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A new method for quantitative intra-oral tooth color determination is presented. Basically, the tooth color is assessed by visual comparison with opaque color standards, which are logically arranged according to three visual color dimensions. The standards were analyzed spectrophotometrically, and the C.I.E. color coordinates were computed. Illumination and observation were standardized during the matching procedure. Two distinct situations, method 1 and method 2, were investigated. The situation in method 1 is to be considered as large window illumination and small window collection of the reflected light. For method 2, the same small window was used for both illumination and observation. Using both methods, the color of a tooth could be quantified into three separate color dimensions. Using method 1, the consistency among 25 examiners was high in determining the color of ten teeth; using method 2, the inter-examiner agreement was low. For the same tooth, different color standards were selected with method 1 or method 2. The standard selected with method 2 often appeared to be in disagreement within clinical expectations. The differences in results between method 1 and method 2 are explained by the optical properties of the translucent dental enamel (e.g., volume reflection). Method 1 allows for reproducible quantification of clinical tooth discoloration according to C.I.E. color specifications and can possibly be applied in prosthetic dentistry.

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This paper discusses the error made when measuring the color of translucent materials, using the same window for illumination and light collection. Two methods, based on largewindow illumination and small -window collection are described.

Summary. A method has been developed for producing measurable and reproducible coronal colour changes in teeth in vitro. Two tecfhniques with different access preparations were assessed for the prevention of dehydration of enamel. Rclative discoloration was also compared in freshly extracted teeth and teeth which had been stored in ethanol. The most reproducible results were obtained with an immersion technique of humidity control and with apical access to the pulp chamber. Freshly extracted teeth or teeth stred in ethanol appeared to be equally suitable for determining the relative staining of the crown compared with the original tooth colour. It is considered that the method could be applied to studies for investigating the discolouring properties of endodontic materials.