Feasibility of Gloss Measurement on Coated Enamel Using Digital Imaging

Objectives: Previous work has shown the ability to measure gloss differences on dry enamel after exposure to acidic beverages. Our present objective was to demonstrate the potential of digital imaging techniques to maintain ability to differentiate gloss on enamel surfaces coated with thin films of water and saliva. Methods: A stained, glossy, extracted human incisor was mounted in acrylic resin. The tooth was then treated with acid to dull the surface, peroxide to whiten the enamel, and finally prophy polished to restore gloss. This generated enamel surfaces representing combinations of stained or white and glossy or dull. At each stage digital images were captured with the surface treated as dry, blotted with water, and coated with a thin saliva film. The digital imaging system employed was designed to reproducibly control imaging conditions including lighting, distance, and position. Images were converted to 8-bit monochrome digital format and regions of high gloss were identified as pixels with luminescence values 65% above background. The degree of specular highlights or ‘Sparkle' was quantified by determining the difference in average grayscale intensity between enamel regions of high specular reflection and the baseline crown. All measurements were performed in triplicate. Results: Sparkle values on both stained and white enamel produced consistently higher measurements compared to corresponding dull surfaces. Addition of water or saliva at the enamel surface reduced contrast in Sparkle compared to dry enamel, however measured difference in dull and glossy surfaces maintained statistical significance (p<0.05) for all three surface coatings. Conclusions: The ability to differentiate between dull and glossy enamel surfaces was maintained when thin moisture and saliva coatings were applied. This demonstrates the potential to measure gloss changes on oral surfaces in the mouth and to relate the measurements to what is perceived naturally by an observer.