Stress analysis in the mandibular condyle during prolonged clenching: a theoretical approach with the finite element method

Dental Implant Treatment in Bruxers: A Case Report and Literature Review

This case report presents a literature review and a case report of a full-mouth implant rehabilitation for a 65-year-old woman with a history of Bruxism. The patient's oral condition showed dentition with severe occlusal wear, extensive dental work, and missing teeth replaced with bridges and implants. The existing dental work was failing due to recurrent caries and the mechanical failure of long-span bridges. The unique aspect of the treatment presented in this report is the management of existing osseointegrated implants of different systems with different platform designs, which adds to the treatment's complexity. The existing implants were incorporated into the planned treatment, and other implants were added to support maxillary zirconia and mandibular hybrid full-arch prostheses. After 2 years of function, extensive wear was evident on the milled acrylic, even though an occlusal guard was used. New acrylic teeth were processed using the same milled titanium bar of the mandibular hybrid prosthesis, and the occlusal surfaces of the acrylic teeth were protected with gold onlays. The patient is seen regularly for maintenance every 6 months with no further complications. Careful evaluation, planning, and treatment execution are paramount in managing patients with a history of bruxism. Patients should be prepared and informed about possible mechanical failure and seen regularly for maintenance.

A Comparative Study of Temporomandibular Joints in Adults with Definite Sleep Bruxism on Magnetic Resonance Imaging and Cone-Beam Computer Tomography Images

Objective: The aim was to study the imaging characteristics of the temporomandibular joint (TMJ) of definite sleep bruxers through magnetic resonance imaging (MRI) and cone-beam computer tomography (CBCT). Methods: Nineteen definite sleep bruxers diagnosed by polysomnography and twenty asymptomatic non-bruxers matched by age, gender, and education level participated in this study. After obtaining MRI and CBCT images of all TMJs of the subjects, evaluation and measurement were conducted, respectively. The analyzed parameters included disc position, disc configuration, joint effusion (JE), joint space or condyle position, and condylar bony changes. Results: Of the 38 joints in the study group, disc deformity and disc displacement of TMJs were both 57.9% when the mouth was closed, and 76.3% showed condylar bony changes, while when the mouth was open, 82% of all TMJs showed physiological biconcave discs. Comparison of joint space revealed that the anterior space was larger in the study group. There was no significant difference between the mild and the moderate to severe sleep bruxism subgroups in the changes of TMJ. Conclusion: The results demonstrated that a higher prevalence of disc deformity, disc displacement, JE, and condylar bony changes occurred in temporomandibular joints of sleep bruxers. These changes were not related to the severity of sleep bruxism.

Comparative evaluation of trabecular bone structures of bruxist and non-bruxist individuals with bone apposition in the mandible angle region by fractal analysis

OBJECTIVE

This study aimed to compare the trabecular internal structure of different regions of the mandible according to the grades of appositional classification in the mandible angle region in probable bruxist individuals and non-bruxist G0(Convex course of the basal cortex, no directional change, no bone apposition) individuals by measuring fractal dimension (FD) on panoramic radiographs.

METHODS

200 sample jaws, bilaterally, of 80 probable bruxists and 20 non-bruxist G0 individuals were included in the study. According to the classification in the literature, each mandible angle apposition severity was classified as G0-G1-G2-G3. FD was calculated by selecting the region of interest (ROI) area of 7 regions from each sample. Gender differences in changes between ROIs in radiographs and independent samples t-test were evaluated. Relation between categorical variables was determined by chi-square test (p < .05).

RESULTS

In the comparison of the probable bruxist and non-bruxist G0 groups, FD was found to be statistically significantly higher in the mandible angle (p = 0.013) and cortical bone (p = 0.000) regions in the probable bruxist group than in the non-bruxist G0 group. There is a statistically significant difference between probable bruxist G0 and non-bruxist G0 grades in terms of FD averages in cortical bone (p < 0.001). A statistically significant difference was found in the relationship of ROIs with gender in canine apex (p = 0.021) and canine distal (p = 0.041) regions.

CONCLUSION

FD was found to be higher in the mandibular angle region and cortical bone in probable bruxist individuals than in non-bruxist G0 individuals. Morphological changes seen in the mandible angulus region may be a finding that may raise suspicion for bruxism for clinicians.

Arthroscopic discopexy versus natural course of temporomandibular joint anterior disc displacement: a longitudinal study of clinical and radiological outcomes

The aim of this study was to assess the various outcomes of arthroscopic discopexy compared to the natural course of anterior disc displacement (ADD) longitudinally in the same patients. A retrospective review was performed of 108 patients (152 joints) who experienced the natural course of ADD for a period of time and then underwent arthroscopic discopexy. The outcome was evaluated clinically and by magnetic resonance imaging. The natural course of ADD showed significant deterioration in pain, diet, and quality of life, and also a significant reduction in inter-incisal opening (all P < 0.001), while significant improvements in all clinical parameters were observed at the final postoperative follow-up (all P < 0.001, compared to the last preoperative visit). During the natural course, there was a significant shortening of condylar height, mandibular height, and disc length, and an increase in disc displacement distance (all P < 0.001). Postoperative follow-up revealed the restoration of condylar height and mandibular height, and all discs were significantly repositioned with an increased disc length (unfolded) (all P < 0.001). Bearing in mind the assumption of a low evidence base due to bias resulting from the retrospective non-double-blinded study design and the variable duration of the natural disease course prior to surgery, this study found that the natural course of ADD led to degenerative changes in the joint structures and clinical symptoms, whereas arthroscopic discopexy led to a restoration of the bony structures and the alleviation of clinical symptoms.

Bone apposition at the mandibular angles as a radiological sign of bruxism: a retrospective study

Background

The main objective of this investigation was to determine on panoramic radiographs the prevalence of macroscopically visible alterations (bone apposition in combination with directional change) in the mandibular angle region in bruxism patients. Another aim was to describe and detect different morphological characteristics of the jaw angles.

Methods

Two hundred panoramic radiographs were studied: 100 images of adults with clinically diagnosed bruxism (73 women, 27 men, age range 21–83 years), 100 images of a comparison group consisting of adolescents (66 girls, 34 boys, age range 12–18 years).

Results

The morphological changes of the 400 jaw angles could be classified into four degrees. In the adult group, almost half of mandibular angles showed bone apposition. Conversely, the prevalence in the control group was zero. The localization of the appositions corresponds to the insertions of the masseter and medial pterygoid muscles at the mandibular angle.

Conclusions

The bone apposition at the mandibular angles should be interpreted as a functional adaptation to the long-term increased loads that occur during the contraction of the jaw closing muscles due to bruxism. Hence, radiologically diagnosed bone apposition may serve as an indication or confirmation of bruxism.

The magnetic resonance imaging evaluation of condylar new bone remodeling after Yang's TMJ arthroscopic surgery

To evaluate the post-operative condylar bone remodeling after the treatment of Yang's arthroscopic surgery. Consecutive cases from Jan 2017 to May 2018 that received Yang's arthroscopic surgery were included in this study, the TMJ MRI examinations were performed preoperatively and postoperatively (follow up for 1 year or more), and condylar bone remodeling was estimated. A total of 229 patients (29 male and 200 female) were included in the study, 161 patients had new bone formation, and the average age was 17.5 ± 2.1a. There was no new bone formation in 68 patients with an average age of 24.5 ± 0.7a. The percentage of new bone formation patients in 10-15 years of age was 94.33% and decreases as the age increases. In the position of new bone formation, the posterior slope of condyle was the most (129 joints), the second was the top of condyle (54 joints), the third was around condyle (33 joints), only 25 joints had new bone on the anterior slope of condyle. After TMJ arthroscopic surgery, the condyle has the ability to form new bone, and the younger the age, the stronger the ability of new bone formation. The formation of new bone was most in posterior slope and least in anterior slope of condyle.

A rat model for inducing temporomandibular anterior disc displacement experimentally

The aim of this study was to establish an experimental rat model of temporomandibular joint (TMJ) anterior disc displacement (ADD). A pilot study was conducted to determine the most appropriate surgical protocol. In the main experiment, 40 rats were used. Twenty-four rats were subjected to ADD in the right TMJ, and subsequently thereafter six, nine, and nine rats were sacrificed at 1, 4, and 8 weeks, respectively, for gross evaluation. Twelve rats that underwent a sham operation were equally divided and sacrificed at each of the above time points. Four non-treated control rats were sacrificed at the beginning of the study. TMJ blocks were harvested for radiological and histological assessment. Gross examination showed that 14 rats in the ADD group (58.3%) had anterior displacement of the TMJ disc. In the ADD joints, posterior condylar cartilage thickness decreased during the follow-up period; however, there was no significant difference between the sham-treated and ADD joints, or among the follow-up time points (P > 0.05). The anterior condylar cartilage exhibited obvious qualitative alterations. Radiologic signs of osteoarthrosis appeared after ADD surgery, but this became attenuated with time. The model investigated in this study successfully induced ADD in rats, and should be useful for assessment of progressive changes in the TMJ following ADD.

Experimental study on mandibular length and facial symmetry of low estrogen level and anterior disc displacement of temporomandibular joint

This study was aimed at elucidating the changes of mandible symmetry in a rabbit model with low estrogen levels induced by ovariectomy (OVX) combined with temporomandibular joint (TMJ) anterior disc displacement without reduction (ADDWoR). 32 growing rabbits were randomly allocated into 4 groups; OVX group, ADDWoR group, OVX+ ADDWoR group and control group. In OVX and OVX+ ADDWoR groups, bilateral OVX was performed and then the serum level of 17β-estradiol was evaluated every week. In ADDWoR group and OVX+ ADDWoR group, the right TMJ was surgically opened and the disc was displaced anteriorly and the left TMJ was also surgically opened and closed without any manipulation of the disc. All rabbits had CT scan before and at the end of the study and the mandible measurements were performed on the 3D-reconstructed model. The mandible in ADDWoR group was consistently shorter on the right side resulting in a midline shift to the ipsilateral side. While in OVX+ ADDWoR group, the mandibular length of the right side was more shorter than in ADDWoR group, moreover, mandibular deviation was therefore more severe. In OVX group, there was no difference regarding the length of mandible compared to the control group. There was no difference regarding the mandibular length between left and right sides in the control group.

Design and manufacturing of patient-specific orthodontic appliances by computer-aided engineering techniques

Orthodontic treatments are usually performed using fixed brackets or removable oral appliances, which are traditionally made from alginate impressions and wax registrations. Among removable devices, eruption guidance appliances are used for early orthodontic treatments in order to intercept and prevent malocclusion problems. Commercially available eruption guidance appliances, however, are symmetric devices produced using a few standard sizes. For this reason, they are not able to meet all the specific patient's needs since the actual dental anatomies present various geometries and asymmetric conditions. In this article, a computer-aided design-based methodology for the design and manufacturing of a patient-specific eruption guidance appliances is presented. The proposed approach is based on the digitalization of several steps of the overall process: from the digital reconstruction of patients' anatomies to the manufacturing of customized appliances. A finite element model has been developed to evaluate the temporomandibular joint disks stress level caused by using symmetric eruption guidance appliances with different teeth misalignment conditions. The developed model can then be used to guide the design of a patient-specific appliance with the aim at reducing the patient discomfort. At this purpose, two different customization levels are proposed in order to face both arches and single tooth misalignment issues. A low-cost manufacturing process, based on an additive manufacturing technique, is finally presented and discussed.

Disk displacement, eccentric condylar position, osteoarthrosis - misnomers for variations of normality? Results and interpretations from an MRI study in two age cohorts

Background

Clinical decision-making and prognostic statements in individuals with manifest or suspected temporomandibular disorders (TMDs) may involve assessment of (a) the position of articular disc relative to the mandibular condyle, (b) the location of the condyle relative to the temporal joint surfaces, and (c) the depth of the glenoid fossa of the temporomandibular joints (TMJs). The aim of this study was twofold: (1) Determination of the prevalence of these variables in two representative population-based birth cohorts. (2) Reinterpretation of the clinical significance of the findings.

Methods

From existing magnetic resonance imaging (MRI) scans of the TMJs that had been taken in 2005 and 2006 from 72 subjects born between 1930 and 1932 and between 1950 and 1952, respectively, the condylar position at closed jaw was calculated as percentage displacement of the condyle from absolute centricity. By using the criteria introduced by Orsini et al. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 86:489-97, 1998), a textbook-like disc position at closed jaw was distinguished from an anterior location. TMJ morphology of the temporal joint surfaces was assessed at open jaw by measuring the depth of the glenoid fossa, using the method proposed by Muto et al. (J Oral Maxillofac Surg 52:1269-72, 1994).

Frequency distributions were recorded for the condylar and disc positions at closed jaw.

Student’s t-test with independent samples was used as test of significance to detect differences of condylar positions between the age cohorts (1930 vs. 1950) and the sexes. The significance levels were set at 5%. First, the results from the measurement of the age cohorts were compared without differentiation of sexes, i.e., age cohort 1930–1932 versus age cohort 1950–1952. Subsequently, the age cohorts were compared by sex, i.e., men in cohort 1930–1932 versus men in cohort 1950–1952, and women in cohort 1930–1932 women men in cohort 1950–1952.

Results

In both cohorts, condylar position was characterized by great variability. About 50% of the condyles were located centrically, while the other half was either in an anterior or in a posterior position. In both female cohorts, a posterior position predominated, whereas a centric position prevailed among men. Around 75% of the discs were positioned textbook-like, while the remaining forth was located anteriorly. Age had no statistically significant influence on condylar or on disc position. Conversely, comparison between the age groups revealed a statistically significant decrease of the depth of the glenoid fossa in both older cohorts. This age-dependent changes may be interpreted as flattening of the temporal joint surfaces.

Conclusions

We call for a re-interpretation of imaging findings because they may insinuate pathology which usually is not present. Instead, anterior or posterior positions of the mandibular condyle as well as an anterior location of the articular disc should be construed as a variation of normalcy. Likewise, flattening of articular surfaces of the TMJs may be considered as normal adaptive responses to increased loading, rather than pathological degenerative changes.

Trial registration

Not applicable.

Hydrostatic Compress Force Enhances the Viability and Decreases the Apoptosis of Condylar Chondrocytes through Integrin-FAK-ERK/PI3K Pathway

Reduced mechanical stimuli in many pathological cases, such as hemimastication and limited masticatory movements, can significantly affect the metabolic activity of mandibular condylar chondrocytes and the growth of mandibles. However, the molecular mechanisms for these phenomena remain unclear. In this study, we hypothesized that integrin-focal adhesion kinase (FAK)-ERK (extracellular signal-regulated kinase)/PI3K (phosphatidylinositol-3-kinase) signaling pathway mediated the cellular response of condylar chondrocytes to mechanical loading. Primary condylar chondrocytes were exposed to hydrostatic compressive forces (HCFs) of different magnitudes (0, 50, 100, 150, 200, and 250 kPa) for 2 h. We measured the viability, morphology, and apoptosis of the chondrocytes with different treatments as well as the gene, protein expression, and phosphorylation of mechanosensitivity-related molecules, such as integrin α2, integrin α5, integrin β1, FAK, ERK, and PI3K. HCFs could significantly increase the viability and surface area of condylar chondrocytes and decrease their apoptosis in a dose-dependent manner. HCF of 250 kPa resulted in a 1.51 ± 0.02-fold increase of cell viability and reduced the ratio of apoptotic cells from 18.10% ± 0.56% to 7.30% ± 1.43%. HCFs could significantly enhance the mRNA and protein expression of integrin α2, integrin α5, and integrin β1 in a dose-dependent manner, but not ERK1, ERK2, or PI3K. Instead, HCF could significantly increase phosphorylation levels of FAK, ERK1/2, and PI3K in a dose-dependent manner. Cilengitide, the potent integrin inhibitor, could dose-dependently block such effects of HCFs. HCFs enhances the viability and decreases the apoptosis of condylar chondrocytes through the integrin-FAK-ERK/PI3K pathway.

Disc positions and condylar changes induced by different stretching forces in the model for anterior disc displacement of temporomandibular joint

OBJECTIVE

The aim of this study was to compare the disc positions and condylar changes induced by different stretching forces in the modified animal model for anterior disc displacement (ADD) of the temporomandibular joint.

METHODS

In the experimental group, 30 rabbits were equally divided into 3 subgroups and underwent surgical ADD via different stretching forces: group A with 0.5 N, group B with 1 N, and group C with 2 N. In the sham group, 6 rabbits underwent the same surgery without the disc being pulled anteriorly. The diagnosis of ADD was made when the anterior band of the disc was located anteriorly to the articular eminence. Histologic and radiographic changes of the condyles were observed under light microscopy and micro-computed tomography scanning 1 week after surgery.

RESULTS

The success rates of ADD were both 100% in groups B and C and 70% in group A. The correlations between the stretching force and severity of ADD, the stretching force and severity of cartilage changes, and the severity of ADD and cartilage changes were statistically significant (P < 0.01). The most advanced ADD and severest condylar changes were induced in group C. Condylar remodeling and scleroses were found in micro-computed tomography scans.

CONCLUSIONS

The rabbit model for ADD has been successfully established in this study, which is feasible and minimally invasive. The stretching force of at least 1 N could induce the disc displaced successfully. Larger stretching force would induce severer ADD and condylar degenerative changes.

3D reconstruction of TMJ after resection of the cyst and the stress-strain analyses

The aim of this article is 3D analysis of the temporomandibular joint (TMJ) patient, who underwent surgery, during which the right TMJ was resected along with the ramus of mandible and consequently the joint was reconstructed with subtotal replacement. The main goal is to give a suitable formulation of mathematical model, which describes the changes of stresses in TMJ incurred after the surgery. The TMJ is a complex, sensitive and highly mobile joint which works bilaterally so each side influences the contralateral joint and because of this the distribution of the stresses is changed in the healthy joint as well. Detailed knowledge about function these are necessary for clinical application of temporomandibular joint prosthesis and also help us estimate the lifetime of the prosthesis a possibilities of alteration in the contra lateral joint components. The geometry for the 3D models is taken from the CT scan date and its numerical solution is based on the theory of semi-coercive unilateral contact problems in linear elasticity. This article provides medical part with case report, discretion of treatment, than the methods of mathematical modeling and his possibilities are described and finally results are reported.

Dynamic compressive properties of articular cartilages in the porcine temporomandibular joint

The mandibular condylar and temporal cartilages in the temporomandibular joint (TMJ) play an important role as a stress absorber during function. However, relatively little information is available on its viscoelastic properties in dynamic compression, particularly in a physiological range of frequencies. We hypothesized that these properties are region-specific and depend on loading frequency. To characterize the viscoelastic properties of both cartilages, we performed dynamic indentation tests over a wide range of loading frequencies. Nine porcine TMJs were used; the articular surface was divided into five regions: anterior; central; posterior; medial and lateral. Sinusoidal compressive strain was applied with an amplitude of 1.0% and a frequency range between 0.01 and 10 Hz. In both cartilages, the dynamic storage modulus increased with frequency, and the value was the highest in the lateral region. These values of E' in the temporal cartilage were smaller than those in the mandibular condylar cartilage in all five regions except the lateral region. The Loss tangent values were higher in the temporal cartilage (0.35-0.65) than in the mandibular condylar one (0.2-0.45), which means that the temporal cartilage presents higher viscosity. The present results suggest that the dynamic compressive moduli in both cartilages are region-specific and dependent on the loading frequency, which might have important implications for the transmission of load in the TMJ.

Enhancement of biomechanical behavior on osseointegration of implant with SLAffinity

The purpose of this study was to investigate stresses resulting from different thicknesses of hydroxyapatite- and titanium dioxide (TiO(2))-treated layers at the interface between temporomandibular joint (TMJ) implants and bones using three-dimensional finite element models. For ensuring osseointegration of implant treatment, one must examine the stresses of interface between implant and bone tissue. Treated layers on TMJ implants are a very important factor in clinical application. Several studies have investigated finite element models for TMJs, but few have examined a model for TMJ implants with treated layers. In this study, TMJ models were reconstructed using computer tomography data, and the effects of treated layer thickness on the stress field during jaw movement were investigated; this index has not yet been reported with respect to TMJ implant. The maximum stresses in the bone occurred at the position of the first screw. Data analysis indicated a greater decrease in this stress in the case of using TMJ implants with TiO(2)-treated layers, and the stresses decreased with increasing layer thicknesses. Results confirmed that the treated layers improve biomechanical properties of the TMJ implants and release abnormal stress concentration in them. The results of our study offer the potential clinical benefit of inducing superior biomechanical behavior in TMJ implants.

Influence of psychosocial factors and habitual behavior in temporomandibular disorder-related symptoms in a working population in Japan

Background:

The symptoms of temporomandibular disorders (TMD) are directly influenced by numerous factors, and it is thought that additional factors exert indirect influences. However, the relationships between TMD-related symptoms (TRS) and these contributing factors are largely unknown. Thus, the goal of the present study was to investigate influences on TRS in a working population by determining the prevalence of TRS, analyzing contributing factors, and determining their relative influences on TRS.

Materials and Methods:

The study subjects were 2203 adults who worked for a single company. Subjects completed a questionnaire assessing TRS, psychosocial factors (stress, anxiety, depressed mood, and chronic fatigue), tooth-contacting habit, and sleep bruxism-related morning symptoms, using a 5-point numeric rating scale. Our analysis proceeded in 2 phases. First, all variables of the descriptor were divided into parts by using an exploratory factor analysis. Second, this factorial structure was verified by using a confirmatory factor analysis with structural equation modeling.

Results:

Of 2203 employees, 362 reported experiencing TRS (16.4%). Structural equation modeling generated a final model with a goodness of fit index of 0.991, an adjusted goodness of fit index of 0.984, and a root mean square error of approximately 0.021. These indices indicate a strong structural model. The standardized path coefficients for “habitual behavioral factors and TRS,” “psychosocial factors and habitual behavioral factors,” “psychosocial factors and TRS,” and “gender and habitual behavior factors” were 0.48, 0.38, 0.14, and 0.18, respectively.

Conclusions:

Habitual behavioral factors exert a stronger effect on TRS than do psychosocial factors.

Shear mechanics of the TMJ disc: relationship to common clinical observations

The temporomandibular joint (TMJ) is a complex hinge and gliding joint that induces significant shear loads onto the fibrocartilage TMJ disc during jaw motion. The purpose of this study was to assess regional variation in the disc's shear loading characteristics under physiologically relevant loads and to associate those mechanical findings with common clinical observations of disc fatigue and damage. Porcine TMJ discs were compressed between an axially translating bottom platen and a 2.5-cm-diameter indenter within a hydrated testing chamber. Discs were cyclically sheared at 0.5, 1, or 5 Hz to 1, 3, or 5% shear strain. Within the anterior and intermediate regions of the disc when sheared in the anteroposterior direction, both shear and compressive moduli experienced a significant decrease from instantaneous to steady state, while the posterior region's compressive modulus decreased approximately 5%, and no significant loss of shear modulus was noted. All regions retained their shear modulus within 0.5% of instantaneous values when shear was applied in the mediolateral direction. The results of the disc's regional shear mechanics suggest an observable and predictable link with the common clinical observation that the posterior region of the disc is most often the zone in which fatigue occurs, which may lead to disc damage and perforation.

Combined multi-body and finite element investigation of the effect of the seat height on acetabular implant stability during the activity of getting up

An important question in assessing the stability of a total hip arthroplasty is the effect of daily physical activities of patients. The aim of this study is to examine these effects when standing up from three different seat heights. A musculoskeletal body model has been modified to simulate the three different seat heights. The calculated muscle forces have been transferred to a finite element model of a pelvis. The pelvis model was created from a hemipelvis CT dataset. As an implant component, a metal socket with a polyethylene insert was used. A primary implantation situation was modelled. For the analysed patient activities the highest hip contact forces and the highest micromotions occur at the beginning of the motion. The results of this study show that standing up from a certain seat height can have a significant influence on the micromotions in the implant-bone interface.

Current computational modelling trends in craniomandibular biomechanics and their clinical implications

Computational models of interactions in the craniomandibular apparatus are used with increasing frequency to study biomechanics in normal and abnormal masticatory systems. Methods and assumptions in these models can be difficult to assess by those unfamiliar with current practices in this field; health professionals are often faced with evaluating the appropriateness, validity and significance of models which are perhaps more familiar to the engineering community. This selective review offers a foundation for assessing the strength and implications of a craniomandibular modelling study. It explores different models used in general science and engineering and focuses on current best practices in biomechanics. The problem of validation is considered at some length, because this is not always fully realisable in living subjects. Rigid-body, finite element and combined approaches are discussed, with examples of their application to basic and clinically relevant problems. Some advanced software platforms currently available for modelling craniomandibular systems are mentioned. Recent studies of the face, masticatory muscles, tongue, craniomandibular skeleton, temporomandibular joint, dentition and dental implants are reviewed, and the significance of non-linear and non-isotropic material properties is emphasised. The unique challenges in clinical application are discussed, and the review concludes by posing some questions which one might reasonably expect to find answered in plausible modelling studies of the masticatory apparatus.