Effects of the different materials and thicknesses on endocrown stress distribution

To analyze the effects of different restorations and the thickness of the occlusal space on the stress distribution of endodontically treated molars with endocrowns.

The finite element model of the restoration of the first mandibular molar was created, and four different endocrown materials were used including two resin based ceramics (Lava Ultimate, Vita Enamic), one lithium disilicate ceramic (IPS e.max CAD) and one zirconia ceramics (Cercon), and four kinds of surface space thickness were designed: 1 mm, 2 mm, 3 mm and 4 mm. A total of 600 N was loaded to simulate the maximum bite force in the vertical and inclined directions, and the finite element software ANSYS 10.0 was used to analyze the stress distribution.

The vertical loading analysis showed that the crown stress of the 1 mm-Cercon group was the highest at 211.30 MPa, and that of the 4 mm-Lava Ultimate group was the lowest at 11.56 MPa; the highest dentin stress was 38.84 MPa in the 3 mm-Lava Ultimate group, and the lowest was 11.68 MPa in 1 mm-Cercon group. The stress in the periodontal ligament and alveolar bone had little change. The inclined loading analysis showed that the crown stress of the 1 mm-Cercon group was the highest at 78.73 MPa and that of the 1 mm-Lava Ultimate group was the lowest at 35.51 MPa; the highest dentin stress was 41.63 MPa in the 1 mm-Cercon cervical group, and the lowest was 10.81 MPa in the 4 mm-Cercon coronal group. The stress concentration of cement and cervical dentin under inclined loading was higher than that under vertical loading.

The results of finite element analysis show that the elastic modulus of the endocrown increases, the stress of the crown restoration shows an upward trend, and the stress in the tooth shows a downward trend. With increasing crown thickness, the stress of the crown prosthesis decreased.