ABSTRACT
Objective@#To analyze the effects of different restorations and the thickness of the occlusal space on the stress distribution of endodontically treated molars with endocrowns.@*Methods @# 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@*Results@#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.@* Conclusion @# 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.
ABSTRACT
Objective@# 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.@*Methods@#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.@*Results@#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.@*Conclusion@# 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.
ABSTRACT
@#An id eal balance between the post length within root and the coronal extension should exist. Some theories advocated the use of the longest post as possible as the apical seal is not disturbed. Others advocated that the post should be longer than the crown or that the post should be a certain fraction of the length of the root. The conventional post length has been equal to 2/3-3/4 of the root length from half a century ago. Most of these theories have emphasized the post length in order to achieve sufficient retention and rigidity for coronal restoration. However, dental materials are evolving.With the use of fiber post and resin cement, stress distribution and post retention are improved over conventional metal post and zinc phosphate or glass-ionomer cement. Therefore, with improved bonding strength of fiber post, the post length within root should be minimized to maintain sufficient coronal rigidity. Factors affecting fracture resistance balance of a post-and-core system include the amount of Ferrule height (FH), Post length in root (PLIR), Post length in bone (PLIB), Abutment height (AH), Core length (CL) and Post length out of bone (PLOB). In view of the factors mentioned above, this paper investigated the mechanical factorsin a post-and-core system with literature review.