Observations on the growth of temporalis muscle: A 3D CT imaging study.

This study investigates the hypothesis that there is, during childhood, a disproportionate age-related expansion of the origin of temporalis muscle compared to the growth of the underlying skull. Lateral projections of 50 randomly selected 3D reformatted computerized tomographic (CT) scans (yielding 100 temporalis muscles) of children aged >0.6 to 15 years scanned for conditions that did not affect the shape of their head or face were windowed to provide the optimum delineation of temporalis muscle against the underlying bone. Vertical and anterior-posterior measurements of the muscle made independently by two observers were compared with those of the skull along the same planes. The development of the anterior temporal crest was also assessed. The intraclass correlation coefficient for differences in the measurements made by each observer ranged from good to excellent. The muscle and skull measurements were used to produce a ratio of muscle-to-skull lengths in both vertical and horizontal planes. Analysis of these ratios showed a statistically significant increase in the vertical reach of temporalis with age (Pearson correlation coefficient (R) =0.7826; p < 0.05) compared to the growth of the skull along the planes chosen for the study-but less so for its horizontal reach (R = 0.5073. p < .001). There were no significant differences between right/left or male/female measurements. There was also a substantial level of agreement between both observers in their assessment of the development of the temporal crest. The mean age of children in whom a fully formed temporal crest could be identified (10.6 years) was significantly greater (p < 0.001) than that of the 38 remaining subjects (6.0 years). These results confirm that there is, in response to increased masticatory/dietary demands during childhood, a disproportionate increase in the vertical and (to a lesser extent) horizontal reach of temporalis muscle over its origin from the temporal, frontal, sphenoid, and parietal bones compared the growth of the skull. It is proposed that surgical interference with this normal process is responsible for the soft tissue component of late-developing deformity that can occur following early (at 6-18 months of age) operations for the correction of trigonocephalic head shape associated with metopic synostosis.

The effect of the Botulinum toxin-A on craniofacial development: an experimental study.

In this study, we developed a novel experimental model to evaluate muscular action on bone formation and remodeling by the help of Botulinum toxin-A (BTX). Forty-nine 15-day-old male Wistar rats were put into 4 groups randomly. Group 1 was the control group. BTX 0.4 IU (0.05 mL) was injected into the right masseter muscle in group 2 and into right temporalis muscle in group 3. The same volume of sterile saline was given into the both above-mentioned muscles in group 4. At the end of the fourth month, all animals were killed. Histology and weight of the masseter and temporalis muscles were studied. Thirty different osteometric measurements were also taken from skulls. Significant atrophy in BTX injected muscles was observed in groups 2 and 3. In group 4 (saline injection), only few osteometric measurements were significantly reduced, indicating the effect of the injection itself. Both groups 2 and 3 have apparent decrease in nasal bone, premaxilla, maxilla, and zygomatic dimensions on the injected side. When masseter group was compared with control and saline groups, no significant difference was found in skull base dimensions and mandibular length. In contrast, temporal group has also shown significant decrease in skull base dimensions. Our conclusions are as follows: (1) With this model, it is possible to study muscular action on bone formation and modeling without any surgical intervention, that is, by avoiding surgical artifacts, such as scar and contracture; (2) denervation of the skeletal muscles with BTX during the growing phase does effect bone development in a negative way; (3) pediatric use of the BTX deserves reevaluation under the light of these findings.

Long-term registration of daily jaw muscle activity in juvenile rabbits.

Understanding control of muscles during various tasks and their adaptive changes requires information on all motor behavior used throughout the day. The total duration of muscle activity depends on the magnitude of its activation and can change during maturation. Therefore, the purpose of this study was to examine the duration of muscle activity (i.e. duty time) exceeding various activity levels in maturing jaw muscles. A telemetric device was implanted into nine juvenile male New Zealand White rabbits to continuously record muscle activity during maturation weeks 9-14. Electrodes were inserted into digastric, superficial and deep masseter, medial pterygoid, and temporalis muscles. Duty times (expressed as a percentage of time) were calculated for activation exceeding different levels (5-90%) of EMG peak activity per 24-h period. At 10 weeks of age, for activation exceeding the 5% level, the duty time of the temporalis (20.0+/-5.2%) was statistically significantly higher than that of the medial pterygoid (11.2+/-1.5%), digastric (11.0+/-5.1%), superficial (12.6+/-5.6%), and deep masseter (8.6+/-5.5%). Duty times declined with increasing activity level. For activation exceeding the 40% level the duty times of the superficial masseter and medial pterygoid were significantly higher than those of the other muscles. During maturation none of the muscles showed a significant change in duty time. However, for activation exceeding the 5% level, the inter-individual variation in duty time decreased significantly for the digastric, and superficial and deep masseter.

Effects of post-natal serotonin levels on craniofacial complex.

Although the role of serotonin (5-hydroxytryptamine or 5-HT) in pre-natal craniofacial growth and development has been studied, no research has been done on the effects of serotonin on post-natal craniofacial growth and development. The following experimental question was tested: What effect does increasing in vivo serotonin levels adjacent to trigeminal motoneurons have on post-natal craniofacial structures in young, actively growing rats? Forty male Sprague-Dawley rats were divided into 4 experimental groups (10% serotonin microspheres, 15% serotonin microspheres, blank microspheres, sham surgeries) and underwent stereotactic neurosurgery at post-natal day 35; 5 rats of each group were killed at 14 and 21 post-surgical days for data collection. Statistical analyses by mixed-model, 4 x 2 repeated-measures ANOVA, and post hoc Fisher LSD tests revealed significant (P < or = 0.05, 0.01) differences between groups and sides for muscle weight, cranial dimension, and TMJ dimension data. Data described here indicate that significant alterations of post-natal craniofacial structures can be caused by altered in vivo levels of serotonin adjacent to trigeminal motoneurons.

Avaliaçäo cefalométrica e eletromiográfica em pacientes jovens submetidos à expansäo rápida da maxila / Cephalometric and eletromiographic evaluation in young patients submitted to rapid expansion of the maxila

A expansäo rápida da maxila introduz modificaçöes oclusais nítidas e alteraçöes esqueléticas, com possíveis reflexos nos músculos elevadores da mandíbula. O objetivo deste trabalho foi verificar cefalometricamente as alteraçöes dentoesqueléticas ocorridas e determinar o comportamento neurofisiológico dos músculos masséteres e temporais, por meio da duraçäo do período de silêncio eletromiográfico (PS), induzido pela percussäo do mento. A amostra consistiu de 15 pacientes leucodermas, brasileiros, na faixa etária de 11 a 17 anos, com atresia lateral da maxila e submetidos à expansäo rápida deste osso; avaliados nas fases pré e pós-expansäo, pós-contençäo e 1 ano após a expansäo. Os resultados obtidos e analisados estatisticamente permitiram-nos concluir que: - as alteraçöes introduzidas pela expansäo rápida mostraram-se näo significantes estatisticamente, com tendencia à recidiva. O deslocamento para baixo da maxila, associado a uma discreta extrusäo dos primeiros molares superiores, promoveram pequenas alteraçöes verticais na face, com consequente aumento médio de 2 mm na altura facial ântero-inferior e de 1,5º na convexidade facial. A verticalizaçäo dos incisivos superiores (ñ1º), com influência sobre o lábio correspondente, induziu o ângulo nasolabial a uma suave tendência de aumento. A ligeira vestibulizaçäo dos incisivos inferiores mostrou-se inconclusiva pela possível influência da mecânica ortodôntica corretiva. - a duraçäo média do período de silêncio eletromiográfico, nas referidas fases estudadas, foi de: 40,01, 52,11, 45,67, e 40,80 ms, respectivamente. Possivelmente influenciada pelo discreto aumento na dimensäo vertical, a duraçäo do PS apresentou uma tendência à reduçäo, conforme a condiçäo oclusal tornou-se mais favorável. Este método mostrou-se capaz de evidenciar quantitativamente o grau de equilíbrio neurofisiológico dos músculos em estudo

Growth patterns of the rabbit masticatory muscles.

The post-natal growth of the masticatory muscles in the rabbit was examined. By means of anatomical dissection and measurement, total muscle length, muscle fiber length, and muscle weight were determined in animals varying in age between one week and 36 months and exhibiting a 50-fold weight increase. Growth data were fitted by linear regression models with facial skull length used as the independent variable. Many deviations occur from size-dependent isometric growth. The muscles can be divided into three groups, according to their pattern of weight increase: The jaw openers grow negatively allometrically, and their contribution to total muscle weight decreases with time; the temporal muscle grows negatively allometrically, but its relative weight proportion remains about the same; the masseter and medial pterygoid muscles have positively allometric growth, and their contribution to total muscle weight increases strongly. Generally, the length of the muscles and of their fibers increases at lower rates than does the length of the facial skull. After weaning, the rate of longitudinal growth drops steeply in some muscles. Total fiber area or physiological cross-section (PCS) of muscles is computed from weight and fiber length. It increases positively allometrically in the jaw closers and negatively allometrically in the jaw openers. In the lateral pterygoid muscle, the increase of PCS changes from negatively- to positively-allometric growth after weaning. The study demonstrates that individual oral muscles follow different patterns of longitudinal and cross-sectional growth, so that their functional capacities (force, range of contraction) and mutual functional relationships are age-dependent.

[Postnatal development of the masticatory muscles of the Wistar rat (Rattus norvegicus Berkenhout). A histochemical study]. / Postnatale Entwicklung der Kaumuskulatur der Wistarratte (Rattus norvegicus BERKENHOUT). Eine histochemische Studie.

Muscle biopsies of the mandible adductors of the Wistar rat (Rattus norvegicus Berkenhout) have been analyzed enzyme-histochemically for the investigation of the postnatal development (42.-126. d post partum) of their muscle fibers with special regards to the fiber types. The following methods have been used in this investigation: myofibrillar adenosine triphosphatase (ATP-ase) with different pre-incubations, Sudan black B (triglycerides), periodic acid-Schiff reagent (PAS) (glycogen), Gomori modified Trichrome staining. Quantitative analysis of muscle fibre-type composition and muscle fibre size was done from different regions of muscle sections. Estimation of the fiber size was carried out by measuring the minimum diameter of each type of muscle fibre.

Frequency analyses of EMG power spectra of anterior temporal and masseter muscles in children and adults.

To study the functional change of masticatory muscles during growth and development, frequency analyses of surface electromyogram (EMG) power spectra were carried out. The subjects were six children (five males and one female), aged 4.5 +/- 0.2 years, having full deciduous dentition (Hellman's dental age IIA) and six adults (four males and two females), aged 27.7 +/- 3.8 years, having full permanent dentition. EMG signals were recorded bilaterally by using bipolar silver-surface electrodes from the anterior temporal and masseter muscles while the subjects were chewing gum and while performing maximum clenching in the intercuspal position. A fast Fourier transform algorithm was used to obtain the power-spectral density function and the power spectra of the EMG signals. Since the total power value from 62.5 to 1000 Hz was 100 percent, the frequencies at 25, 50, 75, and 90 percent of the cumulative power were calculated. The results showed that the frequencies at every percent of the cumulative power were age-dependent and that the EMG power spectra patterns in adult muscles were shifted to significantly lower frequencies than those in child muscles. The shift was probably caused by differences in the proportion of fiber type and fiber size between muscles of children and adults.

Postnatal development of the mouse temporal muscle and effects of a fine-grained diet on the muscle spindle.

The postnatal development of the mouse temporal muscle and effects of a fine-grained diet on muscle spindles were investigated. On d 25 after birth, 3 types of extrafusal muscle fibers could be distinguished on the basis of SDH activity, but not on the basis of their diameters. And in 50-d-old mice, 3 types of the muscle fibers had different diameters each other. In intrafusal muscle fibers, the postnatal changes of the SDH activity were similar to those of extrafusal muscle fibers, but the diameter distribution showed unimodal statistical distribution from 10th to 50th postnatal day. On the other hand, in control 180-d-old mice, 80 percent of muscle spindles in the temporal muscle had complete annulospiral endings, but the ratio of muscle spindles with complete annulospiral endings was decreased significantly in mice fed a fine-grained diet. The diet also decreased the diameter of the endings significantly. These results suggest that the main changes in the morphological and functional properties of the mouse temporal muscle occur in during and early after weaning period, and that normal mastication is needed to maintain the homeostatic condition of the mouse temporal muscle.

[Animal experiment studies on the effect of unilateral tooth extraction on the growth of the skull and masticatory muscles. III. The masticatory muscles]. / Tierexperimentelle Untersuchungen über den Einfluss von unilateralen Zahnentfernungen auf das Wachstum des Schädels und der Kaumuskulatur. III. Kaumuskulatur (Schluss).

All continuous teeth were unilaterally extracted on the right side of the upper and lower jaws of 57 male and female Vietnamese belly pig. The animals were slaughtered 6, 7, 8, 9, 10, 11 and 12 after the extraction. Our investigations into quantitative changes in the masticatory musculature after unilateral extraction showed the dry weight of the musculature on the extraction side was reduced. This reduction was greatest in the case of the M. temporalis. The findings relating to the muscles are consistent with the results of the skull evaluations reported in the first 2 publications, with indicated that tooth extraction leads to only local changes in the jaw during postnatal development. The findings published in the 3 publications of this series relating to the bones and muscles are discussed.

Growth and allometry in primate masticatory muscles.

A study of the dry weight of primate and non-primate masticatory musculature permitted possible allometric and ontogenetic influences on this musculature to be explored. Using weight as an indicator of adult body size, all of the masticatory muscles examined (anterior temporalis, posterior temporalis, masseter, medial pterygoid, lateral pterygoid, digastrics, and total adductor mass) are isometric. This is true even when prosimians and non-primates are removed from consideration, leaving only adult anthropoid primates. Thus, size-related changes do not affect the masticatory musculature of anthropoids differently from the musculature of examined prosimians and non-primates. However, other measures of body size (skull length, head and body length) reveal a different picture. Yet, irrespective of the indicator of body size chosen, the allometric properties of the masticatory muscles appear similar and the fluctuations of the various muscle indices therefore reflect functional changes, and are not caused by allometry. Exudate-eating and frugivory are discussed in relation to body size and the development of the mandibular depressor muscles. The logs of the masticatory muscles do not show a significant correlation with age, except when species are followed across age grades. For the five anthropoid species for which this is possible, the medial and lateral pterygoid and digastric muscles are still not correlated with age. When all examined species are considered, some muscle ratios correlate significantly with age. Following anthropoid species across age grades singles out an early surge in growth of the medial pterygoid muscle over the masseter muscle, a situation which was apparent also in the general age correlation.