The effect of toothpaste concentration on enamel and dentine wear in vitro

To determine the effect of toothpaste concentration on enamel and dentine wear in vitro and to model the effects of toothpaste abrasion upon dilution during toothbrushing in vivo.

Polished human enamel/dentine specimens were indented with a Knoop diamond and the enamel-dentine junction profiled. Specimens were brushed for 1200s with toothpastes with differing relative dentine abrasivity (RDA), either Toothpaste A (RDA=90) or Toothpaste B (RDA=200), using a toothbrush mounted in a brushing machine. The toothpastes were dispersed in water and 1% sodium carboxymethyl cellulose to give a range of toothpaste concentrations. After brushing the Knoop indent length and the enamel-dentine step were remeasured and the wear to the enamel and dentine calculated. An equation for modelling the decrease in toothpaste concentration with brushing time was found using published in vivo data and used to estimate the level of dentine wear during in vivo brushing.

The mean enamel wear was in the range 0.03-0.11μm and there was only a small but non-significant (p>0.05) increase in enamel wear with toothpaste concentration. The mean dentine wear was in the range 0.28-27.63μm and the dentine wear increased significantly (p<0.05) with toothpaste concentration, with Toothpaste B giving more wear than Toothpaste A. Analysis with published in vivo data showed that 50% of dentine wear occurs in the first 20s of brushing and that the wear approaches a plateau value with brushing time as the toothpaste concentration is reduced.

Enamel wear increases only slightly with toothpaste concentration whereas dentine wear increases with toothpaste concentration.