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

Clinical application of customized total temporomandibular joint prosthesis by 3D printing: a five-year follow-up study

OBJECTIVES

This study aims to evaluate the clinical efficacy and stability of customized total temporomandibular joint (TMJ) prosthesis by 3D printing from TMJ Yang's prosthesis system after five-years follow-up.

MATERIALS AND METHODS

This prospective single-center case series study recruited patients required total TMJ prosthesis replacement from March 2016 to September 2022. Patient information was collected and followed up at 1 month, 3 months, 6 months, 1 year, 2 years and 5 years post-surgery. Using CT and panoramic scans to evaluate the prosthesis' position and bone integration. Pain, diet and mandibular function were evaluated by VAS score, and maximum interincisal opening, mouth opening deviation and mandibular maximum forward and lateral movement were recorded. Statistical analyses include descriptive statistics for demographic characteristics and paired t-tests and ANOVA for quantitative analysis.

RESULTS

49 consecutive patients with an average age of 52.88 ± 13.78 years were included. The mean follow-up time was 5.00 ± 1.88 years. There were no postoperative infections, and the wound healed well. Patients' postoperative facial shape and occlusion remained unchanged except for one patient improved the facial shape by second-stage genioplasty. The position of the prosthesis was stable and the bone integration was satisfactory. After surgery, pain, mandibular function, and diet improved significantly (P < 0.05) and remained stable 1 year later. The maximum interincisal opening increased (P < 0.05), with mouth opening deviation and movement on the affected side similar to preoperative levels, but movement on the unaffected side and forward movement decreased slightly.

CONCLUSIONS

The customized total TMJ prosthesis by 3D printing from TMJ Yang's prosthesis system is safe, stable and effective during five years' clinical application.

CLINICAL RELEVANCE

This study provides a new, safe and effective prosthesis option for temporomandibular joint reconstruction.

Custom design of a temporomandibular joint prosthesis: A kinematic approach evaluated by finite element analysis

STATEMENT OF PROBLEM

Designing temporomandibular joint (TMJ) prostheses that accurately replicate natural kinematic movement and stress distribution remains a challenge because standardized methods for determining the prosthetic kinematic center are lacking. Current designs often rely on empirical placements without considering individualized kinematic parameters, which can compromise functionality and longevity.

PURPOSE

The purpose of this study was to establish an optimal prosthetic kinematic center location for a custom TMJ prosthesis based on invariant TMJ anatomic landmarks to improve design efficiency, kinematic accuracy, and standardization in patient-specific applications.

MATERIAL AND METHODS

A woman diagnosed with TMJ dysfunction was selected for this study. A 3-dimensional model of her TMJ was reconstructed from computed tomography scans to create a custom prosthesis based on the Walter Lorenz model. Finite element analysis simulated mechanical responses to prosthetic kinematic center placements using anatomic references to guide positioning. Analyses included von Mises stress, minimum principal stress, and kinematic translation under set boundary conditions. The TMJ prosthesis was evaluated based on bone mechanical properties and constraints to replicate natural joint movement accurately.

RESULTS

The optimized prosthetic kinematic center location improved anteroposterior movement, effectively addressing translational deficiencies often caused by lateral pterygoid muscle resection. Maximum von Mises stress was recorded at 31 MPa, and minimum principal stress at -52.68 MPa, both within the material's tolerance, confirming structural stability. These results demonstrate consistent stress distribution and alignment with natural TMJ kinematics, suggesting potential improvements in prosthetic performance and patient comfort.

CONCLUSIONS

This prosthetic kinematic center-based design approach enhances kinematic precision and biomechanical function in TMJ prostheses, closely aligning prosthetic movement with natural condylar action. The method provides a standardized framework for individualized TMJ prosthesis design, potentially extending prosthesis longevity and functionality. Studies with larger sample sizes are recommended to verify the clinical applicability and long-term benefits of this approach.

Identification of potential immune-related genes and infiltrations in temporomandibular joint osteoarthritis

Objective

The aim of this study was to investigate the potential inflammatory cytokines and chemokines markers for temporomandibular joint osteoarthritis (TMJOA) diagnosis using a bioinformatics analysis.

Methods

The differentially expressed genes of mRNA (DEGs) and transcripts of lncRNA (DETs) were identified between TMJOA samples and normal controls curated from GSE205389 by the "DESeq. 2" R package. KEGG and GO were conducted using the R package "ggplot2" and "clusterProfiler". A PPI network was constructed to identify hub genes by using the STRING and Cytoscape. The co-expression network was constructed between mRNA and lncRNA to check the potential regulation and function of lncRNA on protein-coding genes. Finally, the immune cell infiltration analysis was conducted with CIBERSORTx and confirmed with xCells.

Results

The authors identified 171 DEGs and DETs, of which the DEGs were closely related to immune response, T-cell activation, cytokine-cytokine-receptor interaction, and the muscle system process. PPI network of the DEGs screened the top 10 hub genes, including IL6, IL1B, IL10, CCL2, CCL5, CXCL1, CXCL10, ICAM1, CSF1 and MMP1. Additionally, the immune cell infiltration analysis showed that CD8+ T cells, M1 macrophage and B cells infiltration were increased in TMJOA samples. Finally, the authors demonstrated that the co-expression between mRNA and lncRNA was mainly enriched in inflammatory and muscle-related pathways.

Conclusions

The authors found that immune and muscle system-related pathways as well as the immune infiltration played a significant role in the TMJOA development. Additionally, inflammatory cytokines and chemokines could be crucial markers for early-stage TMJOA diagnosis and personalized treatment strategies.

Evaluation of grafts fixation techniques for temporomandibular joint reconstruction with medial femoral condyle flap: A numerical study

Reconstruction for large-scale temporomandibular joint (TMJ) defects can be challenging. Previously, we utilized the medial femoral condyle (MFC) flap for TMJ reconstruction. However, the optimal fixation method remains uncertain. In this study, finite element analysis was used to study the effects of three different fixation types of bone graft: overlap type, bevel type, and flush type. Models of different fixation types of MFC flap were reconstructed from CT images. A standard internal fixation model for extracapsular condylar fracture was also included as a control. Displacement of bone graft, deformation of plates and screws, and stress distribution of plates, screws, and cortical and cancellous of the bone graft were analyzed by finite element analysis to investigate their biomechanical features. The displacement of the bone graft and deformation of plates and screws in three different fixation types showed no significant difference. The overlap type and flush type of fixation displayed the lowest and highest stress respectively. All three fixation types could satisfy the mechanical requirement and face no risk of breakage and the major displacement of the MFC bone graft. These results provide insights into the optimal fixation approach for MFC bone grafts, offering valuable guidance and reference for clinical application.

Improved stomatognathic model for highly realistic finite element analysis of temporomandibular joint biomechanics

BACKGROUND

Mechanical response analysis of the temporomandibular joint (TMJ) is crucial for understanding the occurrence and development of diseases. However, the realistic modeling of the TMJ remains challenging because of its complex composition and multivariate associations.

OBJECTIVE

This study aims to develop a highly realistic stomatognathic model that accurately represents the geometric accuracy, structural integrity, and material properties. And further optimizes the interference and establishes the application range of the simplifications and the assumptions.

METHODS

Geometric reconstruction of the bone was based on high-resolution image data, with the accuracy of the occlusal surface ensured by plaster cast model registration. Soft tissues such as cartilage, the disc, the periodontal ligament (PDL), and disc attachments often need to be approximated or assumed. Therefore, the finite element methods (FEM) was used to optimize these assumptions, including 1) the biomechanical effects of the thickness and modulus of the PDL, 2) the approximation of the geometry and material behavior of the disc, and 3) the simplification of the loading and boundary conditions.

RESULTS

1) The deformation of the PDL causes tooth movement, which spreads to the distal condyle and further effects the TMJ load situation, 2) Disc reconstructed by MRI and hyperelastic material behavior are necessary for accurate TMJ loading analyses, 3) The loss of relative sliding movement between teeth interferes with realistic TMJ loading.

CONCLUSION

The improved stomatognathic model delivers highly realistic and validated simulation, offering theoretical guidance for virtual treatments and TMJ multivariate overload studies.

Biomechanical effects of functional clear aligners on the stomatognathic system in teens with class II malocclusion: a new model through finite element analysis

OBJECTIVES

The Functional Clear Aligner (FCA) is a novel orthodontic appliance designed for the treatment of Class II malocclusion with mandibular retrognathia in adolescents. The aim of this study was to investigate the biomechanical characteristics of the masticatory muscles, jawbone, and temporomandibular joint (TMJ) during mandibular advancement using either FCA or Class II elastics combined with clear aligner (Class II elastics) through finite element analysis.

MATERIALS AND METHODS

A 3D finite element model of the 'muscle-jawbone-TMJ-appliance' system was constructed based on CBCT and MRI images of a boy with skeletal Class II malocclusion. Masticatory muscles included masseter, temporal, medial pterygoid, and lateral pterygoid muscles. The TMJ consists of the temporal bone's glenoid fossa, disc, and mandibular condyle. To observe the biomechanical characteristics of the muscles and TMJ during orthodontic appliance wearing and the retention phase, two different protocols were used: Model 1: The mandibular advancement using FCA; Model 2: The mandibular advancement using Class II elastics.

RESULTS

The FCA group produced greater and more coordinated masticatory muscle forces compared to the Class II elastics group. Temporal and masseter muscles exhibited the most pronounced variation in muscle strength during mandibular advancement. The FCA group exhibited greater TMJ region stress compared to the Class II elastics group. Interestingly, the stress on the articular discs in both models decreased over time. Tensile stresses were observed in both the condyle and the posterior region of the articular fossa.

CONCLUSION

During skeletal Class II malocclusion treatment, masticatory muscle forces and stress on the TMJ were higher in the FCA group compared to the Class II elastics group. In both models, stress cushioning was provided by the articular disc.

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.

An Overview of Clinical Conditions and a Systematic Review of Personalized TMJ Replacement

The temporomandibular joint (TMJ) is a complex structure in the cranio-maxillomandibular region. The pathological changes of the joint cause deficiencies at different levels, making its replacement necessary in some cases. The aim of this article is to analyze the current indications, treatment and criteria, and follow-up using a systematic review and case series. A systematic review was carried out, identifying the indications for the use of a customized TMJ prosthesis and evaluating criteria and validation in the international literature. After review and exclusion, 8 articles were included with a minimum follow-up of 12 months. The age of the subjects was between 18 and 47 years old. In 226 patients, 310 TMJ prostheses were installed, 168 bilaterally and 142 unilaterally. In most of the articles, a good condition in the follow-up was observed, with a reduction in pain and better conditions of mandibular movement and function. TMJ prosthesis and replacement is a protocolized, defined, stable, and predictable procedure. Indications and criteria must be evaluated by specialists and patients related to the pathology involved in TMJ deformity or degeneration. Randomized research with an accurate diagnosis and follow-up is necessary to obtain the best indication for this treatment.

GLX351322, a Novel NADPH Oxidase 4 Inhibitor, Attenuates TMJ Osteoarthritis by Inhibiting the ROS/MAPK/NF-κB Signaling Pathways

As a degenerative disease in joints, temporomandibular joint osteoarthritis (TMJOA) is characterized by progressive cartilage degradation, subchondral bone remodeling, and chronic synovitis, severely undermining functions and quality of life in patients. NADPH oxidase 4 (NOX4) contributes to reactive oxygen species (ROS) production and inflammatory pathway activation in osteoarthritis, which has attracted increasing attention in research in recent years. GLX351322 (GLX), a novel NOX4 inhibitor, exerts a protective effect on chondrocytes. However, whether it has a therapeutic effect on ROS production and inflammatory responses in synovial macrophages remains to be evaluated. In this study, we examined the effect of GLX on LPS-induced ROS production and inflammatory responses in vitro and on complete Freund's adjuvant (CFA)-induced TMJ inflammation in vivo. We found that GLX could depress LPS-induced intracellular ROS production and inflammatory response without cytotoxicity by inhibiting the ROS/MAPK/NF-κB signaling pathways. In line with in vitro observations, GLX markedly attenuated the synovial inflammatory reaction in the TMJ, thus protecting the condylar structure from severe damage. Taken together, our results suggest that GLX intervention or NOX4 inhibition is a promising curative strategy for TMJOA and other inflammatory diseases.

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.

Biomechanical comparative analysis of temporomandibular joint, glenoid fossa and head of the condyle of conventional models prothesis with new PEEK design

This article reviews the design of the temporomandibular joint (TMJ) prostheses used for TMJ joint replacement from 2000 to 2020. The TMJ is a complex joint, with distinct anatomical and functional characteristics making it challenging to maintain. Many authors from the early 20th century reported techniques for TMJ reconstruction, with the goal of restoring its shape and ideal function. Many prototypes have been developed in pursuit of an ideal prosthesis that adheres to the principles of biomechanics and biocompatibility, with good long-term performance and lower cost. The TMJ prosthesis is divided in two parts: the glenoid fossa and the mandibular ramus component. These two parts are fixed with metal screws in the glenoid fossa and fixed in the zygomatic arch with 4 or 5 screws. The mandibular part is fixed to the mandible ramus with 8 or 9 titanium screws. In our review, since 2000 to 2020, little has changed to improve the design and allow for natural mandible movement. From 2000 to 2006, 48 TMJ surgeries were performed using UHMWPE with this design. All patients had good results, preserving opening mouth and lateral movements. All the designs are similar in principle. The glenoid fossa, which resembles a box, limiting the rotation and translation movement. It is known that lateral movements are lost in function as the lateral pterygoid muscle is detached.

The Use of Customized Three-Dimensionally Printed Mandible Prostheses with a Pressure-Reducing Device: A Finite Element Analysis in Different Chewing Positions, Biomechanical Testing, and In Vivo Animal Study Using Lanyu Pigs

Segmental bony defects of the mandible constitute a complete loss of the regional part of the mandible. Although several types of customized three-dimension-printed mandible prostheses (CMPs) have been developed, this technique has yet to be widely used. We used CMP with a pressure-reducing device (PRD) to investigate its clinical applicability. First, we used the finite element analysis (FEA). We designed four models of CMP (P1 to P4), and the result showed that CMP with posterior PRD deployment (P4 group) had the maximum total deformation in the protrusion and right excursion positions, and in clenching and left excursion positions, posterior screws had the minimum von Mises stress. Second, the P4 CMP-PRD was produced using LaserCUSING from titanium alloy (Ti-6Al-4V). The fracture test result revealed that the maximum static pressure that could be withstood was 189 N, and a fatigue test was conducted for 5,000,000 cycles. Third, animal study was conducted on five male 4-month-old Lanyu pigs. Four animals completed the experiment. Two animals had CMP exposure in the oral cavity, but there was no significant inflammation, and one animal had a rear wing fracture. According to a CT scan, the lingual cortex of the mandible crawled along the CMP surface, and a bony front-to-back connection was noted in one animal. A histological examination indicated that CMP was significantly less reactive than control materials (p = 0.0170). Adequate PRD deployment in CMP may solve a challenge associated with CMP, thus promoting its use in clinical practice.

Biomechanical analysis of a temporomandibular joint prosthesis for lateral pterygoid muscle reattachment

OBJECTIVE

To analyze the biomechanical properties of a novel temporomandibular joint (TMJ) prosthesis with an attachment area for the lateral pterygoid muscle (LPM).

STUDY DESIGN

Three prosthesis models were created and compared using finite element analysis for the displacement, stress, and strain when simulating the maximum bite force loading. A verification experiment and a compression test were conducted.

RESULTS

The displacement, stress, and strain of the novel TMJ prosthesis were larger than the solid condylar neck prosthesis and similar to the slotted condylar neck prosthesis, but the values were far less than the yield strength of titanium alloy. The maximum stress and strain in the novel TMJ prosthesis was concentrated in the inner and boundary areas of the LPM reattachment region beside the thinnest part of the prosthesis neck. The difference in the strain values measured using the verification test and those using finite element analysis was <20%. Compression testing of the novel TMJ prosthesis revealed that the mandible fractured when the force reached 588.97 N, whereas the prosthesis itself did not break or deform.

CONCLUSIONS

The mechanical distribution of the novel prosthesis was feasible under maximum bite force for potential clinical application.

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.

Patient specific total temporomandibular joint reconstruction: A review of biomaterial, designs, fabrication and outcomes

Purpose

The aim of this article was to systematically review the available literature on patient specific total temporomandibular joint total joint replacement (PS-TMJR) implants for their biomaterial, designs, fabrication techniques and their outcomes.

Methods

A literature review was conducted using PubMed, and science direct databases using the key words three-dimensional printing, 3D printing, CAD CAM, computer aided designing, computer aided manufacturing, additive technology, custom made implants, patient specific implants in combination with Temporomandibular joint, TMJ surgery.

Results

The search revealed 2760 articles, of which 374 were in English and discussed TMJ reconstruction. Further filtering shortlisted 74 articles that discussed PS-TMJR. Duplicates were removed and additional added from article references. 39 articles describing biomaterial, designing and fabrication of PS-TMJR implants and their outcomes were selected for analysis.

Conclusions

Although PS-TMJR implants allow a better anatomical fit, improved fixation, and safeguard various structures such as the inferior alveolar nerve, they vary in designs, material and fabrication techniques. However, PS-TMJR printed with SLM and EBM technologies have yet to be compared with the conventional ones in terms of mechanical strength, and clinical outcome. With emerging bioprinting technologies, even newer biomaterials should be considered for 3D printing of PS-TMJR devices designed to achieve harmony in function between the joint device, bone and masticatory muscles.

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.

Impact of technology in temporomandibular joint reconstruction surgeries: A systematic review

OBJECTIVES

The digital technologies, in recent years, have integrated with temporomandibular joint reconstruction surgeries (TRS). Therefore, a systematic study was conducted to assess the impact of digital technologies in TRS. Besides, a brief comparison between the CAD/CAM and 3D printing (3DP) technologies is presented.

MATERIALS & METHODS

We searched in PubMed, ProQuest and Science direct using PRISMA guidelines. Population = Patients undergoing TRS, Intervention=CAD/CAM or 3DP, Comparison= conventional TRS (cTRS) vs technology integrated TRS (tiTRS), Outcome= Advantages/disadvantages of technology and Subjective/objective symptoms, Study design= Type of study. The quality of observational study was assessed using ROBINS-1 Assessment tool.

RESULTS

Out of 632 articles, 30 articles for CAD/CAM and 3DP were included in the study. A majority of TRS were done for ankylosis (new or re-entry), earlier failed surgery, osteoarthritis and neoplastic cases. The articles were divided into two groups. Group I: CAD/CAM(n = 16), Group II: 3DP (n = 14).

DISCUSSION

tiTRS had definite advantages over cTRS with lesser surgery time, defined osteotomies, précised implant fitting and better final result outcome however, evidence for tiTRS in long-term follow-up is inconclusive. The cost, time, infrastructure and ethical/regulatory issues are the downsides of assisted surgeries. It was observed that 3DP technology is versatile and its adaptation in the fabrication of customized implants has outpaced CAD/CAM technology. However, literature data is feeble qualitatively and quantitatively.

CONCLUSION

The TRS has leveraged the flexibility and precision of assisted surgeries. In future, tiTRS could successfully replace cTRS, provided that shortcomings should be dealt so that the technology can benefit the masses.

Clinical and radiological outcomes of Chinese customized three-dimensionally printed total temporomandibular joint prostheses: A prospective case series study

PURPOSE

Temporomandibular joint (TMJ) diseases are highly prevalent in China. However, no commercialized custom-made prostheses are available now. This study introduces a three-dimensionally (3D) printed customized total TMJ prosthesis manufactured by a standardized workflow.

MATERIALS AND METHODS

Consecutive patients with end-stage TMJ diseases were recruited from Jan 2018 to Sep 2018. The computed tomography (CT) data for patients were obtained and transformed into the Mimics 18.0 software preoperatively for designing of prostheses and digital templates. 3D printing, friction spot welding and computer-assisted manufacture (CAM) were used to fabricate different components of the prosthesis. The clinical and radiographic evaluations were performed postoperatively.

RESULTS

A series of 9 patients were included. All the prostheses were placed smoothly and fixed stably during surgical procedure. Without severe postoperative complications, all patients exhibited significant improvements in maximum mouth opening, pain, diet, and mandibular function, with good facial symmetry. For the whole prosthesis, the average mean deviation was 0.432 mm (range: from 0.279 to 0.561 mm).

CONCLUSIONS

This study suggests that Chinese customized 3D-printed total TMJ prostheses produces excellent short-term clinical outcomes, with high accuracy in implantation.

Morphological study of safe fixation region of temporomandibular joint prosthesis in Chinese northeast population with 3-dimensional computed tomographic image

This study aimed to measure temporomandibular joint (TMJ) with 3-dimensional (3D) reconstruction technique in Chinese northeast population, and to clarify the region for fixation and to provide morphological basis for the application of TMJ prosthesis in Chinese setting.Computed tomography (CT) scan and 3D reconstruction were performed with 132 individuals. Structural markers and measurements were further performed with a 3D model of the total TMJ, including the width, thickness and angle of zygomatic arch, the width and height of articular fossa, as well as the area, width, thickness and angle of mandible in the fixation region of the TMJ prosthesis. All the measured indicators values were compared between bilateral sides and gender groups.There was no statistical difference in the measured indicators between the left side and the right side (P > .05). However, certain parameters, including S, L5, L7, P4, and P5, were significantly different among males and females (P < .05).In this study, 3D CT image was used to obtain the measurement data of TMJ, which provided data support for the clinical application of TMJ prosthesis in Chinese population.

Finite element analysis of patient-specific TMJ implants to replace bilateral joints with simultaneous correction of facial deformity

Introduction

Finite element analysis (FEA) is a method to mimic the biomechanical behaviour of an object under various loading scenarios, and may be used during virtual planning of the TMJ prosthesis. Here we present an interesting case report where FEA was done to biomechanically evaluate patient specific total joint replacement prosthesis for bilateral TMJ replacement.

Case report

A 22 year old young girl visited our outpatient clinic with a chief complaint of retruded chin and limited mouth opening for the last 15 years. After clinical and radiographic examination, her corrective surgery was virtually planned on Mimics software. The Implants were studied under simulated loading scenarios in ANSYS to understand the structural integrity of the implant for different loading conditions.

Results

Maximum Von-Mises Stress on Condylar component is 151.9 MPa and Maximum Von-Mises Stress on Fossa component is 0.377 MPa. The minimum safety factor of the fossa component was about 15, which is safe enough to complete 100 million cycles. The maximum von-mises stress were detected at the screw holes in the condylar components of the implant. The screw holes were therefore the areas prone to highest chance of failure in the design.

Conclusion

We conclude that FEA based biomechanical analysis is important prerequisite during customized reconstruction of TMJ. In today's scenario of patient specific TMJ reconstruction, FEA based designing and planning of stress distribution along the bone and calculation of maximum strain in the prosthesis, further aids in the proper designing of this implant and enhances the post-operative clinical results.

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.

Computer-assisted surgery for replacement of the temporomandibular joint with customized prostheses: can we validate the results?

PURPOSE

Replacing the temporomandibular joint poses an important challenge to maxillofacial surgeons, and for certain disorders, it represents the treatment's gold standard. Computer-assisted surgery (comprising preoperative virtual planning, virtual intraoperative navigation and 3D printing) is a useful tool for this type of surgery. However, we do not know if and how much the final position of the prosthesis differs, in absolute values, from what was planned virtually in the preoperative phase. We propose a comparative result validation system for temporomandibular joint replacement METHODS: In the present study, we propose a comparative validation system using overlapping images, between the model obtained with preoperative virtual planning and the postoperative result.

RESULTS

The mean difference for all screws of the glenoid prosthesis was 2.08 mm (range, 1.20-3.03) and for all screws of the condylar prosthesis it was 2.33 mm (range, 1.16-3.56). Mean overall difference between both prostheses in all patients was 2.21 mm (range, 1.16-3.56).

CONCLUSIONS

The validation system proposed by overlapping pre- and postoperative images in temporomandibular joint replacement allowed us to establish differences in absolute values between the virtual preoperative model and the actual postoperative result expressed in millimeters.

Patient-specific finite element models of the human mandible: Lack of consensus on current set-ups

The use of finite element analysis (FEA) has increased rapidly over the last decennia and has become a popular tool to design implants, osteosynthesis plates and prostheses. With increasing computer capacity and the availability of software applications, it has become easier to employ the FEA. However, there seems to be no consensus on the input variables that should be applied to representative FEA models of the human mandible. This review aims to find a consensus on how to define the representative input factors for a FEA model of the human mandible. A literature search carried out in the PubMed and Embase database resulted in 137 matches. Seven papers were included in this current study. Within the search results, only a few FEA models had been validated. The material properties and FEA approaches varied considerably, and the available validations are not strong enough for a general consensus. Further validations are required, preferably using the same measuring workflow to obtain insight into the broad array of mandibular variations. A lot of work is still required to establish validated FEA settings and to prevent assumptions when it comes to FEA applications.

A review on computer-aided design and manufacturing of patient-specific maxillofacial implants

Introduction: Various prefabricated maxillofacial implants are used in the clinical routine for the surgical treatment of patients. In addition to these prefabricated implants, customized CAD/CAM implants become increasingly important for a more precise replacement of damaged anatomical structures. This paper reviews the design and manufacturing of patient-specific implants for the maxillofacial area.Areas covered: The contribution of this publication is to give a state-of-the-art overview in the usage of customized facial implants. Moreover, it provides future perspectives, including 3D printing technologies, for the manufacturing of patient-individual facial implants that are based on patient's data acquisitions, like Computed Tomography (CT) or Magnetic Resonance Imaging (MRI).Expert opinion: The main target of this review is to present various designing software and 3D manufacturing technologies that have been applied to fabricate facial implants. In doing so, different CAD designing software's are discussed, which are based on various methods and have been implemented and evaluated by researchers. Finally, recent 3D printing technologies that have been applied to manufacture patient-individual implants will be introduced and discussed.

Endoscopically assisted fixation of the custom-made total temporomandibular joint prosthesis in TMJ Yang's system through a modified preauricular approach

This article describes the experience with the endoscopically assisted fixation of the customized total temporomandibular joint (TMJ) prosthesis in TMJ Yang's system only through a modified preauricular approach. Twenty patients (23 joints) treated with the custom-made total TMJ prosthesis were retrospectively recruited. An endoscopically assisted technique was used through a modified preauricular approach to fix the mandibular component for all these patients. These reconstructions were evaluated by surgical records, clinical examinations, and radiographic observations. All patients had successful fixation of the prosthesis. No patient had permanent weakness of the facial nerve and malocclusion or any other severe complications. The mean operative time was 111 min per joint (range, 85-133 min). The average surgical bleeding was 195 ml per side. The mean follow-up period was 16.2 months (range, 5-32 months). The mean scores were 8.3 for surgical satisfaction and 9.2 for scar healing evaluation. All patients experienced positive clinical outcomes, with a mean 75.2% reduction in pain and 53.7% increase in mouth opening with significant differences (P<0.05). The endoscopically assisted TMJ reconstruction with the customized prosthesis in TMJ Yang's system through the modified preauricular approach could produce good aesthetic and functional results.

An innovative total temporomandibular joint prosthesis with customized design and 3D printing additive fabrication: a prospective clinical study

Background

Total temporomandibular joint (TMJ) prosthesis is an effective and reliable method of joint reconstruction. However, there is still an urgent need to design a new TMJ prosthesis because of no commercially available TMJ prosthesis appropriate for the clinical application on the Chinese population. This study was introduced to prospectively confirm the safety and effectiveness of a new TMJ prosthesis with customized design and 3D printing additive fabrication in clinical application.

Methods

Patients with unilateral end-stage TMJ osteoarthrosis were recruited in this study from Nov 2016 to Mar 2017. Computed tomography scans for all patients were obtained and transformed into three-dimensional (3D) reconstruction models. The customized TMJ prosthesis consisted of three components including the fossa, condylar head, and mandibular handle units, which were designed based on the anatomy of the TMJ and were fabricated using the 3D printing technology. The prominent characters of the prosthesis were the customized design of the fossa component with a single ultra-high-molecular-weight polyethylene and the connection mechanism between the condylar head (Co–Cr–Mo alloy) and mandibular handle components (Ti6Al4 V alloy). The clinical follow-up, radiographic evaluation and laboratory indices were all done to analyze the prosthesis’ outcomes in the clinical application.

Results

12 consecutive patients were included in the study. There were no complications (infection of the surgical wound, damage of liver and kidney, displacement, breakage, or loosening of the prosthesis) found after surgery. Pain, diet, mandibular function, and maximal interincisal opening showed significant improvements after surgery. But the lateral movement was limited to the non-operated side and the mandible deviated towards the operated side on opening mouth following surgery.

Conclusions

The presented TMJ prosthesis is considered an innovative product in TMJ Yang’s system, which is unique compared to other prostheses for the special design and 3D printing additive manufacture. Moreover, the prosthesis is very safe and efficient for clinical use.

Trial registration Prospective reports on Chinese customized total temporomandibular joint prosthesis reconstruction cases, ChiCTR-ONC-16009712. Registered 22 Nov 2016, http://www.chictr.org.cn/showproj.aspx?proj=16091