Comparison of Brushing Machines in the in vitro Assessment of Toothpaste Abrasivity

Brushing of tooth specimens for in vitro assessment of toothpaste abrasivity should provide adequate abrasion for reproducible quantitation. A number of toothbrushing machines have been developed, although few comparative studies have been undertaken. Objectives: to assess the performance of four different designs of brushing machine in the in vitro assessment of toothpaste abrasivity. Methods: sound non-irradiated human teeth extracted for orthodontic purposes were resin embedded according to BS 5136 / BS EN IOS 11609 for abrasivity assessment of toothpastes and flat dentin and enamel specimens were prepared by grinding and polishing. Specimens (n=6 per treatment) were brushed (1000 strokes for dentin, 10,000 strokes for enamel) with slurries of Prayon calcium pyrophosphate in 0.5% Hercules 7MF carboxymethylcellulose with sequential dilution using one of four designs of brushing machine : flat-bed, vertical action, rotary action and V8 crossing action. Before and after brushing, surface profiles of each specimen were undertaken on a Taylor-Hobson Talysurf 2 profilometer to quantify the amount of abrasion. Results: The mean ± standard deviation values for depth of abrasion of specimens after brushing with each machine were : Flat-bed : enamel 0.0450±0.0085microns, dentin 0.5275±0.1150microns; Vertical action : enamel 0.3986±0.2284microns, dentin 0.7515±0.5159microns; Rotary action ; enamel 0.8867±0.0985microns, dentin 3.8046±0.6209microns; V8 cross action : enamel 0.1194±0.0402microns, dentin 0.6332±0.2398microns. Conclusions: We conclude that the greatest and most reproducible depth of abrasion was seen with the rotary action brushing machine under these experimental conditions and provides an appropriate methodology for in vitro assessment of toothpaste abrasivity.