[Numeric simulation of functional remodeling of the anterior alveolar bone].

OBJECTIVE: To study the remodeling of the anterior alveolar bone with parodontium under physiology loading using finite element method (FEM) and theory of bone remodeling. METHODS: A FEM model of the maxillary central incisor with parodontium was established, and the change of bone density during the remodeling of alveolar bone was investigated under physiology loading (60 - 150 N) based on the theory of bone remodeling about strain energy density (SED). The finite element analysis software Abaqus user material subroutine (UMAT) were used. RESULTS: With the increase of physiology loading, the pressure stress on the buccal cervical margin increased gradually while the density was decreased gradually. The cortical bone was lower than its initial density 1.74 g/cm(3), which was 1.74 - 1.63 g/cm(3). The density of cancellous bone was 0.90 - 0.77 g/cm(3), which was lower than its intial density 0.90 g/cm(3). The lingual cervical margin was under tensile stress which also increased with loading, the density had no significant change. When the achieve to 120 N, the density of cortical bone was 1.74 - 1.73 g/cm(3). No significant change was found in the cancellous bone. CONCLUSIONS: The simulation of the perodontium remodeling is achieved and proved to be effective by the relevant research based on the method of the study. And the result will be helpful to form the basis of analysis bone remodeling process and predict the results in the clinical work.

[The study of cyclic fatigue and lifetime for all-ceramic crown after cementation].

OBJECTIVE: To study mechanical and cyclic fatigue behavior of IPS Empress2 under cyclic loading, and to establish guidelines for the use and design of all-ceramic crowns. METHODS: A 3-D finit element method model of tooth and crown were established. The strength and lifetime of all-ceramic crowns under cyclic loading in centric occlusion were investigated using computational techniques of the Abaqus and MSC Fatigue software. RESULTS: Most of the fatigue and fracture of all-ceramic crown occurred within the veneering material at cervical marginal of the crown. The number of loading cycles before failure occurred varied within specified limits 2,506,109-6,950,243. The lifetime of the crown decreased significantly as loading increased and decreased gradually as loading time increased as well. CONCLUSIONS: The mechanical and fatigue behavior of ceramic materials and restorations need to be improved before clinical use in order to guarantee clinical long-term success of all-ceramic crown. properly in order to increase the longevity of all-ceramic crowns.

[Cloning and prokaryotic expression of recombinant Jo-1 antigen and identification of its antigen specificity].

AIM: To obtain highly purified Jo-1 autoantigens. METHODS: The full length of DNA sequence coding for Jo-1 (histidyl-tRNA synthetase) was obtained from human placenta by RT-PCR and then it was inserted into pTYB11 or pMAL-c to construct the expression vectors pTYB11-Jo-1 and pMAL-c-Jo-1. The recombinant plasmids were transformed into ER2566 and BL21 of E.coli, respectively. RESULTS: The fusion Jo-1 antigens were expressed, Western blot analysis demonstrated they responded specifically to anti-Jo-1 antibody from the patients with autoimmune disease polymyositis and dermatomyositis, but did not respond to normal sera and 188 sera containing anti-RNP, Sm, Ro/La or RNP/Ro antibodies from rheumatosis patients. CONCLUSION: The expressed protein of pMAL-c-Jo-1 is soluble, which accounts for more then 50% of total proteins of cells and can be purified by affinity chromatography. The purified proteins can be used as reagents for determining the anti Jo-1 antibody in the serum of patients.

[The simulation of articulation to anterior teeth with three-dimensional dynamic finite element methods].

PURPOSE: To study the stresses and movement of central incisor with three-dimensional dynamic finite element method, in order to understand and describe the process of occluding. METHODS: A three-dimensional dynamic finite element model of central incisor was established, and the definition of contact between the surfaces of occlusive contact was defined as Hard Contact (ABAQUS) to simulate the process of occluding. RESULTS: The stresses on the central incisor varied with the time of overbite and the movement of teeth during dynamic occluding. Higher stresses were observed in the areas of buccal-lingual cervical marginal on the upper teeth, but in the near-far cervical marginal on the lower. CONCLUSIONS: Dynamic finite element method can help to picture the process of articulation and the conditions of teeth momentarily, and could be used for the research of oral biomechanics effectively.

Three-dimensional finite element analysis of weakened roots restored with different cements in combination with titanium alloy posts.

BACKGROUND: It is very difficult and relatively unpredictable to preserve and restore severely weakened pulpless roots. To provide much needed benefit basis for clinical practice, this study was carried out to analyze the stress distribution in weakened roots restored with different cements in combination with titanium alloy posts. Finite element analysis (FEA) was employed in the study. METHODS: A pseudo three-dimensional model of a maxillary central incisor with flared root canal, theoretically restored with titanium alloy posts in combination with different cements, was established. The analysis was performed by use of ANSYS software. The tooth was assumed to be isotropic, homogenous and elastic. A load of 100 N at an angle of 45 degrees to the longitudinal axis was applied at the palatal surface of the crown. The distributions of stresses in weakened roots filled with cements of different elastic modulus were analyzed by the three-dimensional FEA model. RESULTS: Several stress trends were observed when the stress cloud atlas obtained in the study was analyzed. With the increase of the elastic modulus of cements from 1.8 GPa to 22.4 GPa, the stress values in dentin decreased from 39.58 MPa to 31.43 MPa and from 24.51 MPa to 20.76 MPa (respectively, for maximum principle stress values and Von Mises stress values). When Panavia F and zinc phosphate cement were used, the stress peak values in dentin were very small with no significant difference observed, and the Von Mises stress values were 20.87 MPa and 20.76 MPa respectively. On the other hand, maximum principle stress value and Von Mises stress value in cement layer increased with the increase of the elastic modulus of cements. CONCLUSIONS: The result of this study demonstrated that elastic modulus was indeed one of the important parameters to evaluate property of the cements. Our three-dimensional FEA model study also found that the cement with elastic modulus similar to that of dentin could reinforce weakened root and reduce the stress in dentin. Thus, it may be a better choice for the restoration of weakened roots in clinical practice.

Effects of insulin-like growth factor I on the development of osteoblasts in hyperglycemia.

The delayed wound healing of tooth extraction, the activation of alveolar absorption and the being hindered bone formation around the implants in diabetes are difficult to be solved for dentists. So, the aim of the study was to investigate the influences of hyperglycemia and insulin-like growth factor I (IGF-I) on osteoblasts. Osteoblasts were cultured in different conditions: normal glucose, mimic hyperglycemia, hyperglycemia with IGF-I, hyperglycemia with insulin. The proliferation and mineralization of osteoblasts were observed. As abnormal transport of glucose involved in the development of chronic complications in diabetes. The expression of glucose transporter 1 (GLUT1) was further evaluated by RT-PCR, immunofluorescence and Western blot in different groups. These results showed that hyperglycemia increased the proliferation and inhibited the mineralization of osteoblasts, while IGF-I seemed to reverse these effects. The levels of GLUT1 mRNA and protein in hyperglycemia were elevated by 51% and 35%, respectively, compared with that in normal glucose, while the levels in hyperglycemia with IGF-I were almost the same as that in normal glucose. In conclusion, the increased expression of GLUT1 may contribute to the delayed mineralization of osteoblasts in hyperglycemia. Also IGF-I may be a new drug for diabetic bone disease through normalizing the expression of GLUT1.

[The study of viscoelastic residual stresses of ceramic-metal bond].

OBJECTIVE: To study the residual stresses of ceramic-metal bond at viscoelastic and elastic phases during cooling of porcelain-fused-to-metal in order to precisely calculate the ceramic-metal bond strength and improve the restorations. METHODS: The finite element model was set up according the crack initiation test (three-point flexure bond test) based on ISO Standard, elements of viscoelastic and themal-displacement were used to part the model. The result at viscoelastic phases was used as initiation condition of elastic phases to add up. RESULTS: The compressive stress was caused by metal during cooling occurred in the ceramic. The shear stress induced by loading was offset by thermal shear stress. Load tensile stress and the thermal compressive stress vertical of interface concentrated at the end of the bond interface, but the tensile was greatly higher. CONCLUSION: The residual stress is very important to metal-ceramic restorations, and the viscoelastic behavior of porcelain greatly influences it. If the metal and ceramic are compatible,the components stresses of the residual stresses may benefit to ceramic-metal bond, and can be taken as a part of bond stresses.