OBJECTIVES: This study aimed to construct the finite element model of the mandibular first molar with the invisible appliance and explore the dentition movement characteristics of the mandibular first molar when using micro-implant anchorage and different initial positions of the first molar. METHODS: Models of the mandible, tooth, periodontal membrane, and invisible appliance were constructed using cone beam computed tomography (CBCT) data. The two groups were divided into the non-anchorage group and the micro-implant group (between the roots of the first molar and the second molar) based on whether the elastic traction of the micro-implant was assisted or not. The two groups were divided into the following conditions based on the starting position of the first molar: Working condition 1: the distance between the first molar and the second premolar was 0 mm; working condition 2: the distance between the first molar and the second premolar was 1 mm; working condition 3: the distance between the first molar and the second premolar was 2 mm; working condition 4: the distance between the first molar and the second premolar was 3 mm. The data characte-ristics of total displacement and displacement in each direction of dentition were analyzed. RESULTS: In the non-ancho-rage group, all the other teeth showed reverse movement except for the first molar which was moved distally. Meanwhile, in the micro-implant group, except for a small amount of mesial movement of the second molar in wor-king condition 1, the whole dentition in other working conditions presented distal movement and anterior teeth showed lingual movement, among which the distal displacement of the first molar in working condition 4 was the largest. With the change of the initial position of the first molar to the distal, the movement of the first molar to the distal, the premolar to the mesial, and the anterior to the lip increased, while the movement of the second molar to the mesial decreased. CONCLUSIONS The micro-implant can effectively protect the anterior anchorage, increase the expression rate of molar distancing, and avoid the round-trip movement of the second molar. The initial position of the first molar movement is related to the amount of distancing and the remaining tooth movement.
Finite Element Analysis ; Molar ; Bicuspid ; Periodontal Ligament ; Tooth Movement Techniques/methods* ; Orthodontic Appliances, Removable

OBJECTIVES: This study aimed to explore the stress distribution of surface-mounted inlays with two ceramic materials and different strategies for fiber post-restoration on pulp-penetrating non-carious cervical lesion in a maxillary first premolar to provide minimally invasive and reasonable restorative methods. METHODS: The cone beam computed tomography data of the standard right upper first premolar were selected. Healthy control (HC) and defective control (DC) finite element models were established. Then, eight experimental models were established according to two different ceramic materials (IPS e.max CAD [LD] and Lava Ultimate [LU]) and different locations of fiber post (without fiber post [NP], fiber post in buccal root canal [B], fiber post in palatal root canal [P], fiber post in both root canals [BP]), namely, LD_NP, LD_B, LD_P, LD_BP, LU_NP, LU_B, LU_P, and LU_BP. Axial load F1 and lateral load F2 were applied. Maximum principal stress and displacement of the buccal tip were investigated using finite element analysis software. Then, the percentage change of the following indicators in each experimental group was analyzed: stress of defective tip with group DC, stress of enamel and dentine, and displacement of buccal tips with group HC. It was considered similar when the percentage change was less than 5%. RESULTS: LD and LU groups could effectively reduce the stress of the defective tip, but the decreasing amplitude in the former was greater than that of the latter. For the stress of surface-mounted inlays and resin adhesive layer, LD groups were higher than LU groups, and no significant difference in stress peak was found among different experimental groups in the same material. In addition, fiber posts in double root canals could significantly reduce buccal tip displacement. CONCLUSIONS For pulp-penetrating non-carious cervical lesions, the restorative strategy of surface-mounted inlays could be applied. Compared with Lava Ultimate, IPS e.max CAD could better protect the defective tip tooth. Furthermore, fiber posts in double root canals could decrease overall deformation and increase the retention of surface-mounted inlays.
Inlays ; Finite Element Analysis ; Composite Resins ; Bicuspid ; Ceramics ; Dental Stress Analysis

OBJECTIVE: To compare the biomechanical differences among the five internal fixation modes in treatment of Day type Ⅱ crescent fracture dislocation of pelvis (CFDP), and find an internal fixation mode which was the most consistent with mechanical principles. METHODS: Based on the pelvic CT data of a healthy adult male volunteer, a Day type Ⅱ CFDP finite element model was established by using Mimics 17.0, ANSYS 12.0-ICEM, Abaqus 2020, and SolidWorks 2012 softwares. After verifying the validity of the finite element model by comparing the anatomical parameters with the three-dimensional reconstruction model and the mechanical validity verification, the fracture and dislocated joint of models were fixed with S ₁ sacroiliac screw combined with 1 LC-Ⅱ screw (S ₁+LC-Ⅱ group), S ₁ sacroiliac screw combined with 2 LC-Ⅱ screws (S ₁+2LC-Ⅱ group), S ₁ sacroiliac screw combined with 2 posterior iliac screws (S ₁+2PIS group), S ₁ and S ₂ sacroiliac screws combined with 1 LC-Ⅱ screw (S ₁+S ₂+LC-Ⅱ group), S ₂-alar-iliac (S ₂AI) screw combined with 1 LC-Ⅱ screw (S ₂AI+LC-Ⅱ group), respectively. After each internal fixation model was loaded with a force of 600 N in the standing position, the maximum displacement of the crescent fracture fragments, the maximum stress of the internal fixation (the maximum stress of the screw at the ilium fracture and the maximum stress of the screw at the sacroiliac joint), sacroiliac joint displacement, and bone stress distribution around internal fixation were observed in 5 groups. RESULTS: The finite element model in this study has been verified to be effective. After loading 600 N stress, there was a certain displacement of the crescent fracture of pelvis in each internal fixation model, among which the S ₁+LC-Ⅱ group was the largest, the S ₁+2LC-Ⅱ group and the S ₁+2PIS group were the smallest. The maximum stress of the internal fixation mainly concentrated at the sacroiliac joint and the fracture line of crescent fracture. The maximum stress of the screw at the sacroiliac joint was the largest in the S ₁+LC-Ⅱ group and the smallest in the S ₂AI+LC-Ⅱ group. The maximum stress of the screw at the ilium fracture was the largest in the S ₁+2PIS group and the smallest in the S ₁+2LC-Ⅱ group. The displacement of the sacroiliac joint was the largest in the S ₁+LC-Ⅱ group and the smallest in the S ₁+S ₂+LC-Ⅱ group. In each internal fixation model, the maximum stress around the sacroiliac screws concentrated on the contact surface between the screw and the cortical bone, the maximum stress around the screws at the iliac bone concentrated on the cancellous bone of the fracture line, and the maximum stress around the S ₂AI screw concentrated on the cancellous bone on the iliac side. The maximum bone stress around the screws at the sacroiliac joint was the largest in the S ₁+LC-Ⅱ group and the smallest in the S ₂AI+LC-Ⅱ group. The maximum bone stress around the screws at the ilium was the largest in the S ₁+2PIS group and the smallest in the S ₁+LC-Ⅱ group. CONCLUSION For the treatment of Day type Ⅱ CFDP, it is recommended to choose S ₁ sacroiliac screw combined with 1 LC-Ⅱ screw for internal fixation, which can achieve a firm fixation effect without increasing the number of screws.
Adult ; Male ; Humans ; Finite Element Analysis ; Fracture Fixation, Internal/methods* ; Fractures, Bone/surgery* ; Pelvis ; Spinal Fractures/surgery* ; Fracture Dislocation/surgery* ; Joint Dislocations/surgery* ; Biomechanical Phenomena

OBJECTIVE: To discuss the influence of artificial ankle elastic improved inserts (hereinafter referred to as "improved inserts") in reducing prosthesis micromotion and improving joint surface contact mechanics by finite element analysis. METHODS: Based on the original insert of INBONE Ⅱ implant system (model A), four kinds of improved inserts were constructed by adding arc or platform type flexible layer with thickness of 1.3 or 2.6 mm, respectively. They were Flying goose type_1.3 elastic improved insert (model B), Flying goose type_2.6 elastic improved insert (model C), Platform type_1.3 elastic improved insert (model D), Platform type_2.6 elastic improved insert (model E). Then, the CT data of right ankle at neutral position of a healthy adult male volunteer was collected, and finite element models of total ankle replacement (TAR) was constructed based on model A-E prostheses by software of Mimics 19.0, Geomagic wrap 2017, Creo 6.0, Hypermesh 14.0, and Abaqus 6.14. Finally, the differences of bone-metal prosthesis interface micromotion and articular surface contact behavior between different models were investigated under ISO gait load. RESULTS: The tibia/talus-metal prosthesis interfaces micromotion of the five TAR models gradually increased during the support phase, then gradually fell back after entering the swing phase. The improved models (models B-E) showed lower bone-metal prosthesis interface micromotion when compared with the original model (model A), but there was no significant difference among models A-E ( P>0.05). The maximum micromotion of tibia appeared at the dome of the tibial bone groove, and the ​​micromotion area was the largest in model A and the smallest in model E. The maximum micromotion of talus appeared at the posterior surface of the central bone groove, and there was no difference in the micromotion area among models A-E. The contact area of the articular surface of the insert/talus prosthesis in each group increased in the support phase and decreased in the swing phase during the gait cycle. Compared with model A, the articular surface contact area of models B-E increased, but there was no significant difference among models A-E ( P>0.05). The change trend of the maximum stress on the articular surface of the inserts/talus prosthesis was similar to that of the contact area. Only the maximum contact stress of the insert joint surface of models D and E was lower than that of model A, while the maximum contact stress of the talar prosthesis joint surface of models B-E was lower than that of model A, but there was no significant difference among models A-E ( P>0.05). The high stress area of the lateral articular surface of the improved inserts significantly reduced, and the articular surface stress distribution of the talus prosthesis was more uniform. CONCLUSION Adding a flexible layer in the insert can improve the elasticity of the overall component, which is beneficial to absorb the impact force of the artificial ankle joint, thereby reducing interface micromotion and improving contact behavior. The mechanical properties of the inserts designed with the platform type and thicker flexible layer are better.
Adult ; Male ; Humans ; Ankle ; Ankle Joint/surgery* ; Finite Element Analysis ; Tibia/surgery* ; Talus ; Stress, Mechanical ; Biomechanical Phenomena

OBJECTIVE: To establish finite element models of different preserved angles of osteonecrosis of the femoral head (ONFH) for the biomechanical analysis, and to provide mechanical evidence for predicting the risk of ONFH collapse with anterior preserved angle (APA) and lateral preserved angle (LPA). METHODS: A healthy adult was selected as the study object, and the CT data of the left femoral head was acquired and imported into Mimics 21.0 software to reconstruct a complete proximal femur model and construct 3 models of necrotic area with equal volume and different morphology, all models were imported into Solidworks 2022 software to construct 21 finite element models of ONFH with LPA of 45°, 50°, 55°, 60°, 65°, 70°, and 75° when APA was 45°, respectively, and 21 finite element models of ONFH with APA of 45°, 50°, 55°, 60°, 65°, 70°, 75° when LPA was 45°, respectively. According to the physiological load condition of the femoral head, the distal femur was completely fixed, and a force with an angle of 25°, downward direction, and a magnitude of 3.5 times the subject's body mass was applied to the weight-bearing area of the femoral head surface. The maximum Von Mises stress of the surface of the femoral head and the necrotic area and the maximum displacement of the weight-bearing area of the femoral head were calculated and observed by Abaqus 2021 software. RESULTS: The finite element models of ONFH were basically consistent with biomechanics of ONFH. Under the same loading condition, there was stress concentration around the necrotic area in the 42 ONFH models with different preserved angles composed of 3 necrotic areas with equal volume and different morphology. When APA was 60°, the maximum Von Mises stress of the surface of the femoral head and the necrotic area and the maximum displacement of the weight-bearing area of the femoral head of the ONFH models with LPA<60° were significantly higher than those of the models with LPA≥60° ( P<0.05); there was no significant difference in each index among the ONFH models with LPA≥60° ( P>0.05). When LPA was 60°, each index of the ONFH models with APA<60° were significantly higher than those of the models with APA≥60° ( P<0.05); there was no significant difference in each index among the ONFH models with APA≥60° ( P>0.05). CONCLUSION From the perspective of biomechanics, when a preserved angle of ONFH is less than its critical value, the stress concentration phenomenon in the femoral head is more pronounced, suggesting that the necrotic femoral head may have a higher risk of collapse in this state.
Adult ; Humans ; Femur Head/surgery* ; Finite Element Analysis ; Stress, Mechanical ; Femur/diagnostic imaging* ; Femur Head Necrosis/surgery*

OBJECTIVE: To conduct a preliminary study on joint injuries of anterior and calcaneal fibular ligaments of the lateral ankle joint, and to analyze mechanism of action of shaking and poking in treating ankle joint and biomechanical properties of ankle during the recovery of joint injuries. METHODS: CT scan was performed on a male volunteer with right ankle sprain. Mimics 10.0, Solidworks 2016, Hypermesh 12.0 and Abaqus 6.13 software were used to establish 3D nonlinear finite element analysis model of foot and ankle, and the validity of model was verified. Combined with clinical study, the finite element simulation analysis was carried out on the toe flexion, dorsiflexion, varus and valgus of ankle joint under different treatment periods by adjusting elastic modulus of ligament to simulate ligament injury. RESULTS: With the treatment of shake and prick and recovery of ligament injury, the maximum stress and area with large stress on tibial pitch and fibular joint surface gradually increased under the four working conditions, and the stress value of the maximum stress ligament gradually increased, and the stress of the anterior and calcaneal fibular ligament dispersed and transferred, and the axial force gradually decreased. CONCLUSION The finite element method was used to simulate the mechanical condition of the shaking and stamping technique, and the changes of the forces of the ligament and articular surface before and after treatment of anterior and calcaneal ligament combined injury of ankle talus were intuitively observed. The treatment effect was quantified, and could provid objective and scientific basis for clinical promotion and application of this technique.
Male ; Humans ; Ankle Joint ; Finite Element Analysis ; Ligaments, Articular ; Sprains and Strains/therapy* ; Ankle Injuries/therapy*

OBJECTIVE: The purpose of this study is to explore the biomechanical characteristics of the tibia after unicompartmental knee arthroplasty with different distributions of two-pin holes, and to optimize the two-pin holes scheme to reduce the risk of tibial fractures after unicompartmental knee arthroplasty. METHODS: Lower limbs model is segmented and reconstructed from computed tomography images. Four combinations of two pin holes created for tibial cutting guide placement are simulated with finite element analysis. RESULTS: In the third mode, the positioning hole at the proximal medial edge of the tibial plateau has the highest stress value, and the position of the positioning hole near the medial edge of the proximal tibial plateau appears stress concentration. CONCLUSIONS The present study revealed that placing tibial cutting guide holding pins centrally would lower the risks of periprosthetic fracture of the medial tibial plateau.
Arthroplasty, Replacement, Knee ; Tibia/surgery* ; Lower Extremity ; Finite Element Analysis ; Tomography, X-Ray Computed

OBJECTIVE: To investigate the biomechanical characteristics of retinaculum in the treatment of femoral neck fractures. METHODS: The CT data of a 75-year-old female volunteer was processed by software to construct an intact femur model and femoral neck fracture model fixed with three cannulated screws, which were divided into models with retinaculum or not. The Von-Mises stress distribution and displacement were compared to analyze the stability differences between the different models to study the mechanical characteristics of the retinaculum in the treatment of femoral neck fractures. RESULTS: In the intact femur, the most obvious displacement appeared in the weight-bearing area of the femoral head, with retinaculum 0.381 37 mm, and without retinaculum 0.381 68 mm. The most concentrated part of the Von-Mises stress distribution was located in the medial and inferior part of the femoral neck, with retinaculum 11.80 MPa, without retinaculum 11.91 MPa. In the femoral neck fracture fixed with three cannulated screws model, the most obvious position of displacement also appeared in the weight-bearing area of the femoral head, with retinaculum 0.457 27 mm, without retinaculum 0.458 63 mm. The most concentrated part of the Von-Mises located at the medical and inferior part of the femoral neck, with retinaculum 59.22 MPa, without retinaculum 59.14 MPa. For the cannulated screws, the Von-Mises force peaks all appeared in the posterior and superior screw, with retinaculum 107.48 MPa, without retinaculum 110.84 MPa. Among the three screws, the Von-Mises stress of the anterior-superior screw was the smallest, which was 67.88 MPa vs 68.76 MPa in the retinaculum and non-retinaculum groups, respectively. CONCLUSION The complete retinaculum has little effect on the stability of intact femur and femoral neck fractures with anatomical reduction after internal fixation, and cannot effectively improve the stability of the fracture end after the fracture.
Female ; Humans ; Aged ; Finite Element Analysis ; Femoral Neck Fractures/surgery* ; Fracture Fixation, Internal ; Bone Screws ; Femur Neck ; Biomechanical Phenomena

OBJECTIVE: To investigate the biomechanical characteristics of different internal fixations for Pauwels type Ⅲ femoral neck fracture with defect, and provide reference for the treatment of femoral neck fracture. METHODS: Three-dimensional (3D) finite element models of femoral neck fractures were established based on CT images, including fracture and fracture with defects. Four internal fixations were simulated, namely, inverted cannulated screw(ICS), ICS combined with medial buttress plate, the femoral neck system (FNS) and FNS combined with medial buttress plate. The von Mises stress, model stiffness and fracture displacements of fracture models under 2 100 N axial loads were measured and compared. RESULTS: When femoral neck fracture was fixed by ICS and FNS, the peak stress was mainly concentrated on the surface of the screw near the fracture line, and the peak stress of FNS is higher than that of ICS;When the medial buttress plate was combined, the peak stress was increased and transferred to medial buttress plate, with more obvious of ICS fixation. For the same fracture model, the stiffness of FNS was higher than that of ICS. Compared with femoral neck fracture with defects, fracture model showed higher stiffness in the same internal fixation. The use of medial buttress plate increased model stiffness, but ICS increased more than FNS. The fracture displacement of ICS model exceeded that of FNS. CONCLUSION For Pauwels type Ⅲ femoral neck fracture with defects, FNS had better biomechanical properties than ICS. ICS combined with medial buttress plate can better enhance fixation stability and non-locking plate is recommended. FNS had the capability of shear resistance and needn't combine with medial buttress plate.
Humans ; Femoral Neck Fractures/surgery* ; Fracture Fixation, Internal/methods* ; Bone Screws ; Bone Plates ; Biomechanical Phenomena ; Finite Element Analysis

OBJECTIVE: With the help of finite element analysis, to explore the effect of proximal humeral bone cement enhanced screw plate fixation on the stability of internal fixation of osteoporotic proximal humeral fracture. METHODS: The digital model of unstable proximal humeral fracture with metaphyseal bone defect was made, and the finite element models of proximal humeral fracture bone cement enhanced screw plate fixation and common screw plate fixation were established respectively. The stress of cancellous bone around the screw, the overall stiffness, the maximum stress of the plate and the maximum stress of the screw were analyzed. RESULTS: The maximum stresses of cancellous bone around 6 screws at the head of proximal humeral with bone cement enhanced screw plate fixation were 1.07 MPa for No.1 nail, 0.43 MPa for No.2 nail, 1.16 MPa for No.3 nail, 0.34 MPa for No.4 nail, 1.99 MPa for No.5 nail and 1.57 MPa for No.6 nail. These with common screw plate fixation were:2.68 MPa for No.1 nail, 0.67 MPa for No.2 nail, 4.37 MPa for No.3 nail, 0.75 MPa for No.4 nail, 3.30 MPa for No.5 nail and 2.47 MPa for No.6 nail. Overall stiffness of the two models is 448 N/mm for bone cement structure and 434 N/mm for common structure. The maximum stress of plate appears in the joint hole:701MPa for bone cement structure and 42 0MPa for common structure. The maximum stress of screws appeared at the tail end of No.4 nail:284 MPa for bone cement structure and 240.8 MPa for common structure. CONCLUSION Through finite element analysis, it is proved that the proximal humerus bone cement enhanced screw plate fixation of osteoporotic proximal humeral fracture can effectively reduce the stress of cancellous bone around the screw and enhance the initial stability after fracture operation, thus preventing from penetrating out and humeral head collapsing.
Humans ; Finite Element Analysis ; Bone Cements ; Polymethyl Methacrylate ; Biomechanical Phenomena ; Shoulder Fractures/surgery* ; Fracture Fixation, Internal ; Humeral Head ; Bone Screws ; Bone Plates