Persistence of scratching induced by toothpaste brushing of denture acrylic

During the manufacture of a new denture, extensive care is taken to ensure the creation of a high quality polished finish that resists colonization and subsequent fouling by bacteria. However, this pristine state does not last long. With repeated daily use of toothpastes that typically contain abrasives optimized primarily for use on enamel, scratches may develop especially if the brushing is consistently applied along a preferred direction. Although the initial increase in surface roughness resulting from this abrasive action is significant, the cumulative effect of daily brushing is less certain. With continued usage, existing scratch features could either persist or be obliterated by the development of new features. Objectives: To study the effect of multiaxial brushing with toothpaste on the potential formation and removal of visible scratches on acrylic substrates. Methods: Substrates of either Lucitone 199 denture acrylic or Acrylite industrial acrylic were prepared for this study. All samples were polished to a uniform surface roughness (Ra ca. 0.07 microns) comparable to that achieved during denture manufacture. Substrates were then subjected to various sequences of automated brushing using a combination of silica based toothpaste and Oral-B toothbrushes in a downforce standardized V-8 Cross Brushing machine. The resulting surface condition of the substrates was assessed both qualitatively and quantitatively using digital imaging analysis and a glossmeter. Results: Scratches formed during early stages of the automated brushing sequence were generally not “polished out” with subsequent brushing, even when applied in a direction normal to initial brushing. Once lost, surface gloss was never recovered. Conclusions: Long-term brushing with abrasive-containing toothpastes tends to accumulate scratches which collectively increase surface roughness which could detract from denture appearance. Disclosure: Research supported by GlaxoSmithKline