Influence of luting space settings and polymerization-induced cement shrinkage and deformation/adaptation of CAD/CAM crowns

This study aimed to evaluate the adaptation of CAD/CAM crowns and the impact of resin cement polymerization contraction on crown deformation under different cementation configurations. Thirty human molars were randomly divided into three groups (n = 10) to manufacture ceramic crowns with three different cementation space configurations: LD40 (40 μm), LD80 (80 μm), and LD160 (160 μm). The samples were subjected to computerized microtomography scanning for measuring internal and marginal adaptation, and internal fit was analyzed at occlusal, axial, axiogingival points. Five light-curing protocols were used to verify the wavelength spectrum peak of the curing device and the irradiance delivered using two situations: with 0 mm sensor distance and through a ceramic of differing thickness, and an external crown deformation (ECD) test. The highest statistically significant vertical fit was obtained for group LD40, independent of region. LD160 yielded the highest ECD values, independent of positioning of the buccal and distal strain gauge. The highest internal fit was observed at occlusal and axial points of the LD160 group (P<0.001), and LD80 yielded the lowest values at the axiogingival point (p = 0.003, p = 0.006). The irradiance delivered was reduced significantly upon interposition of the ceramic block to the sensor. The peak wavelength for curing was similar among the LD groups. The luting space configurations significantly influenced vertical fit and the ECD results for the CAD/CAM ceramics owing to polymerization shrinkage. Finally, variations in ceramic thickness at different sites affected both the irradiance by the curing device and ECD results.