Effect of ethanol-wet-bonding technique on resineenamel bonds

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1 Journal of Dental Sciences (2014) 9, 16e22 Available online at journal homepage: ORIGINAL ARTICLE Effect of ethanol-wet-bonding technique on resineenamel bonds Muhammet Kerim Ayar*, Cemal Yesilyurt, Cemile Kedici Alp, Tahsin Yildirim Department of Operative Dentistry, Faculty of Dentistry, Karadeniz Technical University, Trabzon, Turkey Received 21 November 2011; Final revision received 27 October 2012 Available online 8 January 2013 KEYWORDS adhesion; ethanol-wet-bonding; micro-tensile test Abstract Background/purpose: It was reported that more stable resin dentin bonds were achieved by using ethanol-wet bonding. Because it would be difficult to saturate acid-etched dentin with ethanol without saturation enamel, the study was conducted to evaluate the microtensile bond strength (mtbs) of adhesive resins bonded to enamel using water- and ethanolwet-bonding techniques. Materials and methods: Flat enamel surfaces from extracted bovine incisor teeth were conditioned with 37% H 3 PO 4 (for 15 seconds) before bonding. Two commercial adhesives (Single Bond 2 and All Bond 3) were applied to enamel using water- and ethanol-wet-bonding techniques (for 1 minute) as follows: group I, Single Bond 2 and water-wet bonding; group II, All Bond 3 and water-wet bonding; group III, Single Bond 2 and ethanol-wet-bonding; and group IV, All Bond 3 and ethanol-wet-bonding. Resin-bonded teeth were stored in distilled water (for 24 hours) and sectioned in beams for mtbs testing. mtbs results were analyzed by a two-way AN- OVA and LSD test. The resineenamel interfaces were examined by SEM. Results: The following mean mtbs values were obtained: 17.4 MPa for group I, 26.4 MPa for group II, 28.7 MPa for group III, and 31 MPa for group IV. For both adhesives, the obtained adhesive-enamel mtbs values with the ethanol-wet-bonding technique were significantly higher than those of the water-wet-bonding technique (P < 0.05). Conclusion: The ethanol-wet-bonding technique may increase the bond strength of commercial adhesives to enamel. The chemical composition of the adhesives can affect the bond strength of adhesives when bonding to acid-etched enamel, using the ethanol-wet-bonding technique. Some adhesive systems used in the present study may simultaneously be applied to enamel and * Corresponding author. Department of Operative Dentistry, Faculty of Dentistry, Karadeniz Technical University, Trabzon 61080, Turkey. address: kerimayar@ktu.edu.tr (M.K. Ayar) /$36 Copyright ª 2012, Association for Dental Sciences of the Republic of China. Published by Elsevier Taiwan LLC. All rights reserved.

2 Enamel bonding with an ethanol-wet-bonding technique 17 dentin using ethanol-wet-bonding. Furthermore, deploying ethanol-wet-bonding for the tested commercial adhesives to enamel can increase the adhesion abilities of these adhesives to enamel. Copyright ª 2012, Association for Dental Sciences of the Republic of China. Published by Elsevier Taiwan LLC. All rights reserved. Introduction In spite of all the achieved improvements in adhesive dentistry, 1 there is a consensus that the stability of resinedentin bonds is problematic. 2e5 It is well known that resin bonding as a process is far more complex than most dentists realize, and a great number of factors, including water sorption and hydrolysis of the adhesive resin, incomplete resin infiltration, incomplete solvent evaporation, and imperfect monomer/polymer conversion, influence the bonding effectiveness of dental adhesives. 2,3,6 Dental bonding systems are resin blends that possess both hydrophilic and hydrophobic properties, and are thus called amphiphilic. In other words, adhesives are compounds containing both hydrophilic and hydrophobic monomers. 7 Bisphenol A diglycidyl methacrylate (Bis-GMA) monomer is the main component of most dental adhesive systems. 6 However, due to the presence of water in the current wet-bonding techniques, 8 there is the potential for phase separation of the hydrophobic Bis-GMA monomer, which has limited water solubility. To avoid this problem, a hydrophobic Bis-GMA monomer is blended with the hydrophilic 2-hydroxyethyl methacrylate (HEMA) monomer. 3 However, nanoleakage studies identified water-filled channels within hybrid layers, which indicated that not all of the residual water was removed. 9,10 Recent studies revealed that the most important factor in the failure of resinebiomaterial interfaces, was to increase the hydrophilicity of current dental adhesives. 5 With the aim of optimizing the penetration of hydrophobic monomers, like Bis-GMA, into the wet demineralized dentin, 11 a new technique was developed called ethanol-wetbonding. This technique is used to chemically dehydrate the exposed collagen matrices without causing their collapse. 6,12 The potential of the ethanol-wet-bonding technique to create durable resinedentin bonds, by replacing most of the water in the demineralized collagen matrices, was demonstrated by in vitro studies using experimental and commercial adhesives. 13e17 The use of ethanol to saturate demineralized dentin matrices, instead of water, facilitates infiltration of dimethacrylates through the interfibrillar spaces. 18 Ethanolwet-bonding permits adhesives to achieve better sealing between the resin rags and tubule walls. 19 Therefore, ethanol-wet-bonding can increase the durability of resin dentin bonds over longer time periods. Although there are many advantages of ethanol-wetbonding, it includes several shortcomings, and certain things must be considered. There are concerns about its biocompatibility and sensitivity to water contamination, and it also requires additional steps and time for the bonding procedure. 6,13,16,20 However, when dentin is saturated with ethanol, it is difficult to keep the enamel wet with water or dry at the same time, like trying to keep enamel dry and the dentin wet. 21 As to clinical considerations, if the enamel can be bonded effectively while it is wet with ethanol, the overall dentin-bonding procedure using ethanol-wet-bonding can be significantly simplified. Therefore, in this study, we assessed the effect of ethanolwet bonding on resineenamel bond strengths. The null hypothesis was that there was no significant influence of ethanol-wet-bonding on the adhesion of two commercial etch-and-rinse adhesives to enamel, compared to the conventional wet-bonding technique. Materials and methods Two commercially available etch-and-rinse adhesives were used in the present study. The adhesives used and their compositions are shown in Table 1. Specimen preparation and bonding procedures Eight freshly extracted bovine incisors were used in the present study. Teeth were stored in a 0.2% sodium azide solution at 4 C prior to use. Following separation of crowns from roots, the crowns were positioned on an acrylic block with the labial surface parallel to the floor. Labial surfaces of the teeth were flattened with a diamond bur (Microdont ISO , São Paulo, Brazil). Teeth were divided into four groups (n Z 2) according to the Table 1 Chemical formulations of the tested adhesives. Adhesive Composition Single Bond 2, 3M ESPE, St. Paul, MN, USA Bis-GMA, HEMA, ethanol, water, polyalkenoic acid copolymer (Lot number: ) AllBond 3, Bisco Inc., Schaumburg, IL, USA Part a: ethanol, MgNTG-GMA (Lot number: ) Part b: Bis-GMA, BPDM, HEMA, photointiators, stabilizers (Lot number: ) All Bond Resin: Bis-GMA, UDMA, TEGDMA, glass Filler (Lot number: ) Bis-GMA Z bisphenol A diglycidyl methacrylate; BPDM Z biphenyl dimethacrylate or 4,4 -dimethacryloyloxyethyloxycarbonylbiphenyl- 3,3 -dicarboxylic acid; HEMA Z 2-hydroxyethyl methacrylate; MgNTG-GMA Z magnesium nitric-triglycidyl glycidyl methacrylate.

3 18 M.K. Ayar et al bonding techniques (water-wet-bonding or ethanol-wetbonding technique) and adhesive agents (Single Bond 2 or All Bond 3) as follows; group I, Single Bond 2 with water-wet bonding; group II, All Bond 3 with water-wet bonding; group III, Single Bond 2 with ethanol-wet-bonding; and group IV, All Bond 3 with ethanol-wet-bonding. In all groups, prepared enamel surfaces were etched with a 37% phosphoric acid gel (Etch 37, Bisco, Schaumburg, IL, USA) for 15 seconds, rinsed, and left moist with water. The adhesive agents were applied to the moist surfaces in the water-wet-bonding technique groups (groups I and II) according to the manufacturer s instructions. For groups III and IV, the ethanol-wet-bonding technique was used. Briefly, ethanol-wet-bonded surfaces were achieved by covering the conditioned, water-rinsed enamel surfaces with absolute (99.5%) ethanol (Tekkim, Bursa, Turkey) for 1 minute. The procedure was performed by keeping the enamel surfaces visibly moist with ethanol prior to application of the resin blends. Then, the remaining bonding procedures were performed according to the respectiveadhesivemanufacturer s instructions. Resin composite (Quadrant Universal LC, Cavex, Haarlem, The Netherlands), 4 mm thick, was built up using an incremental technique (four increments), and each increment from the occlusal surface was cured for 40 seconds using a curing unit with an intensity of 700 mw/cm 2 (Astralis 3, Ivoclar, Vivadent, Schaan, Liechtenstein). Prior to mtbs testing, samples were stored in water for 24 hours. mtbs test All composite-resineenamel samples were sectioned into beams, with an approximate cross-sectional area of 1 mm 2, by a non-trimming method. We generated 60w70 sticks for each experimental subgroup. The mtbs of each stick was tested by attaching it to a movable jig, which was attached to a mtbs tester (Bisco) with cyanoacrylate adhesive (Zapit, Dental Venture of America, Corona, CA, USA). The sticks were stressed to failure in tension, using the mtbs tester at a cross-head speed of 1.5 mm/minute. Fractured specimens were examined with a stereomicroscope (Olympus SZ-CTV, Tokyo, Japan) at 40 magnification, to determine the mode of failure. Failure modes were classified as adhesive, cohesive (composite/dentin), or mixed. Only specimens that presented the adhesive failure mode were included in the statistical analysis. The number of sticks tested and percentages of all failure modes are presented in Table 2. Specimen preparation for scanning electron microscopic (SEM) analysis Four bovine teeth were used to analyze the enamel hybrid layers under SEM. First, all teeth were separated into two halves with a low-speed diamond saw under copious water. Tooth halves were divided into four groups, with two coupled halves each. One half of a tooth was subjected to water-wet bonding, while the other half of the same tooth was subjected to ethanol-wet-bonding. Labial surfaces of the obtained halves were ground as described above. Adhesive application protocols were applied to each half, according to the assigned groups. Composite was built up to a 2 mm height. The enamel-bonding interface was assessed by SEM performed on two sections cut perpendicularly throughout the resin-bonded enamel surface of each tooth half, with a diamond saw under copious water. Cross-sections were polished by wet grinding using 2500-grit SiC paper and immersion for 20 seconds in 2 mol/l HCl, to delineate the resin-infiltrated enamel. After air-drying and sputtercoating with gold, each section was analyzed in a JEOL JSM-6400 SEM (Tokyo, Japan). Representative micrographs were obtained at a magnification of Statistical analyses Distributions and equalities of variances of the mtbs data were respectively analyzed using one-sample Kolmogorov- Smirnov and Levene s tests. Interactions between bonding techniques and adhesives were analyzed using a two-way analysis of variance (ANOVA). A least significant difference (LSD) test was applied for post-hoc comparisons. All statistical tests were performed using SPSS 13 (SPSS, Chicago, IL, USA), and statistical significance was set to P < Results The mtbs, standard deviations (SD), number of the sticks, and percentages of failure modes of each group are summarized in Table 2. There was a statistically significant interaction observed between the wet-bonding technique and adhesive systems (P < 0.05). The different bonding techniques and adhesives resulted in statistical differences (P < 0.001). Group I (Single Bond 2 with water-wet bonding) yielded the lowest Table 2 Results of the microtensile bonding test ranked according to group numbers and adhesive failure (PF) percentages. Number of sticks with adhesive (n) failure are also presented. Different superscripted letters indicate significant differences. Bonding technique Adhesives Microtensile bond strength (MPa) as determined by number of beams (n) PF (%) Water wet bonding Single Bond 2 (Group I) All Bond 3 (Group II) Ethanol-wet-bonding Single Bond 2 (Group III) All Bond 3 (Group IV) c (n Z 24) 58.5 b (n Z 28) 46.6 a,b (n Z 41) 60.2 a (n Z 23) 37.7

4 Enamel bonding with an ethanol-wet-bonding technique 19 bond strengths, with significant differences among all groups. Group III yielded bond strengths with no significant difference from those of groups II and IV. There was no statistically significant difference between groups III and IV (P Z 0.179). The mean mtbs value of group IV (All Bond 3 with ethanol-wet-bonding) was the highest among all groups (Table 2). The frequency of pre-test failures was higher in group I than in the other groups. SEM micrographs of adhesive resins applied to etchedenamel, wetted with ethanosl or water, revealed longer and smoother resin tag formation in group III, while there were slight differences between groups II and IV, in terms of the resin tag formation length and smoothness. However, the presence of a gray band covering the tips of resin tags may indicate that a more-acid-resistant layer was obvious in group IV (Fig. 1). Discussion The pivotal bonding mechanism of the current etch-andrinse resin adhesives to dental substrates, is micromechanical interlocking, which is a diffusion-dependent phenomenon. Infiltration of resin monomers into the dentin and enamel depends on several factors related to both adhesive resins, including the molecular weights of the comonomers 22 and the necessity for good matching of solubility parameters of the monomer/solvent blends with the substrate being penetrated 6 and related substrates. 23 The inherent wetness of dentin makes it a difficult substrate on which to achieve durable bonds between adhesive resin and dentin. 23 Solvents such as ethanol, deployed in primers, aim to help displace water from the dentin surface, which facilitates penetration of the resin monomers into microporosities of the exposed, aciddemineralized collagen network. 24 Unlike dentin, enamel is not inherently wet and consists of a collagen-free, almost completely mineralized structure. 25 Meanwhile, it was thought that considerably more water might be retained in micropores of etched enamel after air-drying, 26 allowing non-uniform resin infiltration into acid-etched enamel. 27 Previously, it was suggested that removal of retained waterby drying using absolute ethanol, might increase the enamel resin adaptation. 26 In the case of ethanol-wet-bonding, the etched enamel surfaces were kept moist with pure ethanol prior to resin application. Results of the present study suggest that the ethanol layer on the etched surface did not hamper the adhesive abilities of the tested adhesives. The present study revealed that wetting etched and visibly moist enamel with absolute ethanol for 1 minute improved the initial bond strengths of all of the tested adhesives. In terms of failure modes, it was determined that adhesive failure was dominant in all Single Bond groups (groups I and Figure 1 SEM micrographs of adhesive resins applied to etched-enamel-wet with ethanol or water after 2 mol/l HCI treatment for 20 seconds. (A) SEM micrograph of Single Bond 2 applied to etched-enamel-wet with water; (B) SEM micrograph of Single Bond 2 applied to etched-enamel-wet with ethanol showing longer and smoother resin tag formation (black arrow). It seems that resin had penetrated into deeper interprismatic areas; (C) SEM micrograph of All Bond 3 applied to etched-enamel-wet with water; (D) SEM micrograph of All Bond 3 applied to etched-enamel-wet with ethanol showing slightly better resin tag formation than those of the former group. Gray band over tips of resin tags, possibly consists of residual apatite after 2 mol/l HCI treatment for 20 seconds is remarkable.

5 20 M.K. Ayar et al III) regardless of the bonding technique. However, it seems that ethanol-wet-bonding affected the failure mode pattern of All Bond 3. Although adhesive failure was dominant in the All Bond 3 group with water-wet bonding (group II), cohesive failure in the enamel was more frequent in the All Bond 3 group with ethanol-wet-bonding (group IV). In short, high bond strength demonstrated morecohesive failure in the enamel (Table 2). The main principles of the ethanol-wet-bonding concept were explained using solubility parameter theories. 6 First, according to solubility parameter theories, ethanol, with a lower hydrogen bond capacity than water, maintains the stability of the demineralized dentin matrix against surface tension forces, and keeps interfibrillar spaces open when demineralized collagen matrices are saturated with ethanol, thus allowing better resin infiltration. 6,12 Second, ethanol is a more-suitable solvent than water for most resin monomers, 13,19 and it consequently allows resins to infiltrate ethanol-saturated collagen matrices without phase separation. 6,12 In the case of etched enamel consisting of hydroxyapatite and keratin-like organic matrices 28 with higher stiffness than demineralized dentin matrix, 29 enamel, even after etching, was not as delicate against surface tension forces that occur during solvent evaporation. For that reason, the first principle of the ethanol-wet-bonding concept did not contribute to the results of the present study. Meanwhile, the latter principle was quite explanatory in several ways, including: (1) increasing resin infiltration as a result of increased solubility of monomers in ethanolsaturated etched enamel; (2) preventing phase separation of monomer blends during infiltration; and (3) enhancing mechanical properties of the resulting polymer, because of enhanced resin infiltration due to the absence of water and the polymerization of monomers due to phase separation. It is clear that increasing the solubility of a resin in a medium improves resin infiltration and prevents phase separation. 19 Substitution of water in nanoscale spaces around and within enamel crystallites (inter- and intracrystallite spaces) and enamel rods affected by acid etching with ethanol, prior to resin infiltration, facilitates resin infiltration into these nanoscale spaces, due to their good solubility in ethanol. 18 Indeed, there are always nanoscale voids and channels filled with water around and within enamel crystallites and rods. Water constitutes about 5e10% by volume of enamel, making the enamel porous. 25 It is well known that these nanovoids and nanochannels play a critical role in the caries process. Recently, it was shown that a novel caries-prevention method, which uses a similar ethanoldehydration protocol prior to application of a resin infiltrant to fill and block these nanovoids and nanochannels, was efficient in clinically arresting the dental caries process. 30,31 Indirect evidence from clinical and in vitro studies associated with resin infiltration techniques, showed that they arrested and prevented dental caries, 32 suggesting that nanovoids within the subsurface enamel are filled with resin monomers via chemical dehydration of etched enamel by ethanol. Therefore, it is meaningful to speculate that due to substitution of water within nanovoids and nanochannels around enamel crystals with ethanol, adhesive resin monomers can efficiently infiltrate these nanovoids, facilitating an extension of microscale retention of etch-and-rinse adhesives to nanoscale retention, which may explain results of the present study. Indeed, as noted by Tay et al, 33 nano-retention means encapsulation of individual enamel crystallites by resin, which occurs 34 when deploying hydrophilic total etching adhesives. With the results of the present study in mind, ethanol-wet-bonding may improve current nano-retention abilities of tested hydrophilic adhesives, due to the aforementioned aspects. Furthermore, the success of ethanol-wet-bonding on enamel bonding can partly be attributed to the higher degree of conversion of resin monomers, and prevention of nano- and microphase separation of resin monomer blends, 35 due to the nearly complete removal of water from the demineralized enamel by chemical dehydration of the demineralized enamel zone, which contains a higher extent of water than sound enamel due to the ethanol. It is known that the presence of water during polymerization of monomers results in a porous permeable polymer, 9 and it was recently shown that 10% residual ethanol even significantly enhanced the degree of conversion of monomers. 35,36 Therefore, mechanical properties of the resulting hybrid zone are greater. 37 Although ethanol-wet-bonding was developed to allow hydrophobic resin adhesives to bond to dentin, with the aim of reducing water sorption over time, it appears that a number of studies on ethanol-wet-bonding with commercial and more-hydrophilic adhesives are increasing over time, 14,38,39 and also in vivo studies on ethanol-wetbonding are ongoing. 7 As the effects of ethanol-wetbonding on the durability of hydrophilic-resin dentin were promising according to previous studies, this interest indicates that ethanol-wet-bonding is not so far from clinical practice. Therefore, commercially available dental adhesives, Single Bond 2, a simplified etch-and-rinse adhesive, and All-Bond 3, a conventional etch-and-rinse adhesive, were selected as resin adhesives in the present study. According to the results of the present study, ethanolwet-bonding increased the bond strengths of all tested adhesives to enamel. Results of the two-way ANOVA indicated that ethanol-wet-bonding resulted in significant improvement of the bond strength of Single Bond 2 compared to that of All Bond 3. More recently, Pashley et al found that ethanol-wet-bonding improved the durability of resinedentin bonds using Single Bond Therefore, it was speculated that Single Bond 2 can simultaneously be used with ethanol-wet-bonding for dentin and enamel bonding, despite there being limited information on the effects of ethanol-wet-bonding on the adhesiveness of commercial adhesives to dentin and enamel. However, results of the present study indicate some implications of ethanol-wet-bonding on enamel for clinical practice, since enhancing the quality of resineenamel bonding may improve the clinical performance of toothcolored restorations that involve enamel borders, at least in reducing the incidence of marginal discoloration. Improved, more-durable resineenamel bonds may be achieved by ethanol-wet-bonding in the future. Moreover, improved resineenamel bonds may increase the durability of resinedentin bonds obtained via ethanol-wet-bonding. It is well known that evidence from water storage-aging

6 Enamel bonding with an ethanol-wet-bonding technique 21 studies suggested that resinedentin bonds were protected by resineenamel interfaces. 40,41 Here, it was speculated that if the durability of resineenamel bonds with ethanolwet-bonding are greater than the conventional method, resinedentin bonds should also be more durable at the same time. Although the number of teeth employed in each group was rather small and intertooth differences existed which may have affected the results of the present study, the higher means and standard deviations obtained from specimens of a smaller diameter, make the mtbs test discriminative enough for detecting differences arising from treatment variables with the use of a smaller number of tooth specimens. 42 Moreover, a previous study showed that intratooth variations (i.e., the number of beams from each tooth) were either similar or even larger than intertooth variations. 43 In conclusion, according to the results of the present study, ethanol-wet-bonding has the potential to improve resineenamel hybridization, because of increasing infiltration of monomer blends into the etched enamel, preventing phase separation of the monomers, and enhancing their polymerization. The ethanol-wet-bonding technique on dentin and enamel may be used simultaneously and may provide the potential to create more-durable resinedentin bonds, thanks to a more-qualified resineenamel hybrid zone. In the future, there is a need to assess the durability of resineenamel bonds and resinedentin bonds with enamel borders, using ethanol-wet-bonding with different dehydration protocols. Conflicts of interest The authors have no conflicts of interest relevant to this article. References 1. Albers HF. Resin Bonding. Tooth-Colored Restoratives: Principles and Techniques, 9th ed. London: BC Decker, e 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;24:90e Spencer P, Wang Y. Adhesive phase separation at the dentin interface under wet bonding conditions. J Biomed Mater Res 2002;62:447e Spencer P, Ye Q, Park J, et al. Adhesive/dentin interface: the weak link in the composite restoration. Ann Biomed Engin 2010;38:1989e Tay FR, Pashley DH. Have dentin adhesives become too hydrophilic? J Can Dent Assoc 2003;69:726e Pashley DH, Tay FR, Carvalho RM, 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: 7e Breschi L, Mazzoni A, De Stefano D, Ferrari M. Adhesion to intraradicular dentin: a review. J Adhes Sci Technol 2009;7: 1053e Kanca J. Improving bond strength through acid etching of dentin and bonding to wet dentin surfaces. J Am Dent Assoc 1992;123:35e Tay FR, Pashley DH, Yoshiyama M. Two modes of nanoleakage expression in single-step adhesives. J Dent Res 2002;81:472e Tay FR, Pashley DH. Water treeingea potential mechanism for degradation of dentin adhesives. Am J Dent 2003;16:6e Tay FR, Pashley DH, Kapur RR, et al. Bonding BisGMA to dentinea proof of concept for hydrophobic dentin bonding. J Dent Res 2007;86:1034e SadekFT, Pashley DH, Nishitani Y, et al. Application of hydrophobic resin adhesives to acid-etched dentin with an alternative wet bonding technique. J Biomed Mater Res Part A 2008;84A:19e Hosaka K, Nishitani Y, Tagami J, et al. Durability of resin-dentin bonds to water- vs. ethanol-saturated dentin. J Dent Res 2009; 88:146e Pashley DH, Tay FR, Breschi L, et al. State of the art etch-andrinse adhesives. Dent Mater 2011;27:1e Sadek FT, Braga RR, Muench A, Liu Y, Pashley DH, Tay FR. Ethanol wet-bonding challenges current anti-degradation strategy. J Dent Res 2010;89:1499e Sadek FT, Mazzoni A, Breschi L, Tay FR, Braga RR. Six-month evaluation of adhesives interface created by a hydrophobic adhesive to acid-etched ethanol-wet bonded dentine with simplified dehydration protocols. J Dent 2010;38:276e Sadek FT, Castellan CS, Braga RR, et al. One-year stability of resin-dentin bonds created with a hydrophobic ethanol-wet bonding technique. Dent Mater: Official Publ Acad Dent Mater 2010;26:380e Becker TD, Agee KA, Joyce AP, et al. Infiltration/evaporationinduced shrinkage of demineralized dentin by solvated model adhesives. J Biomed Mater Res Part B: Appl Biomater 2007; 80B:156e Sauro S, Watson TF, Mannocci F, et al. Two-photon laser confocal microscopy of micropermeability of resin-dentin bonds made with water or ethanol wet bonding. J Biomed Mater Res Part B: Appl Biomater 2009;90B:327e Osorio E, Toledano M, Aguilera FS, Tay FR, Osorio R. Ethanol wet-bonding technique sensitivity assessed by AFM. J Dent Res 2010;89:1264e Kanca J. Resin bonding to wet substrate. II. Bonding to enamel. Quintessence Int 1992;23:625e Eick JD, Gwinnett AJ, Pashley DH, Robinson SJ. Current concepts on adhesion to dentin. Crit Rev Oral Biol Med 1997;8:306e Perdigão J. Dentin bondingevariables related to the clinical situation and the substrate treatment. Dent Mater 2010;26:e24e Tay FR, Gwinnett JA, Wei SHY. Micromorphological spectrum from overdrying to overwetting acid-conditioned dentin in water-free, acetone-based, single-bottle primer/adhesives. Dent Mater 1996;12:236e Berkovitz BKB, Holland GR, Moxham BJ. Enamel. Oral Anatomy, Histology & Embryology. London: Mosby, e Qvist V, Qvist J. Effect of ethanol and NPG-GMA on replica patterns on composite restorations performed in vivo in acidetched cavities. Scand J Dent Res 1985;93:371e Miyazaki M, Sato H, Onose H, Moore BK, Platt JA. Analysis of the enamel/adhesive resin interface with laser Raman microscopy. Oper Dent 2003;28:136e Spears IR. A three-dimensional finite element model of prismatic enamel: a re-appraisal of the data on the Young s modulus of enamel. J Dent Res 1997;76:1690e Sano H, Ciucchi B, Matthews WG, Pashley DH. Tensile properties of mineralized and demineralized human and bovine dentin. J Dent Res 1994;73: Ekstrand KR, Bakhshandeh A, Martignon S. Treatment of proximal superficial caries lesions on primary molar teeth with resin infiltration and fluoride varnish versus fluoride varnish only: efficacy after 1 year. Caries Res 2010;44:41e Paris S, Hopfenmuller W, Meyer-Lueckel H. Resin infiltration of caries lesions: an efficacy randomized trial. J Dent Res 2010; 89:823e6.

7 22 M.K. Ayar et al 32. Kielbassa AM, Muller J, Gernhardt CR. Closing the gap between oral hygiene and minimally invasive dentistry: a review on the resin infiltration technique of incipient (proximal) enamel lesions. Quintessence Int 2009;40:663e Tay FR, Pashley DH. Etched enamel structure and topography: interface with materials. In: Eliades G, ed. Dental Hard Tissues and Bonding: Interfacial Phenomena and Related Properties. New York: Springer, Hannig M, Bock H, Bott B, Hoth-Hannig W. Inter-crystallite nanoretention of self-etching adhesives at enamel imaged by transmission electron microscopy. Eur J Oral Sci 2002;110:464e Ye Q, Park JG, Topp E, Wang Y, Misra A, Spencer P. In vitro performance of nano-heterogeneous dentin adhesive. J Dent Res 2008;87:829e Cadenaro M, Breschi L, Rueggeberg FA, et al. Effects of residual ethanol on the rate and degree of conversion of five experimental resins. Dent Mater 2009;25:621e Ye Q, Spencer P, Wang Y, Misra A. Relationship of solvent to the photopolymerization process, properties, and structure in model dentin adhesives. JBiomedMaterResPartA2007;80:342e Sauro S, Toledano M, Aguilera FS, et al. Resin-dentin bonds to EDTA-treated vs. acid-etched dentin using ethanol wetbonding. Dent Mater 2010;26:368e Carvalho CA, Cantoro A, Mazzoni A, Goracci C, Breschi L, Ferrari M. Effect of ethanol application on post-luting to intraradicular dentine. Int Endod J 2009;42:129e De Munck J, Van Meerbeek B, Yoshida Y, et al. Four-year water degradation of total-etch adhesives bonded to dentin. J Dent Res 2003;82:136e Gamborgi GP, Loguercio AD, Reis A. Influence of enamel border and regional variability on durability of resin-dentin bonds. J Dent 2007;35:371e Tay FR, Pashley DH, Yiu CKY, Sanares AME, Wei SHY. 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: 27e Loguercio AD, Barroso LP, Grande RH, Reis A. Comparison of intra- and intertooth resin-dentin bond strength variability. J Adhes Dent 2005;7:151e8.