Abrasive Particle Size and Enamel Surface Finish

Objectives: Recently reported data demonstrated that abrasive particle size has significant influence on enamel surface finish in terms of gloss, wear depth and surface roughness (J Dent Res (Spec Iss A): 727, 2011). Since most abrasive systems used in toothpastes will display a distribution of particle size, the objective of this study was to examine the effects of mixing two defined sizes of abrasive particles (3µm and ultra-fine 0.05µm) which individually show very different abrasive effects on surface finish of enamel. Methods: Eight bovine enamel specimens per treatment group were prepared to a) 1200-grit SiC and 3 µm diamond finish (Polished group), and b) P800 ground finish (Roughened group) and surface profiled. Specimens were double-brushed sequentially for 3,000, 5,000 and 10,000 strokes in a reciprocal action brushing simulator using slurries containing 1.0 w/w% abrasive (100% ultra-fine, 3:1 ultra-fine:3µm, 1:1 ultra-fine:3µm; 1:3 ultra-fine:3µm and 100% 3µm) in carboxymethyl cellulose plus glycerol. Oral B P35 toothbrush was used for the brushing with 150 g load at 20 °C. After brushing, specimens were surface-profiled for wear depth and surface analysis and surface gloss assessed with a glossmeter. Results: For wear depth and surface roughness, the mixed abrasives showed a relatively close relationship to the proportional properties of the two abrasive particle sizes present in the slurries. However, for surface gloss (a sensitive measure of surface finish), the benefits of use of an optimal particle size alone were lost when mixed with a more abrasive particle size, the latter of which tends to dominate the surface finish. Conclusions: The selection of optimal abrasive particle size for use in toothpastes can have appreciable influence on the wear and surface finish of enamel after brushing.