Interaction between toothpaste abrasivity and toothbrush filament stiffness on the development of erosive/abrasive lesions in vitro.

OBJECTIVES: To investigate the loss of enamel and dentin surface caused by the interaction between abrasives in toothpaste and toothbrush filament stiffness.

METHODS: The study followed a 2 (high-level or low-level abrasive; silica) × 3 (filament stiffness; soft, medium or hard) × 2 (cycling time; 3 or 5 days) factorial design. Polished bovine enamel and dentin specimens (n = 8 each per group) were subjected to 5 days of erosion/abrasion cycling: erosion (5 minutes, four times daily, 0.3% citric acid, pH 3.75); abrasion (15 seconds, twice daily, 45 strokes each, 150 g load, automated brushing machine); and fluoride treatment [15 seconds with abrasion and 45 seconds without abrasion; 275 p.p.m. fluoride (F- ) as sodium fluoride (NaF) in abrasive slurry]. Enamel and dentin specimens were exposed to artificial saliva between erosion and abrasion/F- treatment (1 hour) and at all other times (overnight). Non-contact profilometry was used to determine surface loss (SL) after 3 and 5 days of cycling. Data were analysed using three-way analysis of variance (ANOVA) (factors: abrasive/filament stiffness/time), with separate analyses conducted for enamel and dentin.

RESULTS: For enamel, only 'cycling time' was found to affect SL, with 5 days of cycling resulting in a greater SL than 3 days of cycling. Overall, there was little SL for enamel (range: 0.76-1.85 μm). For dentin (SL range: 1.87-5.91 μm), significantly higher SL was found for 5 days of cycling versus 3 days of cycling, with particularly large differences for hard stiffness/high-level abrasive and medium stiffness/low-level abrasive. For high-level abrasive, after 5 days of cycling hard stiffness resulted in significantly higher SL than did medium stiffness, with no other significant differences according to stiffness. Overall, high-level abrasive resulted in significantly higher SL than did low-level abrasive, with strong effects for all combinations, except medium stiffness after 5 days.

CONCLUSION: The interplay between abrasivity and filament stiffness appears to be more relevant for dentin than for enamel.