Computertomographische Untersuchung von Muskelvolumen, -querschnitt und -dichte bei Dysgnathiepatienten

Chewing pattern and muscular activation in open bite patients

Different studies have indicated, in open bite patients, that masticatory muscles tend to generate a small maximum bite force and to show a reduced cross-sectional area with a lower EMG activity. The aim of this study was to evaluate the kinematics parameters of the chewing cycles and the activation of masseters and anterior temporalis muscles of patients with anterior dental open bite malocclusion. There have been no previous reports evaluating both kinematic values and EMG activity of patients with anterior open bite during chewing. Fifty-two young patients (23 boys and 29 girls; mean age±SD 11.5±1.2 and 10.2±1.6years, respectively) with anterior open bite malocclusion and 21 subjects with normal occlusion were selected for the study. Kinematics parameters and surface electromyography (EMG) were simultaneously recorded during chewing a hard bolus with a kinesiograph K7-I Myotronics-Usa. The results showed a statistically significant difference between the open bite patients and the control group for a narrower chewing pattern, a shorter total and closing duration of the chewing pattern, a lower peak of both the anterior temporalis and the masseter of the bolus side. In this study, it has been observed that open bite patients, lacking the inputs from the anterior guidance, that are considered important information for establishing the motor scheme of the chewing pattern, show narrower chewing pattern, shorter lasting chewing cycles and lower muscular activation with respect to the control group.

The adaptive response of jaw muscles to varying functional demands

Jaw muscles are versatile entities that are able to adapt their anatomical characteristics, such as size, cross-sectional area, and fibre properties, to altered functional demands. The dynamic nature of muscle fibres allows them to change their phenotype to optimize the required contractile function while minimizing energy use. Changes in these anatomical parameters are associated with changes in neuromuscular activity as the pattern of muscle activation by the central nervous system plays an important role in the modulation of muscle properties. This review summarizes the adaptive response of jaw muscles to various stimuli or perturbations in the orofacial system and addresses general changes in muscles as they adapt, specific adaptive changes in jaw muscles under various physiologic and pathologic conditions, and their adaptive response to non-surgical and surgical therapeutic interventions. Although the jaw muscles are used concertedly in the masticatory system, their adaptive changes are not always uniform and vary with the nature, intensity, and duration of the stimulus. In general, stretch, increases neuromuscular activity, and resistance training result in hypertrophy, elicits increases in mitochondrial content and cross-sectional area of the fibres, and may change the fibre-type composition of the muscle towards a larger percentage of slow-type fibres. In contrast, changes in the opposite direction occur when neuromuscular activity is reduced, the muscle is immobilized in a shortened position, or paralysed. The broad range of stimuli that affect the properties of jaw muscles might help explain the large variability in the anatomical and physiological characteristics found among individuals, muscles, and muscle portions.

Myosin heavy chain mRNA isoforms in masseter muscle before and after orthognathic surgery

OBJECTIVES

Orthognathic surgery leads to changed jaw position and force vector of mastication to which the muscles must adapt. The aim of the present study was to determine the relative expression of myosin heavy chain (MyHC) messenger RNA (mRNA) isoforms in different types of human masseter muscle fiber under consideration of change in the number of occlusal contacts before and 6 months after surgery.

STUDY DESIGN

Muscle biopsies were taken from the anterior and posterior parts of both sides in 30 patients with prognathic and retrognathic mandibles. Specific mRNA MyHC analysis was made by real-time polymerase chain reaction to quantify the isoforms I, IIa, and IId/x.

RESULTS

There was a shift in the relative content from type I (46% before, 37% after) to type IIa (29% before, 42% after). This shift correlates with number of teeth in occlusion.

CONCLUSIONS

Correlation between isoform shift and number of teeth in occlusion indicates higher mastication force which stabilizes the treatment result.