In dental offices, tooth whitening is the treatment that mostly increases in numbers in the last years. This protocol is considered an aesthetic one due to the benefits to patients’ sense of welfare, by the improvement on the smile aspect. However, literature shows that, after the procedure, patients may experience pain sensitivity. In this context, the present study utilized a SEM technique to compare the whitening on the superficial posterior tooth face, in three different cases: using a peroxide gel only, peroxide gel associated to light and light only. The results showed that the abrasion in teeth surface is greater with the use of gel than with light only.