Numerical investigation of macro- and micro-mechanics of a ceramic veneer bonded with various cement thicknesses using the typical and submodeling finite element approaches

Objectives: This study investigates the influence of cement thickness on the macro- and micro-mechanical responses in a ceramic veneer adjacent to an incisal overlapped incisor. Methods: Seven finite element (FE) ceramic veneer macro-models with different cement thicknesses (10-180 μm) were generated. A 10 N load was applied with an angulation of 60° to the longitudinal tooth axis. Seven FE micro-models corresponding to the macro-models were constructed at an enamel-adhesive interface where the stress concentration was found. Based on an interfacial scanning electron microscope (SEM) micrograph, morphology of resin tags in the micro-models was generated. The micro-model boundary conditions were determined from the macro-model results. The principal stress on each node in the macro- and micro-models was calculated to investigate interfacial mechanics. A tensile test was performed to obtain an ultimate cement tensile strength to determine the material failure parameters. Results: The highest stress concentration within the cement was found at the resin tag base of the enamel-adhesive interface in lingual side. Maximum stress values from 10.6 to 14.7 MPa for the micro-models were higher (44-48%) than that from 7.2 to 10.0 MPa for the macro-models when the cement layers increased. Based on the ultimate tensile strength (11.8 MPa), bonding failure could found when the micro-models with the cement layers presented more than about 50 μm. This seems to correspond with data from previous studies. Conclusions: Higher stresses develop in the adhesive as the cement thickness increases. Cement thicknesses less than 50 μm might reduce the adhesive bonding failure.