Hiroko Agematsu

Morphologic characteristics of the superior pharyngeal constrictor muscle in relation to the function during swallowing.

To clarify the morphologic characteristics of the superior pharyngeal constrictor muscle, which plays an important role in swallowing, the gross anatomy of the pterygopharyngeal, buccopharyngeal, mylopharyngeal, and glossopharyngeal parts of the muscle was examined. Morphology of the origin of the muscle at the buccopharyngeal part could be divided into three types: type A, membranous morphology from superior to inferior areas; type B, membranous only in superior area; and type C, complete lack of membrane. In all three types, the muscle at the buccopharyngeal part transitionally originated from the buccinator muscle. Morphology of the origin of the muscle at the mylopharyngeal part could be divided into two types: type A, tip of the origin on the mylohyoid line; and type B, tip of the origin away from the mylohyoid line. The present study found that the superior pharyngeal constrictor muscle is attached to the buccinator muscle (which plays an important role in mastication) with mucosa and originates from the mandible and root of the tongue. These findings suggest that the superior pharyngeal constrictor muscle may also play an important role in the expression of smooth coordinated movements associated with ingestion, from mastication to swallowing.

Changes in Muscle-fiber Properties of the Murine Digastric Muscle Before and After Weaning

Abstract The digastric muscle is one of the suprahyoid muscles and consists of the anterior and posterior bellies. Because muscle fiber alignments in these two bellies are different, the functional roles are said to be different. Since the digastric muscle relates to mastication, its functions may change markedly before and after weaning, but many details remain unknown. The aim of this study was to clarify changes in muscle fiber properties of the anterior and posterior bellies of the digastric muscle in mice before and after weaning. Expressions of myosin heavy chain (MyHC) isoforms were assessed at the protein and transcriptional levels. Expression of the MyHC-2b isoform, an isoform displaying fast, strong contraction, was greater in the anterior belly than in the posterior belly after weaning. This suggests that, in mice, the anterior belly of the digastric muscle needs to move rapidly anteroposteriorly for mastication, compared with the posterior belly.

Immuno-scanning electron microscope characterization of large tubules in human deciduous dentin

This study was undertaken to elucidate the type and origin of collagen fibrils which construct the large tubules in deciduous coronal dentin by scanning electron microscope and anti‐types I and III collagen antibody procedures.

Three-Dimensional Analysis of the Internal Structure of the Mandibular Condyle in Dentulous and Edentulous Jaws Using Micro-CT

Abstract This study clarifies the internal structure of the mandibular condyle in dentulous and edentulous jaws; three-dimensional observation and morphological measurements were performed using micro-CT. The materials used in this study were 14 mandibular condyles each removed from the dentulous and edentulous cadavers. Internal structures of the mandibular condyle were morphologically analyzed in three anatomical planes. Additionally, morphometrical observations of the trabecular bone structure at five regions of interest and cortical bone thickness were performed. The mandibular condyle of dentulous jaws consisted predominantly of regularly aligned plate-shaped trabeculae. Conversely, edentulous jaws were predominantly irregularly aligned narrow rod-shaped trabeculae. The results of morphometrical analysis showed that trabecular separation (Tb.Sp) in the central region of the mandibular condyle most closely reflected the difference between dentulous and edentulous jaws. These results suggest that, in edentulous jaws, reduced masticatory function due to tooth loss affects the internal structures of mandibular condyle.

Morphologic Characteristics of Palatopharyngeal Muscle

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.

Changes in the Myosin Heavy Chain 2a and 2b Isoforms of the Anterior Belly of the Digastric Muscle Before and After Weaning in Mice

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.

Three-dimensional analysis of pulp chambers in mandibular first deciduous molars

Abstract In crown restoration, it is important to understand the internal anatomical feature of each tooth, as the morphology of human deciduous teeth is particularly complex. The purpose of this study was to clarify threedimensionally the topographic relationship between the crown contour and the pulp chamber of the mandibular first deciduous molars using a micro-CT system. Fifteen mandibular first deciduous molars obtained from the dried skulls of Indian children in the deciduous dentition period were used as specimens. Three-dimensional reconstructed images were reproduced by combining the two-dimensional slice imaging data using a micro-CT system. Crown contours and shapes of the pulp chamber were observed from various directions. In addition, the thickness of tooth substance at each pulp horn was also measured. In observations of the topographic relationship between the crown contour and the pulp chamber, the pulp horn of the mesiobuccal pulp chamber was found to project the most to the cusp side. The distance between the pulp horn and enamel surface was also shortest (2.45±0.30mm) in this region. Furthermore, in teeth with a deep, wide trigonid notch, the lateral wall of the mesiobuccal pulp chamber projected in the mesial direction. These results suggest that in preparation of cavities in mandibular first deciduous molars, close attention must be focused on pulp exposure in the pulp horn of the mesiobuccal pulp chamber. In addition, the lateral wall of the mesiobuccal pulp chamber should be noted in teeth with the deep, wide trigonid notch.

Three-dimensional observation of internal structure in the region of mandibular deciduous canine using Micro-CT

Abstract The objective of this study is to clarify the changes in the internal structure of the surrounding area in deciduous canine and in relation to the development of successive permanent teeth. We observed the mandibles of the dry skulls of Indian children, using Micro-CT, and measured height of the compact bone at the mandibular base. When the first molars reached the occlusal line in addition to the deciduous dentition stage, the superoinferior position of canine bony crypt located lower than that of other permanent teeth. After this eruption stage, the bony crypts of canine showed inferior growth, resulting in compact substances resorption of the mandibular base. When the central and lateral incisors reached the occlusal line, resorption of compact substance was advanced, but adjunction was observed after deciduous canine shed. Trabecular bone appeared for some directions in the region of sponge bone. The height of compact bone at the mandibular base was measured to elucidate the changes of the compact substance inside of the mandibular base with advancement of the dental eruption stage. The result of measurements quantitatively showed that the bone resorption advanced to the state of central and lateral incisors reached the occlusal line and adjunction occurred after deciduous canine shed.