Sakaguchi R L, Borgersen S E
Minnesota Dental Research Center for Biomaterials and Biomechanics, Minneapolis 55455.
Int J Oral Maxillofac Implants. 1993;8(6):655-61.
The treatment design of most dental restorations is largely empirical and based on the experience of the individual practitioner. Because the biomechanical aspects of implant-supported restorations are difficult to assess on an individual basis, there is a possibility for compromised biomechanical performance of the implant-retained restoration to achieve satisfactory esthetics and phonetics. Through repeated loading cycles, the restoration or its components may fatigue and fail. This study evaluated the biomechanical behavior of the crown component relative to the gold retaining screw and abutment under load to provide insight into the mechanism of loosening and fracture of the retaining screw. A two-dimensional finite element model of the dental implant components was developed for nonlinear contact analysis. A simulation of tightening of the retaining screw was followed by axial loading of a cusp tip on the implant-supported crown. Loading of the cusp tip resulted in separation of the contact between (1) the gold retaining screw and abutment, and (2) the crown and the abutment. Repeated loading and unloading cycles resulted in alternating contact and separation between the retaining screw head base and the crown. Clinical findings of screw loosening and failure probably result from these separation events and from elevated strains in the screw as demonstrated by the model.
