The Effect of Marginal Preparation Type on an All-Ceramic Anterior Crown: A Finite Element Study

Objectives: The aim of the study was to evaluate and compared the effects of 2 different tooth preparation designs on the stress distribution in tooth, cement, core and two ceramic layers of all ceramic anterior crown using the 3 Dimensional (3D) Finite-Element-Analysis (FEA) method. Anterior tooth-crown configuration composed of both layers of restoration is lacking.

Materials and Methods: 1 mm circumferential shoulder and chamfer finish line preparations were performed with rounded shoulder and chamfer diamond cylindrical burs with rounded angles on 2 maxillary central teeth. 1 mm thickness of the frameworks were (IPS e.max Press, Ivoclar-Vivadent, Schaan, Liechtenstein) prepared by pressing technique. After scanning the frameworks for FEA, dentin and enamel ceramics (IPS e.max Ceram, Ivoclar-Vivadent) were applied. Each ceramic layer was scanned for finite-element models. The Variolink II (Ivoclar-Vivadent) was used as a luting material and modeled. A 200 N static load was applied at 45° to the palatal surface. 3D-FEA was performed with I-DEAS software.

Results: Rounded-shoulder model showed higher Von Mises stress values in prepared tooth, core, resin cement, and both two layers of the ceramic than chamfer model. Rounded-shoulder preparation type within all evaluated models had more dispersed stress distribution localization areas than chamfer preparation type’s models. The highest Von-Mises stress values were found within the first ceramic layer of the shoulder model (26.5 MPa) on 1/3 of the buccal surface. Low stress values were found at dentin tooth structures for both chamfer and rounded-shoulder models.

Conclusions: Rounded-shoulder preparation type showed higher Von-Mises stress values at both layers of crown. Minimum Von-Mises stress values were found at dentin regardless of the preparation type.