A new optical 3-D device for the detection of wear

For the clinical performance of new dental restorative materials to be accurately assessed, the three-dimensional anatomical changes of the functional surfaces of the restoration must be elucidated over time. To this end, a highly accurate 3-D optical scanner has been developed that utilizes the principles of triangulation and a reference-free automated 3-D superimposition software. The aim of this study was to assess the accuracy and the precision of the new system with and without referenced positioning. Additionally, the ability of the system to determine wear of posterior fillings three-dimensionally has been shown. Gypsum replicas of restored teeth were evaluated. The tooth surfaces were scanned with a resolution of 250,000 surface points within a measuring time of 20 to 40 sec. The results show that the precision and accuracy of 3-D data acquisition depend on the surface inclination. Up to an angle of 60 degrees, the precision is better than 3 mu m, and the accuracy is better than 6 mu m If exact repositioning of the object before and after occlusal loading is possible, e.g., with in vitro studies, differences on the surface can be determined with a precision of 2.2 mu m. In reference-free measurements, which are a necessity in clinical studies, the 3-D data acquisition in combination with the automatic matching program can detect wear with an accuracy of 10 mu m The application of this measuring device for the detection of wear of a composite filling functioning in the mouth has been shown. Since this measuring technique is automated, and measurements of high accuracy can be attained in a short period of time, this system offers the possibility for complex analyses of three-dimensional wear to be conducted on a large number of samples in clinical studies.