Histomorphometrical aspects of the postnatal development of masticatory muscle in the muscular dystrophic mouse.

Histomorphological and histomorphometrical observations were used to describe the development of masticatory muscles from normal and muscular dystrophic mice. The masseter and the digastric muscle were described from the birth to 35-40 week of age. It has not been possible by histomorphological criteria to separate dystrophic muscles from normal muscles at birth. From 2 weeks onwards marked differences between the affected and unaffected muscles appeared, as the affected fibres from this age are rounded with marked variations in size. Central nucleation is frequent and there is an increased amount of connective tissue between the fibres. The histomorphometrical observations revealed an increase in mean size of the fibres with age, both in normal and dystrophic masticatory muscles. The fibre size variance which has been shown to be a reliable parameter for description of degree of affection of dystrophic muscles, increased with increasing age in both groups. However, the variance is at all ages greater in the dystrophic muscles than in the normal ones, and is always greater in the masseter muscle than in the digastric muscle. There seems to be some small differences between male and female masticatory muscles, whereas no differences could be revealed between muscles from normal and heterozygous animals. Possible explanations of the obvious differences in degree and progression of the disease between the masseter and digastric muscle are proposed.

Os penis of the rat. VI. Scanning electron microscopy of the surfaces of the mature bone.

Observations on the ultrastructural appearance of the surfaces of the mature os penis in the rat reveal that a majority of its surfaces may be classified as prolonged resting surfaces on very slow growing surfaces. Although a vast majority of the bone consists of bone tissue types which usually only form a small part of human and laboratory animal bones, their surface appearances resemble to a high degree surface appearances described for ordinary bone tissue types. Thus, surface morphology need not reflect tissue type variance. However, certain minor deviations from usual descriptions of surface appearances were observed. Such deviations are for instance the combination of partly mineralized fiber bundles and a fully mineralized amorphous ground substance on some of the observed surfaces. The combination may be a result of an extremely slow growth or a lost ability of the ageing bone forming cell to produce organized tissue.

Presence of alpha-naphthyl acetate esterase enzymes in dental and oral epithelium of guinea pig embryos.

This study examines the distribution of alpha-naphthyl acetate esterase enzymes in reduced enamel epithelium, i.e., post secretory ameloblasts (PSA) and external cells of reduced enamel epithelium (ERE) of continuously growing incisor and molar tooth germs and in the covering oral epithelium (OE). Jaws of guinea pig embryos, 25-50 days of gestation age, were pretreated, frozen, serially cut, and incubated with alpha-naphthyl acetate as substrate and hexazotized pararosaniline as capture agent for demonstration of enzyme activity. In addition, sections were preincubated with various inhibitors of enzyme activity. A strong enzyme reaction, essentially unaffected by pretreatment procedures, was demonstrated in all cells of PSA and ERE, and in suprabasal cells of OE. Preliminary characterization of the alpha-naphthyl acetate esterase enzymes by means of inhibitors suggests a prevailing presence of B-esterase enzymes in both oral and dental epithelia. PSA were selectively stained when 2 x 10(-3) M arsanilic acid was used as inhibitor, ERE were selectively inhibited by 10(-5) M eserine, and cells of OE were selectively stained when 2 x 10(-3) M HgCl2 was used as inhibitor. We therefore conclude that the alpha-naphthyl acetate esterase enzymes in combination with inhibitors may serve as histochemical markers for discrimination of dental and oral epithelium in the guinea pig prior to eruption of teeth.

Histomorphometrical analysis of the influence of soft diet on masticatory muscle development in the muscular dystrophic mouse.

The known difference in the severity of dystrophy between the masseter and the digastric muscle of the mouse (dy/dy C57BL/J6) may be attributed to the differences in muscle work load. This possibility was tested by subjecting 3-week-old mice (normal and dystrophic) to a soft diet for 4 weeks. Microscopic examination of haematoxylin-eosin stained sections of these muscles showed that the fibre size dispersion (a measure of disease severity) decreased slightly but significantly in the masseters of mice on a soft diet. It was thus possible to improve the condition of dystrophic masticatory muscles by changing their function. Body weight curves measured during the experimental period suggest that the dystrophic mice may have been under weight because of malnutrition due to lack of sufficient masticatory power.

Skull development in the muscular dystrophic mouse.

Roentgencephalometric tracings of skulls of 7-week-old normal and muscular dystrophic mice were compared. A marked size reduction of the dystrophic skulls relative to the normal ones was observed. However, the visceral parts of the dystrophic skull were more reduced in size than the neural parts. Marked differences in shape were also noticed. Differences in angular values were primarily found between skull parts, whereas angles between adjacent bones were remarkably similar in the two groups. Only a few exceptions of this condition were observed, as angles between adjacent bones in the posterior part of the cranial vault of the dystrophic animals differed from those of the normal animals. The observed differences between normal and dystrophic mice skulls may chiefly be explained as the results of differences in the action of diseased and normal muscles on bone.

Non-specific esterases and esterproteases in masticatory muscles from the muscular dystrophic mouse.

With the aid of histochemical and electrophoretic techniques activities for esterase and esterprotease were investigated in the digastric and masseter muscles from normal and dystrophic mice. The substrates used were alpha-naphthyl acetate and N-acetyl-L-alanine alpha-naphthyl ester. According to the microscopic observations of the dystrophic muscles the histopathological changes in the masseter muscle were much more pronounced than in the digastric muscle. The connective tissue surrounding the myofibers of the dystrophic masseter contained a large number of cells with pronounced enzyme activity. Among them were mast cells that were strongly stained for esterprotease. The connective tissue of the dystrophic digastricus was much less infiltrated with cellular elements reacting for esterprotease. In zymograms the normal digastricus, the dystrophic masseter and the dystrophic digastricus showed a strong activity for certain isoenzymes that were absent or weakly expressed in the normal masseter.

Incidence of centrally positioned nuclei in mouse masticatory muscle fibers.

Cross-sections of normal digastric, temporalis and masseter muscles from 7- and 30-week-old mice were studied for centrally positioned nuclei. Such nuclei were inhomogeneously distributed throughout each muscle and varied markedly between specimens. The incidence of centrally positioned nuclei in the digastric muscle (mean +/- SD: 0.029 +/- 0.015, n = 25) was significantly higher (p less than 0.001) than that in the temporalis (mean +/- SD: 0.011 +/- 0.010, n = 25) and masseter muscles (mean +/- SD: 0.005 +/- 0.007, n = 9), but did not differ between the two latter muscles (p = 0.41). Furthermore, the frequency in a given muscle was apparently age-independent. A connection between fiber type and centrally positioned nuclei is suggested.

Esterase profile of human masseter muscle.

The esterase profile of fresh human masseter muscle was investigated by use of histochemistry and electrophoresis. The histochemical methods included reactions for alpha-naphthyl esterase, myofibrillar ATPase, reverse myofibrillar ATPase and succinic dehydrogenase. In frozen sections of the muscle the coloured reaction product for esterases was present both as a diffuse sarcoplasmic coloration and as distinct granules. The intensity of diffuse reaction was used to classify the muscle fibres as strongly, moderately and weakly reacting. The fibres with strong esterase activity belonged to Type I and iiC. iM and Type II A fibres showed a moderate esterase reaction and Type II B fibres had a low activity. The electrophoretic gels stained for esterase activity showed that the human masseter muscle possesses a slow migrating double band with high enzyme activity and a cascade of faster migrating isoenzymes. In isoelectric focused gels the major esterases showed isoelectric points around pH 5.

Masticatory muscles in the muscular dystrophic mouse. Aspects of the age-related progression of the disease.

Cross-sections of normal and dystrophic digastric and masseter muscles from 7- and 35- to 40-week-old mice were studied in the light microscope. Comparisons of mean cell size, cell size variance and number of centrally positioned nuclei in a given number of fibers were carried out. The masseter muscle seems at both ages to be far more affected by the disease than the digastric muscle. However, the progression of the disease from 7 to 40 weeks is more pronounced in the digastric muscle than in the masseter muscle.

Studies on orthocephalization: growth behavior of the rat skull in the period 13-49 days as described by the finite element method.

Rat cranial skeletal growth was studied, using a cross-sectional data set, for the period 13-49 days by the application of the concepts of continuum mechanics and the numerical techniques of the finite element method (FEM). In contrast to the methods of conventional craniometry (CM) and roentgenographic cephalometry (RCM) the FEM permits fine scale, reference frame invariant descriptions and analysis of growth behavior. This advantage was demonstrated by a numerical example of the use of FEM. The skull was discretized into a number of two-dimensional, triangular elements, whose enclosed areas corresponded closely to both specific skeletal structures and to related functional matrices. Since it was assumed presently that the growth behavior of all of the points enclosed within a given element was similar, the application of the functional matrix hypothesis permitted an integrated description of the growth of the skeletal structure and functional matrix related to each element. The principal locus of rotation of the facial skull, relative to the cranial base, is the inferior frontoethmoidal articulation, a motion that includes a rigid body rotation. Other active and passive skeletal and visceral growth events associated with orthocephalization were located and described. Finally it was shown that the morphogenetically important growth behavior of other portions of the rat head were not directly involved in orthocephalization.

Studies on orthocephalization. 10. Behaviour of the visceral part of the rat head during the first 14 days after gestation.

The present paper considers the significance of interosseous flexions of the palatal complex in the process of orthocephalization of the rat skull between birth and 7 d p.n. The study is based on a sample of 90 rats divided into 4 age groups, i.e. 0, 4, 7, and 14 d. These rats have been X-rayed, and their photographs subsequently analysed. During the studied period, the constituents of the bony palate, i.e. the horizontal part of the palatine bone, the palatal process of maxilla and the palatal part of premaxilla, increase markedly in length, but with individual differences in growth rate. There is, in the period, a marked decrease in angulation between the cranial base and the palatal plane. This means that the rat skull becomes more orthocranial. There is also a straightening (orthopalatalization) of the palate, as the angle between maxilla and premaxilla becomes more obtuse, and a marked decrease in angulation between the palatine bone and the cranial base. The patterns of angular changes suggest that the process of orthocephalization in the period between birth and 14 d p.n. primarily is a result of an upwards rotation of the palatine bone relative to the cranial base, while interosseous deflections in the palate only play a minor role.

Pyogenic granuloma: evaluation of oral conditions.

A consecutive series of 43 pyogenic granulomata in the oral cavity is presented. Most were located to the marginal vestibular gingivae and only a minority (12%) of these had a history of trauma whereas 70% in extragingival locations had a previous history of injury. On the basis of an evaluation of oral conditions the aetiology and the pathogenesis of the pyogenic granuloma are discussed. Trauma, microtrauma due to toothbrushing and gingival inflammation seem to be pathogenetic elements. It is suggested that the granuloma is a localised tissue response to a non-specific irritant.

Histomorphometry of masticatory muscles in the muscular dystrophic mouse.

Cross sections of normal and dystrophic digastric, masseter and temporalis muscles from 7-week-old mice were studied by histomorphological and histomorphometrical methods in the light microscope. The histomorphological part of the study revealed marked differences in morphology between normal and dystrophic muscles. Mutual differences between the dystrophic muscles were also observed. Comparisons of the parameters chosen for the histomorphometrical part of the study, i.e., cell size and number of centrally positioned nuclei in a given number of fibers, revealed that the digastric muscle seems to be the least affected and the masseter muscle the most affected by the disease.

Os penis of the rat. V. The distal cartilage process.

The morphogenesis and morphology of the distally positioned cartilage of the os penis, the processus cartilagineus, are described in rats aged from 1 to 100 days. Based on observations of metachromacy of the process stained with toluidine blue it was found that a processus cartilagineus only exists in the period between 35 and 50 days of age. Before 35 days, the structure consists of connective tissue proper, and after 50 days the cartilage starts to calcify partially. The present paper also initiates studies of experimentally caused alterations of the normal development of the processus cartilagineus by subjecting 35-day-old rats to castration, with subsequent sacrifice at 100 days. Castration at that age causes a complete interruption of normal development of the processus cartilagineus as the structure in 100-day-old castrated rats has distinct morphological characteristics in common with those of 35-day-old normal rats. The present paper, thus, confirms that normal development of the processus cartilagineus seems to be male-hormone-dependent.

Finite element method modeling of craniofacial growth.

The application of the concepts of continuum mechanics and of the numerical techniques of the finite element method permits the development of a new and potentially clinically useful method of describing craniofacial skeletal growth. This new method differs from those associated with customary roentgenographic cephalometry in that its descriptions and analyses are invariant; that is, they are independent of any method of registration and superimposition. Such invariance avoids the principal geometric constraint explicit in all analytical methods associated with conventional roentgenographic cephalometry. The conceptual and mathematical bases of the finite element method (FEM) are presented and illustrated by the numerical and graphic descriptions of the two-dimensional growth of the rat skull, for which two sets of longitudinal growth data are used. In practice, the FEM permits analysis of the skull at a scale significantly finer than previously possible, by considering cranial structure as consisting of a relatively large number of contiguous finite elements. For each such element, independently, it is then possible to describe and depict both the magnitude and the direction of temporal size and shape changes occurring in that element relative to itself at some initial time. It is emphasized that such descriptions are completely independent of any local reference frame.

Studies on orthocephalization. 8. Behaviour of the visceral part of the rat head in the period between 7 and 60 days after gestation.

The present paper considers the significance of interosseous flexions of the palatal complex in the process of orthocephalization of the rat skull between 7 and 60 d after birth. The study is based on a sample of 25 female rats who have been X-rayed at 7, 14, 30, and 60 d with subsequent analysis of the photographs obtained. During this period the constituents of the bony palate, i.e. the palatine bone, the palatal process of maxilla and the palatal part of premaxilla grow steadily but with decreasing rate of increase with age. The premaxilla grows the most, while the palatal bone grows the least. The angle between the cranial base and the palatal plane decreases, i.e. the rat skull becomes more orthocranial with age. At the same time, the palate becomes more orthopalatal, primarily by an increase in the angle between the palatine bone and maxilla. As the angle between the cranial base and the palatine bone after 14 d increases, i.e. rotates in the opposite direction of the palatal plane, it may be concluded that the process of orthocephalization in this period is caused by the deflexion of the angle between the palatine bone and maxilla, while it before 14 d is caused by a combination of an interosseous deflexion in the palate and an upwards rotation of the palatine bone relative to the cranial base.

An allometric network model of craniofacial growth.

This study of cranial skeletal growth kinematics details the conceptual principles underlying the development of an allometric network model of such growth. This model is tested by the analysis of longitudinal rat and cross-sectional human growth data and by comparison of this model with a previously described allometric centered model. It is shown that the network model is superior to the centered model in three ways: (1) The allometric network model permits growth prediction when allometric constants are known; (2) the network model has significantly smaller errors than the centered model; and (3) the network model is capable of displaying growth kinematics of both the neural and facial skulls while in time there are marked transformations, such as relative rotations of two sets of cranial anatomic points.

The growth of the first cervical vertebra in the rat.

With the help of in vivo marking with alizarin red S, the patterns of growth of the first cervical vertebra are demonstrated. Major parts of the developmental events which take place during growth (differential bone formation on the bone ends facing the synchondroses, closure of the dorsal synchondrosis at 14 days, closure of the ventral synchondroses at 35 to 40 days) may be explained by the influence that a capsular matrix exerts on its protecting and supporting skeletal unit. A demonstrated continued increase of the dorsoventral diameter of the bone is suggested to be an adjustive growth process related to the translative movements of foramen magnum, a topic that has been poorly understood and incompletely investigated.