Morphological design of occlusal wear facets for the mandibular first molar crown using different bite registration methods

Purpose To compare the accuracy of occlusal wear facet morphology designed using different bite registration methods for mandibular first molar crowns. Materials and methods The posterior teeth and intraoral intercuspal occlusions of 12 participants were scanned. The abutment shape of the mandibular first molars for complete crowns was virtually designed, and the anatomic coping design method was used to design crowns. In the anatomic coping design, digital wax patterns were constructed by elevating the wear facets on the original surface of the first molars and then adjusting the facets with 2 types of virtual occlusions determined by buccal bite registration (BBR) or segmented tooth registration (STR) methods, where the displacement of teeth under bite force was considered (STR) or not (BBR). The occlusal distance between the original wear facets and the antagonists as well as 3D deviations between the facets on the designed crowns and on the surfaces of the original teeth were measured. Paired-samples t-test was used to analyze the results (alpha = 0.05). Results Regarding occlusal distance, the mean 3D deviation and the root mean square (RMS) values of BBR were greater than those of the STR groups (p < 0.001 and p = 0.008). The mean 3D deviations of the crowns of the BBR and STR groups were 0.19 +/- 0.04 mm and 0.14 +/- 0.06 mm, respectively and the RMS values were 0.22 +/- 0.03 mm and 0.18 +/- 0.04 mm (p < 0.001), respectively. Conclusions The morphology of occlusal wear facets of mandibular first molar crowns designed with the occlusion constructed using the segmented tooth registration method are more coincident with the original morphology.