Comparative study of wear of enamel induced by alternating and simultaneous combinations of abrasion and erosion in vitro.

Two types of interaction of erosive and abrasive forces with human enamel were analysed in an in vitro study. To simulate toothbrushing or chewing after an acidic challenge, enamel specimens were eroded in 0.3% citric acid (pH 3.2), then brushed with or without silica abrasive. To simulate simultaneous erosion and abrasion, as would occur during chewing of abrasive acidic food, enamel specimens were abraded in a toothbrushing machine, with and without silica abrasive, while immersed in citric acid. Enamel wear was measured by profilometry. In both experiments the combination of erosion and abrasion resulted in significantly greater wear than erosion alone, but no significant differences in wear after brushing with or without abrasive were found. Simultaneous erosion and abrasion resulted in about 50% more wear than alternating erosion and abrasion. It is concluded that softened enamel is highly unstable and potentially easily removed by short and relatively gentle physical action. Chewing of acidic foods with some abrasive properties might cause enhanced tooth wear.