Investigation of stress distributions against functional forces of CAD/CAM porcelain lamina veneer restorations: A three-dimensional finite element analysis study

In this in vitro study, it was aimed to examine the stress distributions of porcelain lamina veneers (PLV), which is one of the treatments applied in the clinic, against three different functional forces after they were prepared with different preparation depths and different CAD/CAM material combinations with one type of adhesive and one type of preparation, using three dimensional finite element analysis. In this study, a three dimensional simulation model simulating the maxillary central incisor was used. The preparation model was created in the form of incisal bevel preparation in all teeth. The cervical margin was placed 1 mm coronal to the enamel-cementum junction and all preparation edges were prepared as a chamfer preparation step. The preparatios were determined in four different depths as 0.3, 0.5, 0.7 and 0.9 mm, respectively, and for each restoration model, IPS Empress CAD (Ivoclar Vivadent, Schaan, Liechtenstein), IPS e.max CAD (Ivoclar Vivadent, Schaan, Liechtenstein) and Vita Enamic (VITA Zahnfabrik, Essen, Germany) were used as three different materials. All restorations were cemented using a light-cured Variolink Veneer (Ivoclar Vivadent, Schaan, Liechtenstein) resin cement and the cement layer thickness was determined as 100 µm in the restoration models. The models were fixed by restricting all degrees of looseness from the nodal points located in the upper and posterior regions of the cortical and trabecular bone, preventing movement in all three axes. Analysis was performed by applying 100 N to the palatal surface of the insical edges at three different angles (0°, 60° and 120°) to simulate intercuspal and protrusive motion. The stress distribution and intensities on the finite element model are given as both color coding and numerical values. When the obtained data were examined, the tensile and compressive tensile stresses on the PLVs produced from different CAD/CAM blocks differed. As a result of increasing veneer thickness with depth of preparation, PLVs created less tensile stress in deeper preparations. As the angle of the functional forces on the palatal tooth surface increased, the stresses on the PLVs increased. As the material hardness increased, the stresses in PLV's also increased.