Computer-assisted morphological analysis of dental casts with maxillary prognathism and reversed occlusion.

The morphologic characteristics of the dentition with maxillary prognathism and reversed occlusion were examined by a computer-assisted dental cast analysing system. Dental casts with normal occlusion, maxillary prognathism and reversed occlusion were selected and measured by a 3D shape measuring system. The dental arches and anteroposterior occlusal curves were approximated numerically by the polynomial expression with a fourth order and second order coefficients, respectively. The coefficients were analysed statistically. Maxillary dental arches with mandibular prognathism showed a more acuminate shape (V-shape) with a significant larger second order coefficient, while arches with reversed occlusion showed more angulate shapes (U-shape) with significantly smaller second order coefficients compared with arches with normal occlusions. However, a notable difference in the shape of the mandibular dental arches was not observed. The mandibular dental arches with maxillary prognathism were positioned backward relative to maxillary dental arches, while the arches with reversed occlusion were positioned forward. The anteroposterior occlusal curves with maxillary prognathism showed larger curvatures in maxilla and mandible, while the curves with reversed occlusion showed smaller curvatures in mandible comparing with the curves with normal occlusion. These results suggest that the present method could offer a useful and objective examination technique for the diagnosis of malocclusion.

Influence of abutment substrates on the colour of metal-free polymer crowns.

New-generation composite materials have excellent strength and wear resistance, and thus can be used to make metal-free crowns. However, composite materials are translucent, and so when using them to make metal-free crowns, it is necessary to take the effect of the abutments into consideration. In this study, five types of materials including three types of new-generation composite materials, a conventional composite material, and a ceramic material were used to examine the translucency (contrast ratio) of the materials and the effects of the colour of the abutments on the final appearance of metal-free crowns. It was found that the materials varied slightly from one-another in translucency and that it was possible to reproduce the desired colour when gold alloy was used for the background. However, it was difficult to produce an adequate colour match when silver-palladium alloy was used for the background. When a tooth colour material that was darker than the target colour was used for the abutment teeth, some materials could not reproduce the target colour satisfactorily.

Integration of 3-D shapes of dentition and facial morphology using a high-speed laser scanner.

PURPOSE: The purpose of this study was to develop a method to integrate three-dimensional data of dentition and facial morphology measured by a high-speed laser scanner, and visualize them by computer graphics. The accuracy of integration was also examined. MATERIALS AND METHODS: The 3-D shapes of upper and lower dental casts and the face of a subject were measured by a high-speed laser scanner with zoom lens facility. As an interface to integrate the coordinates between dentition and face, an extraoral marker plate attached to the occlusal record plate was devised. It was applied between the upper and lower dental casts, and with the subject, and measured. Integration was attempted by coinciding the data of the interface. The accuracy of integration was examined using the conditions of the marker plate such as surface shape and attachment angle. RESULTS: Integration of the data of dentition and face was accomplished. The 3-D relationship between them could be visualized in any direction or section by computer graphics. For optimal accuracy of integration, the marker plate with a mixed shape of flat and sinusoidal wave attached at 45 degrees to the occlusal record plate showed the most appropriate results. CONCLUSION: An original method to integrate the 3-D data of dentition and face measured by 3-D laser scanner was developed and shown to have acceptable accuracy.