To compare the stress distribution of different all-ceramic restoration materials and thicknesses in dental crown restorations using the finite element method and provide a reference for the selection and design of clinical crown restoration materials.

A finite element model of mandibular first molar implant crown restoration was created, and 6 crown thickness designs and 4 different crown restoration materials were evaluated, namely, resin-based ceramics (Lava Ultimate and Vita Enamic), lithium disilicate glass-ceramics (IPS e.max CAD), and zirconia ceramic (Cercon) designs. The mandibular first molars were loaded at 600 N, and the stress distribution was analyzed by using the finite element software ANSYS 10.0.

The crown stress analysis showed that 156.05 MPa was the highest in 4 mm Cercon group and 18.85 MPa was the lowest in 1 mm Lava Ultimate group. The stress analysis of resin cement showed that 62.52 MPa was the highest in the 4 mm Lava Ultimate group and 16.74 MPa was the lowest in 1 mm IPS e.max CAD group. During the use of the finished platform, the stress concentration of the Lava Ultimate group in the crown prosthesis and resin cement was higher than that of the personalized platform with the same crown thickness.

With increasing crown thickness, the maximum principal stress concentration in crown restoration and resin cement increases. Personalized abutments are more conducive to reducing stress concentrations for resin-based ceramics.

To explore the technology and efficacy of fabrication of a guide and removal of a fiber post by tetrahedron positioning technology at the chair side.

For one patient with acute chronic periapical periodontitis of the left maxillary lateral incisor who needed to have the fiber post removed, the chair side tetrahedral positioning technique was used to make a guide plate to remove the fiber post. Cone beam CT (CBCT) data were imported into the software to design the guide plate for fiber post removal. The guide plate design on CBCT was transferred to a solid model by using tetrahedral positioning technology. The guide plate was made to guide the removal of the fiber post, and then left maxillary lateral incisor root canal was performed. We evaluated the effect of fiber post removal with tetrahedral positioning technology by reviewing the literature.

The guide plate made by tetrahedral positioning technology can accurately locate the position and direction of fiber posts at a low cost and with high speed. After the fiber post was removed, the root canal could be dredged by using root canal preparation instruments. After root canal preparation, the root canal was filled with warm gutta-percha to complete the root canal treatment. After 3 months, the apical radiograph showed that the transmission shadow of the apical area was reduced. The results of the literature review showed that the fiber post removal with guide plates provides a predictable result and a lower risk of iatrogenic damage. Minimally invasive treatment can be carried out, and chair time can be reduced.

On the basis of CBCT data, using tetrahedral positioning technology to make fiber post removal guides can help reduce the risk of fiber post removal and has the characteristics of speed, low cost and short chair side processing. However, the accuracy comparison between tetrahedral positioning technology and 3D printing guides needs further study.

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.