Effects of different cement-restorative material combinations in full-coverage onlay restorations: A FEA study.

Objectives: To test, through FEM analysis, different cement-material combinations in an indirect adhesive restoration scenario generated through Micro-Computed Tomography.

Methods: A reference lower first molar was prepared for an overlay restoration and scanned with an intraoral camera. The restoration was milled with a reinforced lithium silicate and cemented with a dual cure resin cement. A geometrical model was segmented from a micro-CT scan generating separate volumes of enamel, dentin and restorative materials. The 3D Finite Element (FE) model was subsequently built-up (Meshlab, ISTI, CNR, Pisa, Italy) and an axial chewing load was simulated (Altair Hyperworks, Troy, Michigan, USA) considering the volumes as linear and elastic. Data concerning the tooth-restoration interface were analyzed in terms of shear stress and normal pressure. Different restoration materials and cements were tested in order to evaluate the effects of the combination between the main categories of dental materials applied for IAR and dual or light curing cements.

Results: Concerning tooth-cement interface, stresses in the range from 2*10^-2 to 9*10^-3Gpa, depending on observation axes, were recorded. As regards restorative material variable, resin-matrix ceramic models were subjected to the highest stresses, followed by glass-matrix ceramic and polycrystalline ceramic. Regarding the cement variable, small differences and quantitatively negligible were found in all models when comparing light-curable composite and dual-curing resin cement. Concerning cement-restoration interface, stresses in the range from 1.551*10^-2 to 2.679*10^-3Gpa were recorded. Resin-matrix ceramic showed a wider stressed area both in normal pressure and shear stresses. Concerning the cement variable, small differences were found both in terms of pattern and intensity, especially when applied under the resin-matrix ceramic.

Significance: Resin-matrix ceramic models showed higher stresses in both interfaces, due to the flexion of the restoration at given load. The absence of axial walls in the vestibular and buccal aspect, as well as the reduced occlusal thickness of the restoration, enhances this phenomenon. Cement type seems to have an influence only when undergoing resin-matrix ceramics, better performing when having a reduced polymerization shrinkage.