Experimental validation of a finite element model of the temporomandibular joint

Applied use of biomechanical measurements from human tissues for the development of medical skills trainers: a scoping review

OBJECTIVE

The objective of this review was to identify quantitative biomechanical measurements of human tissues, the methods for obtaining these measurements, and the primary motivations for conducting biomechanical research.

INTRODUCTION

Medical skills trainers are a safe and useful tool for clinicians to use when learning or practicing medical procedures. The haptic fidelity of these devices is often poor, which may be because the synthetic materials chosen for these devices do not have the same mechanical properties as human tissues. This review investigates a heterogeneous body of literature to identify which biomechanical properties are available for human tissues, the methods for obtaining these values, and the primary motivations behind conducting biomechanical tests.

INCLUSION CRITERIA

Studies containing quantitative measurements of the biomechanical properties of human tissues were included. Studies that primarily focused on dynamic and fluid mechanical properties were excluded. Additionally, studies only containing animal, in silico , or synthetic materials were excluded from this review.

METHODS

This scoping review followed the JBI methodology for scoping reviews and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR). Sources of evidence were extracted from CINAHL (EBSCO), IEEE Xplore, MEDLINE (PubMed), Scopus, and engineering conference proceedings. The search was limited to the English language. Two independent reviewers screened titles and abstracts as well as full-text reviews. Any conflicts that arose during screening and full-text review were mediated by a third reviewer. Data extraction was conducted by 2 independent reviewers and discrepancies were mediated through discussion. The results are presented in tabular, figure, and narrative formats.

RESULTS

Data were extracted from a total of 186 full-text publications. All of the studies, except for 1, were experimental. Included studies came from 33 countries, with the majority coming from the United States. Ex vivo methods were the predominant approach for extracting human tissue samples, and the most commonly studied tissue type was musculoskeletal. In this study, nearly 200 unique biomechanical values were reported, and the most commonly reported value was Young's (elastic) modulus. The most common type of mechanical test performed was tensile testing, and the most common reason for testing human tissues was to characterize biomechanical properties. Although the number of published studies on biomechanical properties of human tissues has increased over the past 20 years, there are many gaps in the literature. Of the 186 included studies, only 7 used human tissues for the design or validation of medical skills training devices. Furthermore, in studies where biomechanical values for human tissues have been obtained, a lack of standardization in engineering assumptions, methodologies, and tissue preparation may implicate the usefulness of these values.

CONCLUSIONS

This review is the first of its kind to give a broad overview of the biomechanics of human tissues in the published literature. With respect to high-fidelity haptics, there is a large gap in the published literature. Even in instances where biomechanical values are available, comparing or using these values is difficult. This is likely due to the lack of standardization in engineering assumptions, testing methodology, and reporting of the results. It is recommended that journals and experts in engineering fields conduct further research to investigate the feasibility of implementing reporting standards.

REVIEW REGISTRATION

Open Science Framework https://osf.io/fgb34.

3D Printing Experimental Validation of the Finite Element Analysis of the Maxillofacial Model

Contacts used in finite element (FE) models were considered as the best simulation for interactions in the temporomandibular joint (TMJ). However, the precision of simulations should be validated through experiments. Three-dimensional (3D) printing models with the high geometric and loading similarities of the individuals were used in the validation. This study aimed to validate the FE models of the TMJ using 3D printing models. Five asymptomatic subjects were recruited in this study. 3D models of mandible, disc, and maxilla were reconstructed according to cone-beam CT (CBCT) image data. PLA was chosen for 3D printing models from bottom to top. Five pressure forces corresponding to the central occlusion were applied to the 3D printing models. Ten strain rosettes were distributed on the mandible to record the horizontal and vertical strains. Contact was used in the FE models with the same geometries, material properties, loadings, and boundary conditions as 3D printing models to simulate the interaction of the disc-condyle, disc-temporal bone, and upper-lower dentition. The differences of the simulated and experimental results for each sample were less than 5% (maximum 4.92%) under all five loadings. In conclusion, it was accurate to use contact to simulate the interactions in TMJs and upper-lower dentition.

Biomechanical impact of the porous-fibrous tissue behaviour in the temporomandibular joint movements. An in silico approach

The movement of the temporomandibular joint (TMJ) is a function of its complex geometry and its interaction with the surrounding soft tissues. Owing to an increase in the prevalence of temporomandibular joint disorders (TMDs), many computational studies have attempted to characterize its biomechanical behaviour in the last 2 decades. However, most such studies are based on a single computational model that markedly simplifies the complex geometry and mechanical properties of the TMJ's soft tissues. The present study aims to computationally evaluate in a wider sample the importance of considering their complex anatomy and behaviour for simulating both damping and motion responses of this joint. Hence, 6 finite element models of healthy volunteers' TMJ were developed and subjected to both conditions in two different behavioural scenarios. In one, the soft tissues' behaviour was modelled by considering the porous-fibrous properties, whereas in the other case they were simplified assuming isotropic-hyperelastic response, as had been traditionally considered. The damping analysis, which mimic the conditions of an experimental test of the literature, consisted of applying two different compressive loads to the jaw. The motion analysis evaluated the condylar path during the mandible centric depression by the action of muscular forces. From the results of both analyses, the contact pressures, intra-articular fluid pressure, path features, and stress/strain values were compared using the porous-fibrous and isotropic-hyperelastic models. Besides the great differences observed between patients due patient-specific morphology, the porous-fibrous approach yielded results closer to the reference experimental values and to the outcomes of other computational studies of the literature. Our findings underscore, therefore, the importance of considering realistic joint geometries and porous-fibrous contribution in the computational modelling of the TMJ, but also in the design of further joint replacements or in the development of new biomaterials for this joint.

Finite element analysis of subtalar joint arthroereisis on adult-acquired flexible flatfoot deformity using customised sinus tarsi implant

Background

Subtalar arthroereisis may cause sinus tarsi pain complications. In this study, we aimed to introduce a customised implant that facilitated treatment effect and less impingement. The biomechanical outcome between the intact and implant conditions was compared using finite element analysis.

Methods

A female patient with flatfoot (age: 36 years, height: 156 ​cm, body mass: 51 ​kg) was recruited as the model patient. The customised implant was designed from the extracted geometry. Boundary and loading conditions were assumed from the data of a normal participant. Four gait instants, including the ground reaction force first peak (25% stance), valley (45%), initial push-off (60%) and second peak (75%) were analyzed.

Results

The navicular height was elevated by 4.2% at 25% stance, whereas the strain of the spring, plantar cuneonavicular and plantar cuboideonavicular ligaments were reduced. The talonavicular joint force decreased and the calcaneocuboid joint increased by half and 67%, respectively, representing a lateralised load pathway. There was a stress concentration at the sulcus tali reaching 15.29 ​MPa

Conclusion

Subtalar arthroereisis using a customised implant may produce some positive treatment effects in terms of navicular height elevation, ligament strain relief and lateralised joint loading pathway. Although the concentrated stress at the sulcus tali did not exceed the threshold of bone breakdown, we could not rule out the potential of vascular disturbance owing to the remarkable elevation of stress. Future study may enlarge the contact area of the bone–implant interface by considering customisation based on the dynamic change of the sinus tarsi during walking gait.

The translational potential of this article

Geometry mismatch of prefabricated implants could be the reason for complications. With the advancement of 3D printing, customising implant becomes possible and may improve treatment outcome. This study implemented a theoretical model approach to explore its potential under a simulation of walking.

A three dimensional (3D) musculoskeletal finite element analysis of DARSN temporomandibular joint (TMJ) prosthesis for total unilateral alloplastic joint replacement

PURPOSE

The purpose of this study was to evaluate the strain and stress distribution for DARSN alloplastic unilateral temporomandibular joint (TMJ) prosthesis and the effects on contralateral natural joint using a finite element analysis (FEA).

METHODS

The replacement of the TMJ may have complications like infection, failure of hardware, facial paralysis and perforation. The understanding of the mechanical forces exerted by muscles of mastication and jaw movement on the joint helps in identifying the regions on alloplastic TMJ with various maximum forces, which makes that area more prone for failure of hardware. A three dimensional structural FEA was applied using a validated finite element model (FEM) where the areas of stress and strain were evaluated in the alloplastic joint and the contralateral natural joint. As the pattern of stress and strain can be influenced by the materials used for alloplastic joint and geometry of the design, mechanical property of bone and the attached musculature were also considered while construction the FEM analysis.

RESULTS

The forces of the muscles of mastication has a vital role on the amount of stress and strain present across the alloplastic joint. Masseter and temporalis exhibited the greatest resultant force on the alloplastic as well as the natural condyle with a magnitude of 272 N and 329 N. This study assessed the maximum stress and strain on the condyle-ramus unit and fossa.

CONCLUSION

FEA shows that alloplastic DARSN TMJ prosthesis distributes stress and strain equally between the alloplastic joint site and the contralateral natural joint causing minimal adverse effects to the natural joint. FEA also evaluated the stress and strain on alloplastic component and resulted in drawing clinical implications for operating surgical team.

Finite Element Evaluation of Stable Fixation in Combined Mandibular Fractures

PURPOSE

The fixation of combined mandibular fractures, especially symphyseal-condylar fractures, although occurring commonly and having a higher complication rate in the clinic, is rarely investigated regarding predictable therapeutic approaches. Thus this study's aim was to assess different forms of condylar fixation when combined with symphyseal fracture fixation.

MATERIALS AND METHODS

Using finite element models, we analyzed the stress distribution that occurs when a condylar fracture is fixed with 1 miniplate, 2 miniplates, or a trapezoidal condylar miniplate and when a symphyseal fracture is fixed with 2 parallel plates, 2 perpendicular plates, or 2 lag screws. The null hypothesis was that there would be no differences among the different fixation techniques.

RESULTS

The results showed a stress concentration in the anterior region of the condyle, close to the sigmoid notch. Moreover, adequate fixation in the symphysis could result in less tension at the condylar region. Therefore, when the symphysis was fixed with a lag-screw technique, condylar fixation was less required, showing a more adequate stress distribution when the condyle was fixed with 1 or 2 plates. Conversely, when the symphyseal fixation was less effective, by use of perpendicular plates, there was a change in the stress distribution at the condylar region, altering fixation behavior and resulting in more tension and displacement in the condyle, especially when a trapezoidal plate was used.

CONCLUSIONS

A lag screw and parallel double plates appear to be suitable for symphyseal fixation, whereas 2 straightly positioned plates and a trapezoidal plate are suitable for condylar fixation. However, the combination of perpendicular plates in symphyseal fixation and a trapezoidal plate in condylar fixation showed an altered stress distribution.

A new condyle implant design concept for an alloplastic temporomandibular joint in bone resorption cases

The purpose of this article is to present and evaluate an innovative intramedullary implant concept developed for total alloplastic reconstruction in bone resorption cases. The main goal of this innovative concept is to avoid the main problems experienced with temporomandibular (TMJ) devices on the market, associated with bone fixation and changes in kinematics. A three-dimensional finite element model was developed based on computed tomography (CT) scan images, before and after implantation of the innovative implant concept. To validate the numerical model, a clean cadaveric condyle was instrumented with four rosettes and loaded before and after implantation with the innovative concept TMJ implant. The experimental results validate the numerical models comparing the intact and implanted condyles, as they present good correlation. They show that the most critical region is around rosette #1, with an increase in strains in the proximal region of the condyle of 140%. The maximum principal strain and stress generated with the implant is less than 2200 με and 75 MPa in the posterior region of the cortical bone. Shortly after insertion of this press-fit implant, stress and strain results appear to be within the normal limits and show some similarities with the intact condyle. If these responses do not change over time, the screw fixation used at present could be avoided or replaced. This solution reduces bone resection and lessens surgical damage to the muscles.

Experimental and numerical predictions of Biomet(®) alloplastic implant in a cadaveric mandibular ramus

The purpose of this study was to evaluate experimentally the behaviors of an intact and an implanted cadaveric ramus, to compare and analyze load mechanism transfers between two validated finite element models. The intact, clean cadaveric ramus was instrumented with four rosettes and loaded with the temporal reaction load. Next, the Biomet microfixation implant was fixed to the same cadaveric mandibular ramus after resection. The mandibular ramus was reconstructed from computed tomographic images, and two finite element models were developed. The experimental results for the mandibular ramus present a linear behavior of up to 300 N load in the condyle, with the Biomet implant influencing strain distribution; the maximum influence was near the implant (rosette #4) and approximately 59%. The experimental and numerical results present a good correlation, with the best correlation in the intact ramus condition, where R(2) reaches 0.935 and the slope of the regression line is 1.045. The numerical results show that screw #1 is the most critical, with maximum principal strains in the bone around 21,000 με, indicating possible bone fatigue and fracture. The experimental results show that the Biomet temporomandibular joint mandibular ramus implant changes the load transfer in the ramus, compared to the intact ramus, with its strain-shielding effect. The numerical results demonstrate that only three screws are important for the Biomet TMJ fixation. These results indicate that including two proximal screws should reduce stresses in the first screws and strains in the bone.

The stock alloplastic temporomandibular joint implant can influence the behavior of the opposite native joint: A numerical study

PURPOSE

The objective of the study was to investigate the effect of total stock temporomandibular implants on load mechanisms in both condyles in a specific patient. The patient presented with a disc with wear, and the introduction of a total temporomandibular prosthesis was simulated to compare the articular behavior.

MATERIAL AND METHODS

Based on specific patient computed tomographic images, two finite element models were created: one model with two intact temporomandibular joints (one joint with pathology), and other model with one implanted joint. The simulations considered the five most important muscles acting in the mandible, and it was possible to evaluate the biomechanical changes in the structures (skull, mandible, and articular disc).

RESULTS

The results revealed more load transfer in the opposite condyle than in the damaged one; the insertion of a total temporomandibular implant changed the load transfer to the opposite condyle. There was decreased stress in the disc by about 50% and increased strain distribution. In the mandibular condyle with implant, the screw fixation is critical, with minimum strain around -9430 με for first screw position. In the cranium, the implant changed the bone strains with a minimum principal strain observed around -2500 με in six screw positions.

CONCLUSION

This study indicates that replacing the damaged joint by an implant in an ideal position will improve joint position and consequently redistribute the loads. The study findings provide strong evidence that placing an implant on one side of the mandible will affect the load distribution on that structure and particularly on the opposite side. The temporomandibular joint changes condyle movement; with an implanted condyle, the movement is almost blocked.

Electromyographic evaluation of the 'vertical' dimension: the Learreta TMJ decompression test

The clinical observation of the incisors overbite is the most common form used to evaluate the occlusal vertical dimension (OVD); however, this technique offers poor information about the compression state of the TMJ. In order to obtain such information, it is necessary to evaluate the electrical activity of the elevator muscles using surface electromyography (EMG). In case of a compressive irritation of the joint receptors, the trigeminal nucleus returns an inhibitory motor response of the elevator muscles that can be measured. The Learreta's EMG decompression test is done by measuring the EMG response of the masticatory muscles at maximal occlusion in four different OVD positions in such a way that the reduction of the TMJ pressure, and subsequently, relief of the inhibitory motor response can be studied. The aim of this study is to illustrate this technique, its clinical use and its limitations.

Finite Element Analysis of a TMJ Implant

To determine the causes of failure of an artificial temporomandibular joint implant, one must study the magnitude and location of the maximum stresses under physiological loading. In this study, we analyzed the stresses in a commercially available TMJ implant, the bone ( i.e., mandible), and the bone-implant interface using a finite element software package. Both titanium and Co-Cr-Mo/Vitallium metals as well as bones with various degrees of osteoporosis were studied. The results of the analysis showed that the maximum stresses occurred at the location of the first screw hole (closest to the condyle) of the implant. In addition, the highest microstrains were observed in the bone adjacent to the first screw hole. The results of our study have potential clinical benefit in terms of improved implant design and hence better performance.