Mind the gap: internal fit of fixed dental prostheses

Abstract

Whether single crowns and three-unit bridges produced by computer-aided design and computer-aided manufacturing (CAD-CAM) have an internal fit comparable to crowns and three-unit bridges made by lost-wax metal casting technique is unknown. The primary aim of the thesis is to evaluate the internal fit of fixed dental prostheses (FDPs). The secondary aims are 1) to compare the internal fit of single crowns of different materials produced by recent digital techniques and the older lost-wax and metal casting technique, 2) to compare the internal fit of three-unit fixed dental prostheses of different materials produced by recent digital techniques and the older lost-wax and metal casting technique, and 3) to use and compare two digital methods (the triple-scan and the dual-scan methods) for the investigation of internal fit The internal fit of 5 groups of 1) single crowns and 2) three-unit bridges produced with the CAD-CAM technique was compared with that of single crowns and three-unit bridges produced in cobalt-chromium with the conventional lost-wax and metal casting technique. Comparison was performed using the triple-scan and the dual-scan protocol. The 5 groups were milled presintered zirconia, milled hot isostatic pressed zirconia, milled lithium disilicate, milled cobalt- chromium, and laser-sintered cobalt-chromium. The cement space was statistically smaller (P<.05) for crowns made by the conventional lost-wax and metal casting technique compared with that of crowns produced by the CAD-CAM technique. No such differences were found for the cement spaces of three-unit bridges. Single crowns made using the conventional lost-wax and metal casting technique seems to have better internal fit than crowns produced using the CAD-CAM technique. For three-unit bridges no such differences is observed. Regarding the test methods the results indicates that the dual-scan method is well suited for the investigation of internal fit of FDPs.