Partial or total fracture of veneered ceramic fixed partial dentures is a major problem in dentistry. Objective: To analyze and optimize the flexural strength of bilayered ceramic specimens and to prevent spallation through controlled heat treatment. Methods: Twenty groups of 10 core/veneer bar specimens (25 mm x 4 mm x 1.5 mm) each were fabricated by hot-pressing and veneering the core ceramic according to recommended procedures. The ceramic combinations used included: I) Empress 2 glass-ceramic core (E2C) with Eris glass veneer (ERV); II) E2C with Empress 2 glass veneer (E2V); III) an experimental lithia-disilicate-based core ceramic (EXC) with ERV; and IV) EXC with E2V. The core/veneer ceramic specimens were subjected to four-point flexure after heating them for 1 h either at the glass transition temperature (T_g) or at temperatures that were either 10ºC or 20ºC above or below T_g. The specimens were cooled to room temperature (~ 1 min) after each of the thermal treatments. The veneer layer was subjected to tensile stress during flexure testing. The flexure strength of veneered specimens was calculated using composite beam theory. Residual stresses within the veneer layer were calculated using a fracture mechanics equation. Results: For all specimens, crack initiation occurred within the ceramic veneer surface of the specimens. There were statistically significant differences among the flexural strengths of the heat-treated specimen groups (p £ 0.05). The flexural strength ranged between 115 and 152 MPa. Residual compressive stresses ranged between 54 and 115 MPa. There was a statistically significant difference among the mean residual stresses of the heat-treated specimens (p £ 0.05). Conclusions: Compressive residual stress can be optimized to prevent spallation of veneered lithia-disilicate based core ceramics by controlling heat treatment. This study was supported by NIH/NIDCR Grant No. DE 06672.

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