40 specimens were prepared from fresh-extracted human molars and further embedded using the acrylic resin. Specimens were randomly divided into 2 groups according to the treatment before in vivo erosion (n=20): CPP-ACP for 3 min (CPP-ACP group) and deionized water for 3 min (control group). 10 healthy volunteers were recruited and customized maxillary appliance containing 4 specimens (2 from CPP-ACP group and 2 from control group) was fabricated for each volunteer. Participants were instructed to drink 150 ml cola in 5 min using the gargling method after placing appliances intraorally for 2 h. The in vivo attacks were performed 4 X 5 min with 1-h interval daily over 7 d. The surface microhardness and surface microstructure of the specimens were evaluated at the baseline and after the treatment. The data were statistically analyzed using three-way ANOVA and post hoc tests. Data were considered statistically significant at a level of P <0.05.

Inclusion Criteria:

• 18 to 60 years of age and in good general health
• Dental erosion and wear degree is 0-1

Exclusion Criteria:

• Systemic diseases or oral mucosal disorders
• Current orthodontic treatment
• Pregnancy
• Known allergies to the experimental drink
• Had been given drugs which lead to dry oral more regularly within half a year