Construction and assessment of a three-dimensional finite element model of mandibualr second molar mesialization using customized lingual appliance and mini-implant / 中华口腔医学杂志

Objective@#To construct a three-dimensional (3D) finite element model and analyze the biomechanical characteristics during mandibular second molar mesialization using customized lingual appliances and mini-implant.@*Methods@#One adult student volunteer from The First Affiliated Hospital of Zhengzhou University with lower left first molar extraction was selected. After CT scanning, Mimics, Geomagic, ANSYS were employed to develop a 3D finite element model including customized lingual brackets, stainless steel lingual arch wire, buccal buckles, lower dentition, periodontal ligaments and alveolar bone. Four different loading methods (1. the force of 1.470 N loaded at the lingual side only; 2, 3, 4. the forces of 0.490, 0.735 and 0.980 N loaded at both buccal and lingual sides, respectively.) were included. The initial displacements of the lower second molar and stress distribution in the periodontal ligaments were analyzed.@*Results@#More uniform stress distributions in the periodontal membrane of mandibular left second molar were found when the mesial force were loaded at both buccal and lingual sides than the force loaded at lingual side only. More inclination of the second molar was observed when force loaded at both sides than at lingual side only. With the values of the force increased, the mesial inclination potential of the second molar, the initial movement of the second molar and the stress distribution in the periodontal membrane increased. Under the force of 0.735 N at both buccal and lingual sides, mesially inclined initial displacements of the mandibuar second molar were observed and the stress values of von Mises was in the suitable area.@*Conclusions@#Less second molar rotation was found when the force loaded at both buccal and lingual sides than loaded at lingual side only. However, force loaded at both sides would increase the measial inclination potential of the second molar.

Construction of a finite element model based on lunate sagittal Micro-CT images and its stress analysis / 中国组织工程研究

BACKGROUND: Biomechanical mechanisms are complex, and previous studiers focus on the stress conduction in the carpus. However, the stress distribution and characteristics of trabecula in the carpus are rarely reported.OBJECTIVE: To investigate the stress distribution and deformation characteristics of the normal lunate through a two-dimensional sagittal finite element model.METHODS: A normal cadaveric lunate sample was scanned with Micro-CT and the central sagittal image was chosen for further finite element analysis (FEA). The chosen image was processed and imported into the finite element analysis software (Ansys 14.0). A two-dimensional sagittal finite element model of the lunate bone was established. Axial pressure was applied to the model with the wrist held in different positions, and nine regions of interests (ROIs) were identified, for which stress and displacement nephograms were created. These included the first principal stress (S1, the maximum stress in a principal plane), the third principal stress (S3, the minimal stress in a principal plane), shear stress (SXY, the component of stress coplanar with a material cross section), von Mises stress (SEQV, yielding begins when the elastic energy of distortion reaches a critical value)and displacement of each ROI (UY, displacement on the vertical plane of the lunate) which were calculated and compared.RESULTS AND CONCLUSION: (1) The stresses on ROIs located in the proximal and volar cortices of the lunate bone were much higher than those in the distal and dorsal cortices. At the proximal lunate, S1 was less than S3; however at the distal lunate, S1 was greater than S3. The ROIs of the distal and proximal ends of the lunate bone received much higher stress than the ROIs of the middle part. As for axial trabecular displacement,both distal and proximal ROIs were compressed by axial pressure. However, the dorsal and the volar parts of the proximal lunate moved in different directions at different wrist postures. Besides, the stress values and magnitudes of displacement were elevated in wrist flexion and extension compared to neutral position.Furthermore, the stress concentration zones (the proximal volar ROI, the proximal dorsal ROI, the distal volar ROI, and the distal dorsal ROI) had different directions of shear stress and displacement in different wrist postures. (2) These results suggest that when stress is loaded on a normal lunate model, four stress concentration zones, the proximal volar ROI, the proximal dorsal ROI, the distal volar ROI, and the distal dorsal ROI are found. The wrist postures can significantly affect the value and distribution of axial stress on the sagittal lunate.

Digital modeling for the individual mandibular 3D mesh scaffold based on 3D printing technology / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate an ideal modeling method of designing 3D mesh scaffold substitutes based on tissue engineering to restore mandibular bone defects. By analyzing the theoretical model from titanium scaffolds fabricated by 3D printing, the feasibility and effectiveness of the proposed methodology were verified.</p><p><b>METHODS</b>Based on the CT scanned data of a subject, the Mimics 15.0 and Geomagic studio 12.0 reverse engineering software were adopted to generate surface model of mandibular bone and the defect area was separated from the 3D model of bone. Then prosthesis was designed via mirror algorithm, in which outer shape was used as the external shape of scaffold. Unigraphics software NX 8.5 was applied on Boolean calculation of subtraction between prosthesis and regular microstructure structure and ANSYS 14.0 software was used to design the inner construction of 3D mesh scaffolds. The topological structure and the geometrical parameters of 3D mesh titanium scaffolds were adjusted according to the aim of optimized structure and maximal strength with minimal weight. The 3D mesh scaffolds solid model through two kinds of computer-aided methods was input into 3D printing equipment to fabricate titanium scaffolds.</p><p><b>RESULTS</b>Individual scaffolds were designed successfully by two modeling methods. The finite element optimization made 10% decrease of the stress peak and volume decrease of 43%, and the porosity increased to 76.32%. This modeling method was validated by 3D printing titanium scaffold to be feasible and effective.</p><p><b>CONCLUSIONS</b>3D printing technology combined with finite element topology optimization to obtain the ideal mandibular 3D mesh scaffold is feasible and effective.</p>

Three-dimensional finite element analysis on half of the structure defect with post core and all-ceramic crown restoration of mandibular first molar / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To make a mechanical analysis on three-dimensional finite element models of the mandibular first molar defect restored with post core and all-ceramic crown, and to provide a guideline for planning restoration for such kind of tooth structure defect.</p><p><b>METHODS</b>Cone-beam CT based three dimensional finite element models of post and core restored first mandibular molars were established, with 6 different ferrule designs (the ferrule with only 180 axial wall on different locations). The von Misses criterion was applied for comparing the maximum von Misses stress value of dentin and stress concentration areas in six models which restored with fiber post or cast NiGr alloy post core or Au alloy post core under the maximum, vertical, inclined and horizontal direct loads.</p><p><b>RESULTS</b>The restoration effects in six models were compared, and the maximum von Misses stress concentration areas were not obviously different. The maximum von Misses stress value of NiCr alloy post core and crown was 62.81 MPa. Under horizontal load, the maximum von Misses stress value of dentin increased remarkably.</p><p><b>CONCLUSIONS</b>The location of residual dentin has little influence on the stress distribution, when restored by post core and crown. Au alloy post core and crown or fiber post core and crown are superior to NiCr alloy post core and crown.</p>

Finite element analysis of the maxillary central incisor with crown lengthening surgery and post-core restoration in management of crown-root fracture / 北京大学学报(医学版)

Objective:To construct the finite element models of maxillary central incisor and the simu-lations with crown lengthening surgery and post-core restoration in management of different crown-root fracture types, to investigate the stress intensity and distributions of these models mentioned above, and to analyze the indications of crown lengthening from the point of view of mechanics. Methods:An extrac-ted maxillary central incisor and alveolar bone plaster model were scanned by Micro-CT and dental impression scanner ( 3shape D700 ) respectively. Then the 3D finite element models of the maxillary central incisor and 9 simulations with crown lengthening surgery and post-core restoration were construc-ted by Mimics 10. 0, Geomagic studio 9. 0 and ANSYS 14. 0 software. The oblique static force (100 N) was applied to the palatal surface ( the junctional area of the incisal 1/3 and middle 1/3 ) , at 45 degrees to the longitudinal axis, then the von Mises stress of dentin, periodontal ligament, alveolar bone, post and core, as well as the periodontal ligament area, were calculated. Results:A total of 10 high-precision three-dimensional finite element models of maxillary central incisor were established. The von Mises stress of models: post >dentin >alveolar bone >core >periodontal ligament, and the von Mises stress increased linearly with the augmentation of fracture degree ( besides the core) . The periodontal ligament area of the crown lengthening was reduced by 12% to 33%. The von Mises stress of periodontal ligament of the B2L2c, B2L3c, B3L1c, B3L2c, B3L3c models exceeded their threshold limit value, respective-ly. Conclusion: The maxillary central incisors with the labial fracture greater than three-quarter crown length and the palatal fracture deeper than 1 mm below the alveolar crest are not the ideal indications of the crown lengthening surgery.

Influence of attachment type on stress distribution of implant-supported removable partial dentures / 北京大学学报(医学版)

Objective: To compare influences of different retention attachments on stress among supporting structures .Methods: By 3-dimensional laser scanner and reverse engineering computer aided design ( CAD) software , a basic partially edentulous digital model with mandibular premolar and molar missing was established .Implant attachment and removable partial dentures ( RPD) were added into the basic model to build three kinds of models: RPD only, RPD +implant +Locator attachment , and RPD +implant +Magfit attachment .Vertical and inclined loads were put on artificial teeth unilaterally . By means of 3-dimensional finite element analysis , the stress distribution and displacement of the main supportive structures were compared . Results: A complete 3-dimensional finite element model was established , which contained tooth structure , and periodontal structures .The displacement of the denture was smaller in Locator (9.38μm vertically, 45.48μm obliquely) and Magfit models (9.54μm vertically, 39.45 μm obliquely) compared with non-implant RPD model (95.27 μm vertically, 155.70 μm oblique-ly) .Compared with the two different attachments , cortical bone stress value was higher in Locator model ( Locator model 10.850 MPa vertically , 43.760 MPa obliquely;Magfit model 7.100 MPa vertically , 19.260 MPa obliquely).The stress value of abutment periodontal ligamentin Magfit model (0.420 MPa vertically) was lower than that in Locator model (0.520 MPa vertically).Conclusion:The existence of implant could reduce maximum von Mises value of each supportive structure when Kennedy Ⅰpartially edentulous mandible was restored .Comparing the structure of Magfit and Locator attachment , the contact of Magfit attachment was rigid , while Locator was resilient .Locator attachment could improve stability of the denture dramatical -ly.Locator had stronger effect on defending horizontal movement of the denture .

THE EFFECT OF INTRA-ARTICULAR CONTACT ON THREE-DIMENSIONAL NONLINEAR SIMULATION OF HUMAN TEMPOROMANDIBULAR JOINT FORCES / 解放军医学杂志

Purpose: To analyze the effect of the intraarticufar contact of the temporomandibular joint ( TMJ ) on three dimensional nonlinear simulation of human TMJ forces in order to simulate the distribution and transfer of TMJ forces more realistically and logically. Materials and Methods: Combining helical CT scanning technology with three dimensional finite element method, together with Auto CAD software, three dimensional nonlinear finite element models were developed in vivo for comparison with the changes in the stress within the TMJ in different contact conditions. Results: The stresses on the surfaces of articular disc and condyle in the finite element models with contact elements between the disc and condyle were mainly distributed on their anterior and medial regions, and the stresses on other regions were relatively smaller. But, the stresses of those models without contact element were mainly distributed on their midposterior and medial aspacts. Moreover, the stress values were higher. When the friction coefficient was in the range of 0 0.15, the distribution extent and magnitude of the contact stress between the disc and the condyle in the TMJ were completely same. Meanwhile, the surface stresses on the disc and the condyle were nearly coincident in three ways of disc condyle contact, which were no friction contact, rigid contact and elastic contact. Conclusion: In the issue of disc condyle contact of simulating TMJ forces with three dimensional nonlinear method, the stress distribution in the joint with complete contact relationship between the disc and the condyle conforms more to the physiological condition. The lower friction coefficient ( 0 0.15 ) in the TMJ and various contact patterns between the disc and condyle had no evident influence on the stress distribution in the TMJ. Three dimensional nonlinear analysis for the forces in the TMJ might be more realistic and reasonable because of contact simulation among various structures within the TMJ.