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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 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
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: 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: 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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Objective To study the stress distributions of mandible defect by reconstruction with polyetheretherketone (PEEK) and its composite reconstruction plate through three-dimensional finite element analysis. Methods The finite element models of reconstruction plate of titanium alloy, PEEK, carbon-fiber-reinforced polyetheretherketone (CFR)-PEEK with 30% endless carbon fibers and CFR-PEEK with 68% endless carbon fibers were established by CBCT scanning，Mimics software，SolidWorks, Geomagic Studio and ANSYS Workbench software, and titanium alloy served as control. Two occlusal situations were simulated in the mandible model. Loading I: anterior region loading with 300 N; loading II: left posterior region with 300 N. Results The ratio of the maximum Von Mises stress of the reconstructed plate to its yield strength under two load situations: PEEK system ＞ 30%CFR-PEEK system ＞ titanium alloy system ＞ 68% CFR-PEEK system; the maximum stress of the mandible: PEEK system ＞ 30% CFR-PEEK system ＞ titanium alloy system ＞ 68% CFR-PEEK system. In the PEEK system, the maximum Von Mises stress of reconstructed plate and mandibular exceeded its yield strength under loading I; in the other systems, the maximum Von Mises stresses of mandible and reconstruction plate were below the yield strength. Conclusions The reconstruction plate of CFR-PEEK with 68% endless carbon fibers distributed the stresses in a similar manner as the titanium reconstruction plate, which could meet the mechanical strength requirements of mandible defect reconstruction. The fracture risk of the reconstructed plate was lower than that of titanium alloy, but the incidence of stress shielding was slightly higher. The result can provide references for the selection of materials and clinical application of reconstruction plate for mandibular defects.
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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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@#Unilateral maxillary defects are common clinical maxillofacial deformities. Because of their large area and the complexity of the maxillary structure, the distribution of pressure from dental prostheses and on the sustentacular tissue is usually uneven, which often results in pain or ulceration of the soft tissue and agomphiasis during the therapeutic process. Recently, the finite element method has been used to guide prosthesis design and implantation. This method is conducive to the restoration and stability of the dental prosthesis and the protection of the remaining tissue, which improves restoration quality and patient satisfaction. This paper summarizes the establishment of a three-dimensional finite element model of unilateral maxillary defects and its application in repairing unilateral maxillary defects with traditional prostheses, implant-supported prostheses and surgical flap transplantation combined with prostheses.
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Objective To design two kinds of fixed full-arch implant-supported prosthesis and to investigate their stress distribution in the different vertical heights of the edentulous mandible. Methods The cone-beam computed tomography (CBCT) scan data of the upper denture andmandible were collected to establish the base models of the mandible. The vertical heights of the mandible models were loweredby 0. 5. 10 and 15 mm. and the three-dimensional finite element models of implants with different vertical heights supported by mental foramen 6 parallel implants and supported by “All-on-Four” were established. including 2 groups (8 models); 6-implant group and 4-implant group. A 250 N vertical force was applied to the central fossa of the right mandibular first molar. The stress of each part of the models was analyzed by Ansys 15. 0 software. Results Under the same loading condition. the maximum stress value of the implantswas in the neck of the implants. The maximum stress distribution of 8 models showed that the maximum stress value was 40. 12-49. 06 MPa for the 4-implant group and was 80. 62-109. 64 MPa for the 6-implant group, with the latter being two folds that of the former. In two groups, the maximum stress was the lowest when the vertical height reduction was 5 mm. With the decrease of the mandible vertical height. the stress increased gradually. However, the maximum stress of the 0 mm-height-reduced models was larger than that of 5 mm- height-reducedmodels. Conclusion There is no destructive stress under certain extreme load in both 4-implant group and 6-implant group, with the 4-implant group having a more reasonable stress distribution. The 5 mm-hight-reduced models have the minimum stress, indicating that appropriate vertical height reduction can lead to more reasonable implant stress distribution.
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Objective:To construct three-dimensional(3D)finite element models with 3 different retainer designs.Methods:The intact maxillary first premolar was scanned using Micro-CT.CT images were reconstructed through Mimics 10.0 software and the prima-ry 3D models were gained after improvement in the Geomagic 7.0 software,The abutments and prosthesis of cantilever resin-bonded bridg that could be identified by the FEA software were accomplished.Results:The 3D models of cantilever resin-bonded bridg with 3 different retainer designs were constructed successfully using the maxillary first premolar as the abutment.The mesh number were 553 959,468 134,516 748,respectively.Conclusion:Using Micro-CT and finite element analysis the 3D reconstruction of the cantile-ver resin-bonded bridges may be more accurate for biomechanical analysis.
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BACKGROUND:Creation of a precise finite element model is an important basis for the finite element mechanical analysis of the spine. The reports on the precise finite element model are less. OBJECTIVE:To create L 3-L 5 lumbar three-dimensional finite element model and validate this model with normal CT data. METHODS:A 39-year-old male healthy volunteer with the height of 175 cm and weighted 65 kg was selected, then the L 3-L 5 lumbar spines were scanned with 16 row spiral CT to obtain 101 CT images with the thickness of 1.25 mm. Solid geometric model was established with Geomagic9.0 software, then determined the unit type, divided the finite element mesh, and established the finite element model for loading and calculating. RESULTS AND CONCLUSION:A L 3-L 5 lumbar three-dimensional finite element model was established. It included 213 736 nodes and 799 779 elements. The ranges of motion of L 3-L 4 and L 4-L 5 segments of the model were consistent with cadaveric biomechanical testing results, verified the effectiveness of the model, so the model could be used for experimental research.
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BACKGROUND: Due to dentition defect, dentition loss, periodontal disease, trauma and tumor, many patients have to face insufficient buccal-lingual mandibular width. At present, there is no consistent conclusion in suitable peri-implant buccal-lingual mandibular width. OBJECTIVE: To investigate the stress of implant-bone interface with three-dimensional finite element method, in order to evaluate buccal-lingual mandibular width suitable for implants. METHODS: Classes Ⅰ and Ⅲ mandible implant models (the buccal-lingual width of implant neck region was 1, 1.5, 2, 2.5, 3 and 3.5 mm) were loaded with 200 N forces vertical y and at 60° oblique. Then, the stress and strain in the implant-bone interfacial were analyzed. RESULTS AND CONCLUSION: Almost 2 mm or more than 2 mm of mandible bone width could result in good stress distribution in implant-bone interface. The stress distribution of oblique loading was much greater than that of vertical loading. Proper quantity of peri-implant mandibular width is good for stress distribution in implant-bone interface. In the clinical treatment, the oblique loading should be avoided or reduced.
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PURPOSE: The purpose of this study was to find an inclination slope of the screw thread that is favorable in distributing the stresses to alveolar bone by using three dimensional finite element analysis. MATERIALS AND METHODS: Three types modelling changed implant thread with fixed pitch of 0.8 mm is the single thread implant with 3.8degrees inclination, double thread implant with 7.7degrees inclination and the triple thread implant with 11.5degrees inclination. And three types implant angulation is the 0degrees, 10degrees and 15degrees on alveolar bone. The 9 modelling fabricated for three dimensional finite element analysis that restored prosthesis crown. The crown center applied on 200 N vertical load and 15degrees tilting load. RESULTS: 1. The more tilting of implant angulation, the more Von-Mises stress and Max principal stress is increasing. 2. Von-Mises stress and Max principal stress is increasing when applied 15degrees tilting load than vertical load on the bone. 3. When the number of thread increased, the amount of Von-Mises stress, Max principal stress was reduced since the generated stress was effectively distributed. 4. Since the maximum principal stress affects on the alveolar bone can influence deeply on the longevity of the implants. When comparing the magnitude of the maximum principal stress, the triple thread implant had a least amount of stress. This shows that the triple thread implant gave a best result. CONCLUSION: A triple thread implant to increase in the thread slope inclination and number of thread is more effective on the distribution of stress than the single and double thread implants especially, implant angulation is more tilting than 10degrees on alveolar bone. Thus, effective combination of thread number and thread slope inclination can help prolonging the longevity of implant.
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Crowns , Finite Element Analysis , Longevity , Prostheses and ImplantsABSTRACT
PURPOSE: The change of the marginal bone around dental implants have significance not only for the functional maintenance but also for the esthetic success of the implant. The purpose of this study was to investigate the load transfer of internal conical joint type implant according to marginal bone resorption by using the three-dimensional finite element analysis model. MATERIALS AND METHODS: The internal conical joint type system was selected as an experimental model. Finite element models of bone/implant/prosthesis complex were constructed. A load of 300 N was applied vertically beside 3 mm of implant axis. RESULTS: The pattern of stress distribution according to marginal bone resorption was similar. The maximum equivalent stress of implant was increase according to marginal bone resorption and the largest maximum equivalent stress was shown at model of 1 mm marginal bone resorption. Although marginal bone loss more than 1mm was occurred increasing of stress, the width of the stress increase was decreasing. CONCLUSION: According to these results, the exposure of thin neck portion of internal conical joint type implant is most important factor in stress increasing.
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Bone Resorption , Dental Implants , Finite Element Analysis , Joints , Models, Theoretical , NeckABSTRACT
OBJECTIVE: The purpose of this study was to analyze the stress distribution and the displacement pattern of mandibular anterior teeth under various intrusive force vectors according to the position of orthodontic miniscrews and hooks, using three-dimensional finite element analysis. METHODS: A three-dimensional finite element model was constructed to simulate mandibular teeth, periodontal ligament, and alveolar bone. The displacement of individual tooth on three-dimensional planes and the von Mises stress distribution were compared when various intrusion force vectors were applied. RESULTS: Intrusive forces applied to 4 mandibular anterior teeth largely resulted in remarkable labial tipping of the segment according to the miniscrew position. All 6 mandibular anterior teeth were labially tipped and the stress concentrated on the labiogingival area by intrusive force from miniscrews placed mesial to the canine. The distointrusive force vector led to pure intrusion and the stress was evenly distributed in the whole periodontal ligament when the hook was placed between the central and lateral incisors and the miniscrew was placed distal to the canine. CONCLUSIONS: Within the limits of this study, it can be concluded that predictable pure intrusion of the 6 anterior teeth segment may be accomplished using miniscrews placed distal to the canine and hooks located between the central and lateral incisors.
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Displacement, Psychological , Incisor , Periodontal Ligament , ToothABSTRACT
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Displacement, Psychological , Finite Element Analysis , Mandible , Neck , Polymers , TitaniumABSTRACT
This study evaluated the influence of the type of restoration and the amount of interdental spacing on the stress distribution in maxillary central incisors restored by means of porcelain laminate veneers and direct composite resin restorations. Three-dimensional finite element models were fabricated to represent different types of restorations. Four clinical situations were considered. Type I, closing diastema using composite resin. Labial border of composite resin was extended just enough to cover the interdental space; Type II, closing diastema using composite resin without reduction of labial surface. Labial border of composite resin was extended distally to cover the half of the total labial surface; Type III, closing diastema using composite resin with reduction of labial surface. Labial border of the preparation and restored composite resin was extended distally two-thirds of the total labial surface; Type IV, closing diastema using porcelain laminate veneer with a feathered-edge preparation technique. Four different interdental spaces (1.0, 2.0, 3.0, 4.0 mm) were applied for each type of restorations. For all types of restoration, adding the width of free extension of the porcelain laminate veneer and composite resin increased the stress occurred at the bonding layer. The maximum stress values observed at the bonding layer of Type IV were higher than that of Type I, II and III. However, the increasing rate of maximum stress value of Type IV was lower than that of Type I, II and III.
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Dental Porcelain , Diastema , IncisorABSTRACT
STATEMENT OF PROBLEM: A casting connection technique is widely used for repair, correction and addition to base metal framework. However, a casting connection technique may increase the risk of failure in clinical situations when high stresses exist. PURPOSE: The purpose of this study was to investigate the mechanical retentive groove design comparatively to increase the joint strength by using the three-dimensional finite element analysis model of a 3-unit fixed partial denture. MATERIAL AND METHODS: Ten finite element models were constructed. (Model A: One retentive groove, Model B: Two retentive grooves, Model C: Three retentive grooves, Model D: Four retentive grooves, Model E: One horizontal groove and two vertical grooves, Model F: Two horizontal grooves and one vertical groove, Model G: One groove with the enlarged dimension, Model H: Two grooves with the enlarged dimension, Model I: One groove with the increased height, Model J: One groove with the increased width of base). The vertical force was applied to the mesial and the distal fossa to the casting connection of mandibular first molar. RESULTS: The main factors, affecting joint strength of casting connection were both the retention between the primary cast and the secondary cast and the thickness of the primary cast remaining after preparing retentive groove. The increase of retentive force, according to the numbers and the dimension of retentive groove had an effect on distributing stress. However, in some cases, the increase of retentive force resulted in the increase of stress by reducing thickness of the primary cast in the connection area. CONCLUSION: The design of retentive groove that limits number of retentive groove for metal thickness and increases the depth of retentive groove for retention is highly recommended.