The use of FEM to calculate stresses in connection between zirconia coping and veneering ceramic
Prof. Beata Śmielak1, Prof. Leszek Klimek2, Dr. Jacek Świniarski3, Dr. Kamila Rogowska1
1 Department of Dental Prosthetics, Medical University of Lodz,
2 Department of Materials Research, Institute of Materials Science and Engineering, University of Technology,
3 Department of Strength of Materials, University of Technology
Objectives
To investigate, using the FEM, the infusion of different notching angles with varying groove widths and depths on a zirconium dioxide coping with the aim of establishing the optimal connection conditions with veneering ceramic.
Materials and Methods
Ten rectangular sintered zirconia (3Y-TZP) samples were etched with a neodymium-yag laser Nd:YAG. Then, a profilometer was used to test the depths and spacing of the grooves. A notch profile was used to design the shapes and spacing of the grooves based on a finite element method (FEM) simulating zirconia. The following situations were simulated: an increase in groove width from 100% to 180% and depth from 40% and 80%; and a 40% depth and width. To calculate the stresses in the connection between zirconia coping and veneering ceramic, a model comprising grooves cut perpendicular was adopted. For discretization purposes we used twenty-node solid BRICK elements featuring intermediate nodes with three degrees of freedom in each node. The same load F=1N divided by the number of nodes on the external surface was applied to each node of the outer surface of the base. In subsequent computing variants the F load changed the orientation by angle from 0∘ to 45∘ every 15∘.
Results
The highest level of material strain occurs at angleα= 0∘σredmax =309MPa and the lowest at angleα=45∘σredmax=220MPa. The highest positive stress pressure occurs at angleα= 0∘pmax=251MPa, pmin=-354MPa and the lowest at angleα=15∘, pmax=171 MPa, pmin=-186MPa. In the case of tangential stresses on the coping-veneering ceramic connection, the highest values were noted at angleα= 15∘τmax=44.4 MPa and the lowest at angleα= 45∘τmax=32.7MPa.
Conclusions
To reduce the load on the zirconia-veneering ceramic connection, the notches should be made at an angle ofα=45∘ Maintaining the width of the groove bottom while increasing the depth offers fewer advantages than deepening and narrowing the groove bottom.