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

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.

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 150μm with Venus Flow, Rely-X Veneer and Clearfil AP-X before biaxial flexure testing at 24h 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.

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.

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.