Development of medial pterygoid muscle fibers in rabbits fed with a liquid diet.

OBJECTIVE: This study aimed to investigate the influence of decreased functional load on the medial pterygoid muscle during mastication in rabbits fed with a liquid-diet. MATERIALS AND METHODS: Medial pterygoid muscles from 54 rabbits (solid- and liquid-diet groups, n=48; unweaned group, n=6) were histochemically examined at 4, 9, 12, 18, and 33 weeks after birth. Six fiber types (I, IC, IIC, IIA, IIAB, and IIB) were distinguished via mATPase staining. RESULTS: Significant increases in the diameters of all fiber types were seen up to 33 weeks of age in the solid-diet group; however, no significant increase was noted in fiber types I and IC, from 4 to 33 weeks of age, in the liquid-diet group. The proportion of slow fibers increased up to 12 weeks followed by an increase in the number of fast fibers in the solid-diet group, whereas in the liquid-diet group, the number of slow fiber declined after weaning. CONCLUSIONS: Liquid-diet consumption caused muscle fiber atrophy and an increase in the number of fast fibers during early developmental stages after weaning. Furthermore, the growth pattern of the medial pterygoid muscle in the liquid-diet group was different from that in the solid-diet group.

Histochemical study of rabbit medial pterygoid muscle during postnatal development.

The medial pterygoid muscle is a layered structure like the masseter muscle. This study aimed at investigating the regional differences in fiber type composition and fiber diameter of the medial pterygoid muscle in the rabbit from birth until 33 weeks of age. Histochemical analysis of the medial pterygoid muscle was performed during five developmental stages (4, 9, 12, 18, and 33 weeks after birth) in 30 male Japanese white rabbits. Six fiber types (I, IC, IIC, IIA, IIAB, and IIB) were identified by mATPase staining. An increase in diameter was observed in fiber types I and IC until 9 weeks of age, and in fiber types IIC, IIA, IIAB, and IIB until 33 weeks of age. No significant differences in fiber diameter were noted in the different regions of the pterygoid muscle. Moderate fast to slow fiber type shifts occurred from weeks 4-12; thereafter, a rapid slow to fast fiber type shift was observed. Significant differences in fiber type composition based on regional differences were noted at 4 weeks of age. However, there was no difference in fiber type composition between regions at 33 weeks. In conclusion, it was clear that the diameter and proportion of fast fibers had increased even after reaching sexual maturity in rabbits. In addition, the medial pterygoid muscle tissues appeared to be homogenous at 33 weeks of age with very few differences between regions.

Percentage of lateral pterygoid muscle inserted in the disc of human temporomandibular joint / Porcentaje del músculo pterigoideo lateral inserto en el disco de la articulación temporomandibular humana

Insertion of the upper head of the lateral pterygoid (UHLP) in the temporomandibular joint disc (TMJ) has been linked to anterior displacement of the disc and temporomandibular disfunction. The aim of this study was to determine in human adults, the percentage of muscle fiber in the upper head of the lateral pterygoid muscle inserted in the articular disc. A systematic review of the literature was designed beginning with articles published in Medline, Lilacs and Scielo data bases between the years 1990 and 2010. Key words "Lateral Pterygoid Muscle" and Pterygoid Lateral Muscle" were used, and the term MeSH "Pterygoid Muscle" with Boolean OR "Lateral Ptrerygoid Muscle" AND "Insertion" and the free terms "Pterygoid Lateral Muscle Disc Articular" and "Pterygoid lateral Muscle Meniscus". Of the 156 articles obtained and analyzed, 18 articles meeting eligibility criteria were selected. Based on those articles the percentage of insertion of the CSPL in the TMJ disc was evaluated, each one was subsequently assigned a level of evidence according to OCEBM Oxford Centre Evidence Based Medicine. Only four articles answered the research inquiry, three studies were histological and one used imaging techniques with cross section slices with an adequate evidence level (1B). However, results differed with insertion percentages from 2 percent to 69.8 percent being reported in the superior head of the lateral pterygoid muscle in the articular disc.

La actividad de la inserción de la cabeza superior del pterigoideo lateral (CSPL) en el disco de la articulación temporomandibular (ATM) ha sido vinculada al desplazamiento anterior del disco y disfunción temporomandibular. El propósito de este estudio fue determinar el porcentaje de fibras musculares de la cabeza superior del músculo pterigoideo lateral que se insertan en el disco articular, en humanos adultos. Se diseñó una revisión sistemática de la literatura a partir de artículos primarios publicados en las bases de datos Medline, Lilacs y Scielo entre los años 1990 y 2010. Se utilizaron las palabras clave "Músculo Pterigoideo Lateral" y "Pterygoid Lateral Muscle", el Término MeSH: "Pterygoid Muscle" con los boleanos OR "Lateral Pterygoid Muscle" AND "Insertion" y los Términos Libres: "Pterygoid Lateral Muscle Disc Articular" y "Pterygoid lateral Muscle Meniscus". Se obtuvieron 156 artículos, los cuales fueron analizados y se seleccionaron 18 que cumplieron con los criterios de elegibilidad. En base a estos artículos se evaluó el porcentaje de inserción de la CSPL en el disco de la ATM, posteriormente a cada uno se les otorgó un nivel de evidencia de acuerdo a la clasificación de Oxford Centre Evidence Based Medicine (OCEBM). Solo 4 artículos respondieron a la pregunta de investigación, 3 estudios fueron histológicos y 1 imagenológico, todos con diseños de cortes transversales con buen nivel de evidencia (1b). Sin embargo los resultados fueron disímiles, reportándose porcentajes de inserción del 2 al 69,8 por ciento de la cabeza superior del pterigoideo lateral en el disco articular.

[Comparative morphometric analysis of structural organization of separate heads of the human lateral pterygoid muscle during prenatal period and the first 3 years of the postnatal period].

It was discovered some features in structure and differentiation of different types of the muscular fibers in each of the two heads of the lateral pterygoid muscle during ontogenesis. Taken characteristics gave possibility to think about different functional significance of data of structure in action of the temporomandibular joint of a man.

Expression of unique and developmental myosin heavy chain isoforms in adult human digastric muscle.

Digastric muscle (DGM) is a powerful jaw-opening muscle that participates in chewing, swallowing, breathing, and speech. For better understanding of its contractile properties, five pairs of adult human DGMs were obtained from autopsies and processed with immunocytochemistry and/or immunoblotting. Monoclonal antibodies against alpha-cardiac, slow tonic, neonatal, and embryonic myosin heavy chain (MHC) isoforms were employed to determine whether the DGM fibers contain these MHC isoforms, which have previously been demonstrated in restricted specialized craniocervical skeletal muscles but have not been reported in normal adult human trunk and limb muscles. The results showed expression of all these MHC isoforms in adult human DGMs. About half of the fibers reacted positively to the antibody specific for the alpha-cardiac MHC isoform in DGMs, and the number of these fibers decreased with age. Slow tonic MHC isoform containing fibers accounted for 19% of the total fiber population. Both the alpha-cardiac and slow tonic MHC isoforms were found to coexist mainly with the slow twitch MHC isoform in a fiber. A few DGM fibers expressed the embryonic or neonatal MHC isoform. The findings suggest that human DGM fibers may be specialized to facilitate performance of complex motor behaviors in the upper airway and digestive tract.

Condyle-fossa modifications and muscle interactions during herbst treatment, part 1. New technological methods.

Changes in the condyle, the glenoid fossa, and the muscles of mastication were investigated in subjects undergoing continuous orthopedic advancement of the mandible with a Herbst-block appliance. The total sample consisted of 56 subjects and included 15 nonhuman primates (in the middle mixed, early permanent, and permanent dentitions), 17 human Herbst patients in the early permanent dentition, and 24 human controls from the Burlington Growth Center. The 8 nonhuman primates in the middle mixed dentition were the focus of this study. Mandibular advancement was obtained progressively in 5 animals by adding stops to the telescopic arms of fixed functional Herbst appliances with occlusal coverage; activations of 5.0 mm, 7.0 mm, and 8.0 mm were achieved. Two primates served as controls, and the third was a sham control. Two experimental animals and the 2 controls also wore surgically implanted electromyographic electrodes in the superior and inferior heads of the lateral pterygoid muscles and in the superficial masseter and anterior digastric muscles. Changes in condylar growth direction and amount were assessed with the Björk method from measurements made on serial cephalometric tracings superimposed on metallic implants. Undecalcified sections, treated with intravenous tetracycline vital staining, were viewed with fluorescence microscopy to examine histologic changes in the condyle and the glenoid fossa. New bone formation in the fossa associated with continuous mandibular protrusion was quantified by using computerized histomorphometric analysis of decalcified histological sections and polarized light. The unique combination of permanently implanted electromyographic electrodes, tetracycline vital staining, and histomorphometry represents a significant technological advancement in methods and materials. Together, they demonstrated different muscle-bone interaction results for functional appliances than those reported in previous studies. In Part 1 of this study, we describe and discuss the techniques used in this research and give a brief overview of the findings; in Part 2 (to be published next month), we offer a more in-depth discussion of the results and the implications of our findings.

Volumetric change of the medial pterygoid following distraction osteogenesis of the mandible: an example of the associated soft-tissue changes.

Mandibular distraction osteogenesis lengthens not only the affected skeleton but also the associated muscles of mastication. The purpose of this study was to determine medial pterygoid volume before and after distraction by using computed tomography. Using computed tomographic scans, the volume of the medial pterygoid muscle was determined before and after mandibular distraction in six pediatric patients. In four unilateral distraction patients (average age, 65 months), the average increase of the medial pterygoid muscle on the distracted side of the mandible was 29 percent, and on the contralateral nondistracted side, 10 percent. The average increase in medial pterygoid muscle volume in two bilateral distraction patients (each aged 8 months) was 75 percent. Results of this study demonstrate that distraction osteogenesis of the human mandible not only lengthens deficient bone, but it also increases the volume of the attached musculature.

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.

Effects of covariance model assumptions on hypothesis tests for repeated measurements: analysis of ovarian hormone data and pituitary-pteryomaxillary distance data.

In the analysis of repeated measurements, multivariate methods which account for the correlations among the observations from the same experimental unit are widely used. Two commonly-used multivariate methods are the unstructured multivariate approach and the mixed model approach. The unstructured multivariate approach uses MANOVA types of models and does not require assumptions on the covariance structure. The mixed model approach uses multivariate linear models with random effects and requires covariance structure assumptions. In this paper, we describe the characteristics of tests based on these two methods of analysis and investigate the performance of these tests. We focus particularly on tests for group effects and parallelism of response profiles.

Apoptosis in the development of the temporomandibular joint.

Apoptosis has been shown to be involved in remodeling of organs during development, and derangement of the apoptotic process may result in temporomandibular joint (TMJ) dysfunction or congenital malformation. To investigate the relationship between the development of the TMJ and apoptosis, rat fetuses at 17.5-20.5 days of gestation (E17.5-20.5, vaginal plug=E0) and rats at postnatal days 1, 2, 3, 5, and 10 (P1, 2, 3, 5, and 10) were examined by light (LM) and transmission electron microscopy (TEM) and electrophoretic analysis of DNA fragmentation. At E17.5 and 18.5, a few layers of slender mesenchymal cells which eventually develop into the TMJ disk were observed, although TEM or electrophoresis did not reveal apoptotic cells at these stages. At E19.5 and 20.5, all structures of the TMJ except the lower joint cavity could be distinguished, but at these stages apoptotic cells were not observed. In P1 condyles, apoptotic cells were observed by TEM both at the subsurface of the condyle and in the region at which the lateral pterygoid muscle attaches to the condyle. These apoptotic cells showed irregular chromatin condensation, convolution of the cell membrane, and fragmentation and disintegration of the cytoplasm. Electrophoretic analysis of the P1 condyle further confirmed DNA fragmentation. Apoptosis was not observed in all specimens at the P1 stage. It was confirmed in 8 out of 20 animals (10 out of 27 joints) by TEM and/or electrophoretic analysis. The shape of the upper portion of the condyle flattened progressively from E20.5 to P2. At this stage, the lower joint cavity was developing, as observed by LM. These findings suggest that the morphological changes of the mandibular condyle effected by apoptosis, together with development of the lower joint cavity, play important roles in the postnatal functional adaptation to external stimuli such as mechanical strain.

The development of the temporomandibular joint: a review with regard to the lateral pterygoid muscle.

This review sets out to explore the relationship between the lateral pterygoid muscle and the meniscus. It examines the embryological evidence to explain the controversy surrounding the apparent morphological discrepancy in the attachment of the lateral pterygoid muscle to the meniscus. It shows that the contribution of the lateral pterygoid muscle to the formation of the meniscus remains in dispute. Morphogenetic studies have not been able to support either one or other viewpoint and no direct conclusions can therefore be made on the embryology of the temporomandibular joint.

Metabolic transitions in rat jaw muscles during postnatal development.

The program of acquisition of adult metabolic phenotypes was studied in three jaw muscles in order to determine the link between muscle metabolism and functional development. During early postnatal stages, there were similar transitions in the masseter, anterior digastric, and internal pterygoid muscles with respect to fiber growth, fiber type composition, and whole muscle energy metabolism. Oxidative capacity, as judged by the activities of the enzymes succinate dehydrogenase (SDH), malate dehydrogenase (MDH), and beta-hydroxyacyl CoA dehydrogenase (beta OAC), rose sharply after birth to reach near maximal levels by 3 weeks. The capacities for glycolytic metabolism represented by lactate dehydrogenase (LDH), and for high-energy phosphate metabolism represented by adenylokinase (AK) and creatine kinase (CK) activities, rose gradually, not reaching peak values until 6 weeks or later. Thus, the maturation of oxidative metabolism preceded that of glycolytic metabolism in the developing jaw muscles. This was documented for individual fibers in the masseter muscle. Differential metabolic maturation among the jaw muscles was evident beyond 3 weeks. All three jaw muscles attained their specific adult fiber-type profile by about 6 weeks. This maturation program differed from that of hindlimb muscles [Nemeth et al., J Neurosci 9:2336-2343, 1989] and diaphragm muscle [Kelly et al., J Neurosci 11:1231-1242, 1991], reflecting their differential energy demands for contractile performance.

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.

[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.

Time-dependent effects of a 'functional'-type orthopedic appliance on the rat mandible growth.

The modus operandi and the time-dependent variations in the effects of the LSU-activator, an orthopedic appliance currently used in human orthodontic therapy, was experimentally analyzed in growing rats. This appliance causes a forward positioning of the lower jaw and a restriction of mandibular motility. After a 4-week treatment, the following changes were observed: (i) the growth rate of the condylar cartilage was accelerated, this growth-promoting effect being more pronounced when the LSU-activator was worn during the animal's rest span. (ii) the direction of condylar growth became more backward-oriented; no significant difference between day and night treatment, i.e. during the rest and activity spans could be detected; (iii) the supplementary lengthening of the mandible was greater in rats treated during rest than in rats treated during waking and (iv) the number of serial sarcomeres in the lateral pterygoid muscle was smaller. This growth retardation of the muscle was greater in rest-time than in waking-time treated individuals. The LSU-type activator's action implies a two-step effect: during the time of wearing the appliance, the more forward positioning of the mandible causes a reduced growth of the lateral pterygoid muscle; during the time the LSU-type activator is not worn, the mandible is functioning in a more forward position such a way that it stimulates the growth rate of the condylar cartilage and the subperiosteal ossification of the posterior border of the ramus. It is therefore essential, for a few hours every day, that the mandible be allowed to move freely from the appliance in a more forward position.