A novel longitudinal erosion-abrasion in-situ model was proposed. In an exploratory test (phase 1) toothbrushing effect was investigated using a parallel design, whereas in the main study (phases 1 + 2), a crossover design tested the effect of fluoride dentifrice. In phase 1, 16 subjects (n = 5-6 subjects per group) wore partial dentures with enamel specimens for 28 d and adhered to one of the following treatment regimens: regimen A, erosion only; regimen B, erosion + toothbrushing with fluoride-containing dentifrice [1,100 ppm of fluoride as sodium fluoride (NaF)]; and regimen C, erosion + toothbrushing with placebo dentifrice (0 ppm fluoride). Erosion consisted of the exposure of specimens to grapefruit juice. In regimens B and C, toothbrushing was performed with the test dentifrices 5 min after erosion. For the main study a second phase was carried out in which subjects initially treated with regimen B were treated with regimen C, and vice versa (crossover, n = 11), repeating the same experimental protocol. Enamel wear was measured by optical profilometry at baseline and every 7 d thereafter. In the exploratory test (phase 1), no significant differences were observed among regimens at any of the study time-points. In the main study (phases 1 + 2), higher enamel wear was observed for regimen C than for regimen B. A significant trend was observed for the increase of enamel wear over time. Fluoridated dentifrice reduced the development of erosive-abrasive lesions. The proposed longitudinal model provided adequate responses for erosion-abrasion frequency and fluoride effects.
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