Silica abrasivity and STP: effect on tooth stain removal in-vivo

Objectives: A key objective in whitening dentifrice development is to maximise stain removal performance without incurring excessive abrasivity.  This work investigates how in vivo tooth stain removal by brushing with dentifrice is affected by the abrasivity of the dentifrice silica system and the presence of the chemical stain removal agent sodium tripolyphosphate (STP).

Methods: This was a multi-centre, randomized, evaluator-blind, four-group parallel study, completed by 578 subjects.  Assessment of natural tooth stain was performed using the Lobene stain index (LSI) at baseline, week 6 and week 12. Abrasivity of dentifrices was determined using the Relative Dentine Abrasivity (RDA) test.  Three dentifrices of essentially identical base formulation were prepared with different silica systems of varying abrasivity.  Each contained 10% w/w STP.   A control dentifrice with no STP was also tested. Analysis of covariance was used for analysis of LSIs for week 6 and week 12 data. 

Results: The stain removal and abrasivity results were as follows (values with different superscript letters were significantly different (p<0.05)):

 

Dentifrice	LSI (area x intensity)  reduction 0 to 12 weeks	RDA
Control	0.14a	65 ± 1.7A
Low abrasive + STP	0.22a	91 ± 2.2B
Medium abrasive + STP	0.30b	128 ± 3.6C
High abrasive + STP	0.38b	185 ± 1.3D

Conclusions: This study showed a clear hierarchy of stain removal properties amongst the four dentifrices.  STP increased stain removal in vivo.  The cleaning performance of the dentifrices with different silica systems correlated closely with the abrasivity of the silica system.