Impact of brushing force on abrasion of acid-softened and sound enamel

ObjectiveThe study aimed to analyse the effects of different brushing loads on abrasion of acid-softened and sound enamel surfaces.DesignSound and acid-softened surfaces of each 10 human enamel samples were submitted to brushing abrasion in an automatic brushing machine at 1.5 N (A), 2.5 N (B), 3.5 N (C) or 4.5 N (D) brushing load. Prior to abrasion, demineralisation of half of each enamel surface was performed by storage in hydrochloric acid (pH 2.0) for 60 s. Brushing was carried out (1000 strokes) using a manual toothbrush and toothpaste slurry in a ratio of 1:3. Enamel loss was measured after 10, 20, 50, 100, 150, 200, 250, 300, 350 and 1000 brushing strokes (BS). Pre- and post-brushing values of Knoop indentation length (5 indentations each sample) were measured and mean enamel loss was calculated from the change in indentation depth. Within- and between-group comparisons were performed by ANOVA and t-test followed by Bonferroni-correction.ResultsEnamel loss of acid-softened surfaces was significantly influenced by the brushing load applied and was mostly significantly higher in group D (10–1000 BS: 225–462 nm) compared to A (10–1000 BS: 164–384), B (10–1000 BS: 175–370 nm) and C (10–1000 BS: 191–396 nm). Abrasion of acid-softened enamel was fourfold higher compared to sound surfaces. Sound enamel was significantly influenced by the brushing force at 20–200 brushing strokes only, but revealed no significant differences between groups A–D.ConclusionBrushing load influences abrasion of briefly eroded enamel, but might be of minor importance for abrasion of sound enamel surfaces.