Abrasion of Bovine Enamel With Increasing Surface Loss

Bovine enamel has long been used in toothpaste abrasivity assessment protocols, however, it is not clear how the wear susceptibility of the tissue changes through its thickness. Objectives: Characterise the effects of abrasive wear on sound bovine enamel specimens after successive toothbrushing procedures and grinding/polishing operations, relating abrasion depth, surface roughness and gloss to enamel thickness. Methods: Sixteen sound bovine enamel specimens were prepared to a flat polished (3µm diamond) finish and subjected to a toothbrushing procedure with slurries of Sident 9 silica abrasive in 0.5% carboxymethylcellulose with 10% glycerol, for 10,000 double-strokes (ISO conditions) using a novel tooth-brushing simulator. Brushing parameters were: 120 strokes/min with Oral-B P35 toothbrushes, brush-head loading of 150g at 20^oC. Following each brushing procedure, eight specimens were ground and polished to remove minimal enamel to achieve flatness (~50µm), and eight were ground and polished to remove an increased quantity of enamel (~100µm). Before and after brushing treatments, specimens were surface profiled using a Taylor-Hobson Talysurf Series 2 profilometer to quantify the mean abraded depth and surface roughness. Gloss measurements were taken using a Novo-Curve small area gloss meter. Results: The first 2 successive brushing treatments in each group did not show a significant difference in mean abrasion depth, or mean roughness values, however, successive brushing treatments did demonstrate a significant increase (p<0.05) in abraded depth for both groups. There was a trend towards increasing abrasion depth and increasing roughness with decreasing enamel thickness, however, gloss values did not appear to be affected overall by enamel thickness. Conclusions: The susceptibility of bovine enamel to wear and the surface roughness appear to increase with decreasing enamel thickness. Studies on wear of the enamel surface need to carefully control the depth of enamel tissue examined to ensure reproducibility between studies.