An in vitro screening assay for dental stain cleaning

Bovine teeth (n = 8 per group) were ground/polished to provide flat enamel specimens and ferric-tannate deposits were precipitated onto the enamel surfaces. The ferric-tannate stained enamel specimens were brushed using an in vitro tooth-brushing simulator with slurries containing commercially available toothpaste products, dental abrasive particles, and sodium tripolyphosphate (STP) solutions of different concentrations. The colour of the enamel surfaces was measured using a spectrophotometer before and after stain application as well as after the brushing treatments.

Differences in stain removal efficacy were found between the toothpastes categorised as whitening and non-whitening comprising of different types of dental abrasives (hydrated silica and alumina). A mean value of 27% for stain removal was detected for the three non-whitening toothpastes and 59% of stain removal was detected for the three whitening toothpastes after 1000 strokes. Compared with the slurry with Zeodent 113 abrasive alone, the addition of STP provided better performance for stain removal under the same brushing conditions (mean value of 62% for Zeodent 113 abrasive alone and 72% with the addition of 5% (w/w) STP after 1000 strokes). No difference was evident between the STP concentration of 5% (w/w) and 10% (w/w).

The ferric-tannate/bovine enamel model reported here provides good stain retention, is rapidly and easily prepared, and is shown to be progressively and reproducibly sensitive to toothbrushing using different toothpastes and surfactant/chelating agent solutions. Importantly, it provides good discrimination between various oral hygiene products.

The stain removal assay reported here has considerable potential to enable comparative assessments of different toothpaste types in terms of their cleaning capabilities.