Temporomandibular Joint Shape Research Articles

Temporomandibular joint shape in anthropoid primates varies widely and is patterned by size and phylogeny.

The temporomandibular joint is the direct interface between the mandible and the cranium and is critical for transmitting joint reaction forces and determining mandibular range of motion. As a consequence, understanding variation in the morphology of this joint and how it relates to other aspects of craniofacial form is important for better understanding masticatory function. Here, we present a detailed three-dimensional (3D) geometric morphometric analysis of the cranial component of this joint, the glenoid fossa, across a sample of 17 anthropoid primates, and we evaluate covariation between the glenoid and the cranium and mandible. We find high levels of intraspecific variation in glenoid shape that is likely linked to sexual dimorphism and joint remodeling, and we identify differences in mean glenoid shape across taxonomic groups and in relation to size. Analyses of covariation reveal strong relationships between glenoid shape and a variety of aspects of cranial and mandibular form. Our findings suggest that intraspecific variation in glenoid shape in primates could further be reflective of high levels of functional flexibility in the masticatory apparatus, as has also been suggested for primate jaw kinematics and muscle activation patterns. Conversely, interspecific differences likely reflect larger scale differences between species in body size and/or masticatory function. Results of the covariation analyses dovetail with those examining covariation in the cranium of canids and may be indicative of larger patterns across mammals.

Analysis of temporomandibular joint dysfunction in paediatric patients with unilateral crossbite using automatically generated finite element models

The evaluation of temporomandibular joint (TMJ) dysfunction using finite element models is a time consuming process that requires extensive technical knowledge. We combined a statistical active appearance model with automated modelling algorithms to biomechanically study the relationship between TMJ malformations and dysfunction in radiographs from 20 paediatric patients with unilateral crossbite. A fitting algorithm (fitting error < 4%) recognised the TMJ shape and adjusted the dimensions of each patient-specific 2D FE model, which was then used to compute 2 different joint movements. Significant functional differences were observed between the crossbite and non-cross bite sides, and the shape-function relation was verified.

Morphometric analysis for evaluating the relation between incisal guidance angle, occlusal plane angle, and functional temporomandibular joint shape variation

Objective: The correlations between morphology of the temporomandibular joint structure, the anterior guidance angle, and occlusal plane were investigated.Materials and methods: A cone beam computed tomography analysis was performed in 158 patients (86 women and 72 men). 3D software was employed to obtain the coordinates of the shape of the incisal guidance angle, occlusal guidance angle, articular fossa, and mandibular condyle. Generalized Procrustes analysis including principal components analysis (PCA) were performed and produced principal components (PCs) scores of each shape and their centroid size (CS).Results: A significant Pearson correlation coefficient of 0.3451 (p < .001) was observed between the incisal guidance angle and occlusal plane. The CS also showed a correlation with the incisal guidance angle, but not with the occlusal plane angle. The PCA results revealed that there were no significant correlations between the temporomandibular joint structure (TMJ) shape (fossa and condyle) and the incisal guidance angle.Conclusions: Incisor guidance angle and occlusal plane angle were correlated. In addition, there was a correlation between CS and incisal guidance angle. In the PCA, It can be concluded that the size is more related to the incisor guidance angle than the morphological factors of the constituent components of the TMJ.

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.

Novel 3-dimensional analysis to evaluate temporomandibular joint space and shape.

The purpose of this study was to present and validate a novel semiautomated method for 3-dimensional evaluation of the temporomandibular joint (TMJ) space and condylar and articular shapes using cone-beam computed tomographic data. The protocol for 3-dimensional analysis with the Checkpoint software (Stratovan, Davis, Calif) was established by analyzing cone-beam computed tomographic images of 14 TMJs representing a range of TMJ shape variations. Upon establishment of the novel method, analysis of 5 TMJs was further repeated by several investigators to assess the reliability of theanalysis. Principal components analysis identified 3 key components that characterized how the condylar head shape varied among the 14 TMJs. Principal component analysis allowed determination of the minimum number of landmarks or patch density to define the shape variability in this sample. Average errors of landmark placement ranged from 1.15% to 3.65%, and none of the 121 landmarks showed significant average errors equal to or greater than 5%. Thus, the mean intraobserver difference was small and within the clinically accepted margin of error. Interobserver error was not significantly greater than intraobserver error, indicating that this is a reliable methodology. This novel semiautomatic method is a reliable tool for the 3-dimensional analysis of the TMJ including both the form and the space between the articular eminence and the condylar head.

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.

Dietary correlates of temporomandibular joint morphology in New World primates

Previous analyses of the masticatory apparatus have demonstrated that the shape of the temporomandibular joint (TMJ) is functionally and adaptively linked to variation in feeding behavior and diet in primates. Building on previous research, this study presents an analysis of the link between diet and TMJ morphology in the context of functional and dietary differences among New World primates. To evaluate this proposed relationship, I used three-dimensional morphometric methods to quantify TMJ shape across a sample of 13 platyrrhine species. A broad interspecific analysis of this sample found strong relationships among TMJ size, TMJ shape, and diet, suggesting that both size and diet are significant factors influencing TMJ morphology in New World primates. However, it is likely that at least some of these differences are related to a division of dietary categories along clade lines. A series of hypotheses related to load resistance capabilities and range of motion in the TMJ were then tested among small groups of closely related taxa with documented dietary differences. These pairwise analyses indicate that some aspects of TMJ morphology can be used to differentiate among closely related species with different diets. However, not all of my predictions were upheld. The anteroposterior dimensions of the TMJ were most strongly consistent with hypothesized differences in ingestive/masticatory behaviors and jaw gape, whereas the predictions generated for variation in entoglenoid and articular tubercle height were not upheld. These results imply that while some features can be reliably associated with increased load resistance and facilitation of wider jaw gapes in the masticatory apparatus, other features are less strongly correlated with masticatory function.

A model of temporomandibular joint function in anthropoid primates based on condylar movements during mastication.

The hypothesis that the shape of the bony temporomandibular joint (TMJ) is functionally related to sagittal sliding of the condyle during mastication is tested, and a model of the relation of sagittal sliding to mandibular size, TMJ shape, and diet is developed. Sagittal sliding is defined as fore-aft motion of the condyle during mandibular translation and/or angular rotation. Ascending ramus height is used as a structural correlate of the distance between the condyle and the mandibular axis of rotation (CR). Cineradiographic data on sagittal sliding and gape during mastication in Ateles spp., Macaca fascicularis, Papio anubis, and Pan troglodytes in conjunction with comparative data on mandibular size and TMJ shape are used to evaluate the hypothesis. The results show that 1) linear and angular gape are highly positively correlated with sagittal sliding, 2) pure mandibular translation is rare during mastication, 3) the CR is rarely if ever located at the condyle during mastication, 4) angular gape should be standardized in interindividual comparisons of sagittal sliding, and 5) the height of the ascending ramus (and by inference the CR-to-condyle distance) is highly positively correlated with absolute sagittal sliding. Sagittal sliding relative to the length of the articular eminence was the variable used to explore the relation between TMJ shape and sliding. This variable standardized absolute sagittal sliding relative to joint size. The relative depth and orientation of the articular eminence were not correlated with relative sagittal sliding. The anteroposterior curvature of the condyle was highly negatively correlated with relative sagittal sliding. Flat condyles are associated with large amounts of relative sagittal sliding. A flat condyle increases joint contact area, which reduces joint stress. A flat condyle also increases joint congruence, and this may facilitate the combined sliding and rolling motion of the condyle when the sliding motion is relatively large. The shape of the entoglenoid process was also positively correlated with relative sagittal sliding. A relatively large entoglenoid process may help to guide sagittal sliding and prevent excessive mediolateral sliding of the condyle. The functional model makes a number of predictions about the correlations between food consistency and food object size, mandibular size, TMJ shape, and sagittal sliding of the condyle during mastication and incision.

Evaluation of Temporomandibular Joint Shape and Image Diagnosis.

Tomograms of a temporomandibular joint (TMJ) were analyzed by image processing. The TMJ shape was evaluated from the TMJ space, the space area and the distance between the reference points of the condyle and the glenoid fossa. The shape factors of the condyle and the glenoid fossa were also measured to examine the deformation of the bone. The borderline values were determined from the results obtained by the image analysis and they were used to select an abnormal sample from among many samples. The deformation of the condyle can be detected simply by the shape factor. The error of diagnosis is more than 10% according to the borderline values of the TMJ space and the space area. On the other hand, the error is 2. 4% when the horizontal distance between the reference points is employed. The present system will contribute to the image diagnosis of the TMJ syndrome and evaluate the TMJ shape objectively