The effect of internal roughness and bonding on the fracture resistance and structural reliability of lithium disilicate ceramic.

OBJECTIVE

To evaluate the effect of internal roughness and bonding on the load to failure and structural reliability (Weibull analysis) of a lithium disilicate-based glass ceramic under different testing scenarios.

METHODS

IPS e.max CAD blocks (Ivoclar Vivadent AG) were shaped into cylinders (N=100), crystalized according to the manufacturer's instructions, and randomly assigned into two surface conditions: (1) polished surface (600-grit SiC polish papers), and (2) a roughened surface (air-abrasion with 50μm AlO). Two assemblies were investigated: a ceramic disc isolated (to isolate the effect of roughness); and a simplified tri-layer setup simulating the restoration of a posterior tooth (ceramic+cement+epoxy resin) to evaluated the influence of bonding isolated and the associated effect of both factors. Four different scenarios were tested: (1) isolated disc under static load (n=10); (2) disc bonded to an epoxy resin substrate and tested under a static load (n=10); (3) disc bonded and tested under fatigue (n=20); and (4) simulated-bonding tested statically (n=10). The data of load to failure were submitted to One-way ANOVA and Weibull analysis.

RESULTS

At a non-bonded scenario (isolated disc and simulated-bonding) a polished internal surface presented a higher characteristic strength. However, when bonding was present this difference became inexistent. No difference was found in terms of structural reliability (Weibull moduli) among the groups. FEA analysis shows that with bonding the tensile stress is better distributed, while in a non-bonded scenario higher tensile stresses occur at the bonding interface.

SIGNIFICANCE

A rough internal surface impacted deleteriously the mechanical properties of lithium disilicate ceramic when it was not properly bonded to the substrate. However, bonding to the substrate appeared to play a more significant role in the fracture resistance than internal roughness.