Effect of ion exchange of glazed dental glass ceramics on strength parameters

Ion exchange treatments can significantly increase the strength of dental glass ceramic core materials by induced compressive residual stresses. However, the core materials of dental restorations need to be veneered or at least to be stained and glazed for esthetic and functional reasons. The objective of this study was to determine the effect of different ion exchange treatments on the strength parameters of stained and glazed glass ceramics. Batches of specimens made of a leucite reinforced dental glass with and without staining and glazing layer, untreated, single ion exchanged (KNO3), and dual ion exchanged (1. KNO3/27, 2. 30 mol% NaNO3/70 mol% KNO3) were tested. The strength of the core material was increased from 117 to 213 MPa by single ion exchange. Staining and glazing increased the strength up to 165 MPa. Single ion exchange of the stained and glazed core caused only a slight additional strength increase up to 173 MPa. The dual ion exchanged stained and glazed core exhibit a strength of 195 MPa and decreased the large strength scatter because of a well-designed residual stress profile. We conclude that dual ion exchange treatments could significantly increase the mechanical reliability of stained and glazed glass ceramic restorations.