Flexural strength of the joint between glass-infiltrated alumina frames and the alumina-magnesia modifier.

PURPOSE The purpose of the present study was to evaluate the flexural strength of the joint between glass-infiltrated alumina frames and the experimental adjusting agent (MA modifier) that contains alumina and magnesia. METHODS A commercially available adjusting agent (Optimizer), a slurry of alumina powder (Alumina modifier), and a bulk specimen (joint-free alumina) were used as controls. Beam-shaped alumina specimens were machined from an alumina block. The ends of two alumina beams were positioned at an interval of 1.0 mm and joined with each adjusting agent. The joined specimens were subjected to sintering, glass infiltration firing, glass control firing, and then a three-point bending test was carried out to evaluate the flexural strength. RESULTS The maximum flexural strength was observed in the joint-free alumina, followed by MA modifier, Optimizer and Alumina modifier. With the exception for joint-free alumina, the failure modes after three-point bending test tended to shift from adhesive failure at substrate material-adjusting agent interface to cohesive failure within adjusting agent as the flexural strength increased. CONCLUSIONS The use of MA modifier significantly improved the flexural strength of joined glass-infiltrated alumina frame. The MA modifier could be applied for adjusting the margin as an alternative to Optimizer when fabricating crown and bridge substructures with In-Ceram Alumina system.