Akinobu Usami

Myosin Heavy Chain Isoforms of the Murine Masseter Muscle During Pre- and Post-natal Development

Masticatory muscles that are derived from the branchial arches express different compositions of myosin heavy chain (MHC) isoforms during the transitional phase from suckling to mastication. To clarify the developmental changes of murine masseter muscle, the composition of MHC isoforms was examined using immunohistochemical staining and competitive reverse transcription PCR. We found that MHC1 was expressed transiently in the pre and post‐natal stages. In the compositional change of isoforms, the embryonic type MHCp was expressed consistently, whereas the adult isoforms increased with the developmental process. In particular, a significant change was observed between embryonic days 14 and 16, a stage when murine facial development is conspicuous. This suggests that the development of murine masseter muscle is closely associated with facial development.

Changes in the muscle fibre properties of the mouse temporal muscle after weaning.

To clarify changes in the muscle fibre properties of the temporal muscle related to the start of masticatory movement, we immunohistochemically investigated myosin heavy chain (MyHC) isoform protein expression using pre‐weaning and post‐weaning mice. In addition, we examined the expression of a gene coding for those MyHC proteins. Immediately after weaning, isoforms with fast and potent contractility were frequent. This suggests that the temporal muscle plays an important role in a marked functional change in the oral cavity from lactation to mastication, contributing to oral function in cooperation with other masticatory muscles.

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.

Effects of mechanical stretching on caspase and IGF-1 expression during the proliferation process of myoblasts.

Abstract It has been reported that the synthesis, degradation, and metabolism of muscle proteins in myoblasts, as well as the proliferation and differentiation of cells, are influenced by various related to extracellular signaling molecules, such as neural transmitters, growth factors, and hormones, when muscle tissue has been exposed to mechanical stimulation. However, reports regarding the expression of growth factors during mechanical stimulation of myoblasts are few, and many questions remain unanswered. We examined the mRNA expression of insulin-like growth factor 1 (IGF-1) in myoblasts subjected to mechanical stretching in vitro. In addition, apoptosis caused by intracellular stress has been reported to occur during muscle development at the embryonic stage. To clarify the expression of intracellular stress factors, we here investigated related gene expression. Expression of IGF-1 increased in the early stage of cell stretching, followed by a decrease in the late stage. This suggests that mechanical stimulation resulted in an immediate increase in IGF-1 expression, followed by a decrease as cells acclimated to the inducing environment. Caspase was significantly expressed in a stretch group at 12 hours after the beginning of mechanical stimulation, compared with a control group. This suggests that cellular proliferation is also regulated by intracellular stress factors involving the endoplasmic reticulum, mitochondria, and other organelles during the process of muscle proliferation and differentiation

Root resorption of maxillary primary incisors in relation to position of successive permanent incisors by Micro-CT

The aim of this study is to elucidate the root resorption of primary incisors in relation to the development of permanent incisors. We observed the maxillas of the dry skulls of Indian children, using Micro-CT, and measured distance between the root surface of the primary incisor and the bony crypt of the permanent incisor. The bony crypt of the maxillary permanent incisor, which was situated at the lingual side of the primary incisor, grew upward towards the mouth as the tooth eruption stage proceeded. Root resorption was clearly seen at the primary dentition stage, and it proceeded to from root surface towards root canal at the first molar eruption. With the advance of the stage, the distance between the root surface of the primary incisor and the bony crypt of the permanent incisor became shorter, especially the distance between the root of the primary lateral incisor and the bony crypt of the permanent central incisor did. By using Micro-CT, we could confirm more clearly that the growth of the bony crypt of the central permanent incisor deeply influence the progress of root resorption of the primary lateral incisor.

Topographical relationship between positions of lingual foramina and attachment of mylohyoid muscle in mental region

PurposeLingual foramina can be observed between the lingual aspects of the mandible in humans. A sublingual artery is thought to exist in sublingual space and a submental artery in submaxillary space, which pierce the mandible through lingual foramina. During surgery for oral implant placement between apices of the mental foramen, it is important to determine the existence and positioning of lingual foramina. The purpose of this study was to investigate the positions of lingual foramina in relation to the mylohyoid muscle and vertical position of the mylohyoid line using cone-beam computed tomography (CBCT) images.MethodsWe examined 20 formalin-perfused cadavers. The mylohyoid muscle was dissected and marked with a silicone tube, then CBCT images were obtained to evaluate the relationship of that muscle with lingual foramina.ResultsWe observed 37 lingual foramina in the 20 cadavers. As for vertical positioning, 16 lingual foramina were found in sublingual space, while in horizontal positioning, 6 were found in the anterior region of sublingual space. The ratio of vertical distance from the inferior margin to the mylohyoid line and mental spine was lower in the anterior region as compared to the posterior region.ConclusionIn this study, lingual foramina were found to commonly exist in sublingual space above the mylohyoid muscle and pierce the mesial side. For evaluation of the vertical position of the mylohyoid line, it is better to use the stable mental spine rather than the alveolar process.

The morphological studies of root resorption of maxillary primary canines and their relation with the position of successive permanent teeth using Micro-CT

The purpose of this study is to clarify the root resorption of maxillary primary canines in relation to the development of successive permanent teeth. It was observed the maxilla of dry skulls of Indian children, using Micro-CT, and measured shortest distance between the root surface of maxillary primary canine and the bony crypt of maxillary canine. The bony crypt including successive canine was positioned almost directly above the root of primary canine and located superior to another bony crypts in the primary dentition stage. When the first molars reached the alveolar crest in addition to the primary dentition stage, the bony crypt of canine grew, showing the distal inclination of the superior margin and mesial inclination of the inferior margin. After the stage which is central incisors reached the alveolar crest, root resorption of primary canines was observed on the lingual side nearby the root apex and the bony crypt of canine was adjacent to the nasal cavity. It was quantitatively shown that the distance between the roots of primary maxillary canine and canine bony crypts reduced from central incisors reached the alveolar crest to lateral incisors reached that.

Morphological changes in the zygomatic arch during growth

Abstract Morphometry of the zygomatic arch was obtained using 30 Indian dried skulls at each of Hellmans dental stages: IIA, IIIA, IIIB, IVA, and VA, for a total of 150 skulls 300 sides. The following conclusions were obtained. 1.Though both the height and length of the zygomatic arch increased at all stages from IIA to VA, the rate of increase of the height indicated a value larger than the length. 2.The zygomaticotemporal suture consisted of the vertical element from the upper margin to the center and the horizontal element from the lower side to the margo inferior during the IIA period. This suture changed to a gradual curve from the upper margin to the margo inferior with the movement of the center and the lower side to the rear during the VA period. 3.The degree of interdigitation of the zygomaticotemporal suture increased from the IIA period to the IIIA and IIIB to IVA. These findings suggest that the form of the zygomatic arch and the zygomaticotemporal suture showed growth change adjusting to the functional change in mastication with growth.

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.

Coronal Cementogenesis in Cattle Molar Teeth

Abstract Coronal cementum is generally noted in herbivorous animal teeth. Cementum is occasionally formed in the cervical area and the impacted tooth occlusal surface in humans. Therefore, it is suggested that coronal cementum is formed under certain conditions. In this study, using cattle premolar tooth germs, the relationship between the movement of cementoblasts and the initiation site of cementogenesis was observed, and the following results were obtained: 1. Cementogenesis was initiated in the bottom area of occlusal surface grooves, and gradually progressed toward the cuspal crest area. 2. When reduced enamel epithelial cells migrating from the enamel surface toward the dental sac were at a distance of 20–30 μm from the enamel surface, cementoblasts appeared and cementogenesis was initiated. These findings demonstrated that after the degeneration of reduced epithelium, coronal cementum was gradually formed, showing a relationship between the formation area and progression process of coronal cementum and tooth development, since the completion period for enamel formation differs between areas.