Load transfer in Christensen(®) TMJ in alloplastic total joint replacement for two different mouth apertures

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.

Biological Treatments for Temporomandibular Joint Disc Disorders: Strategies in Tissue Engineering

The temporomandibular joint (TMJ) is an important structure for the masticatory system and the pathologies associated with it affect a large part of the population and impair people's lifestyle. It comprises an articular disc, that presents low regeneration capacities and the existing clinical options for repairing it are not effective. This way, it is imperative to achieve a permanent solution to guarantee a good quality of life for people who suffer from these pathologies. Complete knowledge of the unique characteristics of the disc will make it easier to achieve a successful tissue engineering (TE) construct. Thus, the search for an effective, safe and lasting solution has already started, including materials that replace the disc, is currently growing. The search for a solution based on TE approaches, which involve regenerating the disc. The present work revises the TMJ disc characteristics and its associated diseases. The different materials used for a total disc replacement are presented, highlighting the TE area. A special focus on future trends in the field and part of the solution for the TMJ problems described in this review will involve the development of a promising engineered disc approach through the use of decellularized extracellular matrices.

Evaluation of condylar cortical bone thickness in patient groups with different vertical facial dimensions using cone-beam computed tomography

The aim of this study is to evaluate through computed tomography differences in cortical plate thickness of condyle in patients with a different facial vertical skeletal pattern. The final sample of this retrospective study included CBCT exams of 60 adult subjects (mean age 33.2 ± 5.6), selected from the digital archive of a private practice. The subjects were assigned to 3 different groups according to the values of the Frankfurt-mandibular plane angle: hyper-, normo-, and hypodivergent groups. The volume rendering of the mandible was obtained and three condylar points were marked on it: median pole, lateral pole and the most cranial point. For each considered reference point, the minimum distance between external and internal cortical surface was measured, obtaining three different outcomes: condylar cortical bone thickness of median pole (CCBToMP), lateral pole (CCBToLP) and cranial pole (CCBToCP). The measurements were executed by means of Mimics software by the same expert operator in specific scan views. The cortical bone thickness of hyperdivergent patients was found to be statistically thicker than normodivergent patients and hypodivergent patients. Cortical bone thickness of normodivergent patients was found thicker than hypodivergent patients. All the differences were statistically significant (p < 0.05). The Pearson correlation coefficient showed a statistically significant correlation (p < 0.001) between the Frankfurt-mandibular plane angle and the evaluated cortical bone thickness outcomes. Facial biotype characteristics that define vertical facial skeletal pattern affect the cortical bone thickness of mandibular condyle.

Advancements in temporomandibular joint total joint replacements (TMJR)

The goal of this paper is to review the advantages and disadvantages of the various treatment options of temporomandibular joint (TMJ) total joint replacement (TJR). TMJ articles published within the last 20 years were reviewed to collect the information on non-invasive and invasive TMD treatment methods. Recent technological advancements helped the evolution of treatment methods and offered significant value to TMD patients and surgeons. Considering the TMD levels, the therapeutic procedures can involve general health examiniations, physical therapy, medication, oral rehabilation or as an end stage clinical invention, temporomandibular joint replacement. In fact when intra-articular TMD is present, the effective treatment method appears to be TJR. However, concern for infection, material hypersensitivity, device longevity and screws loosening issues still exists. Further combined research utilizing the knowledge and expertise of, surgeons, material scientists, and bioengineers is needed for the development of improved TMD therapeutic treatment.

Ex-vivo and in vitro validation of an innovative mandibular condyle implant concept

PURPOSE

The purpose of this study is to pre-validate an inovative implant concept, and to compare the behavior of the mandibular condyle against a commercial Biomet implant in an ex vivo model and present results of the first cadaveric studies.

MATERIALS AND METHODS

Three experimental cadaveric condyles were tested under three conditions: one intact, another with the Biomet model, and one with the innovative concept. The condyle was tested with a reaction of 300 N in all situations and the principal strains were measured. Before the geometry of the cadaveric condyle was reconstructed from a microCT scan, and a finite element model was created. Finally, a procedure was carried out with the new implant by two expert surgeons on a two cadaveric head model.

RESULTS

In vitro the mandible condyle presents a linear behavior until maximum load. The strain measured with Biomet implant indicates a strain shielding effect in the proximal region, inducing bone loss in the long term. The lingual side of the Biomet implanted condyle presents an increase of +44% in strain.

CONCLUSION

The new concept was evaluated and showed a similar behavior to the intact model, and better behavior than the Biomet. The innovative concept proves that it is possible to avoid screws for a TMJ fixation and improve the TMJ alloplastic behavior.

Biomechanical simulation of temporomandibular joint replacement (TMJR) devices: a scoping review of the finite element method

The aim of this study was to perform a literature review on the use of finite element modeling (FEM) for the evaluation of the biomechanical behavior of temporomandibular joint replacement (TMJR) devices. An electronic search of online medical and scientific literature database was conducted using selected search terms. The search identified 307 studies, of which 19 were considered relevant to this study. Of the 19 selected studies, 10 (52.6%) investigated the influence of geometry and fixation methods, while two (10.5%) evaluated the behavior of artificial condyle-fossa structures. The TMJR devices assessed in these studies included TMJ Inc. (aka Christensen; 63.2%), Zimmer Biomet (15.7%), Stryker (10.5%), and a theoretical intramedullary condylar component (5.3%); 26.3% of the studies evaluated custom TMJR devices. Such studies provided important data on the distribution of strain and stress through TMJR structural components and surrounding bone by using different software systems and methods. The mean stress values were lower on a custom TMJR condyle-ramus component and the supporting bone than on the stock device. FEM proved to be an accurate and valuable biomechanical simulation tool for studying the current TMJR devices and should be considered a useful tool for the improvement and development of future joint replacement devices.

Numerical model proposed for a temporomandibular joint prosthesis based on the recovery of the healthy movement

The temporomandibular joint (TMJ) is an anatomical set of the buco-maxillary system that allows the movement of the mandible in most varied ways. Several factors can influence the malfunctioning of the joint and lead to the use of a total prosthesis. However, current prostheses do not supply the maximum amplitude of movement during protrusion and opening, due to mainly the anatomical differences between patients. For this reason, this article aims to study the patient's kinematic characteristics for a better comprehension of the problem and, consequently, to develop a numerical model for TMJ prostheses able to recover the healthy movement. The numerical model is based on the development of a mechanical joint whose profile is able to reproduce the movement of the health system. The results obtained through the developed model showed a good agreement with the experimental results, representing, therefore, a promising alternative to approach the problems related to TMJ.

Influences of geometrical and mechanical properties of bone tissues in mandible behaviour - experimental and numerical predictions

The properties and geometry of bone in the mandible play a key role in mandible behaviour during a person's lifetime, and attention needs to be paid to the influence of bone properties. We analysed the effect of bone geometry, size and bone properties in mandible behaviour, experimenting on cadaveric mandibles and FE models. The study was developed using the geometry of a cadaveric mandible without teeth. Three models of cadaveric condyles were experimentally tested with instrumented with four rosettes, and a condyle reaction of 300 N. Four finite element models were considered to validate the experiments and analyse mandible behaviour. One numeric model was simulated with 10 muscles in a quasi-static condition. The experimental results present different condyle stiffness's, of 448, 215 and 254 N/mm. The values presented in the rosettes are influenced by bone geometry and bone thickness; maximum value was -600 με in rosette #4, and the maximum strain difference between mandibles was 111%. The numerical results show that bone density decreases and strain distribution increases in the thinner mandible regions. Nevertheless, the global behaviour of the structure remains similar, but presents different strain magnitudes. The study shows the need to take into account bone characteristics and their evolutions in order to improve implant design and fixation throughout the patient life. The change in bone stiffness promotes a change in maximum strain distribution with same global behaviour.

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.

Christensen vs Biomet Microfixation alloplastic TMJ implant: Are there improvements? A numerical study

The objective of this study was to compare the load transfer mechanism and behavior of two total temporomandibular joint (TMJ) prostheses: Biomet and Christensen TMJ models were simulated. Computed tomography (CT) images from a specific patient were used to generate two models for use in simulation of implantation for the total temporomandibular prostheses. Three finite element models were created in all. One considered the intact temporomandibular joint and two received a temporomandibular implant. In the simulation we considered the five most important muscles acting on the mandible and incisor teeth support. The Christensen model reduced strain in the opposite condyle by around 50% while increasing strain in the implanted condyle. The changes in the posterior side of the implanted condyle present an increase of five times the minimum principal strain, suggesting some bone fatigue. With the Biomet implant, the reduction in strain in the implanted condyle on the posterior side was around 100%, suggesting the possibility of some bone loss proximally near the resection plane. Based on our results, we conclude that in both models the implants influence the behavior of the mandible by improving the symmetry of the mandible and strain distribution. The Biomet implant modifies the behavior of the mandible slightly and presents some improvements over the Christensen TMJ model in strain distribution and tensions in the opposite intact disc similar to the non-implanted situation.

Prosthesis Loading After Temporomandibular Joint Replacement Surgery: A Musculoskeletal Modeling Study

One of the most widely reported complications associated with temporomandibular joint (TMJ) prosthetic total joint replacement (TJR) surgery is condylar component screw loosening and instability. The objective of this study was to develop a musculoskeletal model of the human jaw to assess the influence of prosthetic condylar component orientation and screw placement on condylar component loading during mastication. A three-dimensional model of the jaw comprising the maxilla, mandible, masticatory muscles, articular cartilage, and articular disks was developed. Simulations of mastication and a maximum force bite were performed for the natural TMJ and the TMJ after prosthetic TJR surgery, including cases for mastication where the condylar component was rotated anteriorly by 0 deg, 5 deg, 10 deg, and 15 deg. Three clinically significant screw configurations were investigated: a complete, posterior, and minimal-posterior screw (MPS) configuration. Increases in condylar anterior rotation led to an increase in prosthetic condylar component contact stresses and substantial increases in condylar component screw stresses. The use of more screws in condylar fixation reduced screw stress magnitudes and maximum condylar component stresses. Screws placed superiorly experienced higher stresses than those of all other condylar fixation screws. The results of the present study have important implication for the way in which prosthetic components are placed during TMJ prosthetic TJR surgery.