The influence of the veneering porcelain and different surface treatments on the biaxial flexural strength of a heat-pressed ceramic

Abstract

Statement of problem The strength of all-ceramic restorations can be adversely affected by surface defects, leading to restoration failures. Additionally, when a 2-layer all-ceramic restoration is required for esthetic purposes, part of the stronger ceramic core material is replaced by veneering porcelain. Purpose This study evaluated the effect of different surface treatments on the strength of a ceramic core material and veneering porcelain, as well as the influence of veneering porcelain on the strength of a 2-layer ceramic structure. Material and methods Fifty heat-pressed ceramic cores and 30 veneering porcelain discs (17 mm diameter × 2 mm) were made. From the ceramic core group, 20 discs were selected and reduced to a thickness of 1 mm and veneered with 1 mm of porcelain. These specimens were divided into 2 groups of 10 each. The remaining 30 ceramic core and the 30 veneering porcelain discs were divided into 2 sets of 3 equal sized groups (n=10). Ceramic core groups were prepared for testing having the following surfaces: airborne-particle abrasion, ground, and overglazed. Veneering porcelain groups were tested: as fired (no additional treatment), ground, and overglazed. Biaxial flexural strength was measured using the ball-on-ring test method. All specimens were loaded to fracture. One and 2-way analysis of variance were used to analyze the data (α=.05). Results The ceramic core discs were significantly ( P=.001) stronger than the veneering porcelain discs for the airborne-particle abrasion, as-fired, and ground surface treatments (82 ± 11 MPa vs 51 ± 8 MPa and 93 ± 14 MPa vs 60 ± 6 MPa, respectively). For the overglazed treatment, there was not a significant difference between the core (115 ± 1 4 MPa) and the veneer materials (107 ± 14 MPa). The ground 1-layer core was significantly ( P=.015) stronger (93 ± 14 MPa) than the 2-layer with the core tested in tension (72 ± 19 MPa). There was no significant difference between 1-layer veneer overglazed (107 ± 14 MPa) and 2-layer discs when tested with the veneer in tension (105 ± 16 MPa). Conclusion The overglazed surface treatment significantly improved the strength of the materials tested, as well as the strength of 2-layer discs with the veneer in tension. The veneering porcelain influenced the strength of 2-layer specimens only when tested with the ground ceramic core surface in tension.