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Introduction

The demand for esthetic restorations, the increased fear of amalgam toxicity and the environmental problems associated with mercury have increasingly led universities to teach resin composite for restorations of posterior cavities in many countries .

Despite the current good performance of resin composite in posterior teeth , postoperative sensitivity (POS) was already mentioned to be a problem with resin composite restorations. Early clinical studies have also indicated that up to 30% of the study populations have reported POS following placement of a posterior resin composite restoration , which were mostly attributed to the use of total-etch adhesives (nowadays named etch-and-rinse systems).

Etch-and-rinse systems employ a phosphoric acid to etch enamel and dentin prior to the application of the bonding solution. As a consequence, the smear layer is removed and the dentin tubules are opened, increasing the dentin permeability and hydraulic conductance of dentin . During etching, an excessive demineralization may occur reducing the chances for a complete monomer impregnation into the demineralized dentin .

An incomplete monomer penetration due to over-etching or inadequate adhesive application may leave voids in the hybridized area as well as denuded collagen fibrils allowing dentin fluid movement , under occlusal stress, extreme temperatures and sweet stimuli. This, in turn, sensitizes the nerve endings in the dentin tubules and causes POS.

This fact has led to a widespread belief that self-etch systems lowers the risk of POS as they do not remove, but incorporate the smear layer in the hybridized complex with the advantage of being less technique-sensitive . Although there is a biological plausibility behind this belief with some clinical studies reaching this conclusion , the perception that self-etch adhesives cause less POS than etch-and-rinse systems seems to be more anecdotal than an evidence-based finding , as other clinical trials do not support this trend .

Recently a meta-analysis has pointed out that POS is a very infrequent finding, not affected by the type of adhesive strategy (ER or SE) employed . This study has some limitations. Firstly, the authors have not applied a broad and sensitive search strategy and only one database was used. Secondly, the authors have not searched the grey literature, which is important to minimize publication bias. Lastly, the risk of bias of the included studies was not evaluated, possibly leading to a biased conclusion.

Therefore, we aimed to conduct a systematic review to identify the following focused question: Does the use of a self-etch adhesive compared with an etch-and-rinse system influence the risk and intensity of POS in adult patients with posterior restorations?