Masatsugu Hashimoto

Age estimation based on three-dimensional measurement of mandibular central incisors in Japanese

The purpose of this study was to investigate an age estimation method that considers gender as well as three-dimensional measurement of the components, specifically enamel and dentin. A total of 155 mandibular central incisors aged 12-79 years old which was chosen from the collection stored at the Department of Anatomy in Tokyo Dental College and had no opened apex, caries or restorative treatment, were examined. Samples were scanned using micro-CT HMX225 ACTIS4. Based on the sliced image data, three-dimensional structures were obtained and the volumes of enamel, dentin, and pulp cavity were measured. Regression equations for age estimation were then determined. The accuracy of age estimation equations for each region, volume ratio, and sex was assessed using the determination coefficient R(2) as well as the standard errors of estimated values. The root region alone had a comparable accuracy to that of the whole tooth and the crown region had a relatively lower accuracy. In the whole tooth and the crown region, slightly higher correlations were observed for pulp/tooth volume ratios in which enamel was excluded. Females tended to have higher accuracy compared to males. The estimated age was higher in males compared to females for the same volume ratio of the pulp cavity. The highest correlation in both genders with age was observed for the volume ratio of the pulp cavity to the whole tooth excluding the enamel (males, R(2)=0.67; females, R(2)=0.76). The 95% confidence intervals for the population regression showed different distributions for each sex. In the 95% prediction intervals for age estimation, females tended to have narrower intervals and higher accuracy compared to males. Therefore, the use of gender-specific equations is recommended for age estimation.

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.

Red cell glyoxalase I polymorphism in Japanese: Confirmation of a lowGLO1 frequency

SummaryHaemolysate samples from 414 unrelated Japanese living in Tokyo were examined for GLO phenotypes by starch gel electrophoresis using a tris-citrate-borate-LiOH buffer system, pH 7.4. Three phenotypes were found which were classified as GLO 1 (2; 0.48%) GLO 2-1 (40; 9.66%) and GLO 2 (372; 89.86%). The corresponding gene frequency for GLO1 was 0.0531 and that for GLO2 was 0.9469. It was confirmed that the GLO1 frequency of Japanese is much lower than the values previously reported for Caucasians and Africans.

The Influence of Bite Force on the Internal Structure of the Mandible through Implant—Three-dimensional and Mechanical Analysis Using Micro-CT and Finite Element Method—

Applying appropriate stress through the teeth is considered essential for maintaining the homeostasis of the jaw. The aim of this study was to clarify the effects of pressure applied via endosseous implants on internal structures of the jaw. A mandible with dental implants for 15 years was analyzed by micro-CT to prepare a finite element model of the mandible, including implants and the surrounding internal microstructures. Based on this model, mechanical analysis was conducted by the three-dimensional finite element method. The results showed that stress distribution was seen in the trabecular bone around the implants. It became clear that pressure is transmitted to mandibular internal structures via implants, and stress is dispersed along internal trabecular alignment.

Trial application of oxygen and carbon isotope analysis in tooth enamel for identification of past-war victims for discriminating between Japanese and US soldiers

Stable isotope analysis has undergone rapid development in recent years and yielded significant results in the field of forensic sciences. In particular, carbon and oxygen isotopic ratios in tooth enamel obtained from human remains can provide useful information for the crosschecking of morphological and DNA analyses and facilitate rapid on-site prescreening for the identification of remains. This study analyzes carbon and oxygen isotopic ratios in the tooth enamel of Japanese people born between 1878 and 1930, in order to obtain data for methodological differentiation of Japanese and American remains from the Second World War. The carbon and oxygen isotopic ratios in the tooth enamel of the examined Japanese individuals are compared to previously reported data for American individuals (born post WWII), and statistical analysis is conducted using a discrimination method based on a logistic regression analysis. The discrimination between the Japanese and US populations, including Alaska and Hawaii, is found to be highly accurate. Thus, the present method has potential as a discrimination technique for both populations for use in the examination of mixed remains comprising Japanese and American fallen soldiers.

Evaluation of the Palatal Bone for Placement of Orthodontic Mini-Implants in Japanese Adults

Abstract Mini-implants are increasingly being used for orthodontic anchorage in the palate. The anatomical structure of the jaw must be properly evaluated prior to use; however, there are a few research reports providing basic data regarding the palate. Bone thickness was measured and bone morphology evaluated in the palates of Japanese people. The palates of five Japanese adult cadavers and 15 skulls were examined. The samples were imaged and measured using the micro-CT system. In the mid-palatine suture region, the cortical bone had a complex mesh-like structure and was thicker than surrounding areas. Cortical bone thickness varied depending on the site. The mid-palatine suture region is an ideal site for mini-implant insertion; however, because bone and cortical bone thickness markedly decrease in the lateral region, careful attention should be paid when inserting mini-implants in the midpalatine suture.

Temporomandibular joint ankylosis: a case report.

ABSTRACT 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.