[Effect of the 3/4 crown and porcelain-fused crown restorations on the tooth displacement and the loading force of the supporting tissues]

A mechanical simulation model of tooth and alveolar bone in the application of 3/4 crown and porcelain-fused crown restorations was made and analyzed using three-dimensional finite element technique. The results obtained were as follows. 1. When the physiological tooth mobility was less than 150 microns, the teeth were sufficiently fixed using the splint and the bridge connected with more than two teeth, in the case of 20 percent absorption of the alveolar bone, and more than three teeth in the case of 40 percent absorption. In the case of 60 percent absorption, the teeth were fixed with the splint of six teeth connections, and were fixed with the bridge of five teeth connections. 2. The periodontium supporting force decreased markedly according to the increase of the number of the abutment teeth. 3. The teeth accompanied with the absorption of the alveolar bone were connected, in order to inhibit the tooth mobility and the periodontium supporting force. In this application, it had the inhibitory action when the replacing ratio of metal and ceramics to a crown of the tooth was less than 35 percent. 4. According to the finite element analysis, the design bases of fixed restorations applied in the teeth accompanied with the absorption of the alveolar bone were preferred.