Influence of infrastructure design and ceramic coverage material on stress development in posterior crowns

To evaluate the influence of the infrastructure design and type of ceramic coverage on residual stresses after occlusal loading of crowns with yttria-stabilized zirconium oxide (Y-TZP) infrastructure, analyzed by means of the finite element method.

3D models of a mandibular first molar total crown were constructed with two different types of infrastructures: a coping with a uniform thickness of 0.3 mm, and an anatomic coping with a thickness ranging from 0.3 mm to 1.5 mm, depending on the external anatomy of the crown, and three types of ceramic coverages: feldspathic, leucite- and lithium disilicate-reinforced types. Fusion 360 software ( Autodesk) was used to simulate occlusal loading of 300 N in an area of 1 mm² on the internal slopes of the mesial vestibular cusps.

Higher tensile stress values ( σ1 positive) were observed for the ceramics with anatomic copings (800.3 MPa for feldspathic; 800.1 MPa for leucite, and 799.0 MPa for lithium disilicate), in comparison with the groups of uniform coping (482.0 MPa for feldspathic, 480.0 MPa for leucite, and 479.4 MPa for lithium disilicate). Stress distribution in all the groups followed the same type of pattern, with stresses developing in the load application region and following in the direction of the facial-lingual regions of the coverage crowns. The main maximum peaks of tensile strength were located below the points of load application and on the internal surface of the crown in the distolingual direction. The magnitudes of tensile stress on the anatomic coping ceramics were higher than on the uniform coping ceramics; the different coverage ceramics used did not influence the stress distribution pattern.

Ceramics on copings with a uniform shape resulted in lower values of internal stress development, in comparison with the anatomic-shaped copings, irrespective of the coverage ceramic used.