Temporomandibular Joint Morphology Research Articles

Predilection of chewing side preferences and clinical assessment of its impact on temporomandibular joint

Statement of the Problem: Normal mastication in humans generally favors one side and then the other, but most people chew more on a particular side, which means they have a preferred chewing side (PCS). The relationship between the use of one habitual chewing side and the peripheral factors involved in temporomandibular disorders (TMDs) is not understood yet. Aims and Objectives: The objective of the study is to explore the effect of chewing side preference on temporomandibular joint (TMJ) in adult population. Methods: One hundred and seventy healthy dentate subjects (148 female and 22 male) were selected and clinically examined for this cross-sectional study. Chewing side preference test and TMJ clinical examination were conducted. Subjects were classified into unilateral and bilateral chewers, signs and symptoms of TMDs were recorded. Results: Statistical analysis was performed to evaluate the difference between the subjects regarding preferable chewing side, distribution of subjects with respect to signs and symptoms of TMDs, and frequency of symptoms in habitual chewers using Chi-square test, at 5% significance level. The results showed that among all the subjects, 80% preferred unilateral chewing side and there was a significant correlation with asymmetric factors of TMJ with masticatory side. Conclusion: Within the limitations of the study, it may be concluded that the presence of a PCS affects the morphology and parameters of TMJ. This signifies that it is not only sufficient enough to maintain anatomic health but also dynamic and functional factors should be considered to avoid TMDs.

Food, Form and Function: Motor Control, Movement and Modulation during Mastication in Mammals

Mammalian feeding is one of the many dynamic behaviors in which close form‐function relationships are readily apparent across the phylogeny. The link between masticatory morphology and function, for example, has been highlighted time and again with classic contrasts being made between major dietary groups, such as herbivores and carnivores. These contrasts emphasize differences between the teeth, muscle anatomy, temporomandibular joint (TMJ) and masticatory kinematics. In some cases, masticatory anatomy is hypothesized to significantly limit movement. Yet it has also been shown in diverse species that mastication is a behavior that has the potential for significant functional variability depending on a number of factors, including the textural, mechanical and/or physical properties of the food being consumed and jaw muscle activation patterns that move the jaw and produce the force to break down food. Here, I will explore the relationship between masticatory morphology, jaw‐muscle activity and jaw kinematics in select species representing different dietary groups (e.g., herbivory, carnivory, and omnivory) and examine the effect that food properties have on the dynamic response of the feeding system. Jaw‐muscle activity patterns were collected using electromyography and kinematic data were collected using X‐ray Reconstructing of Moving Morphology (XROMM). In goats (herbivore), increasing food toughness increases total cycle duration and the duration of jaw closing during chewing, whereas increasing food stiffness has little effect on overall temporal dynamics. Differences are observed in the jaw‐muscle firing patterns when chewing on different foods. Kinematic data from pigs (omnivore) reveal that changes in food toughness affect the chewing cycle as a whole, whereas changes in food stiffness alter the relative contribution and duration of the constituent phases of the chewing cycle, while total cycle duration remains more or less constant. Comparisons between ferrets (carnivore) and two closely related omnivorous species, skunks and raccoons in jaw kinematics, also indicate that the morphology of the TMJ and dentition may impact how jaw‐movements are modulated during mastication. Finally, kinematic data also reveal that occlusion is facilitated by rotation of the jaw about a vertical axis (“yaw”), mediolateral translation of the condyles, and/or rotation of the working‐side hemimandible around its long axis (“roll”), yet there are differences in the relative contribution of each type of movement that may be related to tooth and TMJ morphology. Combined, these experimental datasets from different species reveal new complexities to mastication and the modulation of jaw movements in mammals and help to clarify interpretations of function from morphology.Support or Funding InformationThis research was funded by National Science Foundation grants IOS‐0520855, IOS‐1456810 and DBI‐0922988.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Comparison of temporomandibular joint and ramus morphology between class II and class III cases before and after bi-maxillary osteotomy

PurposeThe purpose of this study was to compare changes in temporomandibular joint (TMJ) and ramus morphology between class II and III cases before and after sagittal split ramus osteotomy (SSRO) and Le Fort I osteotomy. Materials and methodsThe subjects were 39 patients (78 sides) who underwent bi-maxillary surgery. They consisted of 2 groups (18 class II cases and 21 class III cases), and were selected randomly from among patients who underwent surgery between 2012 and 2016. The TMJ disc tissue and joint effusion were assessed by magnetic resonance imaging (MRI) and the TMJ space, condylar height, ramus height, ramus inclination and condylar square were assessed by computed tomography (CT), pre- and post-operatively. ResultsThe number of joints with anterior disc displacement in class II was significantly higher than that in class III (p < 0.0001). However, there were no significant differences between the two classes regarding ratio of joint symptoms and ratio of joint effusion pre- and post-operatively. Class II was significantly better than class III regarding reduction ratio of condylar height (p < 0.0001) and square (p = 0.0005). ConclusionThe study findings suggest that condylar morphology could change in both class II and III after bi-maxillary surgery. The findings of the numerical analysis also demonstrated that reduction of condylar volume occurred frequently in class II, although TMJ disc position classification did not change significantly, as previously reported.

Can skull form predict the shape of the temporomandibular joint? A study using geometric morphometrics on the skulls of wolves and domestic dogs

The temporomandibular joint (TMJ) conducts and restrains masticatory movements between the mammalian cranium and the mandible. Through this functional integration, TMJ morphology in wild mammals is strongly correlated with diet, resulting in a wide range of TMJ variations. However, in artificially selected and closely related domestic dogs, dietary specialisations between breeds can be ruled out as a diversifying factor although they display an enormous variation in TMJ morphology. This raises the question of the origin of this variation. Here we hypothesise that, even in the face of reduced functional demands, TMJ shape in dogs can be predicted by skull form; i.e. that the TMJ is still highly integrated in the dog skull. If true, TMJ variation in the dog would be a plain by-product of the enormous cranial variation in dogs and its genetic causes. We addressed this hypothesis using geometric morphometry on a data set of 214 dog and 60 wolf skulls. We digitized 53 three-dimensional landmarks of the skull and the TMJ on CT-based segmentations and compared (1) the variation between domestic dog and wolf TMJs (via principal component analysis) and (2) the pattern of covariation of skull size, flexion and rostrum length with TMJ shape (via regression of centroid size on shape and partial least squares analyses). We show that the TMJ in domestic dogs is significantly more diverse than in wolves: its shape covaries significantly with skull size, flexion and rostrum proportions in patterns which resemble those observed in primates. Similar patterns in canids, which are carnivorous, and primates, which are mostly frugivorous imply the existence of basic TMJ integration patterns which are independent of dietary adaptations. However, only limited amounts of TMJ variation in dogs can be explained by simple covariation with overall skull geometry. This implies that the final TMJ shape is gained partially independently of the rest of the skull.

Revisiting size and scaling in the anthropoid temporomandibular joint

Masticatory morphology in primates is likely under strong selective pressure to maximize feeding efficiency while simultaneously minimizing the occurrence of injury or pathology. As a result, masticatory shape, including aspects of temporomandibular joint (TMJ) morphology, varies widely across primates in relation to feeding behavior and body size. This study examines patterns of allometry in the TMJ of anthropoid primates, with the specific goal of evaluating how allometric patterns may reflect variation in loading and/or range of motion at this joint. Phylogenetic reduced major axis regressions were employed to examine how specific aspects of TMJ morphology scale in relation to body mass and mandible length. Patterns of shape variation across the entire masticatory apparatus were examined by utilizing geometric morphometric techniques. Results reveal that most aspects of TMJ shape scale with either isometry or positive allometry relative to body mass and/or mandible length, though several departures from these patterns were observed. In particular, male cercopithecoids tend to show distinct scaling patterns in TMJ height above the occlusal plane and condylar area, likely reflecting known trade-offs between increased range of motion and force production in this clade, as has been linked to selection for increased male canine size. The geometric morphometric analyses indicate that craniofacial and masticatory shape are strongly allometric, but that glenoid shape variation is less consistently allometric. Notably, different patterns of allometric shape variation were observed in platyrrhines, cercopithecoids, and hominoids, perhaps related to different, and potentially competing, selective pressures in each of these clades.

Morphometric analysis of temporomandibular joint elements

PurposeTo study the morphology of temporomandibular joint (TMJ) elements and examine the feasibility of a novel biofidelic articular disc casting technique. Methods18 formalin-fixed cadavers (77.8% female, 22.2% male) with mean (SD) death age of 71.9 (13.7) years were used for this study. In each specimen the masseter muscle, mandibular ramus, and articular disc were dissected bilaterally and measured for length, width, and thickness. All anatomic measurements were made using a digital slide caliper (Hawk Inc., Cleveland, OH). Further, a novel method for the creation of biofidelic articular disc models was established through trial and error. Models were measured for accuracy against their biological counterparts. ResultsLeft articular disc length and thickness were inversely correlated (r = −0.58, p < 0.049). Direct correlations existed between right disc and ramus thickness (r = 0.56, p < 0.039), masseter length and thickness (r = 0.59, p < 0.009), and masseter width and thickness (r = 0.66, p < 0.003). Comparison of the model measurements with their biological counterparts found no significant differences. DiscussionThese observed correlations between elements of the TMJ hold relevance for oral-maxillofacial surgeons and researchers examining disorders of the TMJ. Additionally, our casting technique proved accurate in modeling human articular discs.

Diagnostic imaging modalities and surgical anatomy of the temporomandibular joint in rabbits

The temporomandibular joint (TMJ) is a condylar synovial joint that, together with the masticatory muscles, controls mandibular movement during mastication. The rabbit is often used as a model species for studying the mechanisms of TMJ diseases, and in regenerative research. However, there are significant differences between rabbit and human TMJs that should be taken into account before using this model for experimental research. Here, we use several analytical approaches (radiography, computed tomography and magnetic resonance imaging) to enable a detailed description and analysis of the rabbit TMJ morphology. Moreover, possible surgical approaches have been introduced with a focus on available access into the rabbit TMJ cavity, which relate our findings to clinical usage.

Comparison of Morphologic Parameters of Temporomandibular Joint for Asymptomatic Subjects Using the Two-Dimensional and Three-Dimensional Measuring Methods.

The differences of temporomandibular joint (TMJ) morphologic parameters by using two-dimensional (2D) and three-dimensional (3D) measuring methods were compared. Ten asymptomatic subjects (26.75 ± 4.89 years) were randomly recruited. The 3D models of the maxilla, mandible, and teeth were reconstructed according to cone-beam computed tomography (CBCT) image data. The morphologic parameters of TMJs were measured by the 2D CBCT measuring method (group A) and the 3D reconstruction model measuring method (group B), respectively. The morphologic parameters in each group were assessed by paired samples t-test, and the statistical significance was achieved when p < 0.05. The horizontal condylar angle (HCA), sagittal ramus angle (SRA), medial joint space (MJS), lateral joint space (LJS), superior joint space (SJS), and anterior joint space (AJS) in group A were significantly smaller than those in group B (p < 0.05). The HCA on the left side was significantly smaller than that on the right side in group A (p < 0.05). However, all the morphologic parameters in group B were not significantly different between left and right sides. In conclusion, there were significant differences for the morphologic parameters of TMJ measured on 2D CBCT and 3D models. 3D measuring method should be used for the detection of TMJ morphology in clinical practice.

Cone-Beam Computed Tomographic Assessment of Temporomandibular Joint Morphology in Patients with Temporomandibular Joint Disc Displacement and in Healthy Subjects: A Pilot Study

Purpose: The purpose of this study was to analyze the size and morphology of mandibular condyle and mandibular fossa between temporomandibular joint (TMJ) disc displacement (DD) patients and healthy subjects using cone-beam computed tomography (CBCT). Methods: Twenty healthy subjects and twenty TMJ DD patients participated in this study respectively. We made five measurements in mandibular condyle (medio-lateral dimension, antero-posterior dimension, condyle height, intercondylar distance and intercondylar angle) and two measurements in mandibular fossa (mandibular fossa depth and articular eminence angle) using CBCT image. Results: There was no difference between two groups in medio-lateral dimension. In case of antero-posterior dimension, average of healthy controls was larger than that of TMJ DD patients, but that was not significant statistically. There were no significant differences between two groups in condyle height. Comparing intercondylar distance and intercondylar angle between two groups, there was no significant difference between two groups. In comparison of mandibular fossa depth and articular eminence angle, there was no significant difference between two groups. Conclusions: We couldn't find any definite relationship between TMJ morphology and TMJ DD.

Morphologic Analysis of the Temporomandibular Joint Between Patients With Facial Asymmetry and Asymptomatic Subjects by 2D and 3D Evaluation: A Preliminary Study.

Signs and symptoms of temporomandibular joint (TMJ) dysfunction are commonly found in patients with facial asymmetry. Previous studies on the TMJ position have been limited to 2-dimensional (2D) radiographs, computed tomography (CT), or cone-beam computed tomography (CBCT). The purpose of this study was to compare the differences of TMJ position by using 2D CBCT and 3D model measurement methods. In addition, the differences of TMJ positions between patients with facial asymmetry and asymptomatic subjects were investigated.We prospectively recruited 5 patients (cases, mean age, 24.8 ± 2.9 years) diagnosed with facial asymmetry and 5 asymptomatic subjects (controls, mean age, 26 ± 1.2 years). The TMJ spaces, condylar and ramus angles were assessed by using 2D and 3D methods. The 3D models of mandible, maxilla, and teeth were reconstructed with the 3D image software. The variables in each group were assessed by t-test and the level of significance was 0.05.There was a significant difference in the horizontal condylar angle (HCA), coronal condylar angle (CCA), sagittal ramus angle (SRA), medial joint space (MJS), lateral joint space (LJS), superior joint space (SJS), and anterior joint space (AJS) measured in the 2D CBCT and in the 3D models (P < 0.05). The case group had significantly smaller SJS compared to the controls on both nondeviation side (P = 0.009) and deviation side (P = 0.004). In the case group, the nondeviation SRA was significantly larger than the deviation side (P = 0.009). There was no significant difference in the coronal condylar width (CCW) in either group. In addition, the anterior disc displacement (ADD) was more likely to occur on the deviated side in the case group.In conclusion, the 3D measurement method is more accurate and effective for clinicians to investigate the morphology of TMJ than the 2D method.

Changes in temporomandibular joint morphology in class II patients treated with fixed mandibular repositioning and evaluated through 3D imaging: a systematic review.

To estimate the effects of skeletal class II malocclusion treatment using fixed mandibular repositioning appliances on the position and morphology of the temporomandibular joint (TMJ). Two independent reviewers performed comprehensive electronic searches of MEDLINE, EMBASE, EBM reviews and Scopus (until May 5, 2015). The references of the identified articles were also manually searched. All studies investigating morphological changes of the TMJ articular disc, condyle and glenoid fossa with 3D imaging following non-surgical fixed mandibular repositioning appliances in growing individuals with class II malocclusions were included in the analysis. Of the 269 articles initially reviewed, only 12 articles used magnetic resonance imaging and two articles used computed tomography (CT) or cone-beam CT images. Treatment effect on condyle and glenoid fossa was discussed in eight articles. Treatment effect on TMJ articular disc position and morphology was discussed in seven articles. All articles showed a high risk of bias due to deficient methodology: inadequate consideration of confounding variables, blinding of image assessment, selection or absence of control group and outcome measurement. Reported changes in osseous remodelling, condylar and disc position were contradictory. The selected articles failed to establish conclusive evidence of the exact nature of TMJ tissue response to fixed mandibular repositioning appliances.

Comparative study of the prevalence of temporomandibular joint osteoarthritic changes in cone beam computed tomograms of patients with or without temporomandibular disorder

To compare the prevalence of temporomandibular joint (TMJ) osteoarthritic changes in cone beam computed tomography (CBCT) images of temporomandibular disorder (TMD) and non-TMD patients. A retrospective analysis of CBCT images of the joints of TMD and non-TMD patients was performed. The presence or absence of osteoarthritic changes (condylar erosion, osteophyte, subcortical cyst, or generalized sclerosis) in each TMJ was evaluated. The prevalence within the two study groups were compared by using Chi-square statistics. At least one type of osteoarthritic change was present in78.6% of joints in the TMD group and 79.7% in the non-TMD group. No significant difference was found in prevalence of osteoarthritic changes between the TMD and non-TMD groups in the overall study sample or within the subsets of gender and age in the groups. The lack of a significant difference in prevalence of TMJ osteoarthritic changes in TMD and non-TMD patients highlights the equivocal relationship between osseous TMJ morphology and degenerative bone disease.

Correlation between temporomandibular joint morphology and disc displacement by MRI.

The aim was to evaluate the morphology of the temporomandibular joint's (TMJs) disc and condyle as well as its correlation with disc displacement, using MRI. 190 TMJs were retrospectively analysed. The condyle morphology of each TMJ was evaluated by two observers using both axial and coronal views, as were their disc morphology and displacement, using sagittal view. Condyle morphology was classified as flat, convex, angled or rounded in the coronal sections and as anterior side flat/posterior side convex, biconvex, anterior side concave/posterior side convex, flat or biconcave in the axial view. Disc morphology was determined as biconcave, biplanar, biconvex, hemiconvex or folded. χ2, Fisher exact and Bonferroni correction tests were used to evaluate the data. ANOVA followed by post hoc Tukey's test was used to evaluate the interaction between age and disc displacement. Anterior disc displacement with reduction; convex condyle morphology in the coronal view; anterior side concave/posterior side convex morphology in the axial view; and biconcave discs were found to be the most prevalent findings. An association was observed between disc morphology and disc displacement (p<0.001). No correlation between condyle morphology and TMJ disc displacement was found (p=0.291 for axial and p=0.14 for coronal views). The results of this study suggest that TMJ disc morphology is associated with disc displacement.

CBCT in orthodontics: assessment of treatment outcomes and indications for its use

Since its introduction into dentistry in 1998, CBCT has become increasingly utilized for orthodontic diagnosis, treatment planning and research. The utilization of CBCT for these purposes has been facilitated by the relative advantages of three-dimensional (3D) over two-dimensional radiography. Despite many suggested indications of CBCT, scientific evidence that its utilization improves diagnosis and treatment plans or outcomes has only recently begun to emerge for some of these applications. This article provides a comprehensive and current review of key studies on the applications of CBCT in orthodontic therapy and for research to decipher treatment outcomes and 3D craniofacial anatomy. The current diagnostic and treatment planning indications for CBCT include impacted teeth, cleft lip and palate and skeletal discrepancies requiring surgical intervention. The use of CBCT in these and other situations such as root resorption, supernumerary teeth, temporomandibular joint (TMJ) pathology, asymmetries and alveolar boundary conditions should be justified on the basis of the merits relative to risks of imaging. CBCT has also been used to assess 3D craniofacial anatomy in health and disease and of treatment outcomes including that of root morphology and angulation; alveolar boundary conditions; maxillary transverse dimensions and maxillary expansion; airway morphology, vertical malocclusion and obstructive sleep apnoea; TMJ morphology and pathology contributing to malocclusion; and temporary anchorage devices. Finally, this article utilizes findings of these studies and current voids in knowledge to provide ideas for future research that could be beneficial for further optimizing the use of CBCT in research and the clinical practice of orthodontics.

Assessment of osseous morphology of temporomandibular joint in asymptomatic participants with chewing-side preference.

Chewing-side preference (CSP) may be associated with temporomandibular disorders. However, little information exists regarding whether CSP will lead to osseous changes of temporomandibular joint (TMJ) in asymptomatic participants. The aim of this study was to investigate the relationship between osseous morphology of TMJ in asymptomatic participants with CSP and without CSP. Of the 121 healthy dentate participants, 35 participants with left CSP, 38 with right CSP and other 48 without CSP were scanned by cone-beam computed tomography. The dimensions of the reconstructed images of opposing TMJs were compared. Statistical analyses were performed using spss 16.0 software. The results showed that there were no significant differences between the dimensions of bilateral structures of the TMJ (P1>0·05) in participants without CSP. However, the posterior-superior, posterior and lateral joint space of the preferred side were smaller than that of the unpreferred side in participants with CSP (P2<0·01) and bilateral TMJ in participants without CSP (P3<0·01). In addition, width of condylar neck of the unpreferred side both in sagittal and perpendicular to the long axis of condyle views was greater than that of the preferred side in participants with CSP (P2<0·01) and bilateral TMJ of participants without CSP (P4<0·01). Also, the inclination of articular eminence of the preferred side in view perpendicular to the long axis of condyle was less than that of the unpreferred side (P2<0·05). These findings suggest CSP affects osseous morphology of TMJ in asymptomatic participants.

Morphological and degenerative changes in a suspected post-traumatic bifid mandibular condyle

Bifid mandibular condyle is a rare anatomical anomaly with uncertain aetiology and pathogenesis. Theories for the developmentof this condition include bony alterations post-trauma, however little evidence exists to support this theory. Furthermore, the likely alterations to joint morphology over time as a result of this condition - including possible degenerative changes - have notbeen highlighted. We describe a case of bifid mandibular condyle attributed to a post-traumatic aetiology with associated degenerative changes in a male Sri Lankan skull of approximately 40 to 50 years of age. Fractures of the left parietal bone, zygomatic bone and damage to the orbit were observed in addition to a bifid left mandibular condyle that had anteromedial and posterolateral condyles and remodeling of the mandible consistent with a fracture of the mandibular neck. Two fossae were notedin the squamous part of the temporal bone that corresponded to the two condyles. Degenerative alterations to both joint surfaces included damage to the articular surface and osteophyte formation around the articular margins. This case provides circumstantial evidence to support the development of bifid mandibular condyles post-trauma with observations including longterm modifications to temporomandibular joint morphology leading to subsequent alterations in masticatory muscle activity, andthe first evidence of degenerative change associated with this condition. Both outcomes will potentially result in a loss in temporomandibular joint function and are clinically relevant consequences of bifid mandibular condyle

Temporomandibular joint morphology and disc position in mandibular prognathism patients with and without asymmetry

The purpose of this study was to investigate the relationship between temporomandibular joint (TMJ) morphology, including the angle of articular eminence and discal tissue in patients with or without asymmetry.

Morphological Changes in the Temporomandibular Joint Before and After Sagittal Splitting Ramus Osteotomy of the Mandible for Skeletal Mandibular Protrusion

Changes of temporomandibular joint (TMJ) morphology were analyzed in 21 patients with mandibular protrusion corrected using bilateral sagittal split ramus osteotomy (SSRO) and mini-plate fixation with TMJ cephalometric laminographs. The condylar pass angle, eminence to the FH plane angle, and total height of fossa and lower height of fossa in both left and right sides, significantly decreased after surgery. The width of the condyle, in both left and right sides, significantly increased after treatment. However, in the joint spaces, there were no significant differences before and after treatment. The amount of change in the eminence to the FH plane angle, total height of fossa and lower height of fossa, before and after surgery, showed significant positive correlations with that of SNB, before and after surgery. These results suggest that adaptive bone remodeling of the TMJ might occur due to the correction of occlusion and craniofacial morphology by SSRO in patients with mandibular protrusion.

Application of a Cephalometric Method to the Temporomandibular Joint in Patients With or Without Alteration in the Orientation of the Mandibular Condyle Axis

In a prior study,1 the spatial relationship of the mandibular condyle was studied through a cephalogram based on laminographies of the temporomandibular joint (TMJ). The present method was developed with the aim of analyzing TMJ morphology and the spatial relationship of the mandibular head within the mandibular fossa, considering references far from these structures, as they may suffer shape alterations. This study was conducted in view of the importance of the study of morphology and the hard structures relationship, which constitutes the temporomandibular joint. Its purpose is to validate a new TMJ cephalogram method by analyzing joints with and without alterations in the orientation of the condylar axis growth. Sixty joints were studied through laminographies in maximal occlusion, examining those joints with and without alterations in the orientation of the axis during condylar growth for subsequent analysis. Results showed that those joints were in a posterior position and rotation of the mandibular head, and that they presented a greater inclination in the articular eminence compared to joints without alterations in the axis orientation. Moreover, a new cephalometric method could be validated, demonstrating that changes in the condylar axis orientation imply pathology; they could also be correlated with changes in the condylar position and in the glenoid fossa morphology.

Dietary correlates of temporomandibular joint morphology in the great apes

Behavioral observations of great apes have consistently identified differences in feeding behavior among species, and these differences have been linked to variation in masticatory form. As the point at which the mandible and cranium articulate, the temporomandibular joint (TMJ) is an important component of the masticatory apparatus. Forces are transmitted between the mandible and cranium via the TMJ, and this joint helps govern mandibular range of motion. This study examined the extent to which TMJ form covaries with feeding behavior in the great apes by testing a series of biomechanical hypotheses relating to specific components of joint shape using linear measurements extracted from three-dimensional coordinate data. Results of these analyses found that taxa differ significantly in TMJ shape, particularly in the mandibular fossa. Chimpanzees have relatively more anteroposteriorly elongated joint surfaces, whereas gorillas tend to have relatively anteroposteriorly compressed joints. Orangutans were most commonly intermediate in form between Pan and Gorilla, perhaps reflecting a trade-off between jaw gape and load resistance capabilities. Importantly, much of the observed variation among taxa reflects differences in morphologies that facilitate gape over force production. These data therefore continue to emphasize the unclear relationship between mandibular loading and bony morphology, but highlight the need for further data regarding food material properties, jaw gape, and ingestive/food processing behaviors.