Abstract
The aim of this study was to evaluate the microtensile bond strength of self-etch adhesive systems to dentin after storage in acids from oral biofilm. Three adhesive systems were used in the study: a two-step self-etch adhesive for use with a silorane-based resin composite (Filtek P90 adhesive system - P90), a two-step self-etch adhesive (Clearfil SE Bond - CSE) and a one-step self-etch adhesive (Adper Easy One - AEO). The bond strength of these products was evaluated by bonding resin composite (Filtek Z350 for CSE and AEO; and Filtek P90 for P90) to 90 bovine dentin tooth fragments, according to the manufacturer's instructions. After 24 h of water storage at 37 °C, the specimens were sectioned into beams (1 mm2) divided and stored in distilled water, lactic acid and propionic acid, for 7 and 30 days. After storage, the specimens were tested for microtensile bond strength. Data were analyzed by three-way ANOVA and Tukey´s test (α=0.05). CSE presented the highest microtensile bond strength after storage in distilled water for 7 and 30 days. The microtensile bond strength of all adhesive systems was lower after storage in lactic acid and propionic acid than after water storage. Significant difference was not found between storage times.
Highlights
The success of dental adhesive restorations depends on several factors [1], a stable bond between resin composites and tooth substrates seems to be one of most important aspects in dental practice [2], as a poor adhesive interface can trigger various deleterious effects that may lead to loss of restoration in long-term observation [3].Irrespective of the hybridization technique, using total-etch or self-etch adhesive systems, the hybrid layer obtained by the interaction between collagen fibers of the demineralized dentin and the resin monomers in dental adhesives, is the main coupling mechanism between tooth and restorative composites [2]
Extremely important for the success of adhesive restorations, the hybrid layer is known to be very susceptible to hydrolysis, which leads to weakening of the dentin-adhesive interface [4]
All adhesive systems presented lower the normal distribution of errors and the homogeneity of μTBS after storage in propionic and lactic acid compared to water storage after 7 days or 30 days storage
Summary
The success of dental adhesive restorations depends on several factors [1], a stable bond between resin composites and tooth substrates seems to be one of most important aspects in dental practice [2], as a poor adhesive interface can trigger various deleterious effects that may lead to loss of restoration in long-term observation [3].Irrespective of the hybridization technique, using total-etch or self-etch adhesive systems, the hybrid layer obtained by the interaction between collagen fibers of the demineralized dentin and the resin monomers in dental adhesives, is the main coupling mechanism between tooth and restorative composites [2]. Extremely important for the success of adhesive restorations, the hybrid layer is known to be very susceptible to hydrolysis, which leads to weakening of the dentin-adhesive interface [4] This phenomenon occurs when using the etch-and-rinse strategy due to the persistence of unprotected collagen at the bottom of the hybrid layer, which can undergo a harmful enzymatic action [2,5]. Despite expectations that this condition would not occur with the self-etch adhesive system [6], a study has shown the existence of partially demineralized non-infiltrated zones under the hybrid layer obtained using these materials [6]. This unexpected condition was found to be caused by the buffering effect of the tooth mineral content on the adhesive acidic monomers [5]
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