Fatigue Testing of Implant Supported Bridge. A Study of All-on-two Concept

Abstract: The conventional implant therapy of patients with edentulous mandibles involves installation of four implants. The treatment is well-studied with high success rate. By reducing number of implants, biological and cost benefits could be made. The aim of the study was to test the mechanical aspects and fatigue resistance of a fixed bridge retained on two implants. The working hypothesis was that the construction would manage mechanical fatigue testing equal to 10 years of intraoral use. A machine to simulate chewing cycles was constructed by two engineering students. The bridge was attached to an aluminium block with two implants. The loading force was 177 N and applied 7 mm posterior from the central point of the right implant. The test came to a halt after 40 minutes because of motor failure which corresponds to 37.2 hr of intraoral use. A new machine made by a professional mechanic is required to redo the test. The height of the most distal points of the bridge on both sides were reduced by 0.3 mm and the most anterior point was increased by 0.2 mm. No plastic deformation of implant heads or change in abutment screw insertion torque was observed. The pressure on the distal cantilever caused deflection of the bridge which could have caused the differences in measurement. In conclusion, a complete bridge retained on two implants cannot stand mechanical pressure of 177 N on such a long cantilever although longer testing time corresponding to at least 10 years of intraoral use is required.