Dpu 10

Five disk-shaped specimens (2.0 mm in diameter × 3.0 mm in thickness) were prepared for each experimental composite. The specimens were embedded in epoxic resin, inside PVC cilinders, with the irradiated surfaces facing a glass plate. After the cure of epoxic resin, the irradiated surfaces were wet polished (DPU 10, Struers, Denmark) with 1200 and 4000 grit SiC paper (250 rpm/60 s in each paper) and five knoop indentations spaced of 500 μm were made in each specimen with 25 g load and dweel time of 15 s (Micromet 5104 / Full MHT software, Buëhler, Lake Bluff, IL, USA). The average of five indentations were take as the KHN for each specimen.

Thirty bovine incisors selected according to similar color and maintained in a 0.2% thymol solution at 4°C for one week were used in this study. Before the specimens' preparation, the teeth were examined under a stereomicroscope at 10x magnification (SZ40, Olympus, Tokyo, Japan) to identify the presence of any defects that could interfere with the obtained results. The roots were separated from the crowns and the teeth were sectioned through the pulp chamber using a low speed water-cooled diamond saw (Isomet 1000, Buehler, Lake Bluff, IL, USA) to obtain enamel/dentin slices from their labial surfaces. The enamel and dentin surfaces of each slice were ground flat with 1200-, 2500-, and 4000-grit SiC papers (DPU-10, Struers, Copenhagen, Denmark), which was controlled with a digital caliper (MPI/E-101, Mitutoyo, Tokyo, Japan), until reaching a thickness of 2.0±0.1 mm (1.0 mm of dentin and 1.0 mm of enamel). Afterwards, disc-shaped enamel/dentin specimens with 8.0 mm in diameter were prepared from each slice by using a diamond bur (#3097, KG Sorensen, Cotia, SP, Brazil) in a highspeed hand piece fixed in a special sample-aligning device. The specimens were randomly divided into three groups of ten specimens according to the three toothpastes analyzed (Figure 1) and kept in artificial saliva at 37°C before taking all measurements.