Efficacy of waiting periods and topical fluoride treatment on toothbrush abrasion of eroded enamel in situ.

The aim of this study was to investigate the effectiveness of both waiting periods between acid exposure and tooth brushing and fluoride applications in preventing toothbrush abrasion of acid-softened enamel surfaces. The study, on 5 subjects, had an in situ crossover design with experimental periods of 5 days each. Human enamel samples were recessed in mouth appliances and at the end of each experimental period, enamel loss was determined profilometrically. Specimens were eroded extraorally (2 x 20 min per day; 0.05 M citric acid), standardized brushing (2 x 30 s per sample per day; powered toothbrush) was performed in situ. The groups were: (1) erosion only, (2) brushing with fluoride-free toothpaste directly after, (3) 2 h after, or (4) before erosion; fluoride application was either (5) brushing with a fluoride toothpaste or (6) brushing with a fluoride toothpaste or gel, and rinsing with a fluoride mouth rinse. Enamel loss was (1) 45.2 +/- 10.8, (2) 79.3 +/- 7.8, (3) 81.7 +/- 9.5, (4) 69.7 +/- 13.8, (5) 51.5 +/- 13.0, and (6) 41.2 +/- 1.8 microm. Brushing without fluoride increased the enamel loss significantly (p < or = 0.001), waiting for 2 h had no protective effect, and brushing before erosion decreased enamel loss values only by 12% (n.s.). In the fluoride groups, enamel loss was significantly lower than after brushing with the fluoride-free toothpaste and comparable to values after erosion only (n.s.). Waiting periods had only a minor effect, whilst the application of fluoride appeared promising.