Particle size effects on abrasion, surface polishing and stain removal efficacy in a tooth model system

Four calcined alumina abrasive particles [ultrafine (0.05 μm), 3 μm, 9 μm and 20 μm] with defined sizes were investigated for their effects on toothbrush abrasion, surface polishing and stain removal in vitro. The existence of a critical particle size (CPS) was shown for the first time in a tooth model system and in the present study a CPS of ~2.3 μm for d10, 4.3 μm for d50 or 7.8 μm for d90 for the calcined alumina abrasives was apparent. The d10, d50 and d90 values indicate that 10%, 50% and 90% of the particles measured were less than or equal to the size stated. This dimension enabled maximum abrasive action on the tested specimens resulting in the largest wear depth, greatest surface polishing and best stain removal. The enamel wear depth decreased when brushed with abrasives above the critical particle size and became almost independent of further particle size increases, which is useful for minimising wear effects in the development of dentifrice. The findings provide new information on abrasive particle size for modification and control of toothpaste abrasivity and cleaning.