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During the process of growth and development, the digastric muscle is subjected to marked functional changes, including the change from suckling to mastication. In particular, because the anterior belly of the digastric muscle, which is one of the suprahyoid muscles, plays an important role in mastication. Therefore, this muscle seems to undergo a marked functional change before and after weaning. However, the details remain unknown. Here, to clarify the changes in the muscle fibre characteristics of the anterior belly of the digastric muscle before and after weaning, we examined myosin heavy chain isoforms at the protein (immunohistochemistry) and mRNA (transcription) levels. As a control, the changes in the muscle fibre characteristics of the sternohyoid muscle, which is anatomically aligned in the same direction as the anterior belly of the digastric muscle, were analyzed. The results showed that, in the anterior belly of the digastric muscle that is involved in mandibular movements in mice, the ratio of a fast-contraction isoform with strong contractile force increased after weaning. We believe that this occurred in response to a functional change from suckling to mastication. On the other hand, there was little change in the composition of sternohyoid muscle. [ABSTRACT FROM AUTHOR]

In an effort to clarify the morphologic characteristics of the palatopharyngeal muscle, we examined its origin, insertion, and positional relationship with other muscles. We found that the origin of the palatopharyngeal muscle was both the oral and the nasal side of the soft palate; it was also attached to both the palatal aponeurosis and the soft palate median. However, in some cases the muscle originated on the nasal side was lacked. When the palatopharyngeal muscle originated from both the oral and the nasal side, it traveled through its insertion via the levator muscle of the palatine velum. This insertion was seen in a wide area and could be divided into three parts: the pharynx anterior, central, and posterior walls. In the central pharyngeal wall, insertion into the pharyngeal aponeurosis, inferior constrictor pharyngeal muscle, and esophagus were observed. The present results suggest that the palatopharyngeal muscle has a close positional relationship with the levator and tensor muscles of the palatine velum, the pharyngeal constrictor muscles, and the esophagus.

Purpose: The present study sought to clarify correlations of accessory nerve innervation in the neck region and innervation of the sternocleidomastoid and trapezius muscles with postoperative dysfunction after functional neck dissection by macroscopic observation., Materials and Methods: The materials used in this study were 35 cadavers provided for anatomical practice to the Department of Anatomy, Tokyo Dental College. The accessory nerve was identified at the anterior margin of the trapezius muscle, and its innervation in the posterior triangle of the neck was examined in detail., Results: The superficial cervical vein vascularizes the anterior margin of the trapezius muscle near an area where the main trunk of the accessory nerve innervates the trapezius muscle. The results showed 3 types of accessory nerve innervation of the sternocleidomastoid muscle: Type A, the not penetrating type; Type B, the partially penetrating type; and Type C, the completely penetrating type. In addition, 5 types of innervation of the trapezius muscle by the main trunk and branches of the accessory nerve were apparent, with the number of branches innervating the muscle ranging from 0 to 4., Conclusions: Dysfunction after functional neck dissection can thus be avoided by paying attention to not only the main trunk of the accessory nerve, but also the branches. Moreover, when identifying accessory nerve innervation of the trapezius muscle, the superficial cervical vein may offer a useful surgical landmark.

The mandibular angle is one of the areas of the mandible that are prone to bone fractures, and the presence of an impacted third molar has been found to be associated with increased risk of angle fractures. The factors involved in bone fractures are the amount and direction of load, and the biomechanical and anatomical properties of bone. In the present study, micro-focused X-ray computed tomography was performed to observe and analyze the three-dimensional (3D) bone microstructure of the mandibular angle, and finite element analysis was conducted to examine the relationship between angle fractures and the presence or absence of mandibular third molars. 3D bone microstructure showed no marked difference between mandibles with and without third molars. Finite element analysis showed that, in the mandible with a third molar, stress was concentrated around the root apex of the third molar, and was transmitted in a direction matching the clinical findings of angle fractures. The results obtained in this study suggest that the presence of an impacted third molar changes the concentration and transmission of stress in the mandible, thus increasing the risk of an angle fracture.

This report is based on a case of temporomandibular joint ankylosis discovered in a cadaver during routine student dissection in the Department of Anatomy at Tokyo Dental College. Extensive osseous ankylosis in the left temporomandibular joint was evident in this case which exhibited a distinctive bird-like facial deformity caused by a mandibular growth disorder. This resulted in the underdevelopment of the mental area in particular. Furthermore, abnormally enlarged antegonal notching was present along the inferior border of the mandible anterior to the angle. Both these manifestations indicated the likelihood that the ankylosis had contributed to the abnormalities and had commenced at an early stage of skeletal development.