The effect of shape and size distribution of abrasive particles on the volume loss of enamel using micro-abrasion

Wear of enamel during tooth brushing is a complex phenomenon with many variables affecting the level of loss. Toothpastes contain angular abrasive particles at a concentration of 12%-15% v/v abrasive designed to remove biofilm and extrinsic stains that also have the potential to harm the tooth enamel resulting in wear. Toothpastes contain multi-modal particles in the size range of 4 mu m-12 mu m. The aim of this paper is to develop an understanding of the relationship between the combined effects of particle shape, size, size distribution and load on the volume loss of enamel under abrasive testing. Micro-abrasion testing using a Nylon ball, to simulate the toothbrush, was undertaken on hydrated bovine enamel disks using volume concentrations of 5% - 20% v/v alumina and silica. Post experimental surface analysis was performed to analyse the wear scar morphology and groove analysis. The synergistic effects were calculated of bimodal particles vs. mono sized particles. Mono-sized particles as compared to bimodal, appeared to give the best outcome and least wear of enamel. A positive synergy existed for the alumina and silica bimodal tests, indicating the bimodal particle distribution was causing fracture of the enamel prisms (rods), followed by micro-chipping and removal of enamel. The magnitude and the distribution of the particle sizes is the most dominant factor in determining the levels of wear, with smaller particles and narrow distributions of the particle size reducing the magnitude of wear. The shape of the particles is also a major factor influencing wear, with the spherical tests generating lower wear rates than the angular tests.