Influence of Toothbrush on the in-vitro Assessment of Toothpaste Abrasivity

The assessment of toothpaste abrasivity in-vitro is an important process by which all dentifrices are classified relative to an abrasive standard. Standardization of the process and the variables involved is critical for comparison of data. The nature of the brush used in abrasivity assessment may represent a significant factor in variability between test centres. Objectives: To investigate the effects of using the BS ISO 11609 recommended medium texture Pepsodent (Pep) and Oral B Compact P35 (OBP35) brush-heads on the abrasivity of a calcium pyrophosphate slurry on enamel and dentine using a newly developed brushing machine. Methods: Sound non-irradiated human teeth, extracted for orthodontic purposes, were resin embedded according to BS 5136 / BS ISO 11609 for abrasivity assessment of toothpastes and flat dentine and enamel specimens were prepared by grinding and polishing to a final 3µm diamond finish. Specimens (n=8 per treatment) were brushed 10,000 double-strokes for enamel and 2,000 double-strokes for dentine, with slurries of Prayon calcium pyrophosphate in 0.5% Hercules 7MF carboxymethylcellulose with 10% glycerol. Brushing was performed at 120 strokes/min with the 2 brush types and brush-head loading of 150g at a temperature of 20°C. Before and after brushing, specimens were profiled on a Taylor-Hobson Talysurf Series 2 profilometer to quantify the amount of abrasion. Results: The mean ± standard deviation values for depth of abrasion of specimens after brushing with each brush-head were : Pep brush : enamel 0.5580±0.2658µm, dentine 5.4408±2.0459µm; OBP35 brush : enamel 1.4019±0.4029µm, dentine 8.1373±1.6238µm. Conclusions: OBP35 toothbrushes caused appreciably more abrasion on both enamel and dentine compared with the Pep toothbrush, which may reflect relative filament stiffness. Although the filament area of the 2 brush types was similar, the filaments of the Pep brush were significantly stiffer. The type of toothbrush used is an important variable to be standardized in abrasivity assessment.