Development of quantitative measurement methods for tooth wear using area and volume of virtual model cusps

Abstract

Objectives: Tooth wear represents the decrease of tooth enamel structure which is the result of the combined effects of many mechanisms. Clinicians must examine the level of tooth wear with specific criteria for the proper diagnosis of the oral health of the patient. Until now, there have been many ways to measure tooth wear. The advantages of qualitative methods are that they are intuitive, rapid, and do not require specific space or equipment. The disadvantages are that the methods are more subjective and require guidelines for training and calibration to ensure the reliability of the data. We have already developed new quantitative methods using virtual models with limitations. Therefore, the purpose of this study was to develop and evaluate easier and more intuitive quantitative parameters using cusp area and volume.

Methods: The subjects in this study are the identical virtual models used in the former study. Ninety maxillary and mandibular dental casts were prepared and rendered as virtual 3D models and stored in the computer hard disc as CAD image files. The same age group classification and NTWI scoring system were also reused. The reference highest point of each cusp was marked on the first molar of the virtual models and a virtual occlusal plane was generated with these reference points. The plane was then lowered vertically from 0.2, 0.4, 0.6, and 0.8 mm to create offset planes. The area and volume of each cusp was then measured and added together at the level of 0.2, 0.4, 0.6, and 0.8 mm, respectively. In addition to the former analysis, the differential characters of each cusp were analyzed.

Results: The scores of the new parameters were better than the former study for the differentiation of the age and new tooth wear index (NTWI) groups. Spearmans ρ coefficients between the total area and each cusp area also showed higher scores in area of 0.6 mm (0.6A) and 0.8A. The mesiolingual cusp (MLC) differed statistically (P < 0.01) with other cusps in the paired t-test. Also, the MLC exhibited the highest percentage of change of 0.6A within the age and NTWI groups. In the case of age groups, the MLC showed the highest score in groups 1 and 2. In the case of the NTWI groups, the MLC was not significantly different in groups 3 and 4. Those results coincided with the opinion that the lingual cusp exhibits rapid wear because it works as a functional cusp.

Conclusions: Although this study has limitations because it is a cross-sectional study, it suggests better quantitative parameters and analysis tools for each cusp wear characteristic. Therefore, these results are helpful to clinicians and researchers who are conducting studies on tooth wear.