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[Fundamental properties of the human lateral pterygoid muscle activity and quantitative observation in relation to vertical dimension and bite force].

The purpose of this study is to investigate the fundamental property of the superior head of the lateral pterygoid muscle (LPT) of the human beings. The experiments were performed on 6 subjects. Electromyographic activity of the superior head of LPT were simultaneously recorded with masseter, temporal and digastric muscle. The findings may be summarized as follows: 1. Superior head of LPT showed the maximum activity during closing and clenching. 2. Superior head of LPT showed remarkable tonic activity at rest position and notable activity during swallowing and passive retrusion. 3. Superior head of LPT activity was related to vertical dimension and bite force quantitatively, but such relationship was quite different from masseter and temporal muscle. 4. Jaw-jerk reflex was evoked by mechanical chin tap in the superior head of LPT, masseter and temporal muscle showing identical time course. 5. Periodontal excitatory reflex was evoked by mechanical tooth stimulation in the superior head of LPT and temporal muscle. From these findings it was concluded that superior head of LPT was qualitatively similar to but quantitatively distinct from jaw closing muscles such as masseter and temporal muscle.

Bite Force↗

Ultrasound image of human masseter muscle related to bite force, electromyography, facial morphology, and occlusal factors.

The thickness of the human masseter muscle, corresponding approximately to a cross-section at the most bulky part of the superficial portion, was measured by ultrasound scanning at three sites 1 cm apart. The study included 13 women, 21-28 yr of age, with a minimum of 24 teeth and without craniomandibular disorders. Ultrasonography produced a well-defined depiction of the muscle with distinct tendinous structures. The average thickness at the measuring sites varied from 8.83 to 11.08 mm with the muscle relaxed, and increased significantly during contraction to average values between 9.84 and 12.57 mm. The study showed a connection between measures of masseter thickness and function of the muscle, as well as parameters generally associated with masseter muscle function. Muscle thickness at the voluminous anterior part of the superficial portion was systematically and significantly correlated to bite force, occlusal tooth contact and cephalometric data (anterior face height, vertical jaw relation and mandibular inclination). In conclusion, ultrasound scanning gave an uncomplicated and a reproducible access to parameters of jaw muscle function and its interaction with the craniomandibular system.

Adult↗

Comparison of jaw-muscle bite-force cross-sections obtained by means of magnetic resonance imaging and high-resolution CT scanning.

Cross-sectional areas of the jaw muscles were determined by means of magnetic resonance imaging (MRI) in 12 healthy adult male subjects. These findings were compared with the cross-sectional areas of the jaw muscles of the same subjects, obtained by means of computer tomography (CT) in a previous study (Weijs and Hillen, 1985). Significant correlations (r greater than 0.7) were found between the CT and MRI cross-sections of the masseter, medial pterygoid, and temporalis muscles. The low correlation between the CT and MRI cross-sections of the lateral pterygoid muscle could be explained by the different imaging techniques (slice thickness) of MRI and CT scanning. CT and MRI cross-sectional areas of the masseter and medial pterygoid muscle (but not the temporalis muscle) showed highly positive and significant correlations with the maximal voluntary bite force. In living subjects, the cross-sections of the masseter and medial pterygoid muscles can be visualized with CT and MRI. Compared with CT, MRI has some advantages, such as the absence of adverse effects (no radiation) and the excellent soft-tissue imaging. Furthermore, a series of frontal, horizontal, sagittal, and angulated MRI scans can be made without modification of the patient's position, facilitating reconstruction of the jaw muscles.

Adult↗

Forces and moments generated at the dental incisors during forceful biting in humans.

A miniature load sensor capable of measuring all forces and all moments simultaneously at a single location in space was used to assess the magnitude and direction of loads that affect the dental incisors during forceful, static biting. While prior approaches have not measured all necessary six degrees of freedom during biting, the complete set of loads is needed to serve as realistic boundary conditions for analytical or computational models of mandibular mechanics. Four subjects were asked to perform controlled and repetitive edge-to-edge incisal biting activities. Customized devices were used to rigidly hold the load sensor in place at pre-specified tooth separations of less than 1 mm. The results yielded force resultants with a magnitude range of 24.5 to 28.4 N. This range was intentionally limited in magnitude to avoid damage to the internal strain gauge assembly of the sensor. In all cases, the highest force component was oriented upwards. An additional simultaneous moment resultant (range: 8.9-17.0 N cm) with a main moment component oriented backwards and downwards towards the oral cavity was also detected. These data suggest that in order for the biting loads to be composed of six DOF, the remaining forces acting on the mandibular force system (i.e. muscular and/or articular) may indeed be non-coplanar and non-concurrent. Although useful for static biting activities, the bulk of the sensor would probably preclude meaningful measurements during dynamic events such as chewing or swallowing.

Adult↗

Sensory components of bite-force response in the rat.

The relative roles of proprioceptive input from the muscles of mastication and the periodontal pressure receptor input from membranes surrounding upper and lower incisors were assessed in animals trained to bite with peak forces within certain bands of forces for water reinforcement. Measures of performance obtained from animals before and after chronic bilateral lesions were made in the mesencephalic nucleus of the trigeminal nerve suggest that proprioceptive input does not play a major role in the differentiation of bite force. However, measures of performance obtained before and after acute peripheral blocking of input from the pressure receptors indicate that these pressure receptors are the main source of input used in bite-force differentiation.

Anesthesia, Local↗

Changes in bite force and muscle forces in the upper extremities after counter irritation.

Today, physical therapy is recognized as an effective, reversible, and conservative treatment for temporomandibular disorders (TMD). The purpose of this investigation is to explore the feasibility of utilizing counter irritation with ischemic pain at a remote site outside of the head and neck region as a method for restoring muscle force in a course of physical therapy. Twenty healthy asymptomatic female subjects were recruited for this study. The experiments were performed over two days, with the two experimental days randomly assigned to the experiment performed with or without counter irritation. The counter irritation was applied to the subject's left hand using a submaximal effort tourniquet procedure. The maximal bite, finger-pinch, and handgrip forces were measured on the right side, and the results from the days with and without the counter irritation were compared. As a result, a significantly higher mean maximal bite force and a trend toward higher finger-pinch force were observed with the irritation than without the irritation, while there was no significant difference in the handgrip force. These findings indicate that counter irritation outside of the head and neck may be useful for increasing bite force, and may be applicable in the treatment of TMD for the restoration of masticatory muscle force.

Adolescent↗

The effect of maximum biting force and bone loss upon masticatory function and dietary selection of the elderly.

Simple methods are described for measuring masticatory effectiveness--the percentage of sugar chewed out of chewing gum in 20 strokes--and the height of residual mandibular bone using callipers. Both are objective methods, they are acceptable to the elderly, appropriate for denture wearers and practicable for use in domiciliary surveys. Using these and other methods, the masticatory effectiveness of housebound pensioners is shown to relate to maximum biting force, denture quality, remaining mandibular bone and dietary selection. However, opinions on the difficulty of mastication are completely unrelated to any of these measures. The level of compensation for inadequate mastication is indicated by the percentage of difficult foods eaten by geriatric hospital inpatients: there was complete overlap of percentages in those endentulous patients using dentures and those without dentures. Presumably many of these patients had adapted to swallowing very poorly chewed food. The contrasts shown between hospital inpatients and old people still at home indicate the progressive consequences of physical and neurological deterioration.

Adult↗

[Condylar displacement and mandibular bending deformation due to bite force].

The purpose of this study was to investigate the influence of the difference of the biting pivot positions, vertical dimensions and mandibular positions on the condylar displacement during clenching. The condylar displacement was measured by the Pantograph using the point of condyle on the Kinematic Axis as the representative and the Path of the Kinematic Axis (PKA) as the standard for the judgement of the displacement. The bending deformation of the mandible was also measured by a multi-vision and image analyzing system in order to correct its influence on the condylar displacement measured. The results were as follows: 1. The direction and magnitude of the condylar displacement changed with the biting pivot position. The bilateral condyles moved upwards deviating from the PKA when clenching on the bilateral 2nd-molar or the bi-or unilateral canine teeth; Whereas the biting-side condyle moved downwards and the idling condyle either moved upwards deviating from the PKA or backwards along the PKA when clenching on the unilateral 2nd-molar. 2. The displacement of the idling condyle was multi-directional when clenching on the habitual closure whereas it was unidirectional and of a smaller magnitude when clenching on the most retruded closure. 3. When clenching on the unilateral 2nd-molar, the mandible on the non-pivot side had an inward and upward bending deformation and the arch width decreased. It can be inferred that the actual idling condylar displacement was more inward and upward than that measured by the Pantograph.

Adult↗

[Equipment for measuring dental bite force (gnathodynamometers].

The authors provide the main technical characteristics of 6 experimental outfits for measuring dental bite. In the outfits, use is made of transducers of different types: capacitive, tensoresistive, fitted with a sensitive element in the form of a beam of equal resistance and converters of varied types. The weight of the outfits is from 10 to 30 g. It is assumed that the industrial manufacture of the most promising models may be commenced after the completion of experimental work.

Bite Force↗