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BACKGROUND: Previous studies have reported that femoral head finite element models are mostly modeled with single or few samples for specific biomechanical research, but there is little research on model stability. OBJECTIVE: To compare the models of normal femoral head and osteonecrosis of the femoral head with multiple samples, and to analyze the accuracy and stability of the models through the comparison of stress distribution and mechanical parameters, so as to provide mechanical basis for prevention and treatment of collapse of osteonecrosis of the femoral head. METHODS: Totally 20 sides uncollapsed of osteonecrosis of the femoral head one year of non-surgical treatment were selected as the experimental group, and the healthy side of 20 patients with unilateral osteonecrosis of the femoral head were set as the normal group. The CT data of the femoral head were collected to establish the finite element model. The stress distribution of normal femoral head and osteonecrosis of the femoral head, the maximum equivalent stress and the maximum total deformation at the weight-bearing area of the femoral head were observed and compared. This study was approved by the Medical Ethics Committee of Wangjing Hospital of China Academy of Chinese Medical Sciences. Patients signed the informed consent. RESULTS AND CONCLUSION: (1) The finite element models of normal proximal femur, non-necrotic proximal femur and necrotic bone were established. The number of elements and nodes were 502 568±114 196, 692 608±154 678; 449 954±125 824, 623 311±171 401; 19 133±13 167, 27 577±19 131, respectively. (2) When the load was set by simulating one-foot standing position, the cloud image showed that when 2.5 times body weight applied to the weight-bearing area of the femoral head; the surface stress of the weight-bearing area of the normal femoral head was uniform. The stress was uniformly distributed in the femoral head along the stress trabeculae, and the calcar femorale bears the most. The stress concentration area appeared on the surface of the weight-bearing area and the necrotic area of osteonecrosis of the femoral head. The stress was scattered and distributed on the inner and outer sides of the femoral neck and the femoral head of osteonecrosis of the femoral head produced more deformation than the normal femoral head. (3) The maximum total deformation of the weight-bearing area of the osteonecrosis of the femoral head and the normal femoral head was (4.14±1.31) mm and (1.36±0.22) mm and the maximum equivalent stress was (1.94±0.77) MPa and (0.75±0.19) MPa, respectively, and with statistically significance (P < 0.05). Moreover, two groups of data tend to be concentrated and the models are stable. Through the comparison of multi-sample normal femoral head and osteonecrosis of the femoral head, the CT gray-assigned method reflects the actual mechanical properties of osteonecrosis of the femoral head, and has good accuracy and stability.
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BACKGROUND: Single-segment and double-segment osteotomies are often used to treat ankylotic kyphosis. However, the selection of preoperative strategies, especially for segmental and osteotomy methods, often depends on clinical experience. At present; there are few reports on the biomechanics of double-segment vertebral column decancellation and vertebral column resection osteotomy. OBJECTIVE: To establish a two-segment osteotomy model for ankylotic kyphosis, and to compare and discuss the total displacement of the spine, stress analysis of the internal fixation system, and equivalent stress intensity of the osteotomy contact surface. METHODS: MIMICS software and Geomagic studio software were used to establish two kinds of models of ankylotic kyphosis with vertebral column resection osteotomy and vertebral column decancellation. Each kind of model was divided into single-segment osteotomy and double-segment osteotomy, i.e., L1 single-segment vertebral column resection osteotomy model, L1 single-segment decancellated osteotomy model, L2 single-segment vertebral column resection osteotomy model, L2 single-segment vertebral column decancellation model, T12L2 double-segment vertebral column resection osteotomy model, T12L2 double-segment vertebral column decancellation model, T12L3 double-segment vertebral column resection osteotomy model, and T12L3 double-segment vertebral column decancellation model. ANASYS software was imported to load model. The whole spine displacement, pedicle screw, connecting rod, and bone interface equivalent stress nephogram were recorded under different conditions of osteotomy. RESULTS AND CONCLUSION: (1) Whether it was vertebral column decancellation or vertebral column resection osteotomy model, the total spinal displacement of single-segment osteotomy was less than that of double-segment osteotomy. The displacement of vertebral column resection osteotomy was less than that of vertebral column decancellation in both single-and double-segment osteotomy models. L2 single-segment vertebral column resection osteotomy model had minimal displacement. (2) Whether it was vertebral column decancellation or vertebral column resection osteotomy model, equivalent stress of the single-segment osteotomy was less than that of the double-segment osteotomy. The equivalent stress of the internal fixation device of the vertebral column resection osteotomy was less than that of vertebral column decancellation in both single-and double-segment osteotomy models. The equivalent stress of the internal fixation device of the L1 single-segment vertebral column resection osteotomy was smallest. (3) The equivalent stress of the osteotomy contact surface of all single-segment osteotomy models was smaller than 28 MPa. In the two-segment osteotomy model, the equivalent stress of the osteotomy contact surface of the vertebral column resection osteotomy was less than that of vertebral column decancellation. (4) These results suggest that the biomechanical stability of the single-segment osteotomy model was better than that of the double-segment osteotomy model. The stability of vertebral column resection osteotomy was better than that of vertebral column decancellation.
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OBJECTIVE@#This study aimed to evaluate the stress distribution of the mandibular first molar with different thicknesses and heights of the axial wall restored by the endocrown with two marginal designs and thus provide a theoretical basis for selecting clinical preparation through the finite-element method.@*METHODS@#Two marginal endocrowns of the mandibular first molar with different axial-wall thicknesses (t=1, 2, 3 mm) and heights (h=2, 3, 4 mm) were established. Group A was the butt-joint design, whereas group B was the shoulder-surrounded design. After applying vertical and oblique loads , the size and distribution of the maximum principal stress and equivalent stress of residual tooth tissue were recorded.@*RESULTS@#The maximum principal stress and equivalent stress distribution of residual tooth tissue were similar among different models. Group A showed a lower maximum principal stress and equivalent stress than group B at the same thickness and height under vertical load. Meanwhile, under oblique load, the maximum principal stress values of groups A and B decreased with increased thickness at constant height. Group A showed lower equivalent stress than group B at the same thickness and height of 2 and 3 mm. However, when the height was 4 mm, the trend was reversed.@*CONCLUSIONS@#In mastication, when bearing the vertical force, the retention of the butt-joint marginal endocrown preferred to the shoulder-surrounded one. Given the higher axial wall of the shoulder-surrounded marginal endocrown, it showed better ability to bear the oblique force than the butt-joint one.
Subject(s)
Crowns , Dental Stress Analysis , Finite Element Analysis , Mastication , MolarABSTRACT
Objective To analyze the influence from size parameters of minimally invasive vascular clamp on mechanical properties of small arteries. Methods The finite element simulation analysis on the process of minimally invasive vascular clamp clamping small arteries was performed. The influence patterns of 5 different sawtooth spacing, sawtooth heights and sawtooth lengths on mechanical properties of small arteries were studied. Results Larger sawtooth spacing led to smaller maximum equivalent stress of the clamped artery. The maximum equivalent stress of the small artery was not linear with the sawtooth height of the vascular clamp. The maximum equivalent stress of the small artery was the smallest and the vascular injury was the minimal when the swatooth height was 75 μm. The sawtooth length of the vascular clamp had an important influence on mechanical properties of clamped small arteries. The maximum equivalent stress of the artery was proportional to the sawtooth length of the vascular clamp. Conclusions The size parameters of minimally invasive vascular clamp had an important influence on mechanical properties in the process of clamping small arteries. The research findings can provide guidance for the design of the minimally invasive vascular clamp.
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Objective: To investigate the stress and stress distribution generated on each component of implant prosthodontic system and surrounding cortical bone when different diameters of screw-access hole (SAH) were prepared on molar crown. Methods: A fimite element(FE) model of partial mandible without first molar was set up, and an Bego implant was insert into it. A total of 5 models of the crown were computer-simulated by varying the diameter (Φ = 0-4 mm) of the SAH. The loading forces were 200 N axially (0°) and 100 N obliquely (45°) respectively on occlusive surface. The FE analysis was performed by computer. Results: Φ ≤3 mm: stress on occlusal surface of crown was almost unchanged and mainly distributed in the loading area. Φ = 4 mm, stress appeared an obvious rise and reached the maximum, the stress concentration under vertical load was changed to the hole margin. In vertical loading, screw could remain at a relatively low stress level when diameter did not exceed 1 mm. No changes on other components was observed. Conclusion: SAH diameter of 1 mm is recommended when a cement-and screw-retained crown is used in posterior region.
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Objective To study the stress distribution on different length of pedicle screws under the physiological load by using the three dimensional finite element analysis. Method A three dimension model of the pedicle screw and L1 vertebral body were constructed with the model meshed on the basis of the finite element method. The feature dimension of pedicle screw in the model was set in a specified varied range. Under the physiological load, the stress on every model with different diameter sizes of pedicle screw was analyzed. ResultsThe stress on every bone model decreased with the increase of stress on screw under the axially pullout force as the length of screw ranged from 30mm to 50mm. And the maximum Equivalent Stress (EQV Stress) in the pedicle screw appeared in the central area of the pedicle screw, the maximum Equivalent Stress (EQV Stress) in the cortical bone appeared in both sides of contact surface, the maximum Equivalent Stress (EQV Stress) of the cancellous bone appeared in both sides of contact surface of the top of pedicle screw and cancellous bone. In a certain external load, with the 50mm length of screw, the load that transfers to the cortical bone and cancellous bone is reduced by 43.1% and 42.3%, respectively, while the maximum Equivalent Stress (EQV Stress) of screw was increased 38%. When L≥45mm, the variable stress on all models become stable. Conclusions While the length of screw is in range of 4.0 mm to 6.5 mm, 30～50 mm ,the increase of pedicle screw length could improve the distribution of axial pullout stress on the screws, cortical bone and cancellous bone. As long as the bone mass allowed, the length of pedicle screws should be not less than 45mm in clinical choice.