Chewing-side preference is one of the risk factors for temporomandibular disorders (TMD), and people with chewing-side preference is more prone to have short and displaced condyles, increased articular eminence inclination and glenoid fossa depth. The proportion of TMD patients with chewing-side preference is often higher than that of the normal subjects. Clinical studies have shown a strong correlation between chewing-side preference and TMD symptoms and signs; and animal studies have shown that chewing-side preference can affect the growth, development, damage and repair of the mandible. After long-term unilateral mastication, changes in the stress within the joint cause the imbalance of temporomandibular joint (TMJ) structural reconstruction, the transformation and even destruction of the fiber structure of masticatory muscle, resulting in uncoordinated movement of bilateral muscles. The joint neurogenic diseases caused by the increase of neuropeptide substance P and calcitonin-gene-related-peptide (CGRP) released locally by TMJ may be the mechanism of TMD. This article reviews the research progress of the influence of chewing-side preference on the structure of TMJ, the relationship between chewing-side preference and TMD, and the related mechanisms.
Humans ; Mastication/physiology* ; Temporomandibular Joint/physiology* ; Temporomandibular Joint Disorders/etiology* ; Mandible/physiology*

OBJECTIVETo investigate the relationship between the contour of articular eminence and traces of the condylar kinematic center during jaw opening movement in healthy subjects, and compare trace characteristics of condylar kinematic center and MRI findings in TMD patients.

METHODSIn 10 healthy subjects, jaw-opening motion was recorded. The kinematic center and terminal hinge axis point of the condyle were used as trace reference points. The contour of articular eminence was examined by MRI. Seven patients with TMD signs and/or symptoms (disk displacement) were selected for this study. The condylar trace was recorded during jaw protrusion and opening-closing. The internal derangement in temporomandibular joints was detected by MRI and defined as: (1). normal disk position, (2). disk displacement with reduction, (3). disk displacement without reduction.

RESULTSIn healthy subjects, most of the opening traces of the kinematic center coincided with the contour of articular eminence (8/10 joints in left, 9/10 joints in right). For terminal hinge axis point, no trace coincided with the contour of articular eminence (0/20 joints in left and right). In TMD patients, according to MRI findings, the condylar traces of kinematic center in 3 normal disk position joints showed normal shape. However, in 6 disk displacements with reduction joints and 5 disk displacement without reduction joints, the condylar traces of kinematic center showed irregular patterns except 1 disk displacement with reduction joint.

CONCLUSIONSIn comparison with the terminal hinge axis point, the opening traces of the kinematic center can be interpreted as the translatory movement of the condyle/disc along the articular eminence. The study suggests the use of kinematic center in condylar movement studies.

Adolescent ; Adult ; Humans ; Magnetic Resonance Imaging ; Mandibular Condyle ; physiology ; Temporomandibular Joint ; physiology ; Temporomandibular Joint Disorders ; physiopathology

OBJECTIVETo investigate the regulation of stress distribution on TMJ when the location of occlusal load on the mandibular second molar was changed by using the 3-dimensional Finite Element Method (FEM).

METHODSA 3-dimensional FEM TMJ model including left mandibular second molar and mandible was established. In finite element analysis software ANSYS the same boundary constraints were applied to the TMJ FEM model with different load cases. The occlusal loads were applied to simulate ICO load, distal load, and buccal load and the stress values of condyles of the FEM model were calculated.

RESULTSAs the occlusal load was applied to different tooth contact areas with various shapes, the stress distributions of bilateral condyles were found different and asymmetrical. The condyle stress on TMJ FEM model in three loading cases was diverse, not only in stress character but also in stress distribution style. The maximum value of Von Mises in the opposite condyle was 51.513 MPa when ICO load was applied. But when the distal load or the buccal load was applied, the maximum value of Von Mises in the opposite condyle increased to 72.145 MPa or 69.566 Mpa respectively.

CONCLUSIONSThe same level but in different direction of occlusal load that resulted from difference of loading spots by changing the occlusal contact area, would induce different stress features on bilateral condyles.

Bite Force ; Dental Stress Analysis ; Finite Element Analysis ; Humans ; Mandible ; physiology ; Molar ; physiology ; Temporomandibular Joint ; physiology

OBJECTIVETo explore the six degrees of freedom of jaw opening and closing movement with motion capture and analysis system to establish a quantitative method for studying mandibular movement and a digital basis for virtual reality study of mandibular movement.

METHODSIn a male adult with normal dentition without temporomandibular joint disorders, 3 fluorescent markers were pasted in the upper dentition and 4 in the lower dentition. Six cameras of the motion capture system were arranged in a semi-circular fashion. The subject sat in front of the camera at an 80-cm distance with the Frankfort plane kept parallel to the horizontal plane. The degree-of-freedom (3 linear displacement and 3 angular displacement) of jaw opening and closing movement was obtained by collecting the marker motion.

RESULTSSix degrees of freedom of jaw opening and closing were obtained using the motion capture system. The maximum linear displacements of X, Y and Z axes were 5.888 089 cm, 0.782 269 cm, and 0.138 931 cm, and the minimum linear displacements were -3.649 83 cm, -35.961 2 cm, -5.818 63 cm, respectively. The maximum angular displacements of X, Y and Z axes were 0.760 088°, 2.803 753°, and 0.786 493°, with the minimum angular displacements of -2.526 18°, -0.625 94°, and -25.429 8°, respectively. Variations of linear displacements during jaw opening and closing occurred mainly in the Y axis, and those of angular displacement occurred mainly in the Z axis.

CONCLUSIONThe six degree-of-freedom of mandibular movement can be accurately obtained with the motion capture system to allow quantitative examination of the mandibular movement.

Adult ; Humans ; Male ; Mandible ; physiology ; Movement ; physiology ; Range of Motion, Articular ; Temporomandibular Joint ; physiology ; Video Recording

OBJECTIVETo analyze the stress distribution in temporomandibular joint (TMJ) with different depth of curve of Spee (CS) by three-dimensional finite element model (3D-FEM).

METHODSFEM with different depth of CS were established. The depth was 2.50, 0 and 4.50 mm (model 0, 1, 2). The stress distribution were analyzed by software Abaqus. The change of stress were analyzed by paried t test.

RESULTSThe stress distribution patterns in TMJ with different depth of CS were similar. The Von Mises on the anterior surface of condyle and the Von Mises on the intermedial zone of the disc was higher. The S. Max. Principal of the condyle was mainly tensile stress. The S. Min. Principal of the condyle was mainly compressive stress. The S. Max. Principal of the disc was mainly tensile stress. The S.Min. Principal of the disc was mainly compressive stress.In model 0, the eviations of the Von Mises, the S.Max. Principal and the S.Min. Principal on the anterior surface of condyle were 0.1057 - 0.2298 MPa, -0.2243 - -0.3738 MPa and -0.3494 - -0.1165 MPa. The eviations of the Von Mises, the S.Max. Principal and the S. Min. Principal on the intermedial zone of the disc were 0.1099 - 0.6880 MPa, -0.3217 - 0 MPa and -1.2000 - -0.1000 MPa. The D-values of of Von Mises of condyle and disk between different models were extremely significant (P < 0.01).

CONCLUSIONSWith the same plane of occlusion, the stress distribution patterns of TMJ with different depth of CS is similar to that of normal occlusion. The final results also validate the anterior surface of condyle and intermediate zone of articular disc are the weight-bearing areas in TMJ. The changes of depth of CS change the value of the stress.

Cephalometry ; Dental Occlusion ; Dental Stress Analysis ; methods ; Finite Element Analysis ; Humans ; Imaging, Three-Dimensional ; methods ; Mandibular Condyle ; physiology ; Stress, Mechanical ; Temporomandibular Joint ; physiology ; Temporomandibular Joint Disc ; physiology

OBJECTIVETo look for the way of three-dimensional simulation of the craniofacial system.

METHODSA three-dimensional laser scanner was used for gypsum models digitization and computed tomography scans was employed for skull reconstruction, then the data of teeth and temporomandibular joint were picked up and integrated. The ARCUS sigma system was used to record spatial mandibular movements. The data of both digital reconstruction and spatial movements were transferred into one coordinate system. The software for three-dimensional simulation was programmed.

RESULTSThe preliminary program could be used to analyze static and dynamic occlusion and gnathic relations, to check the contact points and to show from various visual angles and slices. The occlusal plane, curves, and helical axis were initially defined and displayed.

CONCLUSIONSUsing available instruments and methods, we developed the primary edition for three-dimensional simulation of the craniofacial system. However, it is far from a mature system and there is still plenty of work to be done.

Dental Occlusion ; Humans ; Imaging, Three-Dimensional ; Mandible ; physiology ; Models, Anatomic ; Skull ; Temporomandibular Joint ; physiology ; Tooth

OBJECTIVETo investigate the activities of head, neck and upper trunk muscles with mandibular movement in normal adults.

METHODSThe integral data of surface electromyography (EMG) had been recorded to analyze the activities of anterior temporal (Ta), posterior temporal (Tp), sternocleidomastoid (SCM) and trapezius (TRAP) muscles with mandibular movement in ten normal adults.

RESULTSThe former mentioned muscles acted constantly when the mandible was in the rest position. The activities of Ta, Tp and SCM muscles increased with protrusion of mandible, mouth opening, tapping, maximum clenching, and chewing movements. The amplitudes of the increased activity of these muscles were correlated significantly with each other. When the activities of Ta and Tp muscles increased to 56 times and 25 times respectively, the activity of SCM muscle increased to 5 - 6 times. The activity of trapezius muscle increased with protrusion of mandible and opening movement, but tended to stop with the maximum clenching and chewing movement. The correlations of left and right sides of the same muscles had been found.

CONCLUSIONSThe muscles of head, neck and upper trunk can act as contributors to keep the mandibular positions and take part in the mandibular movements.

Adult ; Electromyography ; Female ; Head Movements ; physiology ; Humans ; Male ; Mandible ; physiology ; Mastication ; physiology ; Movement ; Muscle, Skeletal ; physiology ; Neck Muscles ; physiology ; Range of Motion, Articular ; Shoulder ; physiology ; Temporomandibular Joint ; physiology

INTRODUCTIONTemporomandibular joint disorders (TMJDs) are caused by several factors such as anatomical, neuromuscular and psychological alterations. A relationship has been established between TMJDs and postural alterations, a type of anatomical alteration. An anterior position of the head requires hyperactivity of the posterior neck region and shoulder muscles to prevent the head from falling forward. This compensatory muscular function may cause fatigue, discomfort and trigger point activation. To our knowledge, a method for assessing human postural attitude in more than one plane has not been reported. Thus, the aim of this study was to design a methodology to measure the external human postural attitude in frontal and sagittal planes, with proper validity and reliability analyses.

METHODSThe variable postures of 78 subjects (36 men, 42 women; age 18-24 years) were evaluated. The postural attitudes of the subjects were measured in the frontal and sagittal planes, using an acromiopelvimeter, grid panel and Fox plane.

RESULTSThe method we designed for measuring postural attitudes had adequate reliability and validity, both qualitatively and quantitatively, based on Cohen's Kappa coefficient (> 0.87) and Pearson's correlation coefficient (r = 0.824, > 80%).

CONCLUSIONThis method exhibits adequate metrical properties and can therefore be used in further research on the association of human body posture with skeletal types and TMJDs.

Adolescent ; Adult ; Female ; Humans ; Male ; Movement ; physiology ; Posture ; physiology ; Reproducibility of Results ; Temporomandibular Joint Disorders ; diagnosis ; physiopathology ; Young Adult

OBJECTIVETo investigate the effect of unilateral mastication on glenoid fossae by means of animal experiment.

METHODSAn animal model of unilateral mastication was established by extracting right mandibular molars of Wistar rats. The rats were sacrificed in different period to examine the location changes of glenoid fossae through sagittal and horizontal plane.

RESULTSThe anterior points of glenoid fossae in non-masticatory side of experimental groups were more anterior than those in masticatory sides. The anterior points of the glenoid fossae of non-masticatory sides in experimental groups were more anterior than those of the same sides in the control groups after inducing unilateral mastication for two and four months. After inducing unilateral mastication for two and four months, the anterior and the posterior points of the glenoid fossae of non-masticatory sides in experimental groups became closer to the midline by comparison with masticatory sides as well as the same sides in control groups. Locations of glenoid fossae in masticatory sides showed no changes in comparison with the same side of the control groups.

CONCLUSIONThe forward and inward remodeling of the glenoid fossae can be observed after unilateral mastication was induce to the non-masticatory sides of experimental rats. It is concluded that unilateral mastication might be one of the etiologic factor of temporomandibular joint disorders.

Alveolar Process ; growth & development ; pathology ; Animals ; Facial Asymmetry ; physiopathology ; Female ; Mandible ; growth & development ; pathology ; Mandibular Condyle ; growth & development ; pathology ; Mastication ; physiology ; Maxilla ; growth & development ; Maxillofacial Development ; physiology ; Rats ; Rats, Wistar ; Temporomandibular Joint ; growth & development ; pathology ; Temporomandibular Joint Disc ; physiopathology

This study was conducted to establish a functional mandibular biomechanical model for use in the follow-up biomechanical study of the integrated and fractured mandible. The integrated and dry human mandible was used, and the corresponding maxilla and cranial base was duplicated by resin and plaster. 2-mm silicon rubber was used for simulation of the temporomandibular joint (TMJ) disc. A simulated TMJ and physiological mandibular model was developed by four pairs of muscular loadings (Masseter= 180 N, Temporalis = 190 N, Medial Pterygoideus = 120 N, Lateral Pterygoideus = 40 N) in each muscular center, and the functional loading corresponding with physiological condition was reflected and simulated more realistically when compared with that of the previously reported mandibular models which were developed by occlusion loading or by only one pair of muscles loading. In summary, we have established a functional mandibular model which can be used to analyze the biomechanical behavior in various functional conditions.
Biomechanical Phenomena ; Humans ; Mandible ; physiology ; Masseter Muscle ; anatomy & histology ; physiology ; Masticatory Muscles ; physiology ; Models, Biological ; Pterygoid Muscles ; anatomy & histology ; physiology ; Stress, Mechanical ; Temporal Muscle ; anatomy & histology ; physiology ; Temporomandibular Joint ; physiology