Influence of implant distribution on the biomechanical behaviors of mandibular implant-retained overdentures: a three-dimensional finite element analysis.

OBJECTIVE: To assess stress distribution in peri-implant bone and attachments of mandibular overdentures retained by small diameter implants, and to explore the impact of implant distribution on denture stability. METHODS: Through three-dimensional Finite Element Analysis (3D FEA), four models were established: three models of a two mandibular implants retained overdenture (IOD) and one model of a conventional complete denture (CD). The three IOD models consisted of one with two implants in the bilateral canine area, another with implants in the bilateral lateral incisor area, and the third with one implant in the canine area, and another in the lateral incisor area. Three types of loads were applied on the overdenture for each model: a 100 N vertical load and a inclined load on the left first molar, and a100N vertical load on the lower incisors. The stress distribution in the peri-implant bone, attachments, and the biomechanical behaviors of the overdentures were analyzed. RESULTS: Despite different distribution of implants, the maximum stress values in peri-implant bone remained within the physiological threshold for all models across three loading conditions. The dispersed implant distribution design (implant in the canine area) exhibited the highest maximum stress in peri-implant bone (822.8 µe) and the attachments (275 MPa) among the three IOD models. The CD model demonstrated highest peak pressure on mucosa under three loading conditions (0.8188 Mpa). The contact area between the denture and mucosa of the CD model was smaller than that in the IOD models under molar loading, yet it was larger in the CD model compared to the IOD model under anterior loading. However, the contact area between the denture and mucosa under anterior loading in all models was significantly smaller than those under molar loading. The IOD in all three models exhibited significantly less rotational movement than the complete denture. Different implant positions had minimal impact on the rotational movement of the IOD. CONCLUSION: IOD with implants in canine area exhibited the highest maximum stress in the peri-implant bone and attachments, and demonstrated increased rotational movement. The maximum principal stress was concentrated around the neck of the small diameter one-piece implant, rather than in the abutment. An overdenture retained by two implants showed better stability than a complete denture.

Evaluation of stress and displacement of maxillary canine during the single canine retraction in the maxillary first premolar extraction cases- A finite element study.

OBJECTIVES: This finite element study aimed to simulate maxillary canine movement during anterior teeth retraction. MATERIALS AND METHODS: Three methods of maxillary canine movement including miniscrew sliding with high hooks (MSH), miniscrew sliding with low hooks (MSL), and the traditional sliding method (TS) without using miniscrews were simulated using three-dimensional finite element analysis. The initial displacement of the maxillary canine, the maximum principal stress of the periodontal ligament and the Von Mises stress were calculated. RESULTS: The distolingual tipping movements of the canine were shown in three movement modes. MSH showed a small tendency to lingual tipping movement and a extrusion movement while MSL had the largest lingual inclination. TS demonstrated a tendency toward distolingual torsion displacement. Compressive stress values were mainly concentrated in the range - 0.003 to -0.006 MPa. For tensile stress, the distribution of MSH and MSL was concentrated in the range 0.005 to 0.009 MPa, TS was mainly distributed about 0.003 MPa. Von Mises equivalent stress distribution showed no significant difference. CONCLUSIONS: The loss of tooth torque was inevitable, irrespective of which method was used to close the extraction space. However, miniscrew application and higher hooks reduced the loss of torque and avoided lingual rotation. CLINICAL RELEVANCE: This study shows that miniscrew implants with different hooks can better control the movement of the maxillary canines. The non-invasive nature of the finite element analysis and its good simulation of dental stress and instantaneous motion trend have a clinical advantage in the analysis of tooth movement.

Biomechanical comparison of all-on-4 and all-on-5 implant-supported prostheses with alteration of anterior-posterior spread: a three-dimensional finite element analysis.

Introduction: The all-on-4 concept is widely used in clinical practice. However, the biomechanical changes following the alteration of anterior-posterior (AP) spread in all-on-4 implant-supported prostheses have not been extensively studied. Methods: Three-dimensional finite element analysis was used to compare the biomechanical behavior of all-on-4 and all-on-5 implant-supported prostheses with a change in anterior-posterior (AP) spread. A three-dimensional finite element analysis was performed on a geometrical mandible model containing 4 or 5 implants. Four different implant configurations were modeled by varying the angle of inclination of the distal implants (0°and 30°), including all-on-4a, all-on-4b, all-on-5a, and all-on-5b, and a 100 N force was successively applied to the anterior and unilateral posterior teeth to observe and analyze the differences in the biomechanical behavior of each model under the static influence at different position. Results: Adding an anterior implant to the dental arch according to the all-on-4 concept with a distal 30° tilt angle implant exhibited the best biomechanical behavior. However, when the distal implant was implanted axially, there was no significant difference between the all-on-4 and all-on-5 groups. Discussion: In the all-on-5 group, increasing the AP spread with tilted terminal implants showed better biomechanical behavior. It can be concluded that placing an additional implant in the midline of the atrophic edentulous mandible and increasing the AP spread might be beneficial in improving the biomechanical behavior of tilted distal implants.

Comparative study of biomechanical effects between two types of 2 × 4 techniques employing a rocking-chair archwire: a three-dimensional finite element analysis.

OBJECTIVES: After bonding brackets to the first deciduous molar in a 2 × 4 technique, a three-dimensional finite element analysis (3D FEA) is used to demonstrate the biomechanical changes in an orthodontic system. This study aims to opt for the appropriate type of orthodontic technology by analyzing and comparing the mechanical systems produced by two types of 2 × 4 techniques employing rocking-chair archwires. MATERIALS AND METHODS: Herein, the maxilla and maxillary dentition are modeled by cone beam computed tomography (CBCT) and 3D FEA. Common clinically used 0.016-inch round archwires (material: titanium-molybdenum alloy and stainless-steel) and 0.018-inch round archwires (material: titanium-molybdenum alloy and stainless-steel) are bent into the shape of a rocking chair with a depth of 3 mm. The forces and moments applied to the brackets are transferred to the dentition to evaluate the biomechanical effects of the 2 × 4 technique after the bracket is bonded to the first deciduous molar. RESULTS: For the central incisor, the teeth-moving distance in all three directions increases with bracket bonding to the first deciduous molar applying the 0.016-inch rocking-chair archwire. For the lateral incisor, the tooth root moves toward the gingival side when using 0.016-inch and 0.018-inch archwires. Moreover, for the same archwire size, the lateral incisors move toward the gingival side by bonding the bracket to the first deciduous molar. After bonding a bracket to the first deciduous molar, using rocking-chair archwires of 0.016 inch or 0.018 inch, the buccal movement distance of the first molar crown increases in the X-axis direction. In the Y-axis and Z-axis directions, the modified 2 × 4 technique significantly increases the effect of backward-tipping compared with the traditional 2 × 4 technique. CONCLUSIONS: In clinical practice, the modified 2 × 4 technique can be used to increase the movement distance of anterior teeth to a certain extent and accelerate the orthodontic teeth movement. Moreover, the modified 2 × 4 technique is better in anchorage conservation of the first molar than the traditional technique. CLINICAL RELEVANCE: Although the traditional 2 × 4 technique is widely used in early orthodontic treatment, we found mucosal damage and abnormal archwire deformation might affect orthodontic treatment time and effect. The modified 2 × 4 technique is a novel approach that avoids these drawbacks and improves orthodontic treatment efficiency.

[Three-dimensional finite element analysis of cement flow in abutment margin-crown platform switching].

OBJECTIVE: To analyze the cement flow in the abutment margin-crown platform switching structure by using the three-dimensional finite element analysis, in order to prove that whether the abutment margin-crown platform switching structure can reduce the inflow depth of cement in the implantation adhesive retention. METHODS: By using ANSYS 19.0 software, two models were created, including the one with regular margin and crown (Model one, the traditional group), and the other one with abutment margin-crown platform switching structure (Model two, the platform switching group). Both abutments of the two models were wrapped by gingiva, and the depth of the abutment margins was 1.5 mm submucosal. Two-way fluid structure coupling calculations were produced in two models by using ANSYS 19.0 software. In the two models, the same amount of cement were put between the inner side of the crowns and the abutments. The process of cementing the crown to the abutment was simulated when the crown was 0.6 mm above the abutment. The crown was falling at a constant speed in the whole process spending 0.1 s. Then we observed the cement flow outside the crowns at the time of 0.025 s, 0.05 s, 0.075 s, 0.1 s, and measured the depth of cement over the margins at the time of 0.1 s. RESULTS: At the time of 0 s, 0.025 s, 0.05 s, the cements in the two models were all above the abutment margins. At the time of 0.075 s, in Model one, the gingiva was squeezed by the cement and became deformed, and then a gap was formed between the gingiva and the abutment into which the cement started to flow. In Model two, because of the narrow neck of the crown, the cement flowed out from the gingival as it was pressed by the upward counterforce from the gingival and the abutment margin. At the time of 0.1 s, in Model one, the cement continued to flow deep inside with the gravity force and pressure, and the depth of the cement over the margin was 1 mm. In Model two, the cement continued to flow out from the gingival at the time of 0.075 s, and the depth of the cement over the margin was 0 mm. CONCLUSION: When the abutment was wrapped by the gingiva, the inflow depth of cement in the implantation adhesive retention can be reduced in the abutment margin-crown platform switching structure.

Effect of thread depth and thread pitch on the primary stability of miniscrews receiving a torque load : A finite element analysis.

PURPOSE: We have been developing a new type of miniscrew to specifically withstand orthodontic torque load. This study aimed to investigate the effect of thread depth and thread pitch on the primary stability of these miniscrews if stressed with torque load. METHODS: Finite element analysis (FEA) was used to evaluate the primary stability of the miniscrews. For thread depth analysis, the thread depth was set to 0.1-0.4 mm to construct 7 models. For thread pitch analysis, the thread pitch was set to 0.4-1.0 mm to construct another 7 models. A torque load of 6 Nmm was applied to the miniscrew, and the other parameters were kept constant for the analyses. Maximum equivalent stress (Max EQV) of cortical bone and maximum displacement of the miniscrews (Max DM) were the indicators for primary stability of the miniscrew in the 14 models. RESULTS: In the thread depth analysis, Max DM increased as the miniscrew thread depth increased, while Max EQV was smallest in model 3 (thread depth = 0.2, Max EQV = 8.91 MPa). In the pitch analysis, with an increase of the thread pitch, Max DM generally exhibited a trend to increase, while Max EQV of cortical bone showed a general trend to decrease. CONCLUSION: Considering the data of Max DM and Max EQV, the most appropriate thread depth and thread pitch of the miniscrews in our model was 0.2 and 0.7 mm, respectively. This knowledge may effectively improve the primary stability of newly developed miniscrews.

Three-dimensional finite element analysis of cement flow in abutment margin-crown platform switching / 北京大学学报(医学版)

OBJECTIVE@#To analyze the cement flow in the abutment margin-crown platform switching structure by using the three-dimensional finite element analysis, in order to prove that whether the abutment margin-crown platform switching structure can reduce the inflow depth of cement in the implantation adhesive retention.@*METHODS@#By using ANSYS 19.0 software, two models were created, including the one with regular margin and crown (Model one, the traditional group), and the other one with abutment margin-crown platform switching structure (Model two, the platform switching group). Both abutments of the two models were wrapped by gingiva, and the depth of the abutment margins was 1.5 mm submucosal. Two-way fluid structure coupling calculations were produced in two models by using ANSYS 19.0 software. In the two models, the same amount of cement were put between the inner side of the crowns and the abutments. The process of cementing the crown to the abutment was simulated when the crown was 0.6 mm above the abutment. The crown was falling at a constant speed in the whole process spending 0.1 s. Then we observed the cement flow outside the crowns at the time of 0.025 s, 0.05 s, 0.075 s, 0.1 s, and measured the depth of cement over the margins at the time of 0.1 s.@*RESULTS@#At the time of 0 s, 0.025 s, 0.05 s, the cements in the two models were all above the abutment margins. At the time of 0.075 s, in Model one, the gingiva was squeezed by the cement and became deformed, and then a gap was formed between the gingiva and the abutment into which the cement started to flow. In Model two, because of the narrow neck of the crown, the cement flowed out from the gingival as it was pressed by the upward counterforce from the gingival and the abutment margin. At the time of 0.1 s, in Model one, the cement continued to flow deep inside with the gravity force and pressure, and the depth of the cement over the margin was 1 mm. In Model two, the cement continued to flow out from the gingival at the time of 0.075 s, and the depth of the cement over the margin was 0 mm.@*CONCLUSION@#When the abutment was wrapped by the gingiva, the inflow depth of cement in the implantation adhesive retention can be reduced in the abutment margin-crown platform switching structure.

Three-dimensional finite element analysis of the influence of implant site and axial direction on the immediate weight bearing stress of central incisors in different alveolar fossa shapes / 口腔医学

Objective@#To analyze and investigate the effects of implant location and axial direction on the stress distribution of implants, abutments, central screws, and crowns during immediate loading of maxillary mesial incisors with different alveolar fossa morphology based on three-dimensional finite element method.@*Methods@#Referring to the oral CBCT images of a healthy adult, a three-dimensional finite element model was established for immediate implant loading of maxillary central incisors with three alveolar fossa morphs: labial, intermediate, and palatal; different implant sites(apical site, palatal/labial site) and axes(tooth long axis, alveolar bone long axis) were simulated; the established model was loaded with a force of 100 N. ANSYS software was applied to analyze the stress values of the implants, abutments, central screwss, and crownss. @*Results@#The 3D finite element models of 12 maxillary central incisors with different alveolar sockets were successfully established;the implants and their superstructures were least stressed when the maxillary central incisors with partial labial and partial palatal shape were placed along the long axis of the alveolar bone in the palatal/labial position for immediate implant loading;the implants and their superstructures were least stressed when the maxillary central incisors with central shape were placed along the long axis of the tooth in the palatal position for immediate implant loading. The implant and its superstructure were subjected to the least stress when the implant was placed along the long axis of the tooth in the immediate loading position. @*Conclusion@#The bio-mechanical characteristics of the implant and its superstructure are influenced by the different socket morphology, implantation sites and axes. Therefore, in clinical practice, different implantation axes and implantation sites should be developed for different socket morphs.

Effect of cervical spine motion on displacement of posterolateral annulus fibrosus in cervical spondylotic radiculopathy with contained posterolateral disc herniation: a three-dimensional finite element analysis.

BACKGROUND: Previous studies on dynamic impingement of nerve root in cervical spondylotic radiculopathy (CSR) have focused on effect of cervical spine motion (CSM) on dimensional changes of intervertebral foramen. However, there are few studies to investigate effect of CSM on displacement of posterolateral intervertebral disc until now. The present study aimed to investigate effect of CSM on displacement of posterolateral annulus fibrosus (AF) in CSR with contained posterolateral disc herniation. METHODS: A C5-C6 CSR finite element model with unilateral contained posterolateral disc herniation was generated based on validated C5-C6 normal finite element model. Forward and backward displacement distributions of posterolateral AFs in CSR model and normal model were compared. Changes in forward and backward displacement magnitudes of posterolateral AFs of the herniated side and the healthy side in CSR model, with respect to those of the ipsilateral posterolateral AFs in normal model, were compared. The comparisons were performed under flexion, extension, lateral bendings and axial rotations. RESULTS: There was no difference in deformation trend of posterolateral AF between CSR model and normal model. Bilateral posterolateral AFs mainly moved forward during flexion and backward during extension. Left posterolateral AF mainly moved backward and right posterolateral AF forward during left lateral bending and left axial rotation. Left posterolateral AF mainly moved forward and right posterolateral AF backward during right lateral bending and right axial rotation. However, with respect to forward and backward displacement magnitudes of the ipsilateral posterolateral AFs in normal model, those of the herniated side increased relatively significantly compared with those of the healthy side in CSR model. CONCLUSIONS: Flexion, lateral bending to the healthy side and axial rotation to the healthy side make posterolateral AF of the herniated side mainly move forward, whereas extension, lateral bending to the herniated side and axial rotation to the herniated side make it mainly move backward. These data may help select CSM or positions to diagnose and treat CSR with contained posterolateral disc herniation. Increase in deformation amplitude of posterolateral AF of the herniated side may also be the reason for dynamic impingement of nerve root in CSR with contained posterolateral disc herniation.

[Three-dimensional finite element analysis of Swanson prosthesis-arthroplasty of the first metatarsophalangeal joint combined with osteotomy and bone grafting of the first metatarsal bone for hallux valgus].

Objective: To analyze the biomechanical changes of hallux valus after Swanson prosthesis-arthroplasty of the 1st metatarsophalangeal joint combined with osteotomy and bone grafting of the 1st metatarsal bone by three-dimensional finite element analysis, so as to provide data basis for studying the changes of foot morphology and physiological function after hallux valus correction surgery. Methods: A 65-year-old female patient with severe hallux valus admitted in January 2013 was selected as the research object. The CT data of the right foot was obtained, and the three-dimensional finite element models before and after Swanson prosthesis-arthroplasty of the 1st metatarsophalangeal joint combined with osteotomy and bone grafting of the 1st metatarsal bone were established by Mimics10.01, Geomagic Studio, and ANSYS12.0 software. ANSYS 12.0 software was used for nonlinear static stress analysis, and the hallux valgus angle (HVA), the intermetatarsal angle (IMA), and the von Mises stress distributions of the forefoot plantar surface and the 1st to 5th metatarsal bones were observed before and after operation. Results: The HVA and IMA were 56.3° and 16.3° before operation and 9.2° and 9.8° after operation, respectively. Before operation, the stress on the forefoot was the largest in the 4th metatarsal head zone and the smallest in the 1st metatarsal head zone; the stress on the medial side of the forefoot was significantly smaller than that on the lateral side, and the center of forefoot pressure was located on the lateral side. After operation, the stress on the forefoot was the largest in the 1st metatarsal head zone and the smallest in the 5th metatarsal head zone; the stress on the lateral side of the forefoot was significantly smaller than that on the medial side, and the center of forefoot pressure was located on the medial side. Before operation, the stress of the 5th metatarsal bone was the largest, and the 1st metatarsal bone was the smallest. After operation, the stress of the 1st metatarsal bone was the largest, and the 4th metatarsal bone was the smallest. Conclusion: Swanson prosthesis-arthroplasty of the 1st metatarsophalangeal joint combined with osteotomy and bone grafting of the 1st metatarsal bone can effectively correct hallux valgus and make HVA, IMA, and plantar pressure distribution close to normal. However, postoperative stresses of the 1st to 5th metatarsal bones elevate, which may lead to associated complications.

[Three-dimensional finite element analysis of exo-cortical placement of humeral calcar screw for reconstruction of medial column stability].

Objective: To explore the biomechanical stability of the medial column reconstructed with the exo-cortical placement of humeral calcar screw by three-dimensional finite element analysis. Methods: A 70-year-old female volunteer was selected for CT scan of the proximal humerus, and a wedge osteotomy was performed 5 mm medially inferior to the humeral head to form a three-dimensional finite element model of a 5 mm defect in the medial cortex. Then, the proximal humeral locking plate (PHILOS) was placed. According to distribution of 2 calcar screws, the study were divided into 3 groups: group A, in which 2 calcar screws were inserted into the lower quadrant of the humeral head in the normal direction for supporting the humeral head; group B, in which 1 calcar screw was inserted outside the cortex below the humeral head, and the other was inserted into the humeral head in the normal direction; group C, in which 2 calcar screws were inserted outside the cortex below the humeral head. The models were loaded with axial, shear, and rotational loadings, and the biomechanical stability of the 3 groups was compared by evaluating the peak von mises stress (PVMS) of the proximal humerus and the internal fixator, proximal humeral displacement, neck-shaft angle changes, and the rotational stability of the proximal humerus. Seven cases of proximal humeral fractures with comminuted medial cortex were retrospectively analyzed between January 2017 and December 2020. Locking proximal humeral plate surgery was performed, and one (5 cases) or two (2 cases) calcar screws were inserted into the inferior cortex of the humeral head during the operation, and the effectiveness was observed. Results: Under axial and shear force, the PVMS of the proximal humerus in group B and group C was greater than that in group A, the PVMS of the internal fixator in group B and group C was less than that in group A, while the PVMS of the proximal humerus and internal fixator between group B and group C were similar. The displacement of the proximal humerus and the neck-shaft angle change among the 3 groups were similar under axial and shear force, respectively. Under the rotational torque, compared with group A, the rotation angle of humerus in group B and group C increased slightly, and the rotation stability decreased slightly. All the 7 patients were followed up 6-12 months. All the fractures healed, and the healing time was 8-14 weeks, with an average of 10.9 weeks; the neck-shaft angle changes (the difference between the last follow-up and the immediate postoperative neck-shaft angle) was (1.30±0.42)°, and the Constant score of shoulder joint function was 87.4±4.2; there was no complication such as humeral head varus collapse and screw penetrating the articular surface. Conclusion: For proximal humeral fractures with comminuted medial cortex, exo-cortical placement of 1 or 2 humeral calcar screw of the locking plate outside the inferior cortex of the humeral head can also effectively reconstruct medial column stability, providing an alternative approach for clinical practice.

Influence of different base materials and thicknesses on the fracture resistance of endocrown: A three-dimensional finite element analysis.

INTRODUCTION: To analyze the stress distribution of the all-ceramic endocrown with different base materials and thicknesses using three-dimensional finite element analysis. METHODS: A endodontically treated maxillary premolar was scanned by micro-CT, a three-dimensional finite element model of the endocrown with fluid resin as the base material was divided into control (0 mm), 1 mm, 2 mm, and 3 mm groups according to base thickness. Three kinds of conventional base materials were used and divided into glass ion group (A), fluid resin group (B), and nanocomposite resin group (C), and a three-dimensional finite element model of the endocrown with 1.0 mm thickness of base was established. A static loading with axial and 45° direction was applied to each model, the stress distribution of each part of the endocrown was analyzed under different base materials and thicknesses. RESULTS: The different thickness of the base layer has an influence on the components of the restoration and the tooth. The stress in the control group was the largest. The stress was the lowest when the thickness of the base layer was 1 mm; The maximum of the equivalent stress, the first, second, and third principal stress in the endocrown, abutment, and alveolar bone, are basically the same with the different base materials. The stress on the base layer increases with the elastic modulus of base materials increases. CONCLUSIONS: The base layer played a force buffering effect on the dental body restored with endocrowns, and the effect was the best at 1 mm; The selection of base material has little influence on the whole, but in order to protect the weak tissues of the cavity bottom, the base material with lower elastic modulus can be used.

Role of the proximal tibiofibular joint on the biomechanics of the knee joint: A three-dimensional finite element analysis.

PURPOSE: The proximal tibiofibular joint (PTFJ) is easily ignored, although many diseases of the knee are caused by PTFJ injuries. Therefore, studying PTFJ biomechanics is very important. The effects of PTFJ injury on ankle function have been reported. However, few studies have assessed the effects of PTFJ injury on the knee joint. This study was performed to describe the biomechanical effects of PTFJ on the knee joint according to a three-dimensional finite element model. METHODS: The knee joint of a healthy volunteer was scanned by CT and MRI. CT and MRI scanning data in DICOM format were imported into Mimics software. Subsequently, 3D models of the normal and PTFJ injured knee, including the bone, cartilage, meniscus and ligament structures were established, and their validity was verified on the basis of available studies in literature. The biomechanical changes in the two knee models under different conditions were compared. RESULTS: The validity of the intact model was verified. No significant difference was observed in tibial mobility in the two models under the conditions of 134 N forward, 10 N·m internal rotation and 10 N·m valgus load. After application of 134 N backward, 10 N·m varus and external rotation load with respect to the tibia, the posterior movement of the tibia and the varus and external rotation angles of the tibia were 3.583±0.892 mm, 4.799±0.092° and 18.963±0.027° in the normal knee model, and 5.127±1.224 mm, 5.277±0.104° and 21.399±0.031° in the PTFJ injury model, respectively, and a significant statistical difference was observed. CONCLUSIONS: PTFJ played an important role in maintaining the posterolateral stability of the knee joint and thus deserves more attention in clinical operations.

Malposition of components and Femorotibial mechanical Axis changes on pressure distribution in Total knee arthroplasty.

BACKGROUND: To the best of our knowledge, no report has analyzed the postoperative results of poor prosthesis position, particularly when the femoral and tibial components are abnormally positioned relative to neutral lower limb alignment. We aimed to investigate pressure distribution in the knee at different lower limb alignments with diverse positions of femoral and tibial components. METHODS: We established a three-dimensional model of the lower limb using computed tomography and simulated total knee arthroplasty. Tibial and femoral components were changed to 7°, 5°, and 3° of valgus and neutral and 3°, 5°, and 7° of varus positions in the coronal plane. Finite element analysis was performed after applying pressure to simulate weight-bearing, and pressure distribution on the tibial surface was analyzed. We also conducted biomechanical testing using a weight-bearing rig with six cadavers. We measured the pressure at the tibial surface with the position of different components and lower limb alignment. FINDINGS: Peak pressure on the medial or lateral side of the tibia was determined by the mechanical axis. When tibial components are in 3°,5° and 7° of valgus/varus and femoral components are in 3°,5° and 7° of varus/valgus correspondence, no peak pressure was detected with normal alignment, despite malpositioned components. INTERPRETATION: Lower limb alignment is more critical than the position of the component. Medial and lateral tibial compartment pressures were evenly distributed if the alignment was neutral. Malpositioned femoral or tibial components changed the femorotibial mechanical axis, and peak pressure of the proximal tibia was positively related to alignment.

Effect of Different Customized Abutment Types on Stress Distribution in Implant-Supported Single Crown: A 3D Finite Element Analysis.

PURPOSE: The purpose was to investigate stress distribution among 4 different customized abutment types: titanium abutment (Ti), titanium hybrid-abutment-crown (Ti-Hybrid), zirconia abutment with titanium base (Zir-TiBase), and zirconia hybrid-abutment-crown with titanium base (Zir-Hybrid-TiBase). MATERIALS AND METHODS: To achieve this purpose, 4 types of abutment configurations were simulated. A static load of 200 N (vertical) and 100 N (oblique) were applied to the models. The volume average, maximum, and stress distribution of von Mises stress, including percentage difference, were analyzed with 3D finite element analysis. RESULTS: According to the volume average von Mises stress, the Ti and Zir-TiBase comparison group showed that the Zir-TiBase group dominantly generated the higher value at Ti-base (22.57 MPa) and screw (17.68 MPa). To evaluate the effect of the hybrid-abutment-crown on volume average von Mises stress by comparing the Ti-Hybrid and Zir-Hybrid-TiBase groups, it was revealed that the combination of abutment and crown in the Ti-Hybrid group generated the worst stress concentration at the screw (12.42 MPa), while in the Zir-Hybrid-TiBase group presented stress concentration at the implant (8.90 MPa). CONCLUSIONS: A titanium base improved stress distribution at implant in zirconia abutment with titanium base by absorbing stress itself. Customized titanium hybrid-abutment-crown and zirconia hybrid-abutment-crown with titanium base created concentrated stress at screw and implant; respectively. Both abutment types should be cautiously used and maintenanced regularly.

Development of an optimal relief method for the palatal plate by stress analysis.

BACKGROUND: Plate dentures cannot be easily modified after fabrication; therefore, the sites and magnitude of relief must be effectively assessed at the time of fabrication. However, a considerable variation exists in the magnitude of optimal relief and relief range, and there are no guidelines that present these clearly, leading the dentists to decide subjectively. Thus, this study aims to develop an optimal relief method to improve the stress bearing capacity of the palatal mucosa. METHODS: The objective of this study, namely, the borderline, was set in steps. A three-dimensional finite element model for the pseudopalatal plate was created and used to evaluate the changes in stress distribution in the palatal mucosa due to the selective relief of stresses above the borderline. The resulting data were used to develop the optimal relief method. RESULTS: In the relief model with a borderline of 0.04 MPa or higher, the distribution volume at which a high stress of 0.20 MPa or higher is generated was approximately 800% of that with the no-relief model, and in the relief model with a borderline of 0.06 MPa or higher, the respective ratio was approximately 280%. On the other hand, the relief models with a borderline of 0.14 MPa or higher were approximately 60%. In the mid-palatal relief model, the distribution volume at which a stress of 0.20 MPa or higher was generated was 180% of that in the relief model. CONCLUSIONS: The supportive strength of plates can be increased by selectively applying optimal relief rather than standard relief, allowing for easier and more effective plate-denture treatment.

Isolated medial column stabilization surgery does not benefit adult acquired flatfoot stage IIa nor IIb by three-dimensional finite element biomechanical analysis.

The surgical treatment for stage II adult acquired flat foot deformity (AAFD) remains controversial. Biomechanical effects of medial column stabilization remain unclear. No study has biomechanically assessed the effect of medial column arthrodesis on the whole foot. Our study aimed to mechanically analyze the advantages and disadvantages of this. Stage IIa and IIb AAFD three-dimensional finite element models were established. The application of Geomagic software, Solidwork software, and Abaqus software was used to simulate a medial column stabilization operation (navicular-cuneiform joint fusion, metatarsal-cuneiform joint fusion, or both). The maximum pressure on plantar soft tissue, medial column bone, and medial ligaments was compared before and after simulated single-foot weight loading. Several data were measured to carry out a comprehensive comparison. The maximum plantar stress was located under the first metatarsal head after the simulated medial column stabilization operation. It increased significantly after medial column stabilization in a stage IIa flatfoot model, but did not change significantly after medial column stabilization in stage IIb model. Therefore, after medial column fusion, the stress of the corresponding joint was reduced, but it was increased in the adjacent joints of the medial column. The stresses on medial ligaments and plantar fascia were also not alleviated after medial column fusion. Our results showed isolated medial column stabilization surgery cannot help patients with stage IIa nor IIb flatfoot from the biomechanical point of view, and such stabilization increases stress on the sole, the joints around the fusion sites, medial soft tissue, and ligaments. It can only be used as a combined surgery to stabilize joints with excessive motion and correct the deformity of supination of the forefoot.

The biomechanical effect of the relevant segments after facet-disectomy in different diameters under posterior lumbar percutaneous endoscopes: a three-dimensional finite element analysis.

OBJECTIVE: To evaluate the biomechanical influence after percutaneous endoscopic lumbar facetectomy in different diameters on segmental range of motion (ROM) and intradiscal pressure (IDP) of the relevant segments by establishing three dimensional finite element (FE) model. METHODS: An intact L3-5 model was successfully constructed from the CT of a healthy volunteer as Model A (MA). The Model B (MB), Model C (MC) and Model D (MD) were obtained through facetectomy on L4 inferior facet in diameters 7.5 mm, 10 mm and 15 mm on MA for simulation. The ROM and IDP of L3/4 and L4/5 of four models were all compared in forward flexion, backward extension, left and right bending, left and right rotation. RESULTS: Compared with MA, the ROM of L4/5 of MB, MC and MD all increased. MD changed more significantly than MB and MC in backward extension, right bending and right rotation. But that of MB and MC on L3/4 had no prominent change, while MD had a slight increase in backward extension. The IDP of MB and MC on L4/5 in six states was similar to MA, yet MD increased obviously in backward extension, right bending, left and right rotation. The IDP on L3/4 of MB and MC was resemble to MA in six conditions, nevertheless MD increased slightly only in backward extension. CONCLUSION: Compared with the facetectomy in diameters 7.5 mm and 10 mm, the mechanical effect brought by facetectomy in diameter 15 mm on the operating segment changed more significantly, and had a corresponding effect on the adjacent segments.

Effect of different defect areas of medial femoral condyle cartilage on peripheral cartilage stress: Three-dimensional finite element analysis / 中国组织工程研究

BACKGROUND: Although it has been found in many studies that three-dimensional finite element analysis can be used in the study of knee joint biomechanics, there are few researches on different defect areas of medial condyle cartilage of the femur. OBJECTIVE: To analyze the stress change trend of perimeter articular cartilage before and after the occurrence of different defect areas of medial femoral condyle cartilage, providing biomechanical data for patients with knee medial femoral condyle cartilage defect. METHODS: One normal adult had been selected to establish a three-dimensional finite element model. Material mechanical properties were input to Abaques software with divided grid model. After controlling boundary condition with mechanical load, structural nonlinear finite element was calculated. First, the load stress distribution of knee cartilage and meniscus was observed under normal stress. Articular cartilage stress distribution was observed with load conditions in different defects (0, 6, 8, 10, 12, 14, 16, 18 and 20 mm) of medial femoral condyle. The stress changes on the cartilage were analyzed during the defect of medial femoral condyle. This study was approved by the Ethics Committee of First Affiliated Hospital of Kunming Medical University. The volunteer signed the informed consent. RESULTS AND CONCLUSION: (1) Material properties, boundary conditions and the introduction of loads were defined successfully. The stress cloud chart and its stress data were obtained from different diameter defects of cartilage in medial condyle of knee joint. According to statistical analysis, the stress on the femoral condyle and tibial plateau cartilage had significant changes compared with no defects when the medial femoral condyle cartilage had defects of 10 mm (area 0. 78 cm2) and 12 mm (area 1. 13 cm2). (2) The stress change trend of the cartilage of the medial condyle of the knee joint under the condition of different diameter defects was calculated based on the analysis of the application of three-dimensional finite element method. (3) Results suggest that the defect with the diameter of 10 mm (area 0. 78 cm2) of medial femoral condyle may be the minimum diameter advised for operation intervention of cartilage repair.

Three-dimensional finite element analysis of mini implants supported mandibular overdentures / 中国组织工程研究

BACKGROUND: Overdenture supported by two to four implants located in the mandibular mental foramen area has been widely used in edentulous patients. However, in patients with severe mandibular resorption, it is a challenging to insert conventional implants. Mini-implants are a better choice in these cases. OBJECTIVE: To compare and analyze the biomechanical characteristics of conventional and mini-implants supported mandibular complete overdenture and to reveal the influence of different implant repair methods on implants and its surrounding tissues. METHODS: The cone beam CT data of a healthy patient scheduled to receive complete edentulous implant supported overdenture was obtained. CT data of the patient, implant and attachment data were imported into the software to create four models: 2 normal implants, 4 normal implants, 4 mini implants, and 5 mini implants supported mandibular overdentures respectively. The overdenture was bilaterally subjected to a vertical load of 150 N. The displacement and stress of implants and the stress of bone were compared. RESULTS AND CONCLUSION: For all models, the lowest and highest maximum values of stress in bone were obtained from 4 normal implant model (2.71 MPa) and 4 mini implant model (7.93 MPa). The lowest and highest maximum values of displacement in implant were obtained from 4 normal implant model (1.37 µm) and 2 normal implant model (1.57 µm). Moreover, the lowest and highest maximum values of stress in implant were demonstrated from 4 normal implant model (12.90 MPa) and 4 mini implant model (22.17 MPa). The biomechanical values of mini implant models were higher than those of conventional models. The biomechanical values of all models were below the critical limits. The distribution was more homogenous and the maximum values of displacement in the implant, stress in implant and stress in bone were reduced as the number of implants increased. Three-dimensional finite element analysis revealed that mandibular overdenture supported by four or five mini implants is a reliable treatment option.