Synopsis

Objective:
There is a significant consumer demand for toothpastes that help whiten teeth. Teeth staining is mostly caused by dietary habits and respective extrinsic stains formation.
Comparing different toothpastes whitening claims can be challenging due to variability in test substrate types, dimensions, inter-substrate variability, staining models, etc.
A standardized methodology that quantifies extrinsic stain removal without abrading the surface was developed, by using in-vitro Hydroxyapatite surfaces, as it is human tooth enamel main component.
Stain removal was quantified by CIELab L colour factor (white / black axis) measurements.

Methods:
Different Hydroxyapatite surfaces were tested, using coffee and Yorkshire-tea based-solutions to stain the surfaces at 37 ± 1˚C.
The number of staining cycles needed and type of surface finish (polished or rough surface) were evaluated.
The stained surfaces were brushed with a toothpaste-based dilution and DI water alone, simulating a 3-week teeth-brushing period. The toothpaste prototype used had an abrasive system comprising hydrated silica and calcium carbonate.

Results:
To enable sufficient surface staining, a surface with roughness and a total of four staining cycles were performed. This allowed for the extrinsic stains to adhere to the surfaces. If the surfaces were polished the stains didn’t adhere to the surface.
Following brushing with the diluted toothpaste-medium there was a significant increase in stains removal, as shown by surface whiteness value increase A whiteness increase from 23-129% was noted, depending on the tested surface type.

Conclusions:
In vitro whitening assessment trials by extrinsic stain removal using synthetic substrates would allow sourcing of more homogeneous test surfaces with a bigger surface area.
This laboratory methodology based using in-vitro surfaces could be used for pre-clinical trials product benchmarking screening and claims support.
Keywords
Hydroxyapatite, toothpaste, teeth extrinsic stains, in-vitro test surfaces.