OBJECTIVE There is some evidence that water rinsing immediately after topical fluoride therapy has the potential to reduce the effectiveness of fluoride. The aim was to determine if covering fluoridated teeth with a layer of mousse containing CPP-ACP could prevent the adverse effect of rinsing on fluoride and consequently its buffering effect on dental plaque pH during cariogenic challenge. METHODS This randomized, controlled, crossover, in situ study was conducted on 25 participants. The participants were subjected to acidulated phosphate fluoride (APF) application followed by five treatment protocols: (1) water rinsing after 30 minutes (APF-30) or (2) immediate water rinsing (APF-0); (3) using CPP-ACP immediately before water rinsing (F-CPP-ACP); and two control groups: (4) no fluoride therapy (No-F) and (5) using CPP-ACP and immediate water rinsing (CPP-ACP-0). After 48 hours, teeth were rinsed with 10% sucrose solution and plaque pH was measured before and after 5, 10, 15, 20 and 30 minutes. RESULTS The least pH changes, the lowest pH drop, and the quickest pH recovery were found in the APF-30 and F-CPP-ACP groups. APF-0 ranked in the middle and the highest values were in the control groups. CONCLUSIONS The results show that in the case using CPP-ACP on fluoridated teeth, water rinsing immediately after topical fluoride therapy did not seem to influence the inhibitory effect of fluoride on plaque acidity.