SURFACE-LAYER CHARACTERIZATION AFTER DUAL-ION EXCHANGE OF A LEUCITE-REINFORCED DENTAL PORCELAIN

The dual ion-exchange technique has been shown to improve the strength of feldspathic dental porcelains by first replacing constituent alkal i ions with smaller ions above the strain point, and then exchanging t he smaller ions for larger ions at temperatures below the strain point . The strength increase is directly related to the thickness of the su rface-exchanged layer. This study evaluated the thickness of the excha nged layer after dual ion exchange of a leucite-reinforced dental porc elain. Optec HSP porcelain disks were fabricated, submitted to a dual ion-exchange treatment, and indented at various loads before determini ng the biaxial flexure strength. The mean flexural strength for the io n-exchanged groups was significantly higher than for control groups, e xcept when the depth of the median crack exceeded 138 mu m. Wavelength Dispersive Spectrometry analyses on cross sections showed that the me an potassium amount in the glassy matrix was significantly lower (P < .001) for the treated specimens than for the controls. The mean thickn ess of the exchanged layer after dual ion exchange was estimated al 14 0 mu m.