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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.
Subject(s)
Finite Element Analysis , Cementation/methods , Gingiva , Crowns , Dental Abutments , Dental Cements , Dental Stress AnalysisABSTRACT
Objective To establish the three-dimensional finite element model of lumbar spine(L) 3-5 segments of the normal spine of 14-year-old adolescents to analyze the biomechanical changes of the lumbar spine after different degrees of lumbar foraminal plasty, and to provide reference for improvement of adolescent foraminoplasty. Methods A14-year-old female volunteer with no previous history of lumbar spine was selected to collect lumbar CT image data and we imported it into Mimics 16.0 software for modeling. ABAQUS software was used to conduct finite element model force analysis. Models M
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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.
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【Objective】 To analyze the effect of different range and location of foramen formation on the biomechanics of lumbar spine by three-dimensional finite element analysis （D-FEA）. 【Methods】 A complete model of the lumbar spine （L5）， M0， was developed using the finite element method， and the models M1， M2， M3， M4 and M5 were obtained by sequentially simulating the apical， medial 1/4， 2/4， 3/4 and 4/4 graded resections of the left superior articular process of L5 under a lateral posterior approach with full spinal endoscopy. The displacements were recorded in six conditions： forward flexion， back extension， left and right lateral bending， and left and right lateral rotation. The results were compared between the resected models and the unresected group M0. 【Results】 The three-dimensional finite model of the L4-L5 segment developed in this experiment was valid. Compared with the unresected group M0， the differences in ROM were statistically significant for M1 under forward flexion load （all P<0.05）， M2 under forward flexion and back extension load （all P<0.05）， M3 and M4 under forward flexion， back extension and left and right lateral bending load （all P<0.05）. The differences were statistically significant for M3 and M4 under anterior flexion， posterior extension， left and right lateral flexion， and right rotation loads （all P<0.05）； and for M5 under anterior flexion， posterior extension， left and right lateral flexion and right rotation loads （all P<0.05）. Compared with M0 in the unresected group， the differences were statistically significant for M1 under anterior flexion loads （all P<0.05）， M2 under anterior flexion and left and right rotation loads （all P<0.05）. The differences were statistically significant for M3， M4 and M5 in forward flexion and extension， left and right lateral flexion， and left and right rotational loading （all P<0.05）. 【Conclusion】 In the process of foramen formation， removal of the tip or the medial quarter of the unilateral single segment of the upper articular process of the lumbar spine will affect the stability of the lumbar spine， and increase the maximum value of the stress of the intervertebral disc during the activities of the lumbar spine. Removal of one half or more will significantly damage the biomechanics of the lumbar spine. In order to avoid damaging the normal biomechanics of the lumbar spine， the upper articular process should be protected as much as possible during the whole spinal endoscopic foraminal reconstruction.
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@#Deep bite is a common clinical malocclusion that has a great impact on patients’ facial aesthetics and oral function. Bite opening is the key step in the treatment of deep bite, playing a decisive role in the development of mandible and the progress of orthodontic treatment. Torque and tip control during the correction of deep bites is a hot topic in orthodontics. The three-dimensional finite element method can accurately simulate clinical processes and conduct dynamic stress analysis, which provides the basis of the biomechanical mechanism. This paper reviewed the finite element analysis of various orthodontic systems for bite opening to provide a reference for clinical application. The emergence of mini-implants provided a new idea for anchorage control in bite opening. Finite element studies found that high-positioned mini-implants are beneficial for bodily tooth intrusion and proposed the ideal position for force application. For the finite element simulation of the reverse curve archwire, it was found that the intrusion and inclination of the anterior teeth increased with the curve depth of the archwire. The application of clear aligners has also been flourishing, but these forces are still difficult to effectively control. Finite element studies on their attachment design and corresponding tooth movement may be helpful to open the bite quickly and effectively. However, the existing studies still have modeling limitations. The structural simplification, linearization and nonstandard parameter definition of the model reduce model accuracy. Additionally, the existing research mostly focused on initial tooth movement, and studies on long-term tooth movement after bone remodeling are lacking. These studies are needed in the future.
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Objective @#To analyze the effect of different cavosurface angles on the stress distribution of ClassⅠ cavity composite resin filling of molars through the three-dimensional finite element method and to provide references for the preparation of ClassⅠ cavities.@*Methods@#Three-dimensional finite element models of ClassⅠ composite resin filling of mandibular first molars with three different cavosurface angles (group A: 90°, group B: 120°, group C: 135°) were established. Polymerization shrinkage of composites was simulated with a thermal expansion approach. The mechanical behavior of the restored models in terms of stress and displacement distributions under the combined effects of polymerization shrinkage and occlusal load (600 N) was analyzed.@*Results@# For ClassⅠ cavities with the same cavity size, the total stress of the restoration model and the maximum stress of the enamel in group A were less than those in groups B and C after cavity composite resin restoration with three cavity cavosurface angles (in which the width of the enamel bevel was 1 mm in groups B and C). The maximum stress of the dentin and adhesive was similar in the three groups, the maximum stress of the composite in group C was the largest, and the maximum stress of the composite in group B was the smallest. In terms of stress distribution, the maximum stress in each restoration model was mainly concentrated in the enamel at the cavosurface, near the enamel-dentin interface and at the edge of the restoration material.@*Conclusion@#From the point of reducing the stress of residual tooth tissue, the preparation of 90° angle without enamel bevel is an ideal method for cavity preparation when composite resin is used to fill ClassⅠ cavities of molars.
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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.
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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.
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BACKGROUND: In recent years, most qualitative studies on the mechanism of distal radius fracture are limited to two-dimensional analysis, which is susceptible to many factors, resulting in unsatisfactory results The use of CT data to establish a three-dimensional finite element model can better evaluate human skeletal variation. OBJECTIVE: To establish a three-dimensional finite element model of the radius and ulna, to test the biomechanics of distal radius fracture and to study the mechanism of distal radius fracture. METHODS: Left upper limb of one 50-year-old healthy female was selected to obtain CT imaging data from distal humerus to middle carpal joint. The three-dimensional finite element model of radius and ulna was established by using three-dimensional finite element analysis software Ansys 16.0. The force load of wrist back extension, palm flexion, ulnar deviation, and radial deviation were simulated. The stress of each part ofthe model under different loads was observed and recorded. The fracture formation and crack direction of distal radius at different model angles were analyzed. RESULTS AND CONCLUSION: (1) When the wrist joint was in dorsal extension position, the compressive stress at the midpoint of the dorsal radial margin ofthe forearm pronation and forearm supination increased with the increase ofthe dorsal extension angle, the tension stress on the volar radius of the forearm pronation and forearm supination increased with the increase of the dorsal extension angle. (2) When the wrist joint was in the metacarpal flexion position, the tension stress at the midpoint of the dorsal radius of the forearm pronation and the forearm supination increased with the increase of the metacarpal flexion angle. The compressive stress on the volar radius of the forearm pronation and forearm supination increased with the increase of the palmar flexion angle. (3) When the forearm was pronated dorsiflexion and supinated metacarpal flexion, the radial crack first appeared on the side of the maximum tension on the surface of the distal radius at the junction of cancellous bone and dense bone, the fracture crack developed along the distal metacarpal to the proximal dorsal end and at an angle of 45 degrees to the bone axis. (4) When the forearm was pronated metacarpal flexion and supinated dorsiflexion, the radial crack first appeared on the side of the maximum tension on the surface of the distal radius at the junction of cancellous bone and dense bone, the fracture crack developed along the far back end to the proximal palmar side and at an angle of 45 degrees to the bone axis. (5) To conclude, with the force load on wrist dorsal extension, metacarpal flexion, ulnar deviation, and radial deviation, the fracture first occurs on the maximum surface tension side of the distal radius at the junction of cancellous bone and dense bone, the direction of the crack is related to the directions of shear stress and tension stress.
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BACKGROUND: Most scholars believe that the fracture of the lumbar spine and pedicle is stable, and transvertebral pedicle screw implantation can improve the stability of fractures. However, the diameter of the transvertebral pedicle screw, mechanical stability and safety of the vertebrae still remain controversial. OBJECTIVE: To analyze the effect of pedicle screws of different diameters and pedicle cortex on the mechanical stability of the fractured vertebrae and pedicle by three-dimensional finite element method. METHODS: Based on normal adult L2-L3 CT DICOM data, a mimics software was used to establish a model of the fracture at L2 vertebral body and the pedicle. At the same time, a three-dimensional model of L3 vertebra was created. The L2-L3 model was imported into 3-matic in stl format, and a model of pedicle screws with different diameters (diameter of 6.5 and 6.0 mm, and length of 45 mm) was established. The model was imported into ansys after the material attributes were assigned in the mimics software. A vertical load of 500 N was applied to the upper surface of the L2 vertebral body to simulate the biomechanical performance of a adult with standard body mass after implantation with transvertebral pedicle screw with different diameters under upright condition. RESULTS AND CONCLUSION: (1) After implantation with 6.0 mm screw, the equivalent load on the lower, upper, inner, and outer walls of the pedicle at the junction of the lumbar vertebra and the pedicle was (1.28±0.62), (0.95±0.18), (0.62±0.37), and (0.36±0.16) MPa, respectively. The difference was significant among groups (F=4.298, P < 0.05). (2) After implantation with 6.5 mm screw, the equivalent load on the lower, upper, inner, and outer walls of the pedicle at the junction of the lumbar vertebra and the pedicle was (1.82±0.76), (1.11±0.18), (0.93±0.38), and (0.43±0.14) MPa, respectively. The difference was significant among groups (F=7.034, P < 0.05). (3) The equivalent load on the lower, upper, inner, and outer walls of the 6.5 mm pedicle screw model was significantly higher than that on the 6.0 mm pedicle screw model (P < 0.05). (4) These results imply that the larger the pedicle screw is, the greater the load on the cortical bone at the junction of the lumbar vertebra and the pedicle is, and the stronger the holding force is. The load on the upper, lower, inner and outer walls of the pedicle is positively related to its cortical thickness. The cortical bone of the inferior wall is thickest, the equivalent load it bears is largest, and the cortical bone of the outer wall is thinnest, and it has the smallest equivalent load. The closer the pedicle screw is to the lower medial wall within the pedicle, the stronger the holding force and the better the stability. The closer it is to the upper and outer side walls, the smaller the gripping force and the worse the stability. However, the placement of nails on the upper and outer walls is safer than the placement of nails on the lower inner wall, and the pros and cons need to be weighed in accordance with the experience of the surgeon during placement.
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BACKGROUND: Flatfoot is a commonly seen disease in foot and ankle surgery, and stage II adult acquired flatfoot is mostly seen in clinic, so this stage is a key to treatment. However, medial column instability occurs in stage II adult acquired flatfoot, which is an important cause for arch collapse. Medial column stabilization can correct the deformity to great extent, but there is a lack of biomechanical study to assess the effect of medial column stabilization on the whole foot. OBJECTIVE: To investigate the biomechanical effects of medial column stabilization on stage II adult acquired flatfoot. METHODS: A three-dimensional finite element model of stage IIa and IIb adult acquired flatfoot was established. Geomagic software, Solidwork software and Abaqus software were used to simulate medial column stabilization operation (naviculocuniform joint fusion, tarsometatarsal joint fusion, and both fusion). The maximum pressure of plantar soft tissue, medial column bone and medial ligaments was compared before and after simulated single-foot weight loading. Meanwhile, the related parameters were measured to carry out a comprehensive comparison. RESULTS AND CONCLUSION: (1) The maximum plantar stress was located under the first metatarsal head after the simulated medial column stabilization operation. The maximum plantar stress increased significantly after the medial column stabilization in stage IIa flatfoot model, but did not change significantly after the medial column stabilization in stage IIb model. (2) After medial column fusion, the stress of the corresponding joint was reduced, but increased for the other joints of the first metatarsal column. (3) The stress of medial ligament and plantar fascia was not alleviated after medial column fusion. (4) These results indicate that simple medial column stabilization surgery cannot reduce the pressure of medial column of flatfoot in stage II acquired flatfoot adults. It can only be used as a combined surgery to stabilize joints with excessive motion and correct the deformity of supination of forefoot.
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BACKGROUND: In the treatment with dental implant prosthesis, the stress distribution of marginal bone and implant-bone interface Is affected by the factors of restoration and occlusion. The Internal structure and the stress distribution of Implant-bone Interface determine the long-term life of the implant and the stability of the marginal bone. OBJECTIVE: To analyze the effects of zirconia-based all-ceramic crown and Co-Cr alloy porcelain ceramic crown on the stress distribution of implant-bone interface, implant, prosthesis abutment, retention screw, and the inner structure in three occlusal relationships. METHODS: Using Mimics 17.0 software, the implant model of maxillary central incisor was established based on the cone beam CT of a patient undergoing prosthesis implantation Into the maxillary central incisor. Two kinds of three-dimensional finite element models of zirconia-based all-ceramic crown and Co-Cr alloy porcelain ceramic crown were constructed. The edge to edge occlusion, normal occlusion and deep overbite were simulated to analyze the stress distribution of Implant structure and the Implant-bone Interface in the three occlusal relationships. RESULTS AND CONCLUSION: (1) In the Co-Cr alloy porcelain ceramic crown group, when the occlusal relationship changed from the edge-to-edge occlusion to the normal occlusion and deep overbite relationships, the stress at the occlusal point of the prosthesis increased correspondingly, and the stress at the abutment, Implant and the Implant-bone Interface decreased. In the normal occlusal relationship, the stress at the retention screw was more concentrated than that in the other two occlusal relationships, and its peak value of the equivalent stress was higher. (2) In the zirconia-based all-ceramic crown group, when the occlusal relationship changed from edge-to-edge occlusion to the normal and deep overbite relationships, the stress peaks of the abutment, implant and implant-bone interface decreased gradually. In the normal occlusal relationship, the stress peaks of the occlusal point and the retention screw were higher than those in the other two occlusal relationships. (3) In the edge-to-edge occlusion relationship, the peak of equivalent stress at the occlusal point of the implant prosthesis in the Co-Cr alloy porcelain ceramic crown group was slightly higher than that in the zirconia-based all-ceramic crown group. The peaks of equivalent stress of the abutment, retention screw, Implant, and Implant-bone Interface in the Co-Cr alloy porcelain ceramic crown group were slightly lower than those in the zirconia-based all-ceramic crown group. In the normal occlusal relationship, the peak of equivalent stress at the neck of the implant in the Co-Cr alloy porcelain ceramic crown group was slightly higher than that in the zirconia-based all-ceramic crown group. In the deep overbite relationship, the peaks of the equivalent stress at the occlusal site of the implant prosthesis and the neck of the implant in the Co-Cr alloy porcelain ceramic crown group were higher than those in the zirconia-based all-ceramic crown group. The peaks of equivalent stress of the abutment, retention screw, and implant-bone interface In the Co-Cr alloy porcelain ceramic crown group were slightly lower than those in the zirconia-based all-ceramic crown group. (4) These results showed that different occlusal relationships and different upper structures of the implant prosthesis affected the stress distribution in each part of the implant and at the implant-bone interface. This finding may provide a reference for the prediction of long-term complications of implant prosthesis.
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BACKGROUND: Using interproximal enamel reduction, adding attachments and over-correction are major methods to improve the efficiency of correcting tooth torsion when using clear aligners in the clinic. However, the choice and placement of attachments depend on the experience and habits of orthodontists, and whether the effects are different has not been reported. OBJECTIVE: To explore the effects of rectangular attachment with different thicknesses and locations on the left maxillary canine tooth torsion in clear aligner by three-dimensional finite element analysis. METHODS: The finite element models of the clear aligner-attachment-maxillary canine-periodontal ligament-spongy bone-cortical bone and the clear aligner-maxillary canine-periodontal ligament-spongy bone-cortical bone were established according to the scanning data of in vitro maxillary canine. The models with attachments were divided into four groups based on different thicknesses of attachment, namely 0.5, 0.75,1.0, and 1.5 mm groups. The placement positions were divided into five areas: mesial, distal, occlusal, median, and gingival of canine. 2° clockwise rotation of the tooth axis (X axis) was applied to the clear aligner. The action of the appliance and the canine were calculated by MSC.Marc.Mentat software. Then, the nephograms of stress and displacement, and the maximum stress and displacement values were collected. RESULTS AND CONCLUSION: (1) Whether the rectangular attachment was used or not, the two models’ distribution of canine’s displacement and periodontal stress were the same. The stress values of periodontal ligament were all higher than those without rectangular attachment. (2) With the thickness of rectangular attachment increasing, the maximum displacement values of the canine increased gradually, which were 42.94, 49.32, 52.52 and 59.39 urn, respectively. (3) When the rectangular attachment was placed in different positions, the maximal displacement of canine teeth the attachment of which was placed on the median was almost the same with that of the gingival side. While the changes in the mesial and distal directions were irregular. (4) The use of rectangular attachments makes no effect on the movement of instant canines, which only plays a synergistic role in the control of canine tooth torsion. The thickness of the attachment has a certain effect on the torsion of appliance. When the thickness increases, the maximum displacement of the canine tooth and the stress of the periodontal ligament are increased. In the vertical direction, the closer of the placement is to the crown, the better the control of the rotated canine is.
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BACKGROUND: In contrast to traditional drafting techniques, the superposition structure of the bed air column of spinal manipulation contributes to controlling the duration of traction. Finite element analysis is used to calculate the stress of adjacent lumbar segments with different traction durations. It provides a better theoretical basis for lumbar traction prescription in clinical spinal manipulative bed. OBJECTIVE: To analyze the stress and distribution of adjacent lumbar segments with different traction durations using the finite element analysis when the spine manipulation bed is used for traction. METHODS: A healthy male volunteer, aged 26 years, with a height of 174 cm and a weight of 60 kg, was selected, who was fully informed of the study protocol and signed an informed consent. The study protocol was approved by the Ethics Committee of Rehabilitation Hospital Affiliated to Fujian University of Traditional Chinese Medicine with an approval No. 2016XJS-001-01. According to the CT images of volunteers T12-S1, an effective three-dimensional finite element model of the lumbar spine was established. By means of three-dimensional finite element analysis, the stress changes of the lumbar vertebrae and facet joint adjacent to the L3 were calculated when the traction was maintained for 10, 20 and 30 seconds respectively. The internal law and mechanism of the changes were analyzed and discussed. RESULTS AND CONCLUSION: (1) When the pushing height was 5 cm and the action time was 1.25-17 seconds, the stress value of adjacent lumbar segments increased continuously. For the intervertebral disc, the stress value was 4.60-5.68 MPa for L2-L3, and 5.26-6.61 MPa for L3-L4; for the facet joint, the stress value was 7.01-8.67 MPa for L2-L3 and 5.22-6.50 MPa for L3-L4. (2) The stress of adjacent vertebral segments and facet joints remained basically unchanged after pushing for more than 24 seconds. Therefore, when the spine manipulation bed acts on the lumbar spine, it will not damage the adjacent lumbar segments, and the duration of action should be between 25 and 30 seconds.
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BACKGROUND: In recent years, the finite element analysis of lumbar biomechanics has become a hot topic. Lumbar lordosis is considered to reduce the pressure load on the lumbar intervertebral disc and protect the lumbar spine. OBJECTIVE: To study the biomechanical effects of lumbar traction on L1-L5 lumbar segments in normal physiological curvature, flexion position and maximum overextension position, and to evaluate the optimal physiological curvature of lumbar traction. METHODS: A healthy male volunteer, aged 26 years, with a height of 174 cm and a weight of 60 kg, was selected, who had no history of lumbar spine diseases. With the L3 segment as the traction site, a finite element model of the whole lumbar spine was established based on lateral radiographs of the lumbar spine at the initiation site and during the maximal overextension as photographed by a DR machine. Based on the three-dimensional finite element model of the lumbar spine, the stress values and distributions of the lumbar vertebrae, the intervertebral joints, the intervertebral discs and the anterior longitudinal ligaments of the whole lumbar spine under different physiological curvatures were calculated. The patient was fully informed of the study protocol and signed an informed consent. The study protocol was approved by the Ethics Committee of Rehabilitation Hospital Affiliated to Fujian University of Traditional Chinese Medicine. RESULTS AND CONCLUSION: (1) Under six kinds of simulated working conditions, the range of motion of L1-L2 was 9.31° for flexion and extension, 9.84° for right and left bending, and 4.43° for right and left rotation; the range of motion of L2-L3 was 10.22° for flexion and extension, 12.35° for left and right bending, and 4.57° for left and right rotation; the range of motion of L3-L4 was 11.20° for flexion and extension, 11.63° for left and right bending, and 5.32° for left and right rotation; the range of motion of L4-L5 was 13.16° for flexion and extension, 11.58° for left and right bending, and 5.05° for left and right rotation. Under the normal physiological curvature of the lumbar vertebrae, the stress value of different lumbar spine structures was much greater than the stress value of hyperextension traction. The normal curvature of the anterior longitudinal ligament was 2.47 MPa, and the curvature of hyperextension traction value was 21.20 MPa. The stress value of L3 was the highest, which was four times that of the hyperextension traction. The stress value of the intervertebral joints at L2-L3 and intervertebral disc was highest than that of any other segment of the lumbar spine. These findings indicate that the pressure of lumbar vertebrae, intervertebral joints and intervertebral discs in hyperextension position is less than that in normal physiological curvature traction, and the pressure of anterior longitudinal ligament is always within the safe range. Lumbar traction may have better clinical efficacy and definite security in hyperextension position.
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OBJECTIVE@#To study the comprehensive impact of scar and maxillary expansion combined with protraction on the development of maxilla with cleft lip and palate after repair operation.@*METHODS@#In the original finite element model of the maxilla with cleft palate, a finite element model of the maxilla with cleft lip and palate was established by using Boolean operation in ANSYS. Scar force after cleft lip and palate repair and maxillary expansion force combined with protraction were added simultaneously to process the stress analysis.@*RESULTS@#Maxillary deformation occurred in the three-dimensional direction. The comparison of displacements was as follows: X-axis>Z-axis>Y-axis.@*CONCLUSIONS@#Maxillary growth is significantly inhibited in the three-dimensional direction under the comprehensive impact of scar and maxillary expansion combined with protraction after repair operation, especially transverse and sagittal growth.
Subject(s)
Humans , Cicatrix/pathology , Cleft Lip/surgery , Cleft Palate/surgery , Finite Element Analysis , Maxilla/surgery , Palatal Expansion TechniqueABSTRACT
Objective: To evaluate the biomechanical effects of combined use of miniscrew and clear aligner in different kinds of loading condition on the en-mass retraction of maxillary anterior teeth. Methods: 3 D finite element models of the maxillary bone with miniscrews and clear aligner were reconstructed using the method of reverse engineering with CBCT data of an adult patient who had maxillary first premolars extracted. The orthodontic force was loaded by (1) clear aligner, (2) clear aligner and 1. 47 N force of retraction at appliance and (3) clear aligner and 1. 47 N force of retraction at canine, respectively. Results: Under the working condition of (1), (2) and (3), in sagittal direction, the displacement difference of crown and root of the maxillary central incisor was 1. 12 E-02 mm, 1. 29 E-02 mm and 9. 62 E-03 mm respectively, the displacement of the first molar crown was-2. 49 E-02 mm, -2. 09 E-02 mm and-2. 00 E-02 mm respectively; in vertical direction, extrusion of the maxillary central incisor was 1. 77 E-03 mm, 2. 93 E-03 mm and 6. 53 E-04 mm respectively. Conclusion: The working condition (3) is more advantageous to control the torque of incisors and to save the anchorage of posterior teeth, and more effective to control the extrusion of the incisors.
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@#Important guarantees of the success of root canal therapy include being familiar with the anatomical features of root canal system, good root canal preparation and complete root canal filling. With the development of medical imaging technology, three-dimensional reconstruction technology has been widely applied in root canal morphology, root canal preparation, root canal filling quality, root canal retreatment efficiency, three-dimensional finite elements and other related research. The reconstructed 3D images can be observed qualitatively and quantitatively from different angles and levels, which aid in the understanding of root canal anatomy and evaluation of the operation effect on all aspects of root canal therapy, providing important guiding significance for clinical operation. The application of 3D reconstruction technology based on micro-CT in the research of root canal anatomy, root canal preparation, root canal filling, root canal retreatment efficiency and three-dimensional finite element analysis are reviewed. The results of a literature review showed that the resolution of micro-CT is high. Furthermore, three-dimensional reconstruction can accurately display the fine anatomical morphology of a root canal, accurately measure the volume and morphological changes of root canal before and after root canal preparation, accurately measure the incidence and volume of the void after root canal filling and accurately calculate the volume changes of the root canal filling materials before and after root canal retreatment. Micro-CT is the gold standard for the morphological study of the root canal system and quality analysis of root canal preparation and filling. After three-dimensional reconstruction with micro-CT scans, a three-dimensional finite element model can be established to simulate the process of root canal therapy and stress analysis. This method can be used to analyze the stress distribution of root canal preparation instruments and the influence of root canal preparation on the stress distribution of tooth tissue and the root canal wall in the process of root canal filling. Then, suitable operation methods can be selected to prevent instrument breakage and root fracture. The application of three-dimensional reconstruction-based micro-CT is of great value in the evaluation of root canal morphology and treatment.
ABSTRACT
Objective @#To analyze the initial displacement of the upper central incisor and stress distribution of periodontal ligament under different torque values of upper incisors under the action of a four-curved auxiliary arch to provide a reliable basis for the safety of clinical application of four-curved auxiliary arches.@*Methods @# A three-dimensional finite element model for torque control of upper anterior teeth with a homemade quadrilateral auxiliary arch was established. Four different states were analyzed: molar ligation without extraction space (group A), microimplant ligation without extraction space (group B), molar recovery with extraction space closure (group C) (the adductive traction force was set at 115 g) and microimplant recovery with extraction space closure (group D) (the adductive traction force was set at 115 g). When four types of torque (0.5 N, 1.0 N, 1.5 N, and 2.0 N) were applied. The initial displacement of upper central incisors and the stress distribution of periodontal ligament in 16 groups (A1-A4, B1-B4, C1-C4, D1-D4) were observed.@*Results @#Under different conditions, as the strength of the four-curve auxiliary arch increases, the maxillary anterior teeth has crown labial inclination and a root lingual inclination. The displacement of the incisor tip increases with the increase in the loading force of the torque auxiliary arch, and the displacement of the incisor root apex increases as the force increases. The difference in incisor-apex displacement distance in A1-A4, B1-B4, C1-C4, D2 and D4 groups increased as the torque force increases, while the difference between the D3 group and D1 and D2 groups decreased slightly. The stress of the cervical periodontal ligament of the upper central incisor did not exceed the stress of the periodontal ligament in the following groups: A1, A2, B1, B2, B3, C1, C2, D1, and D2. The stress of the lip side of the upper central incisor did exceed the stress of the periodontal ligament in the following groups: A3, A4, B4, C3, C4, D3, and D4. In other words, when using the four-curved auxiliary arch as an implant anchorage, the force applied in the absence of extraction space should not exceed 1.5 N, and the force applied in the adduction of extraction space should not exceed 1.0 N. When using the nonimplant anchorage, the force applied in the absence of extraction space and the adduction of extraction space should not exceed 1.0 N. In addition, the range of force should not exceed the maximum stress of the periodontal ligament in the cervical region such that the effective and safe torque movement can be achieved. Under other stress conditions, the stress of the labial and cervical periodontal ligament of the upper central incisor exceeded the stress value (2.6 × 10-2MPa). The stress value of periodontal ligament was 2.6 × 10-2MPa in all groups.@*Conclusion@#A four-curved auxiliary arch has a significant effect on the upper anterior teeth, and the use of microimplants can better control root movement such that the crown of upper central incisors cannot be excessively lip inclined.
ABSTRACT
Objective@#To observe the stress distribution according to a model of the bucco-occluso-lingual (BOL) inlay of mandibular first molar after restoration to provide a basis for the clinical treatment of cracked tooth with BOL inlay.@*Methods@#A three-dimensional finite element model of mandibular first molar was established by combining micro-CT scanning technology with Mimics, UG, Ansys and Midas-FEA software. Based on this model, a BOL inlay restoration model was established. The material parameter of inlay IPS e.max CAD was given, and a Von-mises stress distribution nephogram under the same loading condition was obtained. The results of the stress distribution in each model were compared.@*Results @#The stress of intact teeth is mainly concentrated in the central fissure of the occlusal surface at the crown. The stress of the cavity after BOL inlay restoration is mainly concentrated in the mesial and distal walls of the cavity, the axial-pulpal line angle and the gingival wall. The stress of the inlay is mainly distributed at the bottom of the inlay, axial wall and the gingival wall.@*Conclusion@#BOL inlay restoration change the stress distribution in the complete dental model, which relieves the stress concentration in the fossa and groove of the occlusal surface and can play an active role in the treatment of cracked tooth.