Bond strength of self-etching adhesives IntroducIon One of the main problems detected by dental cli- nicians after restoring a Class V cavity is the mar- ginal quality, especially when the cervical margin is placed in dentin.1 This marginal area is of particular interest, as it is more prone to marginal microle- akage.2 This problem occurs because of the mor- phological and dynamic aspects of dentin. A variety of composites and polymerization techniques have been tried to provide better marginal adaptation.1 Another clinical approach to address this problem is the use of different adhesive systems.3 Applying etch-and-rinse adhesives leads to dentin demin- eralization; as a consequence, the opening of den- tin tubules and exposure of collagen fibers occur in this enamel-free area.4 Increased tubular fluid flows might be impeditive to the monomers’ ability to permeate around collagen fibers.5 Another prob- lem is the discrepancy between the depths of de- mineralization and monomer resin infiltration, leav- ing areas in which collagen fibers are exposed and unprotected. As a consequence, nanoleakage may occur within the hybrid layer in gap-free margins.6 Uninfiltrated, exposed collagen fibers are consid- ered the weakest link of the hybrid layer, as they are subjected to hydrolytic degradation by oral or den- tinal fluid.7 As a result, marginal and internal gaps develop.8 On the other hand, the use of self-etching adhesives has been advocated for many clinical ap- plications.9 Their adhesion mechanism favors ad- hesion by simultaneously etching and infiltrating the adhesive monomer into the dentinal surface.10 The original idea behind the use of this category of adhesives was an attempt to avoid not only tubular opening but also collagen fibril exposure. However, it has been reported that nanoleakage along resin/ dentine interfaces is produced by self-etching sys- tems, thus suggesting water movement within res- in-dentine interfaces not only within voids left in un- infiltrated areas of the hybrid layer, but also within the adhesives.11 It has also been claimed that the nanoleakage observed when self-etching adhesives are applied is not necessarily caused by disparities between the depths of demineralization and resin infiltration.12 In fact, the nanoleakage highlighted areas of increased permeability within a polymer- ized resin matrix in which water was incompletely removed, resulting in regions of incomplete polym- erization and/or hydrogel formation.12 Moreover, polymerization shrinkage, compos- ite viscoelastic properties, and adhesion to and the flexibility of cavity walls are additional factors that influence the integrity of this area.13 Clinically, stresses may also be generated at the interface during tooth function. These stresses are even more critical in Class V restorations because they may undergo flexure along with tooth mastication.14 Thermal and/or mechanical stress concentration may lead to the deterioration of preexisting gaps or the formation of new ones.15 It is believed that the presence of gaps, irrespective of their size/exten- sion, adversely affects the longevity of bonded res- torations.16 The aim of this in-vitro study was to evaluate the influence of water storage and thermo-mechanical cycles on the bond strength, microleakage, and in- ternal gaps of composite restorations when various adhesive systems were applied to dentin-margin in Class V preparations (a two-step etch-and-rinse, a two-step self-etching, and a one-step self-etching adhesive). The research hypotheses tested were: (1) microleakage, (2) axial gap width, and (3) bond strength would demonstrate better results when self-etching adhesives are applied in comparison to a conventional etch-and-rinse adhesive system. MAtErIALs And MEtHods Microleakage and adhesive gap extension evaluations Thirty sound human premolars were scaled, cleaned with slurry of pumice and water, and stored in a 0.1% thymol solution at room temperature to prevent bacterial growth. Teeth were obtained and used in accordance with a protocol approved by the Human Assurance Committee (file number: 10- 03-334). Teeth were selected and their roots were embedded in epoxy resin. Class V cavity prepara- tions (2 mm wide x 3 mm long x 1.8 mm deep) were made on the buccal and lingual surfaces at the cement-enamel junction. Cavity dimensions were standardized using a digital caliper (Model CD-6BS; Mitutoyo, Tokyo, Japan). The composition and ap- plication modes of the adhesive systems studied are described in Table 1. The specimens were ran- domly divided into 3 groups (n=20) according to the adhesive system used: a two-step etch-and-rinse system [ASB2] (Adper Single Bond 2 - 3M/ESPE, St. Paul, MN, USA), a two-step self-etching system [ASE] (AdheSE, Ivoclar Vivadent, Schaan, Liechten- 170 European Journal of Dentistry