J. Morlier

Biomechanical Analysis Comparing Natural and Alloplastic Temporomandibular Joint Replacement Using a Finite Element Model

PURPOSE Prosthetic materials and bone present quite different mechanical properties. Consequently, mandible reconstruction with metallic materials (or a mandible condyle implant) modifies the physiologic behavior of the mandible (stress, strain patterns, and condyle displacements). The changing of bone strain distribution results in an adaptation of the temporomandibular joint, including articular contacts. MATERIALS AND METHODS Using a validated finite element model, the natural mandible strains and condyle displacements were evaluated. Modifications of strains and displacements were then assessed for 2 different temporomandibular joint implants. Because materials and geometry play important key roles, mechanical properties of cortical bone were taken into account in models used in finite element analysis. RESULTS The finite element model allowed verification of the worst loading configuration of the mandibular condyle. Replacing the natural condyle by 1 of the 2 tested implants, the results also show the importance of the implant geometry concerning biomechanical mandibular behavior. The implant geometry and stiffness influenced mainly strain distribution. CONCLUSION The different forces applied to the mandible by the elevator muscles, teeth, and joint loads indicate that the finite element model is a relevant tool to optimize implant geometry or, in a subsequent study, to choose a more suitable distribution of the screws. Bone screws (number and position) have a significant influence on mandibular behavior and on implant stress pattern. Stress concentration and implant fracture must be avoided.

Relationships between geometry and kinematic characteristics in the temporomandibular joint

Motions of the temporomandibular joint (TMJ) involve both translation and rotation; however, there may be substantial variations from one human to another, and these variations present significant difficulties when designing TMJ prostheses. The disc–condyle glides along the temporal bone and the condyle centre describe a curve that depends on the individual morphology. This study analyses disc–condyle rotatory and translatory displacements moving all along the temporal bone facets which are mainly composed of two areas: the articular tubercle slope (ATS) and the preglenoid plane separated by the articular tubercle crest. Displacements were quantified using 3D video analysis, and this technique was computer-assisted. From a population of 32 volunteers, we were able to establish a correlation between the kinematic characteristics of the joint and the disc–condyle trajectories. This study quantifies the geometrical characteristics of the ATS and their inter-individual variations, which are useful in TMJ prosthesis design.

Discrimination of objective kinematic characters in temporomandibular joint displacements.

Designing a temporomandibular joint (TMJ) total prosthesis requires the assessment of joint displacements for open/close movements. Current knowledge presents disc-condyle motions as involving both translation and rotation but there may be substantial variations from human to human. The aim of this study is to discriminate objective kinematic characters amongst thirty-two volunteers. The displacements are determined using 3D video analysis. The ratio between rotation and translation can be defined by introducing a coefficient. This coefficient varies relatively to the opening amplitude and presents the same dispersion rate whatever the variations. Then it allows to discriminate amongst volunteers, regardless of any jaw opening values. Three groups can be isolated relatively to three kinematic models: a translatory preponderant group, a common group and a rotatory preponderant group. All subjects in the first group present concomitant rotatory/translatory displacements up to maximal opening. The other two groups present variations due to different quasi-pure rotation phases at the end of the opening movement. These investigations will make it possible to establish a correlation between the kinematic characters and the disc-condyle trajectories. The disc-condyle glides along the temporal facet and the condyle centre describes the tubercular morphology. The temporal facet geometry, useful for the TMJ prosthesis design, will be studied in a next paper.

The influence of condylar geometry and positions of bone fixation screws on a TMJ implant

There are several diseases that can affect the human temporomandibular joint (TMJ), among which we highlight cancer, trauma or fracture, congenital malformation and osteochondritis (Mercuri et al. 2007). TMJ reconstruction was developed to improve mandibular function and reduce disability (Mercuri 2009). Although implants have widely documented records of short-term successes, the recent arrival of failures and complications related to the placement of such implants again feed the discussions (Wolford et al. 2003). In the UK, the three currently available systems were implanted in 60–65 patients annually (Speculand et al. 2000). Total replacement of the TMJ involves the removal of the ‘non-functional’ joint and placing an artificial one. Owing to the nature of the bone structures involved in the joint, design of prostheses is complex. Materials and geometry play an important key role in enhancing the long-term life of the artificial joint (Britton et al. 2002). The most applied TMJ implants are rigid plates. Surgeons spend a very long time bending the plate to fit it to the contours of the bones (Speculand et al. 2000). This study aims to describe the influence on the strain distribution of different geometries and screw fixations.

Stress distribution in the TMJ disc during a jaw opening movement simulated with a 2D finite element model

The temporomandibular joint (TMJ) is one of the most complex joint of the human body. It connects the mandible to the temporal bone. The articular surfaces of this joint are: the mandibular condyle, the glenoid fossa and the articular eminence of the temporal bone. An articular disc is situated between these surfaces. This disc plays an important role in the stress distribution within the joint. Seventy percentage of patients presenting TMJ dysfunctions have disc displacement (Detamore and Athanasiou 2003). During the opening movement, the mandibular condyle makes a combined movement of translation and rotation to traverse the entire temporal articular surface. The disk follows the mandibular condyle during the movement. Its movement is controlled by its attachments to the bones. On its anterior part, it also receives an insertion from the pterygoid lateral muscle. In this study, an opening movement has been simulated quasi-statically using a 2D finite element model of the TMJ.

Mechanical actions and pressure in functioning of the human temporomandibular joint

The human masticatory system is a multiunit biomechanical system resulting of the phylogenesis and ontogenesis process. One of these units is the osteomuscular unit in the temporomandibular joint (TMJ) region that enables the mandible to move with respect to the maxilla due to the muscles contraction (figure 1). Experimental study of the TMJ and especially of the disc must give better understanding processes occurring in the joint and provide new qualitative and quantitative results which are useful for both, theory and clinical practice. Quantitative determination of strains and stresses in the mandible presents a complicated contact mechanical problem. To solve such a problem, it is necessary to find the loads on the TMJ and the disc characteristics. Using a numerical model and an experimental device, this study determines the strains in the bone.

Dynamics and kinematics in tumble turn: an analysis of performance

et al. 1999). Inaddition, they have found that the fastest and slowestyoung freestyle swimmers differed significantly betweenthe 50m time and these two measures of turningperformance (2.5mRTT and 5mRTT) (Blanksby et al.1996). Itwas found earlier that the correlation between thetotal turn time and the event time increased with thedistance of the event (Chow et al. 1984). It is alsonoticeable that turning is faster than stroking (Blanksbyet al. 1996; Blanksby et al. 2004).A successful swim turn results from a multitude offactors and requires a complex series ofmoves to optimisethe total turning performance. The freestyle tumble turncan be divided into approach, rotation, wall contact, glide,underwater propulsion and stroke resumption phases. Thecontact phase could be divided into passive (braking) andactive (push-off)sub-phases.The aim of this study was first to analyse thecorrelations between the turn performance (3mRTT) andkinematic or dynamic factors, and then between each pairoffactors to explain how best turns are realised.

Stabilometric study of changes in body posture during mandibular advancement

About 50% of orthodontic patients present an excessive retrusive mandibular position compared to the whole face. When the latter is important, in growing children, a propulsive splint can have an impact on this orthopaedic problem. Studies tend to prove that the modification of the intermaxillar relations do not always concern the face and very few data deal with the postural consequences of theses appliances (Nobili and Adversi 1996). Orthodontists cannot ignore them. The aim of this work is to study the influence of the mandibular propulsion on the general posture with a stabilometric platform that records the swaying of the centre of foot pressure (CP).

2D-finite element models of the TMJ in three different mandible positions, simulation of clenching

Finite element (FE) method is now largely used to simulate the behaviour of the human joints. Concerning the TMJ, many 2D and 3D FE models were elaborated during the last 10 years. These models were employed to simulate opening (Tanaka et al. 2004; Aoun et al. 2009) and closing movements (Chen et al. 1998), inter-dental clenching (Pérez del Palomar and Doblaré 2006) or pathological cases (Tanaka et al. 2004). In fact, these simulations constitute a useful tool for characterising the mechanical environment of the joint, which is difficult to characterise experimentally. Recently, we have developed a 2D FE model of the TMJ and simulated the opening movement by imposing displacements to the condyle (Aoun et al. 2009). In this paper, three 2D FE models have been elaborated for the TMJ in three static mandible positions. Clenching has been simulated by imposing the forces of the principal muscles. The goal is to completely characterise the behaviour of the natural TMJ, a very important step to realise before designing a TMJ prosthesis.

Trajectories and kinematic characters in temporomandibular joint displacements

Disc-condyle motions associated with open/close movements involve both translation and rotation; however there may be substantial variations from human to human. A study (Coutant et al. 2007) has discriminated objective kinematic characters between 32 volunteers. Three kinematic models have allowed us to isolate three groups. A translatory preponderant group (TG): a maximal amplitude opening is associated with a concomitant displacement involving both rotation and translation. The ratio between these two displacements presents very little variation during the mandible movement. A middle group (CG) and a rotatory preponderant group (RG): a maximal amplitude opening is associated with two kinematic phases, a phase of concomitancy and a closely pure rotatory displacement that occurs for great amplitudes. In these two groups, the rotatory component contribution increases with the amplitude value. However, RG is characterised by a much more pronounced rotatory component which is statistically significant. The aim of the present study is now to determine a correlation within each group between the kinematics characters and the condyle centre trajectories along the temporal facet in a sagittal plane based on a cranial reference frame.