Methods: The FEM 3D models of extracted human premolar were prepared by Ansys 5.7 software. The FEM models were experimentally validated by elastooptic method. Enamel anisotropic and dentine isotropic properties were included. The class 2 cavities were rebuilt by direct (layering technique, 4 layers of resin composite) and indirect restoration (resin composite and ceramic inlays). The models were loaded initially by the shrinkage and finally by shrinkage and 100N. For inlays 100-150μm layer of luting cement separating tooth and restoration was modelled. Each layer of direct restoration was cured separately.
Results: The cup-to cup distance was decreased in all types of restorations by the shrinkage, in layered composite up to 234.8% (0.206μm), resin composite inlay 67% (0.058μm), ceramic inlay 100% (0.087μm). The application of 100N occlusal load on the sound tooth caused 1.67μm (100%) the increase of cup-to-cup distance. The increase was lower in the tooth restored by inlays (resin composite 0.94μm (56,4%), ceramic 0,92μm (55.5%) and higher in direct composite restoration 3.22μm (193.4%). Higher values of von Missess stress were recorded in enamel than dentine. The von Missess stress at the gingival wall of enamel in the direct resin composite restoration was 15.8MPa, composite inlay 9.1MPa and ceramic inlay 10.4MPa. At the gingival area of dentine the values of von Missess stress were 5.2MPa, 10.2MPa and 11.2MPa, respectively.
Conclusions: The values of von Misses stress caused by shrinkage exceed minimal enamel tensile strength and initial bond strength of some materials. Layered resine composite restoration caused the highest cup-to-cup distance changes.
Research supported by National Science Center grant N518283740.