dentistry, Faculty of Dentistry, Karadeniz Technical University, Trabzon, Turkey Received 19 October 2014; revised 15 November 2014; accepted 17 November 2014 Available online 16 December 2014
Abstract Purpose: Available knowledge on whether complicated and time-consuming ethanol application protocols are required for effective bonds between hydrophobic resin adhesive and dentin is inconclusive. Therefore, aim of this study is to evaluate effects of different ethanol application protocols on microtensile bond strength of hydrophobic adhesive to bovine dentin. Materials and methods: Bovine incisors were randomly divided into four groups (n ¼ 3). Standardized dentin cavities were acidetched with 37% H3PO4 and rinsed with water. Single Bond 2 applied to dentin with water-wet bonding was used as a control group. The rest groups had their dentine surface dehydrated according to different ethanol application protocols: Group 1 (Full-ChemicalDehydration-Protocol) ¼ 50%, 70%, 80%, 95% and 3 100%, 30 s for each ethanol application; Group 2 (Simplified-ChemicalDehydration-Protocol I) ¼ 100% ethanol applied for 60 s at one step and Group 3 (Simplified-Chemical-Dehydration-Protocol II) ¼ 100% ethanol applied for only 20 s at one step, respectively. After ethanol applications, a primer (50% HelioBond þ 50% absolute ethanol) was used, followed by the neat HelioBond application. Resin composite build-ups were then done. Results: Group 1 showed higher bond strength (27.46 ± 8.10). Group 1 showed bond strength statistically similar to Group 2 (22.75 ± 8.02) and Group 3 (25.16 ± 7.23) and statistically different to control group (34.06 ± 5.8). Conclusion: Results indicated that different ethanol application protocols may not affect bond strength of hydrophobic adhesive to dentin. However, slight statistical difference existed between control and full chemical dehydration protocol. © 2014, Hosting by Elsevier B.V. on behalf of the Faculty of Dentistry, Tanta University.
Keywords: Ethanol-wet bonding; Bovine dentin; Microtensile bond strength test; Hydrophobic adhesive
1. Introduction The use of increasing concentrations of hydrophilic monomers in current dentin adhesives raises a concern on if such adhesives have become too hydrophilic [1]. Combination of hydrophilic resin monomers with
E-mail addresses: [email protected], [email protected]. Peer review under the responsibility of the Faculty of Dentistry, Tanta University.
adhesive resins results in increases water sorption, and decreases in mechanical properties of these resin adhesives [2]. Therefore, the use of hydrophobic resins for dentin bonding would avoid these problems and increase durability of resin-dentin bonding in theory [3]. Recently, a new concept of wet bonding which is called ethanol-wet bonding was introduced to dental research community [4]. The ultimate aim of this concept is that providing dentin bonding techniques for increasing resin-dentin bond durability through (i)
http://dx.doi.org/10.1016/j.tdj.2014.11.003 1687-8574/© 2014, Hosting by Elsevier B.V. on behalf of the Faculty of Dentistry, Tanta University.
M.K. Ayar / Tanta Dental Journal 11 (2014) 206e212
improving quality of resultant dentin hybrid layer through efficient removal of residue water from interfibrillar spaces without causing significant collapse of collagen matrices by ethanol-dehydration, and (ii) rendering hydrophilic water-saturated dentin into hydrophobic ethanol-saturated dentin to coax applying more hydrophobic adhesive resin for dentin bonding [4e7,10]. According to ethanol wet bonding concept, water exists within interfibrillar spaces would be removed through an ethanol dehydration/saturation which is an individual application and an extra step [6]. As a result, improving resin e collagen ratio within hybrid layer would be achieved theoretically [8]. Although “ethanol-wet-bonding” looks promising [3,7,9e13], it involves an extra step of replacing residue water with ethanol application. Thus, more evidence is needed to justify this extra step [10]. However, it seems that there is no consensus regarding to how ethanol application for dehydration/saturation should be performed when ethanol-wet bonding would be used for dentin bonding under clinical conditions. Consequently, a vast of variability in ethanol application protocols in terms of concentration of ethanol used, number of application step and time of ethanol dehydration/saturation prior to application of hydrophobic adhesive to dentin exist in the literature. For instance, Nishitani et al., applied 100% ethanol for 15 s onto acidetched water-wet dentin surface to convert it to ethanolsaturated dentin surfaces prior to hydrophobic adhesive resin application [5]. Similarly, Sauro et al. [7], and Hosaka et al. [10], deployed ethanol dehydration protocol as a form of delivering 100% ethanol for 60 s in their studies, respectively. On another hand, Sadek et al., suggests that simplified ethanol dehydration techniques would not be efficient in water decontamination of dentin hybrid layer, thus yielding lower bond strengths [6]. Sadek et al., suggest using ethanol application protocol which is called “full chemical dehydration protocol” involves an application of series of increasing ethanol concentrations (50%, 70%, 80%, 95% and three times 100% ethanol for each 30 s, yielding total of 210 s) [6]. Despite that, all aforementioned researchers who were deployed simplified chemical dehydration protocols, achieved relatively high dentin bond strengths with hydrophobic adhesives. Therefore, it seems that a discrepancy regarding to ethanol application protocols of ethanol-wet bonding concept exists in the literature. Consequently, in the present study, effects of three different ethanol application protocols on microtensile bond strength of hydrophobic adhesive to bovine dentin was determined. The null
207
hypothesis tested was that there are no differences among the microtensile bond strengths of the hydrophobic dentin adhesive deployed using three different ethanol application protocols and those obtained from commercially available hydrophilic etch-and-rinse adhesives. 2. Materials and methods 2.1. Study design
Twelve bovine incisors from 2- to 3-yr-old animals were used in the present study. All labial surfaces were ground and flattened under water with a 180 grit SiC paper. On each surface, one standardized cavity was prepared to 8 mm width, 8 mm height and 2 mm depth by means of coarse cylindrical diamond burs.1 Prepared teeth were randomly divided into four groups (N ¼ 3) as following: Group 1 (Full Chemical Dehydration Protocol): Each acid-etched, wet dentin surface was treated with a series of increasing ethanol concentrations (50, 70, 80, 95, and 100% for three times for 30 s each) at seven steps. The ethanol/water mixture or absolute ethanol was dispensed from transfer pipettes to cover the entire dentin surface, replacing the 100% water or preceding ethanol solution that saturated the demineralized collagen matrix. This procedure was meticulously performed to ensure that the dentin surface was always immersed in a liquid phase by keeping it visibly moist prior to the application of subsequent solutions with higher ethanol concentration. Group 2 (Simplified Chemical Dehydration Protocol I): Each acid-etched, wet dentin surface was treated with absolute ethanol for 60 s at one step. Group 3 (Simplified Chemical Dehydration Protocol II): Each acid-etched, wet dentin surface was treated with only absolute ethanol for 15 s at one step. Group 4 (Conventional water-wet bonding technique þ Single Bond; Control): A commercially available hydrophilic etch-and-rinse adhesive (Single Bond 2) was applied to visibly moist, water-saturated demineralized dentin according to the manufacturers' instructions. 2.2. Hydrophobic adhesive
HelioBond2 which is a basically commercially available enamel bonding agent was used as a hydrophobic etch-and-rinse adhesive for dentin in the 1 2
Microdont, Sao Paulo, Brazil. Ivaclar, Vivadent, Schaan, Liechtenstein.
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Table 1 Chemical compositions of the materials used in the present study. HelioBond (Ivoclar, Vivadent, Schaan, Liechtenstein)Bis-GMA, TEGDMA, catalysts, stabilizers Single Bond 2 (3M ESPE, St Paul MN, USA) Dimethacrylates, HEMA, polyalkenoid acid copolymer, fillers, ethanol, water, photoinitiator Valux Plus (3M ESPE, St Paul MN, USA) TEDGMA, Bis-GMA, silane treated ceramic, 2-benzotriazolyl-4-methylphenol TEDGMA: Triethylene glycol dimethacrylate; Bis-BMA: Bisphenol A diglycidyl ether dimethacrylate; HEMA: Hydroxyethyl methacrylate.
Table 2 Immediate microtensile bond strength (mTBS) means and failure distributions. Groups
Details of ethanol application
mTBS (in MPa)
Group 1 (Full Chemical Dehydration Protocol)
50%, 70%, 80%, 95%, and 100% three times for 30 s each
Group 2 (Simplified Chemical Dehydration Protocol II)
100% ethanol for 60 s
Group 3 (Simplified Chemical Dehydration Protocol II)
100% ethanol for 20 s
Group 4 (Water-wet Bonding; Control)
e
27.46 ± 8.10a A>M>C 22.75 ± 8.02a A>M>C 25.16 ± 7.23a A>M>C 34.06 ± 5.8b A>M>C
Means (n ¼ 20) with the same superscript letters are not significantly different (p < 0.05). Failures were classed as adhesive (A), cohesive either in composite or in dentin (C) or mixed (M).
present study. This bonding agent composed of only hydrophobic monomers (50e100% Bis-GMA, 25e50% TEDGMA) (Table 1). Three-step hydrophobic etch-and-rinse adhesive system was designed based on HelioBond. 0.5 ml of absolute ethanol and 0.5 ml neat HelioBond were mixed in the glass tube to ensure miscibility of HelioBond in absolute ethanol by visually. Then, a primer which consists of 50/50 by vol% absolute ethanol and HelioBond was prepared. Two consecutive coats of the primer were used. The first coat was applied to the dentin with agitation for 15 s. A second application of primer was made, giving a total application time of 30 s. Excess solvent was evaporated with a gentle air stream for 10 s. After solvent evaporation, a coat of a neat HelioBond was applied, air-thinned, and light-cured for 20 s prior to composite placement. In each group, wet bonding techniques and adhesive applications were performed as described above, respectively. Light-curings were done with a 3M ELIPAR S10 LED light-curing unit3 with a power output of 1200 mW/cm2. Composite build-ups were constructed with Valux Plus3 in 5 1mm-thick increments. 2.3. Microtensile bond strength test
All bonded teeth were stored in tap water at 37 C for 24 h. Teeth were sectioned into 0.9 mm 0.9 mm dimensioned resin-dentin sticks using low speed 3
3M ESPE, St. Paul, MN, USA.
diamond saw according to non-trimming technique of microtensile bond strength test [14]. Obtained sticks from the same group were pooled, and twenty sticks were randomly selected to perform microtensile bond strength test. Sticks were fixed to test jig using cyanoacrylate, then stress to failure at cross-head speed of 0.5 mm/min using Bisco microtensile tester.4 Fractured sticks were examined using stereomicroscope and failure classed as adhesive, cohesive either in composite or in dentin or mixed. 2.4. Statistical analysis
Normality of distribution and equality of variances of bond strength data from all groups were checked by KolmogoroveSmirnov test and Levene tests, respectively. Since bond strength data were normal and exhibited equal variances, data were analyzed using one-way analysis of variance design and Tukey HSD test, with statistical significances set at p ¼ 0.05. 3. Results The microtensile bond strength test results for hydrophobic adhesive bonded using different ethanol application protocols and control group of one commercially available hydrophilic adhesive bonded using water-wet bonding technique are shown in Table 2 and Fig. 1. 4
Bisco, IL, USA.
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Fig. 1. Bond strength (Mean mTBS, in MPa) for different ethanol application protocol groups and control group. Bar connects results which were not significantly different from one another (ANOVA, Tukey, p ¼ 0.05, n ¼ 20).
The highest bond strength was recorded for group of hydrophilic adhesive bonded using water-wet bonding technique with significant difference from all other groups (p < 0.05). The lowest bond strength was recorded for group of hydrophobic adhesive bonded using simplified chemical dehydration protocol II. However, there was no significant difference among ethanol-wet bonding groups. The failure mode distribution of fractured specimens revealed that adhesive failures were dominant for all groups (Table 2). 4. Discussion The null hypothesis tested in the present study was that there were no differences among the microtensile bond strengths of the hydrophobic dentin adhesive deployed using three different ethanol-dehydration protocols and those obtained from commercially available hydrophilic etch-and-rinse adhesive. Findings indicated that null hypothesis should be partially rejected. All of tested ethanol-wet bonding techniques were not able to provide dentin bond strength for hydrophobic adhesive which is significantly similar to those of commercially available hydrophilic etch-andrinse adhesive deployed with water-wet bonding. However, it seems that different ethanol-dehydration
protocols did not affect bond strength of hydrophobic adhesive to dentin. Therefore, null hypothesis was partially rejected. According to ethanol-wet bonding concept, it is possible to deploy hydrophobic resin monomer blends for bonding to the dentin which is characteristically hydrophilic tissue [15]. To achieve this, replacement water within interfibrillar space of demineralized dentin matrices with ethanol by using ethanol application is mandatory [4]. This procedure renders hydrophilic water-saturated demineralized dentin matrices into more hydrophobic ethanol-saturated demineralized dentin matrices which are more favourably in terms of solubility of infiltrating resin monomers [4,10,16]. It should be noted that these conclusions are based on findings from macro model of hybrid layer [4]. Macro model of hybrid layer (200 mm-thick) is almost 40 times larger than clinical dentin hybrid layer. It had taken nearly 40 min to render macro model of water saturated demineralized dentin to ethanol-saturated demineralized dentin by application of absolute ethanol at one-step [4]. This ethanol application protocol is certainly inadequate to clinic application. If the direct proportion might exist between water replacement rate and dimensions of demineralized dentin matrices, it would be concluded
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that water replacement of clinical demineralized dentin matrices with ethanol might take one minute application of absolute ethanol. However, there is no evidence to support such direct proportion and available information about ethanol application protocols for ethanol-wet bonding in the literature exhibits great variations. For instance, Nishitani et al. [5] applied absolute ethanol onto watersaturated acid-etched dentin for 15 s at one step for deploying experimental hydrophobic resin blends. However, Sauro et al. [7] and Hosaka et al. [10] achieved ethanol-wet bonding substrates by covering water-saturated acid-etched dentin with absolute ethanol for 60 s, respectively. On the other side, long and more complicated ethanol application protocol called full chemical dehydration protocol was also proposed [6]. In the present study, it was found that, all of three different ethanol application protocols provide significantly similar microtensile bond strength for tested hydrophobic adhesive to those of each. Therefore, within limitations of the present study, it can be concluded that ethanol application for 20 s at one step with absolute ethanol was able to bond hydrophobic adhesive to dentin with relatively high initial microtensile bond strength, presenting the simplest way for clinic conditions. The presence of pulpal pressure simulation may play important role on water removal capacities of different ethanol-wet bonding techniques. Gregoire claimed that application of 100% ethanol twice for 10 s remove all excess and loosely bound water from acidetched dentin [17]. It should be noted that pulpal pressure had not simulated in that study. Similarly, Nishitani who applied 100% ethanol for 15 s onto acidetched water-wet dentin obtained comparable bond strength with hydrophobic adhesives when compared to hydrophilic adhesive deployed with water-wet bonding for dentin bonding when pulpal pressure had not simulated [5]. Conversely, Osorio who used an atomic force microscopy to assess the effects of different ethanol application protocols on collapse of dentin matrices claimed that application of 100% ethanol for 60 s might not able to remove water from dentin tubules and demineralized dentin matrices even in the absence of pulpal pressure simulation [18]. However, the findings of the present study support the notion that simplified ethanol wet bonding protocols is able to remove water as necessary to able to bond hydrophobic adhesive to dentin. Importance of pulpal fluid infiltration into acidetched dentin from dentin tubules and underlying sound intertubular dentin on bonding effectiveness of
hydrophobic adhesive deployed with ethanol wet bonding warrants further studies. Sauro claimed that clinical conditions such as lower water permeability of mature highly mineralized dentin than those of unerupted third molar teeth, and reduction of pulpal pressure when local anaesthesia is administered would be important [19]. Therefore, further studies should assess whether dentin substrate permeability might affect bond strength of hydrophobic adhesives to dentin with different ethanol application protocols under pulpal pressure simulation. Although simplest ethanol application protocol was able to bond hydrophobic adhesive to dentin with relatively high initial bond strength, Single Bond 2, a commercial hydrophilic adhesive, was deployed with water-wet bonding yielded significantly higher bond strength when compared to all of three ethanol wet bonding techniques. It should be bearing in mind that, drastic drops at dentin bond strengths of such hydrophilic adhesives after water-storages are well-known in the literature [20]. Therefore, further studies on effects of different ethanol application protocols on long-term bond strength of hydrophobic adhesive to dentin are guaranteed. It appears that vast of initial studies on ethanol-wet bonding deployed non-commercial experimental resin monomer blends, mostly hydrophobic monomers, for dentin bonding expectedly [4e6]. However, it seems that commercial hydrophilic dentin adhesive systems are being used more often in the recent ethanol-wet bonding studies [21e23]. Possibly, efforts to provide evident to constitute a sound clinic protocol for ethanol-wet bonding concept might drive this trend. Therefore, a commercial hydrophobic adhesive system (HelioBond) was used in the present study. HelioBond is a basically solvent-free resin-enamel bonding agent; consist of only hydrophobic resin monomers (50e100% Bis-GMA, 25e50% TEDGMA). It should be noted that HelioBond did not used according to manufacture instructions. To reduce influence of possibility that solubility parameters of neat HelioBond may be not match in favourable way with those of ethanol-saturated demineralized dentin matrices [15], ethanol solvented primer was formulated using neat HelioBond. So that, HelioBond was applied according to three-step etch-and-rinse rinse approach for ethanolwet bonding groups. Microtensile bond strength test, which uses specimens of smaller diameter than conventional tensile bond strength was, was selected as bond strength test in the present study in order to evaluate effects of test variables on bond strength values. The advantage of
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the use of microtensile bond strength test is that this test produces higher means from specimens of smaller diameter. This enables the microtensile bond strength test to be discriminative enough for detecting differences arising from treatment variables with the use of a smaller number of actual tooth specimens [24]. In the present study, bovine incisors were used as dentin bonding specimens. Bovine dentin is an accepted substitute for human dental hard tissue for bond strength studies [25]. In addition, the usage of bovine incisors provides the ready availability and increased homogeneity of the chemical composition of bovine teeth in comparison with human enamel [26]. 5. Conclusion Effects of different ethanol application protocols on initial bond strength of commercial hydrophobic adhesive to dentin were assessed in the present study. These protocols are (I) application of 100% ethanol for 60 s at one step, (II) application of 100% ethanol for 20 s at one step, and (III) full chemical dehydration protocols which involves application of a series of increasing ethanol concentrations (50, 70, 80, 95, and 100% for three times for 30 s each) at seven steps. Results indicated that even simplified ethanol wet bonding technique might able to bond hydrophobic adhesive to dentin with high bond strength. Therefore, results encourage to use simplest ethanol application protocol for ethanol-wet bonding technique for deploying hydrophobic adhesives for dentin bonding. However, further studies involve in vitro ageing regimes and pulp pressure simulation are guaranteed to reach more certain decisions. References [1] Tay FR, Pashley DH. Have dentin adhesives become too hydrophilic? J Can Dent Assoc 2003;69:726e32. [2] Breschi L, Mazzoni A, Ruggeri A, Cadenaro M, Di Lenarda R, De Stefano Dorigo E. Dental adhesion review: aging and stability of the bonded interface. Dent Mater 2008;24:90e101. [3] Sadek FT, Castellan CS, Braga BR, Mai S, Tjaderhane L, Pashley DH, et al. One-year stability of resin-dentin bonds created with a hydrophobic ethanol-wet bonding technique. Dent Mater 2010;26:380e6. [4] Pashley DH, Tay FR, Carvalho RM, Rueggeberg FA, Agee KA, Carrilho MA, et al. From dry bonding to water-wet bonding to ethanol-wet bonding. A review of the interactions between dentin matrix and solvated resins using a macromodel of the hybrid layer. Am J Dent 2007;20:7e20. [5] Nishitani Y, Yoshiyama M, Donnelly A, Agee K, Sword J, Tay FR, et al. Effects of resin hydrophilicity on dentin bond strength. J Dent Res 2006;85:1016e21.
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