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Zafar MS, Ahmed N. Dent Mater J 2015;34: 315–320

The temptation is to always extend the etching time when placing a resin composite, particularly if the classical frosted appearance of the enamel is not achieved, or if the occlusion is considered unfavourable. The aim of this study was to look again, at the effect of different etching times. In this in vitro study, the investigators did not examine bond strengths, but instead measured non-contact surface roughness and surface hardness. Different etching regimens, using 37% phosphoric acid, were carried out on 1 mm buccolingual sectioned slices prepared from 36 extracted premolar teeth. Images of roughness profile showed an increased peak-to-valley distance with increased etching times. This would suggest 'larger resin tags and thicker hybrid layer' that may compromise bond strength. In addition, it was argued that the observed 'decrease in hardness can affect the enamel-materials interface and early failure of material bond.'