In the first phase, the "immediate" objective and subjective evaluation of dental discoloration by spectroscopic (CIE L*a*b* data analysis with DeltaE evaluation) and questionnaire-based analyses will be recorded. Immediate visual analysis of tooth pigmentation will be evaluated by volunteer him/herself, using a mirror, and by a single dentist soon after the end of each treatment. Participants will indicate the presence/absence of dental pigmentation, and to quantify it with a numeric scale (0= no pigmentation to 10= very strong pigmentation).