Bovine incisors were selected, cleaned with a rotating bristle brush and pumice/water slurry, and washed with tap water. Then, enamel slabs with dimensions of were sectioned from the middle third of the crown using a low-speed saw in a cut machine (Labcut 1010, Extec Corp., London, United Kingdom). These slabs were flattened under water cooling on a rotating polishing machine (Ecomet 3, Buehler, Lake Buff, Illinois) using silicon carbide paper (400, 600, and 1200 grits in sequence) and polished with a 1-μm diamond suspension. Then, the samples were visually checked for the absence of cracks or defects with a loupe ( magnification), and baseline surface microhardness analysis (SMH) was performed. Totally, 288 plane enamel blocks without defects, with SMH mean (standard deviation) values of , were selected and sterilized with gamma radiation (25 kGy).