The relation of the temporal muscle to the form of the coronoid process

Osteoma of the lateral pterygoid plate of the sphenoid bone

A rare case is reported of an osteoma protruding into the pterygomandibular space from the lateral pterygoid plate of the sphenoid bone. The procedure of the diagnosis and treatment is described. In this case, computed tomography (CT) was the most useful in making a differential diagnosis. That the pulling force of the medial pterygoid muscle might be a causative agent in the growth of this osteoma is considered.

Adaptations in the temporalis muscles of rabbits after masseter muscle removal

Masseter muscles were surgically removed in six young female rabbits so that we could study adaptations of the superficial temporalis muscles (ST) to increased functional requirements. Eight weeks following surgery, we used morphological measurements, histochemistry, contractile properties in situ, and occlusal force in vivo to compare the muscles in the experimental animals and six control rabbits. Analysis of the results demonstrated a decrease in fatigability of ST after masseter myectomy. Incisal occlusal force decreased by 65% during the first two weeks, and no recovery was observed during the following six weeks. At eight weeks post-surgery, the mass, twitch tensions, and tetanic tensions of ST were not significantly different from those of the controls. An increase in the percent of the cross-sectional area composed of fast fatigue-resistant fibers, a slower time-to-peak twitch tension, and a decrease in fatigability suggest an increase in oxidative metabolism. Analysis of these results suggests that muscles used for highly repetitious activities with submaximal loadings adapt to increased functional requirements by increasing fatigue-resistant properties.

The shape of the mandible

The validity of traditional cephalometric techniques for orthognathic surgical diagnosis and planning remains controversial. This not only reflects the fact that the linear and angular parameters combine size and shape together, but the techniques also generally rely upon non-homologous datum points, with the resultant data being of dubious mathematical significance. In order to circumvent these problems, the technique of medial (symmetric) axis transformation was used to compare mandibular shapes derived from lateral cephalographs of patients with various anomalies. This technique centers on defining the central (medial) axes of mandibular form and is based on equal weighting of points defining the peripheral border independent of cephalographic orientation. Measurement of the derived medial axes and their relative orientation described marked changes in mandibular shape resulting from pathosis and surgical intervention. However, further research is required to ascertain whether this specific technique for the description of biologic shape facilitates orthognathic surgical diagnosis and planning.

Bilateral coronoid hyperplasia resulting in severe limitation of mandibular movement. Report of a case

A case of bilateral coronoid hyperplasia with limitation of mandibular motion in a female patient has been presented. Her symptoms began to develop around the age of 44. We believe that this is the first case to be reported in a female. Also, in all other reported cases symptoms began to develop around the onset of puberty. The literature has been reviewed with specific reference to the etiology of bilateral coronoid hyperplasia. This case brings the total number of reported cases to twenty-two. We hope that if similar cases are identified in female patients the practitioners will report them promptly. Only in this way will we be in a better position to understand the etiology of bilateral coronoid hyperplasia with special reference to heredity.

Canonical correlations between masticatory muscle orientation and dentoskeletal morphology in children

In order to identify associations between the orientation of the superficial masseter and temporalis muscles and dentoskeletal morphology in a sample of fifty-five children with various malocclusions, eight muscle-orientation variables (relative to the occlusal plane) and twenty-three dentoskeletal variables were evaluated from lateral head films. The thirty-one measurements were reduced to six muscle-orientation and sixteen dentoskeletal variables by a principal component analysis. Three canonical correlations were identified between the muscle orientation and dentoskeletal variable groups at the 0.05 level of significance and canonical loadings were determined for each set of variables. The first canonical correlation (r1 = 0.931) represents a growth-related correlation factor between the masticatory muscle insertion positions relative to the occlusal plane and the dimensional and positional changes of craniofacial structures during growth. The second canonical correlation (r2 = 0.846) may account for an operational artifact in the geometric measurement process, and the third canonical correlation (r3 = 0.813) suggests an association between superficial masseter muscle orientation relative to the occlusal plane and mandibular form. This report confirms the usefulness of multivariate statistical methods to extract latent associations between muscle orientation and craniofacial morphology; the results obtained suggest a contribution from the geometric orientation of the masticatory muscles to the development and maintenance of the dentoskeletal system.

Morphologic alterations in Macaca mulatta following destruction of the motor nucleus of the trigeminal nerve

In two adolescent male Macaca mulatta monkeys, small unilateral electrolytic lesions were produced in the motor nucleus of the trigeminal nerve. The side contralateral to the muscle paralysis served as the control side. The animals were killed 130 and 300 days postoperatively. One animal (animal A) was prepared as a dry skull preparation. Alterations in craniofacial form were noted clinically in both animals and included paralysis and atrophy of the muscles of mastication on the lesion side and mandibular asymmetry. In animal A (300 days postoperative survival), alterations in form included dental and mandibular asymmetry, the appearance of an anterior open-bite on the affected side, and a decrease in the size of the intratemporal fossa on the affected side. Remodeling changes were evident in the condylar process, the zygomatic arch, the orbit, and the zygomaticotemporal and zygomaticofrontal sutures on the lesion side but were not apparent on the contralateral side.

Relationship between the development and growth of cranial bones and masticatory muscles in postnatal mice

Development and growth of cranial bones and masticatory muscles in postnatal mice, assessed by roentgenographic cephalometry and histochemistry, revealed that it corresponded to the attachment of the masticatory muscles, but not necessarily to growth and development of the individual muscles. Physiological functions of the dentofacial complex correlated with development of the muscles.

The morphogenetic relationship of the temporal muscle to the coronoid process in human embryos and fetuses

The purpose of this investigation was: (a) to study the developmental relationships of the temporal muscle and the coronoid process during the critical initial stages of morphogenesis and (b) to correlate the developmental stages of the muscle and the bone with data describing the functioning of the muscles of mastication in utero. The heads of 41 human embryos and fetuses, 6 to 11 weeks, estimated fertilization age, were sectioned and examined under light microscopy. The findings are described in terms of six successive stages, each characterized by a major developmental change occurring during that stage. The data indicate that the temporal and masseter muscle anlagen begin to develop prior to the skeleton to which they ultimately become attached. The coronoid process differentiates subsequently as a discrete entity within the mass of the temporal muscle anlage at an estimated fertilization age of 7 to 7.5 weeks (23-24 mm CRL). At approximately eight weeks of age, the coronoid process unites with the main portion of the mandibular ramus. The findings here presented do not support the conclusion that the coronoid process is self-differentiating as Washburn ('47) contended. Instead, the development of this feature of the human mandible represents a response that follows the differentiation of the temporal muscle. This conclusion is consistent with the observations drawn from a number of investigations concerning structural and functional development of the face.

Adult monkey coronoid process after resection of trigeminal nerve motor root

A smaller or absent coronoid process has been reported, by some investigators but not by others, in growing animals following resection of the temporalis muscle. The trauma of resection, altered function, hemorrhage, scar tissue, and changes in vascularity may have influenced the results. The purpose of this experiment was to observe in adult Macaca mulatta the fully grown coronoid process after decreasing or eliminating neurofunctional activity of the temporalis muscle unilaterally without the trauma of local resection. In two males and three females the motor root of the trigeminal nerve which innervates the temporalis muscle was resected intracranially. In three control animals of both sexes the same surgical procedure was performed except for resection of the nerve. At postmortem, one year later, the temporalis muscle mass was atrophic on the resected side. There were no significant morphological differences, however, between the right and left sides of the mandible, including the coronoid process, regardless of which motor root of the fifth nerve had been resected, which side had been sham-operated, or sex. An extensive deposit of calculus on the buccal surfaces of the teeth on the operated nerve side was a consistent, conspicuous finding.

Split-line patterns of the mandible following masseterectomy in adult and growing monkeys

Architectural changes of the mandibular ramus following masseterectomy were analyzed by means of the split-line technique in both adult and growing monkeys. The right masseter muscle was resected in ten tufted capuchin monkeys (Cebus apella) and they were sacrificed following a 12-month period. Along with modifications in the shape of the mandible, the masseterectomy induced structural changes as revealed by alterations in the split-line patterns. These changes were much more evident in the adult animals. In growing monkeys, intrinsic forces determine an architecture of mandibular growth, represented by the direction of the splits. This is not influenced by the lack of mechanical factors like muscle action. Conversely, the final fibrous architecture of the bone in the adult monkey may be modified by extrinsic mechanical factors.

Radiologic examination of trismus as a complication of cancrum oris

In the radiologic examination of trismus complicating cancrum oris, abnormalities can be detected in the soft tissues, osseous tissues, and temporomandibular joint. In the soft tissue, scar formation may show as a depression in the normal smooth, convex contour of the lateral aspect of the face. There may be a myositis ossificans in the soft tissue, producing bony bars that lead to extra-articular ankylosis. By far the most important changes are in the temporomandibular joint, where there can be varying degrees of joint narrowing, sclerosis of the articular cortex, flattening of the mandibular condyle and occasionally also of the eminentia articularis, osteophytosis, and intra-articular bony ankylosis. Hypoplasia may involve the entire hemimandible or be restricted to its condyloid process. The latter may lead to compensatory enlongation and hypertrophy of the coronoid process. Bony ankylosis of the coronoid process to the posterior wall of the maxilla was seen in three cases. The pathogenesis of these changes is discussed.

Effect of removal of the temporal muscle on the coronoid process in guinea pigs: quantitative triple fluorochrome study

A triple fluorochrome labeling sequence was used to measure the osseous activity in the coronoid process after the removal of the temporal muscle. Statistically significant differences between the control and the experimental animals were found for hematoporphyrin, DCAF, DCTC, and total labeled bone.

Secondary enlargement of the mandibular coronoid process

Enlargement of the coronoid process of the mandible is a rare cause of limited jaw movement.

Primary causes fall into two categories: benign tumours and developmental hyperplasia.

Two cases of clinically important enlargement of the coronoid process secondary to other longstanding causes of difficulty in opening the mouth are described.

It is suggested that significant appositional bone growth secondary to abnormal stresses mediated by the tendon of the temporalis muscle does occur.