The strength of a heat-pressed all-ceramic restorative material

A heat-pressed technique (IPS Empress(R), Ivoclar) has been described to construct single unit crowns, inlay/onlays and veneers using precerammed and precoloured glass-ceramic ingots, The aim of the study was to evaluate the strength of materials obtained using this technique. Strengths were determined by means of shell (disc rupture) tests. Seven groups of 10 specimens each were prepared with different combinations of core, incisal and glaze firing. Shell strength values of these seven groups varied between 167 +/- 18 and 81 +/- 9 MPa. After analysis, results showed that there was no statistical difference between groups when the core porcelain was in tension. However, there was a significant difference between those groups in which the lower surface was either core or incisal porcelain. The component thicknesses of the core and incisal materials did not change the strength of the complete specimen.