Application of Metrology in Dentistry

Objectives: Tooth wear measurement requires a sequential measurement of teeth over a period of time. Therefore, the challenge of wear measurement is to find an unchanged common area as reference despite the likelihood of wear occurring anywhere on the tooth. Methods: In this study we propose a methodology that provides a control for the registration process. In this the registration of the common area is based on mathematical calculations and clinical assessment. Two tooth surfaces were digitised and interpolated into 3-D images using a non-contact laser co-ordinate measuring machine. A software package (QMUL, UK) was used to define an arbitrary area as an initial common reference area for the registration, based on clinical assessment. During the registration procedure the software showed the fitness of the common area, in three different colours: the best fitting area in red, the worst fitting area in black, and the average fitting area in blue. These colours were used as a guide to select a better fitting area for the second registration to achieve a better fit. This registration process could be repeated to achieve the best fit. Then a colour coded image would demonstrate the wear (or the difference) of two images where the wear occurred, and at each region, the extent of the wear is demonstrated in different colours. Results: The fit after second registration was 8.7µm, which was better than the first round fit at 74.8 µm. Conclusions: Within the limitations of this study non-contact laser co-ordinate metrology is a promising assessment tool in detecting tooth wear.