Image Analysis and Spectrophotometry to Assess Stain Removal by Toothpastes

Objective: A typical in vitro method for screening the effects of dentifrices on tooth stain build-up and removal has been to measure the absorbance of methyl methacrylate blocks at 295nm or 395nm, stained with a tea and chlorhexidine regime. This study aimed to explore the application of a digital imaging approach, previously devised to measure tooth whiteness, for the measurement of stain inhibition and removal from these blocks, and to compare results with those obtained by absorbance spectrophotometry at a variety of wavelengths. Methods: The camera system designed for this in vitro use consisted of a high-resolution digital camera, four natural colour fluorescent tubes shining at an angle of 45°. Images were taken at 0° viewing geometry using the Avian white standard and then exported to Adobe Photoshop 5.0 software to provide 8-bit digital L (from L,a,b scale) values. Methyl methacrylate blocks were used to test for stain inhibition by alternate exposure to toothpaste and stain, and for stain removal by exposure to toothpaste, once stain had been developed. Results: For Aquafresh Whitening Toothpaste, Boots Advanced Whitening Toothpaste, Rembrandt Whitening Toothpaste and water (control), there was a good correlation between the 295nm absorbancy and the digital L value for both stain removal and stain inhibition. Conclusion: This study suggests that the measurement of stain by image analysis can be a reliable alternative to the spectrophotometric approach.