After the pH cycling, the enamel wear was determined in relation to the reference surfaces with a contact profilometer (Hommel Tester T 1000, Hommelwerke, VS, Schwenningen, Germany). The reference areas (half of the surface), which remained protected by nail varnish over the whole test period, were carefully cleaned with acetone-soaked cotton wool. Five readings were performed on each slab and the average wear depth was calculated (micrometers). These profilometric traces were taken from the reference surface, across the exposed surface.