A COMPARISON OF IN-VIVO AND IN-VITRO STRAIN WITH POSTERIOR FIXED PARTIAL DENTURES

Purpose. Deformation of fixed partial dentures during function has bee n related to clinical failures. However, such deformation has not been measured quantitatively, and the effect on deformation of the viscoel astic behavior of peridental structures is not well understood. The pu rpose of this study was to determine the strain distribution of fixed partial dentures during function and to compare the biomechanical beha vior of fixed partial dentures in vivo and in vitro. Material and meth ods. Three conventional posterior fixed partial dentures and two compl ete crowns were fabricated. Both in vivo and in vitro strain measureme nts of each of the five prostheses were recorded by a strain gauge met hod. A static load was produced through occlusal force in vivo and wit h a universal testing machine in vitro. Results. The resulting differe nce between the strain distribution for the two crowns in vivo and in vitro was negligible, but the whole fixed partial denture demonstrated a substantial amount of strain in vivo. Conclusions. The results of t his study suggest that serious problems with strain may occur in a lon g-span mandibular posterior fixed partial denture.