The aims of this study are to determine the extent to which the ranking order for clinical Contact-Free-Occlusal-Area (CFOA) wear performance of composites correlates with the ranking based on in vitro scratch hardness, and to analyze the extent to which the microstructure influences the overall trend.
Materials and methods
The patient data and CFOA wear measurements of 16 Tetric-C, 17 Tetric-EC, 16 Gradia-DP, 18 Filtek Supreme, 19 Z100 restorations in 31 subjects (8 males, 23 females) of two randomized clinical trials were fitted in a mixed-effect model. The in vivo performance of the restoratives was summarized by ranking the estimated material-related coefficients in the model. Scratch tests on two specimens per composite were run at a constant speed of 0.05 mm/s under indenter with normal loads of 15, 25, and 35 mN. Scratch width, depth and hardness calculated by imaging the scratch tracks were summarized in a model, the material-related coefficients were ranked and correlated with that of in vivo ranking order.
The best in vivo model included as significant factors (p < 0.0001) the variables material, time/month, cavity type, and jaw type. The CFOA wear ranking order – Filtek Supreme, Z100 > Tetric-C, Tetric-EC > Gradia-DP-correlated closely (R2 = 0.991) with the order of scratch hardness – Z100 > Filtek Supreme > Tetric-C, Tetric-EC > Gradia-DP.
Scratch tests could roughly categorize a new material as to whether it will probably exhibit a high or low in vitro scratch resistance and/or clinical CFOA wear rate.