Objectives: The abrasive within a toothpaste is recognised as the principal tooth cleaning component. However, there is little published data regarding the contribution to stain removal of newer abrasive agents such as amorphous silicas, as the focus has been on comparing marketed dentifrices. This study was undertaken to investigate (i) the impact of the level of an abrasive silica on tooth cleaning and abrasivity in vitro in a typical toothpaste formulation, and (ii) to determine whether high silica incorporation levels might offer improved cleaning efficiency. Methods: Abrasive silica level was varied from 0-28% w/w in a base formulation containing sodium fluoride and sodium lauryl sulphate. To control viscosity, the thickening silica component was progressively reduced as abrasive silica level increased. Tooth cleaning was assessed by the Pellicle Cleaning Ratio (PCR) method and also by a natural extrinsic stain removal (NESR) method developed by GlaxoSmithKline. Abrasivity was determined by the Relative Dentine Abrasivity (RDA) method. Results: In the absence of abrasive silica, tooth cleaning performance and abrasivity of this formulation was very low, but rose to levels typical of marketed toothpastes at 14%. PCR increased little further at silica levels above 14%, which was consistent with the NESR results. In contrast, RDA increased markedly between 14% and 28% abrasive silica.

Abrasive silica level, % w/w	PCR (mean ± s.e.)	RDA (mean ± s.e.)
0	13.08 ± 1.73	6.54 ± 0.30
14	71.06 ± 3.03	50.69 ± 2.97
28	80.24 ± 4.21	77.12 ± 2.47

Conclusions: In this toothpaste system, the abrasive silica was shown to be the principal tooth cleaning and abrasive agent. Use of high levels of abrasive silica (28%) gave no clear cleaning benefit versus the more typical level of 14%. Cleaning was most efficient when the level of abrasive, and hence the abrasivity, was low.

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