Erosion and attrition of human enamel in vitro Part I: Interaction effects

Objective. The aim of the study in vitro was to measure the interplay of attrition and erosion of human enamel under several different pH conditions. Materials and methods. Cusp and smooth surface enamel specimens were prepared from unerupted human third molar teeth. Cusp and smooth surface specimens opposed each other in a wear machine under a load of 600 g. The machine simulated tooth grinding for 30 min (2280 wear cycles). Six groups of 10 specimens were worn in the following environmental conditions: saline, citric acid at pH values of 3.2, 5.5 or 7.0 and two cycling groups (pH 3.2/saline or saline/pH 3.2). Additionally, 10 smooth surface specimens were exposed to the same fluids without attrition. Tissue loss on smooth surface specimens was determined by profilometry. The worn specimen surfaces were studied by SEM. Results. Attrition depth in saline and pH 7.0 citric acid was 25.5 μm. At pH 3.2 and 5.5 attrition depths were 6.0 and 4.3 μm, respectively. Cycling in saline/citric acid and vice versa produced attrition depths of 9.2 and 7.9 μm, respectively. In the erosion only specimens lesion depths were 3.0, 1.2 and 0 μm at pH 3.2, 5.5 and 7.0 and saline, respectively. Attrition specimens at pH 7.0 and in saline showed very rough surfaces. At low pH enamel surfaces appeared flat and smooth. Conclusions. Enamel wear in neutral conditions is significantly higher than in acidic conditions (p<0.05), apparently due to a smoothing effect of erosion on contacting surfaces.