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At least 91 records · Page 5Linked to original sources
PubMed1998

[The evolution of the lower jaw and the jaw joint, from reptiles to man].

The evolution of the mandible shows two characteristic features: transformation of the angular, articular and square bones in reptiles into the tympanic bone, malleus and incus of the middle ear respectively; and specific volume expansion of the tooth-bearing bone which in mammals comprises the entire mandible. Posture, locomotion and mastication are the basic evolutionary factors which simultaneously provoked 1) a displacement of the temporal regions, 2) a transformation of the face lowering and widening the lower jaw and 3) an elongation of the sutures uniting the different bones in the reptile jaw bone, progressively leading to their separation and transversal orientation. These transformations were accentuated in the biped. Thus in man the temporomandibular joint is in a very lateral and elevated position near the mastoids. The mandibular condyls are elongated transversally with a medial cantilever. The medial part of the meniscus is drawn medially by the lateral pterygoid while the lateral part is drawn laterally by the temporal and masseter fibers. The ramus is oriented vertically and lies close to the cervical spine. The dental arches are displaced posteriorly on the bone and have lost their anterior abutment. The strongest occlusal forces are displaced to the posterior part of the arches and are transmitted vertically to the intra-articular meniscus. All these phenomena are termed extreme adaptations and the temporomandibular joint would (apparently) suffer if the evolution continued. The architectural features of temporomandibular joint overload can be deducted by comparison with the "ideal" architectural conditions for the craniofacial equilibrium.

Adaptation, Physiological↗
PubMed1985

Relationships between jaw pain and jaw muscle contraction level: underlying factors and treatment effectiveness.

EMG representations of jaw muscle contraction levels were measured in dental patients with TMJ problems in addition to history and physical evidence of bruxing and clenching, TMJ problems alone, bruxing and clenching, and no pain. Patients with TMJ problems plus bruxing/clenching had EMG levels similar to those with clenching and bruxing problems alone. These levels were far higher than those in the groups with similarly low TMJ problems alone and with no pain. The pain groups were normal for anxiety level and life stress. Although a third of the patients produced a conversion V pattern on the MMPI, no effect was seen on treatment effectiveness. All but a few of the mixed TMJ problem/bruxism/clenching patients and of the bruxism/clenching patients showed considerable reduction in pain through use of treatment oriented toward muscle tension awareness and relaxation. The group with TMJ problems and normal masseter muscle tension made little progress.

Anxiety↗
PubMed1987

Brain-stem perturbations during cortically evoked rhythmical jaw movements: effects of activation of brain-stem loci on jaw muscle cycle characteristics.

The purpose of the present study was to further elucidate with the use of microstimulation techniques the influences of rostral pons and midbrain loci on the neuronal networks responsible for cortically induced rhythmical jaw movement (RJM) activity in the anesthetized guinea pig and to establish if these rostral brain-stem loci are capable of modulating the timing as well as the amplitude of rhythmical digastric (DIG) EMG activity. It was found that repetitive electrical stimulation of widespread areas of the rostral pons and mid-brain produced suppression of ongoing cortically induced rhythmical EMG activity. Prior to complete EMG suppression there was a reduction in amplitude of the DIG EMG and an increase in cycle duration. Repetitive stimulation of these suppressive loci also produced a reduction in the amplitude of the short-latency DIG EMG response produced by short pulse train stimulation of the masticatory cortex. This indicates that part of the suppression of cortically induced rhythmical EMG activity was due to a reduction in excitability of the polysynaptic short-latency pathway from cortex to DIG motoneurons. Short pulse train stimulation of these brain-stem suppressive loci during various phases of the rhythmical DIG cycle produced a phase-dependent increase in duration of the ongoing perturbed cycle. The cycles following the stimulus perturbation did not show any compensatory shortening in their durations suggesting that the stimulus produced a true resetting of the cycle. These data suggest that the brain-stem loci that produce suppression of RJMs evoked by repetitive cortical stimulation can affect the excitability of the central circuits responsible for cycle oscillation and timing as well as the excitability of the polysynaptic short-latency corticotrigeminal pathway to DIG motoneurons.

Action Potentials↗
PubMed2001

Activity of jaw-opening and jaw-closing muscles and their influence on dentofacial morphological features in normal adults.

The purpose of this study was to determine the relationship between the dentofacial morphology and the function of masticatory muscles estimated by kinesiological measurements during isotonic jaw-opening (O) and closing (C) muscle contractions. We examined 26 male adult subjects who had no history of masticatory dysfunction. Three kinesiological parameters, the maximum force (F(max)), maximum velocity (V(max)) and maximum power (P(max)) were measured in both O and C muscles. Correlation analysis was performed between these parameters and dentofacial morphological features determined on lateral roentgenographic cephalograms. The F(max) (C), V(max) (O), log O/C of V(max), and P(max) (O) significantly correlated with anterior overbite. P(max) (C) significantly and negatively correlated with SN-ArG. Furthermore, log O/C of P(max) significantly and negatively correlated with SNA, SNB and ArG/GMe, and positively with SN-ArG. These results, combined with our previous findings that electromyographic muscle activity during isometric contraction correlated significantly with mandibular morphology, indicate that the dentofacial morphology is influenced by the function of both O and C muscles.

Adult↗
PubMedDate not supplied

Immediate effect of occlusal contact pattern in lateral jaw position on the EMG activity in jaw-elevator muscles in humans.

PURPOSE: The aim of this study was to investigate the effect of experimental alterations of nonworking-side occlusal contacts on jaw-elevator muscle activity. MATERIALS AND METHODS: Individual devices were fabricated to simulate various lateral occlusal relationships. Twelve human subjects were asked to carry out submaximal lateral clenching, and electromyographic (EMG) activity of the masseter and anterior and posterior temporalis muscles was measured. RESULTS: Clenching in a lateral mandibular position under natural conditions induced an activity pattern with a clear dominance of the anterior and posterior temporalis muscles on the working side. Working-side dominance in the anterior temporalis was reduced moderately when an experimental nonworking-side occlusal contact was added. Dominance decreased dramatically when an experimental nonworking-side interference was added. The working-side activity in the posterior temporalis was also reduced dramatically by an experimental nonworking-side interference, but not by a nonworking-side occlusal contact. None of the experimental contact patterns had a significant effect on the masseter activity. CONCLUSION: These results suggest that the nonworking-side occlusal contacts have a significant effect on clenching-induced temporalis muscle activity.

Adult↗
PubMed1977

Biologic laws governing functions of muscles that move the mandible. Part IV. Degree of jaw separation and potential for maximum jaw separation.

Accurate diagnosis and treatment of the gnathostomatic system require an understanding of both its biomechanics and its physiology. Clinically, the treatment consists of modifying the existing occlusal program to relieve stress from distressed tissues. The objective of treatment is to effect a neuromuscular release of the mandible. This may be accomplished by (1) equilibration of the natural occlusion, (2) orthodontics, (3) restorative procedures, or (4) surgery. Most frequently, however, the treatment entails some combination of these procedures. The criteria for success of treatment are not determined by the method or technique employed but by the neuromuscular response that the treatment produces. The purpose of this article is not to suggest which occlusal scheme produces the most favorable muscle response in the gnathostomatic tissues. Neither is an objective of this article to teach the mandible-manipulation techniques that are needed to identify occlusal irritants, perform occlusal equilibrations, or obtain accurate centric relation recores. The objective of this article is to emphasize that there are definite principles by which the muscles respond to occlusal contacts. Occlusal contacts can excite bruxism and the sequelae to bruxism. Knowledge of the laws which govern functions of the muscles that move the mandible enables the dentist to acquire the mandibular-manipulation skills that are necessary for the effective diagnosis and treatment of occlusal conditions.

Biology↗
PubMed1988

Atypical simple bone cysts of the jaws. II: A possible association with benign fibro-osseous (cemental) lesions of the jaws.

Four cases are described of simple bone cysts of the mandible arising concurrently with benign fibro-osseous (cemental) lesions. Previous reports of such findings, and a possible relationship to the so-called 'cementoma' of the long bones, are considered. The relevance of this to the aetiology is addressed, and it is suggested that at least some cases diagnosed as simple bone cysts are closely related to the fibro-osseous lesions.

Adult↗