Investigation into the relationship between visual perception and instrumental colour measurement of teeth

Individuals desire to seek aesthetic dental treatments such as restoration, dental fillings, and whitening treatments to obtain the ‘perfect’ smile has given rise to research to determine the most accurate method for tooth colour measurement. Accurate tooth colour measurement is essential in producing satisfactory results for restoration and fillings, improving communication between dentist and patient, as well as determining the efficacy of tooth whitening products. Currently there is no ‘gold’ standard method for assessing tooth colour. Gloss, curvature, small size, in vivo location and translucency are attributes of teeth which make accurate colour measurement difficult. The aim of this thesis is to evaluate ‘accuracy’ of tooth colour measurement by exploring some of the issues arising in visual perception, indices, and instrumental colour measurement. A yellowness index (YIO) is developed to assess changes in perceptual yellowness instead of whiteness which highlighted issues in indices and perceptual evaluation. The amount of edge-loss that occurs in the spectrophotometer, spectroradiometer, Vita EasyShade and digital camera was assessed to determine the amount of error produced by each measurement device. A novel approach to the assessment of accuracy is introduced whereby accuracy is expressed by the instrument’s ability to ‘agree’ with visual perception, with perceptual responses as the ‘reference’. Statistical analysis methods r2, percent wrong decisions and STRESS analysis are used in order to assess the correlation between instrumental measurement and visual perception responses (Z-scores). It was found that there is no ‘gold’ standard instrument, but there are indices that produce better correlation between instrumental measurement and visual perception. WIO and YIO produced the best results for the assessment in changes in tooth whiteness and tooth yellowness no matter which instrument was used. The Vita
Easy Shade was found to perform poorly in comparison to all other instruments.