Biomechanical analysis of a temporomandibular joint condylar prosthesis during various clenching tasks

Biomechanical evaluation of various rigid internal fixation modalities for condylar-base-associated multiple mandibular fractures: A finite element analysis

Condylar-base-associated multiple mandibular fractures are more prevalent than single ones. Direct trauma to mandibular symphysis, body or angle are prone to induce indirect condylar fracture. However, little is known about the effects of various rigid internal fixation modalities in condylar base for relevant multiple mandibular fractures, especially when we are confused in the selection of operative approach. Within the finite element analysis, straight-titanium-plate implanting positions in condylar base contained posterolateral zone (I), anterolateral zone (II), and intermediate zone (III). Von Mises stress (SS) in devices and bone and mandibular displacement (DT) were solved, while maximum values (SSmax and DTmax) were documented. For rigid internal fixation in condylar-base-and-symphysis fractures, I + II modality exhibited least SSmax in screws and cortical bone and least DTmax, I + III modality exhibited least SSmax in plates. For rigid internal fixation in condylar-base-and-contralateral-body fractures, I + III modality exhibited least SSmax in screws and cortical bone, I + II modality exhibited least SSmax in plates and least DTmax. For rigid internal fixation in condylar-base-and-contralateral-angle fractures, I + III modality exhibited least DTmax. The findings suggest that either I + II or I + III modality is a valid guaranty for rigid internal fixation of condylar base fractures concomitant with symphysis, contralateral body or angle fractures.

Development and validation of a digital twin of the human lower jaw under impact loading by using non-linear finite element analyses

Mandibular fractures are one of the most frequently observed injuries within craniofacial region mostly due to tumor-related problems and traumatic events, often related to non-linear effects like impact loading. Therefore, a validated digital twin of the mandible is required to develop the best possible patient-specific treatment. However, there is a need to obtain a fully compatible numerical model that can reflect the patients' characteristics, be available and accessible quickly, require an acceptable level of modeling efforts and knowledge to provide accurate, robust and fast results at the same time under highly non-linear effects. In this study, a validated simulation methodology is suggested to develop a digital twin of mandible, capable of predicting the non-linear response of the biomechanical system under impact loading, which then can be utilized to design treatment strategies even for multiple fractures of the mandibular system. Using Computed Tomography data containing cranial (skull) images of a patient, a 3-dimensional mandibular model, which consists cortical and cancellous bones, disks and fossa is obtained with high accuracy that is compatible with anatomical boundaries. A Finite Element Model (FEM) of the biomechanical system is then developed for a three-level validation procedure including (A) modal analysis, (B) dynamic loading and (C) impact loading. For the modal analysis stage: Free-free vibration modes and frequencies of the system are validated against cadaver test results. For the dynamic loading stage: Two different regions of the mandible are loaded, and maximum stress levels of the system are validated against finite element analyses (FEA) results, where the first loading condition (i) transfers a 2000 N force acting on the symphysis region and, the second loading condition (ii) transfers a 2000 N force acting on the left body region. In both cases, equivalent muscle forces dependent on time are applied. For the impact loading stage: Thirteen different human mandibular models with various tooth deficiencies are used under the effects of traumatic impact forces that are generated by using an impact hammer with different initial velocities to transfer the impulse and momentum, where contact forces and fracture patterns are validated against cadaver tests. Five different anatomical regions are selected as the impact site. The results of the analyzes (modal, dynamic and impact) performed to validate the digital twin model are compared with the similar FEA and cadaver test results published in the literature and the results are found to be compatible. It has been evaluated that the digital twin model and numerical models are quite realistic and perform well in terms of predicting the biomechanical behavior of the mandible. The three-level validation methodology that is suggested in this research by utilizing non-linear FEA has provided a reliable road map to develop a digital twin of a biomechanical system with enough confidence that it can be utilized for similar structures to offer patient-specific treatments and can help develop custom or tailor-made implants or prosthesis for best compliance with the patient even considering the most catastrophic effects of impact related trauma.

Computational modelling of the fossa component fixation associated with alloplastic total temporomandibular joint replacements

The alloplastic total temporomandibular joint (TMJ) replacement is a complex surgical approach to end-stage TMJ disorders. The fixation of TMJ prostheses remains a critical issue for implant design and performance. For the fossa component, it is generally considered to use fixation screws to achieve tripod stability. However, the fossa may still come loose, and the mechanism remains unknown. A computational framework, consisting of a musculoskeletal model for calculating muscle and TMJ forces, and a finite element model for the fossa fixation simulation, was developed. A polyethylene (PE) fossa with stock prosthesis design was analyzed to predict contact pressures at the fixation interfaces, and stresses/strains in the fossa implant and bone during the static loading of normal chewing bite and maximum-force bite. The predicted maximum von Mises stresses were 33 MPa and 44 MPa for the bone, 13 MPa and 28 MPa for the PE fossa, and 131 MPa and 244 MPa for the screws, for the normal and maximum bites, respectively; the peak minimum principal strain was in the range of -2514 ∼ -3545 με for the bone. The results show that the sufficient initial mechanical strength of the fossa component fixation can be established using the screws in combination with bone support. The functional loads applied through the prosthetic TMJ bearing can be largely transferred to supporting bone without causing high level stresses. Tightening fixation screws with a pretension of 100 N can reduce transverse load to the screws and help prevent screw loosening. Further research is recommended to accurately quantify the transverse load and its influence on screw loosening during dynamic loading, and the frictional properties at the bone-implant interface.

Biomechanical Evaluation of a Standard Temporomandibular Joint Prosthesis and Screw Arrangement Optimization: A Finite Element Analysis

BACKGROUND AND OBJECTIVE

Artificial total joint replacement is an important method of temporomandibular joint (TMJ) reconstruction, which has been advocated for TMJ osteoarthrosis, ankylosis, tumors, and other diseases. We designed one type of standard TMJ prosthesis fit for Chinese patients. This study aimed to explore the biomechanical behavior of the standard TMJ prosthesis using finite element analysis and selects an optimal screw arrangement scheme for clinical application.

MATERIALS AND METHODS

A female volunteer was recruited for a maxillofacial computed tomography scan, then the Hypermesh software was used to establish a finite element model of a mandibular condyle defect repaired with an artificial TMJ prosthesis. An advanced universal finite element program software was used to calculate the stress and deformation under a simulated maximum bite force loading. Also, the forces of screws under different numbers and arrangements were analyzed. Meanwhile, we designed an experiment to verify the calculation model.

RESULTS

The average maximum stress of the fossa component of the standard prosthesis model was 19.25 MPa. The average maximum stress of the condyle component was 82.58 MPa, mainly concentrated near the top row hole. The fossa component should be fixed with at least 3 screws, and the optimal number of screws was 4. The condyle component should be fixed with at least 4 screws, and its optimal number was 6. The best scheme of screw arrangement was determined. The results of the verification experiment showed that the analysis was reliable.

CONCLUSIONS

The stress distribution of the standard TMJ prosthesis is uniform, meanwhile, the number and arrangement of the screws significantly affect the contact force of the screws.

Evaluation of internal fixation techniques for extracapsular fracture: A finite element analysis and comparison

BACKGROUND AND OBJECTIVES

This study explored the optimal plates and screws fixation for extracapsular fracture by finite element analysis, and provided a biomechanical basis for clinical treatment.

METHODS

Four extracapsular fixation models were built and evaluated: A. One single straight four-hole plate with two bi-cortical screws on both sides and two mono-cortical screws in the middle; B. One single straight four-hole plate with four bi-cortical screws; C. Two straight four-hole plates, each with two bi-cortical screws on both sides and two mono-cortical screws in the middle; D. One L-shape four-hole plate in the back and one straight four-hole plate in the front, each with two bi-cortical screws on both sides and two mono-cortical screws in the middle. Displacements of fractured bone blocks and stress of plates, screws, cortical and cancellous bone and the deformation of plates were analyzed by finite element analysis to investigate their stability in clinical using.

RESULTS

Groups A and B showed larger displacements of the fractured bone block, greater deformation of plates and higher risk of the plate breakage during masticatory motion. Groups C and D exhibited the minimum displacements of the fractured bone block, the stress distribution within the safe range and less deformation of the plates. In addition, double plates fixation and bi-cortical screws exceeded single plate fixation and mono-cortical screws in stability, respectively, while an L-shape plate exhibited no significant differences in the stress dispersion and the displacement reduction.

CONCLUSIONS

Double plates fixation of the extracapsular condylar fracture was a safe and stable way and bi-cortical screws should be selected as far as possible.

A Novel Design Method of Gradient Porous Structure for Stabilized and Lightweight Mandibular Prosthesis

Compared to conventional prostheses with homogenous structures, a stress-optimized functionally gradient prosthesis will better adapt to the host bone due to its mechanical and biological advantages. Therefore, this study aimed to investigate the damage resistance of four regular lattice scaffolds and proposed a new gradient algorithm for stabilized and lightweight mandibular prostheses. Scaffolds with four configurations (regular hexahedron, regular octahedron, rhombic dodecahedron, and body-centered cubic) having different porosities underwent finite element analysis to select an optimal unit cell. Meanwhile, a homogenization algorithm was used to control the maximum stress and increase the porosity of the scaffold by adjusting the strut diameters, thereby avoiding fatigue failure and material wastage. Additionally, the effectiveness of the algorithm was verified by compression tests. The results showed that the load transmission capacity of the scaffold was strongly correlated with both configuration and porosity. Scaffolds with regular hexahedron unit cells can withstand stronger loads at the same porosity. The optimized gradient scaffold showed higher porosity and lower maximum stress than the target stress value, and the compression tests also confirmed the simulation results. A mandibular prosthesis was established using a regular hexahedron unit cell, and the strut diameters were gradually changed according to the proposed algorithm and the simulation results. Compared with the initial homogeneous prosthesis, the optimized gradient prosthesis reduced the maximum stress by 24.48% and increased the porosity by 6.82%, providing a better solution for mandibular reconstruction.

Biomechanical Effects of Different Miniplate Thicknesses and Fixation Methods Applied in BSSO Surgery Under Two Occlusal Conditions

Purpose

Finite element analysis (FEA) was used to evaluate the effects of different thicknesses, numbers, and positions of the miniplate applied in bilateral sagittal split osteotomy (BSSO) under two occlusal conditions.

Methods

An FEA model of the mandibles was constructed and combined with different thicknesses (0.6 or 1 mm), number (one or two), positions (upper or lower) of a miniplate and was divided into six models. In addition, external forces were applied to the muscles to simulate the intercuspal position (ICP) and right unilateral molar clench. This study used the reaction force of the temporomandibular joints and the stress of the mandible as observation indexes.

Results

The results of this study show that, under ICP, the 0.6 mm lower model generated greater TMJ force reaction compared to the 0.6 mm upper model. The same trend was seen in the 1 mm lower model compared to the 1 mm upper model. Regarding the stress of the bone on the screw-implanted sites, under ICP, screw 10 showed greater stress than screw 2, and screw 11 showed greater stress than screw 3. The stress values of the miniplates showed, under ICP, point 1-c was greater than point 3-c, and point 1-b was greater than point 3-b.

Conclusion

In the case of BSSO mandibular advancement surgery, implanting the miniplate at the upper position can reduce the force on the TMJ and the stress on the distal segment of the mandible. The miniplate can also resist the tensile stress more effectively. In addition, implanting two miniplates with thinner sizes may be an alternative in clinical practice.

Novel Design and Optimization of Porous Titanium Structure for Mandibular Reconstruction

A porous material is considered to be a potential material that can be used to repair bone defects. However, the methods of designing of a highly porous structure within the allowable stress range remain to be researched. Therefore, this study was aimed at presenting a method for generating a three-dimensional tetrahedral porous structure characterized by low peak stress and high porosity for the reconstruction of mandibular defects. Firstly, the initial tetrahedral porous structure was fabricated with the strut diameters set to 0.4 mm and a mean cell size of 2.4 mm in the design model space. Following this, the simulation analysis was carried out. Further, a homogenization algorithm was used for homogenizing the stress distribution, increasing porosity, and controlling peak stress of the porous structure by adjusting the strut diameters. The results showed that compared with the initial porous structure, the position of the large stress regions remained unchanged, and the peak stress fluctuated slightly in the mandible and fixation system with the optimized porous structure under two occlusions. The optimized porous structure had a higher porosity and more uniform stress distribution, and the maximum stress was lower than the target stress value. The design and optimization technique of the porous structure presented in this paper can be used to control peak stress, improve porosity, and fabricate a lightweight scaffold, which provides a potential solution for mandibular reconstruction.

Finite element analysis between Hunsuck/Epker and novel modification of Low Z plasty technique of mandibular sagittal split osteotomy

A novel modification of the Low Z plasty (NM-Low Z) technique for bilateral sagittal split osteotomy was recently proposed. The osteotomy line was modified more inferiorly than in the conventional Hunsuck–Epker (HE) approach. The NM-Low Z technique enhances the mandibular setback distance and degree of rotation in severe skeletal discrepancies. This study aimed to investigate the biomechanical behavior under simulated forces, and to compare the NM-Low Z and HE techniques on the mandible with Class III skeletal deformity at 1 week, 3 weeks, and 6 weeks post-operation. Physiological muscular and occlusal loads were simulated using the finite element (FE) method. Stresses on the miniplate, screws, and bone were observed and compared between the two models. The elastic strain at the fracture site was observed for the optimal bone-healing capacity. The NM-Low Z model exhibited a lower stress than the HE model at every stage post-operation. Both models demonstrated elastic strains within the normal range for bone healing. In summary, the biomechanical behavior of the NM-Low Z technique is comparable to that of the conventional EH technique. NM-Low Z could facilitate post-operation skeletal stability by reducing the stress on fixation materials during bone healing.

3D-printed porous condylar prosthesis for temporomandibular joint replacement: Design and biomechanical analysis

BACKGROUND

Customized prosthetic joint replacements have crucial applications in severe temporomandibular joint problems, and the combined use of porous titanium scaffold is a potential method to rehabilitate the patients.

OBJECTIVE

The objective of the study was to develop a design method to obtain a titanium alloy porous condylar prosthesis with good function and esthetic outcomes for mandibular reconstruction.

METHODS

A 3D virtual mandibular model was created from CBCT data. A condylar defect model was subsequently created by virtual condylectomy on the initial mandibular model. The segmented condylar defect model was reconstructed by either solid or porous condyle with a fixation plate. The porous condyle was created by a density-driven modeling scheme with an inhomogeneous tetrahedral lattice structure. The porous condyle, supporting fixation plate, and screw locations were topologically optimized. Biomechanical behaviors of porous and solid condylar prostheses made of Ti-6Al-4V alloy were compared. Finite element analysis (FEA) was used to evaluate maximum stress distribution on both prostheses and the remaining mandibular ramus.

RESULTS

The FEA results showed levels of maximum stresses were 6.6%, 36.4% and 47.8% less for the porous model compared to the solid model for LCI, LRM, and LBM loading conditions. Compared to the solid prosthesis, the porous prosthesis had a weight reduction of 57.7% and the volume of porosity of the porous condyle was 65% after the topological optimization process.

CONCLUSIONS

A custom-made porous condylar prosthesis with fixation plate was designed in this study. The 3D printed Ti-6Al-4V porous condylar prosthesis had reduced weight and effective modulus of elasticity close to that of cortical bone. The.

Biomechanical Analyses of Porous Designs of 3D-Printed Titanium Implant for Mandibular Segmental Osteotomy Defects

Clinically, a reconstruction plate can be used for the facial repair of patients with mandibular segmental defects, but it cannot restore their chewing function. The main purpose of this research is to design a new three-dimensionally (3D) printed porous titanium mandibular implant with both facial restoration and oral chewing function reconstruction. Its biomechanical properties were examined using both finite element analysis (FEA) and in vitro experiments. Cone beam computed tomography images of the mandible of a patient with oral cancer were selected as a reference to create 3D computational models of the bone and of the 3D-printed porous implant. The pores of the porous implant were circles or hexagons of 1 or 2 mm in size. A nonporous implant was fabricated as a control model. For the FEA, two chewing modes, namely right unilateral molar clench and right group function, were set as loading conditions. Regarding the boundary condition, the displacement of both condyles was fixed in all directions. For the in vitro experiments, an occlusal force (100 N) was applied to the abutment of the 3D-printed mandibular implants with and without porous designs as the loading condition. The porous mandibular implants withstood higher stress and strain than the nonporous mandibular implant, but all stress values were lower than the yield strength of Ti-6Al-4V (800 MPa). The strain value of the bone surrounding the mandibular implant was affected not only by the shape and size of the pores but also by the chewing mode. According to Frost's mechanostat theory of bone, higher bone strain under the porous implants might help maintain or improve bone quality and bone strength. The findings of this study serve as a biomechanical reference for the design of 3D-printed titanium mandibular implants and require confirmation through clinical investigations.

Biomechanical analysis of subcondylar fracture fixation using miniplates at different positions and of different lengths

Background

Many types of titanium plates were used to treat subcondylar fracture clinically. However, the efficacy of fixation in different implant positions and lengths of the bone plate has not been thoroughly investigated. Therefore, the primary purpose of this study was to use finite element analysis (FEA) to analyze the biomechanical effects of subcondylar fracture fixation with miniplates at different positions and lengths so that clinicians were able to find a better strategy of fixation to improve the efficacy and outcome of treatment.

Methods

The CAD software was used to combine the mandible, miniplate, and screw to create seven different FEA computer models. These models with subcondylar fracture were fixed with miniplates at different positions and of different lengths. The right unilateral molar clench occlusal mode was applied. The observational indicators were the reaction force at the temporomandibular joint, von Mises stress of the mandibular bone, miniplate and screw, and the sliding distance on the oblique surface of the fracture site at the mandibular condyle.

Results

The results showed the efficacy of fixation was better when two miniplates were used comparing to only one miniplates. Moreover, using longer miniplates for fixation had better results than the short one. Furthermore, fixing miniplates at the posterior portion of subcondylar region would have a better fixation efficacy and less sliding distance (5.46–5.76 μm) than fixing at the anterolateral surface of subcondylar region (6.10–7.00 μm).

Conclusion

Miniplate fixation, which was placed closer to the posterior margin, could effectively reduce the amount of sliding distance in the fracture site, thereby achieving greater stability. Furthermore, fixation efficiency was improved when an additional miniplate was placed at the anterior margin. Our study suggested that the placement of miniplates at the posterior surface and the additional plate could effectively improve stability.

Evaluation of internal fixation techniques for condylar head fractures: A finite element analysis and comparison

OBJECTIVES

This study evaluated optimum stability of different screw techniques for condylar head fractures (CHF) (P close to an M fracture with the lateral pole preserved according to AO classification 2014) by finite element analysis (FEA) and provided a biomechanical basis for clinical treatment.

STUDY DESIGN

Four CHF fixation models were evaluated: (A) single bicortical screw, (B) 2 bicortical screws, (C) 1 bicortical screw and 1 monocortical screw (used as a positional screw) inserted via a 2-hole titanium plate, and (D) 2 bicortical screws inserted via a titanium plate. Stresses were calculated (FEA) to measure mechanical properties.

RESULTS

The displacement for A and C was larger than for B and D. The maximum stress on the screws for A and C exceeded their breaking limit but was safe for B and D. The stress on the titanium plate for C and D was safe. The stress on bone for A and C was larger than for B and D.

CONCLUSIONS

The 2 bicortical screw fixation reduced the stress on implanted materials and surrounding bone tissue. Titanium plates further alleviated the lever action. Two bicortical screw fixation was more reliable for CHF, and early postoperative loading and functional training can be expected.

Mechanical evaluation of a patient-specific additively manufactured subperiosteal jaw implant (AMSJI) using finite-element analysis

Edentulism with associated severe bone loss is a widespread condition that hinders the use of common dental implants. An additively manufactured subperiosteal jaw implant (AMSJI) was designed as an alternative solution for edentulous patients with Cawood and Howell class V-VIII bone atrophy. A biomechanical evaluation of this AMSJI for the maxilla in a Cawood and Howell class V patient was performed via finite-element analysis. Occlusal and bruxism forces were incorporated to assess the loading conditions in the mouth during daily activities. The results revealed a safe performance of the implant structure during the foreseen implantation period of 15 years when exerting average occlusion forces of 200 N. For the deteriorated state of class VIII bone atrophy, increased stresses on the AMSJI were evaluated, which predicted implant fatigue. In addition, excessive bruxism and maximal occlusion forces might induce implant failure due to fatigue. The models predicted bone ingrowth at the implant scaffolds, resulting in extra stability and secondary fixation. For all considered loading conditions, the maximal stresses were located at the AMSJI arms. This area is most sensitive to bending forces and, hence, allows for further design optimization. Finally, the implant is considered safe for normal daily occlusion activities.

Biomechanical analysis of occlusal modes on the periodontal ligament while orthodontic force applied

OBJECTIVE

The study objective was to investigate four common occlusal modes by using the finite element (FE) method and to conduct a biomechanical analysis of the periodontal ligament (PDL) and surrounding bone when orthodontic force is applied.

MATERIALS AND METHODS

A complete mandibular FE model including teeth and the PDL was established on the basis of cone-beam computed tomography images of an artificial mandible. In the FE model, the left and right mandibular first premolars were not modeled because both canines required distal movement. In addition, four occlusal modes were simulated: incisal clench (INC), intercuspal position (ICP), right unilateral molar clench (RMOL), and right group function (RGF). The effects of these four occlusal modes on the von Mises stress and strain of the canine PDLs and bone were analyzed.

RESULTS

Occlusal mode strongly influenced the distribution and value of von Mises strain in the canine PDLs. The maximum von Mises strain values on the canine PDLs were 0.396, 1.811, 0.398, and 1.121 for INC, ICP, RMOL, and RGF, respectively. The four occlusal modes had smaller effects on strain distribution in the cortical bone, cancellous bone, and miniscrews.

CONCLUSION

Occlusal mode strongly influenced von Mises strain on the canine PDLs when orthodontic force was applied.

CLINICAL RELEVANCE

When an FE model is used to analyze the biomechanical behavior of orthodontic treatments, the effect of muscle forces caused by occlusion must be considered.

Biomechanical evaluation of a customized 3D-printed polyetheretherketone condylar prosthesis

The present study aimed to evaluate the biomechanical behavior of a custom 3D-printed polyetheretherketone (PEEK) condylar prosthesis using finite element analysis and mechanical testing. The Mimics software was used to create a 3D model of the mandible, which was then imported into Geomagic Studio software to perform osteotomy of the lesion area. A customized PEEK condyle prosthesis was then designed and the finite element model of the PEEK condyle prosthesis, mandible and fixation screw was established. The maximum stress of the prosthesis and screws, as well as stress and strain of the cortical and cancellous bones in the intercuspal position, incisal clench, left unilateral molar clench and right unilateral molar clench was analyzed. The biomechanical properties of the prosthesis were studied using two models with different lesion ranges. To simulate the actual clinical situation, a special fixture was designed. The compression performance was tested at 1 mm/min for the condyle prosthesis, prepared by fused deposition modeling (FDM). The results of a finite element analysis suggested that the maximum stress of the condyle was 10.733 MPa and the maximum stress of the screw was 9.7075 MPa; both were far less than the yield strength of the material. The maximum force that the two designed prostheses were able to withstand was 3,814.7±442.6 N (Model A) and 4,245.7±348.3 N (Model B). Overall, the customized PEEK condyle prostheses prepared by FDM exhibited a uniform stress distribution and good mechanical properties, providing a theoretical basis for PEEK as a reconstruction material for repairing the temporomandibular joint.

Biomechanical analysis of costochondral graft fracture in temporomandibular joint replacement

This study is the first attempt to explore the reason of costochondral graft fracture after lengthy mandible advancement and bilateral coronoidectomy by combining finite element analysis and mechanical test. Eleven groups of models were established to simulate costochondral graft reconstruction in different degrees of mandible advancement, ranging from 0 to 20 mm, in 2 mm increment. Force and stress distribution in the rib-cartilage area were analyzed by finite element analysis. Mechanical test was used to evaluate the resistance of the rib-cartilage complex. Results showed a sharp increase in horizontal force between 8 and 10 mm mandible advancement, from 26.7 to 196.7 N in the left side, and continue increased after 10 mm, which was beyond bone-cartilage junction resistance according to mechanical test. Therefore, we concluded that bilateral reconstruction with coronoidectomy for lengthy mandible advancement (≥ 10 mm) may lead to prominent increase in shear force and result in a costal-cartilage junction fracture, in this situation, alloplastic prosthesis could be a better choice. We also suggested that coronoidectomy should be carefully considered unless necessary.

Biomechanical Design Application on the Effect of Different Occlusion Conditions on Dental Implants with Different Positions—A Finite Element Analysis

A dental implant is currently the most commonly used treatment for patients with lost teeth. There is no biomechanical reference available to study the effect of different occlusion conditions on dental implants with different positions. Therefore, the aim of this study was to conduct a biomechanical analysis of the impact of four common occlusion conditions on the different positions of dental implants using the finite element method. We built a finite element model that included the entire mandible and implanted seven dental implant fixtures. We also applied external force to the position of muscles on the mandible of the superficial masseter, deep masseter, medial pterygoid, anterior temporalis, middle temporalis, and posterior temporalis to simulate the four clenching tasks, namely the incisal clench (INC), intercuspal position (ICP), right unilateral molar clench (RMOL), and right group function (RGF). The main indicators measured in this study were the reaction force on the temporomandibular joint (TMJ) and the fixed top end of the abutment in the dental implant system, and the stress on the mandible and dental implant systems. The results of the study showed that under the occlusion conditions of RMOL, the dental implant system (113.99 MPa) and the entire mandible (46.036 MPa) experienced significantly higher stress, and the reaction force on the fixed-top end of the abutment in the dental implant system (261.09 N) were also stronger. Under the occlusion of ICP, there was a greater reaction force (365.8 N) on the temporomandibular joint. In addition, it was found that the reaction force on the posterior region (26.968 N to 261.09 N) was not necessarily greater than that on the anterior region (28.819 N to 70.431 N). This information can help clinicians and dental implant researchers understand the impact of different chewing forces on the dental implant system at different positions after the implantation.

Studies on the Performance of Molar Porous Root-Analogue Implant by Finite Element Model Simulation and Verification of a Case Report

PURPOSE

The aim of this study was to evaluate the effect of porous layer thickness in a 3-dimensionally printed 1-piece molar porous root-analogue implant (RAI) on the biomechanical properties of the peri-implant bone and the clinical efficacy of one such implant in a patient.

MATERIALS AND METHODS

Three RAIs with different superficial porous layer thicknesses (0.5 mm, 1 mm, and fully porous) were designed and assembled using a mandible model and then solidified to obtain 3 finite elements models, denoted A, B, and C. Finite element analysis was performed to analyze the stress on the solid and porous structures of the RAIs and the stress and strain experienced by the bone surrounding the implant. RAIs were fabricated by selective laser melting. An unrepairable molar in a single patient was selected for replacement. An RAI was designed and prepared and then implanted into the alveolar bone immediately after minimally invasive extraction of the damaged tooth. Definitive restorations were placed after a 3-month period of uninterrupted healing.

RESULTS

The stress concentration observed in the 3 types of RAI was principally between the solid and porous interface contact points, with maximum stress on the solid and porous structures smaller than that of the respective yield strength. The introduction of a porous structure on the surface of the RAIs increased peri-implant bone stress, which increased with thickness of the porous layer. The 3-dimensionally printed porous RAI exhibited excellent initial stability immediately after implantation. After continual observation for 6 months, it was found that bone surrounding the root had infiltrated into the RAI, achieving good osseointegration.

CONCLUSIONS

Stress shielding can be reduced by decreasing the elastic modulus of the implant, with the interface between implant and bone allowing more appropriate stress conduction. A 1-piece porous RAI fabricated using 3-dimensional printing establishes a new indication for immediate implantation after extraction.

Biomechanical Analysis of the Forces Exerted during Different Occlusion Conditions following Bilateral Sagittal Split Osteotomy Treatment for Mandibular Deficiency

The bilateral sagittal split osteotomy (BSSO) technique is commonly used to correct mandibular deficiency. If the patient is exposed to excessive external forces after the procedure, occlusal changes or nonunion may occur. However, previous studies only focused on single external forces on the mandible and did not conduct relevant research on the forces exerted by different occlusion conditions. The main purpose of this study was to use finite element analysis methods to determine the biomechanics of four common occlusion conditions after BSSO surgical treatment. This study constructed a finite element analysis computer model of a miniplate implanted in the lower jaw. The structure of the model consisted of the mandible, miniplate, and screws. In addition, external forces were applied to the superficial masseter, deep masseter, medial pterygoid, anterior temporalis, middle temporalis, and posterior temporalis muscles to simulate the incisal clench, intercuspal position (ICP), right unilateral molar clench (RMOL), and right group function occlusion conditions. Subsequently, this study observed the effects of these conditions on the miniplate, screws, and mandible, including the von Mises stress values. The results showed that all of the different occlusion conditions that this study evaluated placed high stress on the miniplate. In the ICP and RMOL occlusion conditions, the overall mandibular structure experienced very high stress. The screw on the proximal segment near the bone gap experienced high stress, as did the screw on the buccal side. According to the present analysis, although the data were not directly obtained from clinical practice, the finite element analysis could evaluate the trend of results under different external forces. The result of this study recommended that patients without intermaxillary fixation avoid the ICP and RMOL occlusion conditions. It can be used as a pilot study in the future for providing clinicians more information on the biomechanics of implantation.

Biomechanical evaluation of Chinese customized three-dimensionally printed total temporomandibular joint prostheses: A finite element analysis

PURPOSE

This work aims to evaluate the biomechanical behavior of Chinese customized three-dimensional (3D)-printing total temporomandibular joint (TMJ) prostheses by means of finite element analysis.

METHODS

A 3D model was established by Mimics 18.0, then output in a stereolithography (STL) format. Two models were established to investigate the strain behaviors of an intact mandible and a one-side implanted mandible respectively. Hypermesh and LS-DYNA software were used to establish computer-aided engineering finite element models. The stress distribution on the custom-made total TMJ prosthesis and the strain distribution on the mandible were analyzed by loading maximal masticatory force.

RESULTS

The maximum stress on the surface of the ultra-high-molecular weight polyethylene was 19.61 MPa. With respect to the mandibular component, the maximum stress in the mandibular component was located at the anterior and posterior surface of the condylar neck, reaching 170.01 MPa. The peak von Mises stress was observed on the topside screw of the mandible, which was found to be 236.08 MPa. For the intact model, it was observed that the strain distribution was basically symmetrical. For the model with the prosthesis, the curve of strain distribution was fundamentally consistent with that in the intact mandible, except for the last 24 mm along the control line. A prominent strain decrease between 41.4% and 58.3% was observed in this area.

CONCLUSIONS

Chinese customized 3D-printed total TMJ prostheses exhibit uniform stress distribution without changing the behavior of the opposite side natural joint. Furthermore, the prostheses have a great potential to be improved in design and materials with a promising future.

Finite element analysis of stress distribution on the mandible and condylar fracture osteosynthesis during various clenching tasks

PURPOSE

The purpose of the study was to evaluate the effect of clenching tasks on the stress and strain of condylar osteosynthesis screws and plates, as well as on the stress, strain distribution and displacement on the whole mandible and bone surrounding screws.

METHODS

Three-dimensional finite element models of the mandible, two straight four-hole plates and eight screws were established. Six static clenching tasks were simulated in this study: incisal clench (INC), intercuspal position (ICP), right unilateral molar clench (RMOL), left unilateral molar clench (LMOL), right group function (RGF) and left group function (LGF).

RESULTS

Based on the simulation of the six clenching tasks, none of the inserted screws and plates were broken or bended. For the whole mandibular bone, the maximum von Mises stress and von Mises strain observed were yielded by the ICP. For the bone surrounding the inserted screws, the maximum von Mises stress and von Mises strain were yielded by the LMOL (49.2 MPa and 3795.1 μ).

CONCLUSION

Clenching tasks had significant effects on the stress distribution on the condylar osteosynthesis and the bone surrounding screws. Contralateral occlusion task (LMOL) had the maximal results of von Mises stress and strain and healing problems could be occur, this result confirms the importance of soft diet after surgery.