[The study on retention of adhesive restoration]

Although the prognoses of the adhesive bridges are practically satisfactory, some disconnections have been reported. Physical bite, twisting and tearing forces are considered to be the causes for these disconnections. Paired natural human teeth; 2 incisal and 2 molar teeth, were embedded in cold cured resin for fatigue test and axial reduction was slightly performed. Cast bridges which were designed to come to 30 mm2 in every abutment and to resemble clinical design, were made from two kinds of metal; Ni-Cr alloy and Ag-Pd-Au alloy, and adhered with teeth by Panavia EX (Kurarey Co. Ltd.). Incisal bridges were disconnected easier than molar bridges in the fatigue test. There was no significant difference between 2 kinds of metal. With stereoscopic microscope, cohesive fracture of resin was observed on the region which was farthest from supporting point of fatigue force in incisal bridges. Dimple patterns characteristically in fatigue fracture were also observed in some cases. In modified tensile test of incisal teeth using Ni-Cr alloy, force point was given far 1 mm & 12 mm apart from approximal surface, and various twisting and tearing forces were loaded in 12 mm cases. The cases loaded by higher twisting and tearing forces had significantly smaller bond strength.