The influence of resin flexural modulus on the magnitude of ceramic strengthening

Introduction. The aim was to determine the magnitude of ceramic resin-strengthening with resin-based materials with varying flexural moduli using a regression technique to assess the theoretical strengthening at a 'zero' resin-coating thickness. The hypothesis tested was that experimentally, increasing resin flexural modulus results in increased resin-strengthening observed at a theoretical 'zero' resin-coating thickness. Method. Vitadur Alpha dentin porcelain disk (n = 250) were condensed, fired, alumina particle air abraded and randomly assigned into ten groups. Groups were resin-coated at 50, 100 and 150 mu m with Venus Flow, Rely-X Veneer and Clearfil AP-X before biaxial flexure testing at 24 h and the stress at failure calculated using a multilayer analysis. An analytical methodological approach was undertaken to predict the biaxial flexure stresses under boundary conditions that reflected the experimental test and a finite element model was used to verify the analytical prediction. Results. The magnitude of resin-reinforcement was significantly influenced by resin-coating type (P < 0.001) and resin-coating thickness (P = 0.013), however, a significant interaction was observed between resin-coating type and thickness (P = 0.048). Linear regression identified a 17, 38 and 47% biaxial flexure strength contribution when Venus Flow, Rely-X Veneer and Clearfil AP-X were used, respectively. The finite element model determined the maximum principal stress was within 3.3% of the predicted analytical solution. Significance. Experimentally, the flexural modulus and thickness of resin-based material used to cement DBC or PLV restorations have a significant impact on the magnitude of resin-strengthening observed. However, for resin-based materials with different flexural moduli the variability in the relationships between thickness and observed increases in biaxial flexure strength of the ceramic requires careful characterization to optimize clinical performance. (C) 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.