Spatial Distribution of the Micro-Mechanical Properties in High-Translucent CAD/CAM Resin-Composite Blocks

Industrially cured, high-translucent computer-aided design/computer-aided manufacturing (CAD/CAM) resin-based composites (RBC) are the most recently launched dental restoratives. Clinical treatments and laboratory tests are based on a homogeneous distribution of properties within CAD/CAM blocks to obtain constant and reproducible results. The study therefore aims to determine the spatial distribution of various micro-mechanical parameters (Vickers hardness, Martens hardness, indentation modulus, creep, elastic and total indentation work) in five representative CAD/CAM RBCs. The properties of the tooth structure were evaluated under similar conditions. Filler size and shape were analyzed by scanning electron microscopy. A multivariate analysis (general linear model) identified a very strong influence of the material on all measured properties (p < 0.001; partial eta squared η(P)(2) > 0.943), whereby the most sensitive parameters when identifying differences within regions were the indentation modulus and the elastic indentation work. CAD/CAM RBC blocks show gradually varying properties that can increase or decrease from central to peripheral areas regardless of the chemical composition of the materials or the inorganic filler fraction. The degree of variation in the measured properties is material-specific and less than 8.7%. Clinical applications and in vitro study designs should consider slight inhomogeneity in CAD/CAM RBC blocks, while the location of the regions with best mechanical performance depends on the material.