Sof-Lex system (Batch No. NC11342, 3M ESPE, St. Paul, MN, USA) was used to polish the samples. This system is composed by two wheels, beige and white. Both are of thermoplastic elastomer impregnated with aluminum oxide particles. The beige spiral was used for removing the scratches, smoothing, and finishing and the white one was used for final polishing. For each sample a beige spiral wheel and a white spiral wheel were used once for 1 min (30 s for each wheel). Both wheels were used at a speed of 20,000 revolutions per minute.
After this procedure 80 samples from each group were subjected to submersion in hydrochloric acid. In each group 20 samples were maintained as they resulted after finishing and polishing procedure (subgroup 1), 100 samples were exposed to hydrochloric acid action, and 40 samples followed a toothbrushing simulation process. The distribution of the samples in groups is detailed inFigure 1 .
After this procedure 80 samples from each group were subjected to submersion in hydrochloric acid. In each group 20 samples were maintained as they resulted after finishing and polishing procedure (subgroup 1), 100 samples were exposed to hydrochloric acid action, and 40 samples followed a toothbrushing simulation process. The distribution of the samples in groups is detailed in