Three clinical evaluation for caries diagnosis will be performed: one at baseline, a second at the end of the chewing period (after 12 months from baseline) and a third after 24 months from baseline assessment. A microbiological evaluation for cariogenic bacteria will be performed immediately after the clinical assessments. Mutans streptococci and lactobacilli counts in saliva will be assessed and categorized using the dip-slide technique (CTR bacteria, Ivoclar Vivadent, Germany).