The mandibular second molars show various morphological features in the roots and root canal, and a guttershaped root (GSR) caused by fusion of the mesial and distal roots is frequently encountered. In this study the number of the roots associated with mandibular second molars were observed using dental cone-beam computed tomography (CBCT). For those with a GSR, determination of root morphology and root canal classification were performed. CBCT image data from 173 Japanese mandibular second molars were obtained. Using sliced images, the number of the roots and root morphology were determined. In cases with a GSR, the ratio for the fused roots was determined and root canal morphology features were classified. A GSR was found in 61 (35.3%), with greater prevalence in females. In addition, the overall ratio of the fused part to root thickness in those with a GSR was 48.7%, with no significant difference related to sex. Furthermore, a C-shaped root canal morphology was commonly observed in both males and females with a GSR. In the present cohort examined in Japanese, most of the mandibular second molar were found to have two roots, with a GSR noted in 35.5%. While a GSR was more often observed in females, a C-shaped root canal was the most common root canal morphology in both sexs. It is considered that assessment using CBCT findings is helpful for precise determination of root canal morphology and presence of a GSR in mandibular second molars.

Although the epiglottis plays a vital role in deglutition, histological studies of the epiglottis and surrounding ligaments associated with swallowing dysfunction are limited. Therefore, we performed histological observations to clarify age-related changes in the morphological characteristics of the epiglottis and surrounding structures. Tissue samples comprising the epiglottis and surrounding structures were collected from corpses that were both orally fed and tubefed during their lifetimes. Following hematoxylin and eosin, Elastica Van Gieson, and immunohistochemical staining procedures, the chondrocytes, connective tissue, and glandular tissue were observed under the epiglottis epithelium, and intervening adipose tissue was observed in the surrounding area. Fatty degeneration of acinar cells was also observed in the glandular tissue, possibly because of aging. Bundles of elastic fibers were present around the vascular wall in the periepiglottic ligament, but some were reduced. Furthermore, large amounts of collagen fibers ran toward and through the cartilage, whereas the mesh-like elastic fibers stopped in front of the cartilage. Microfibrils considered to be oxytalan fibers, which are thinner and shorter than elastic fibers, were observed around the vascular wall and in the fiber bundles. Agerelated changes included connective tissue fibrosis shown by the large amount of collagen fibers, atrophy of salivary glands, and an accompanying increase in adipose tissue. Regarding stretchability and elasticity, the elastic fibers may have an auxiliary function for laryngeal elevation during deglutition. This suggests that disuse atrophy of the laryngeal organs with or without oral intake might reduce the amount of elastic fiber in older adults.

A variety of shapes has been reported for the roots and root canals of maxillary first premolars. The purposes of the present study were to determine branching and shapes of the roots of maxillary first premolars, as well as age-related changes using slice images obtained with cone-beam computed tomography (CBCT) for dental use. CBCT-reconstructed images of 125 cases that included maxillary first premolars were used as subjects. Slice images at the cervical one-third, center, and apical one-third positions of the root were prepared. Root branching and number of root canals was determined at each measurement position in the images. The subjects were divided into three groups: younger than 30 years, 30 to 50 years, and over 50 years. The root canal morphology was compared among these age groups. Single-rooted premolars were the most frequent. As for number of root canals, a single-canal premolar was observed at the position of the cervical one-third in 33.6%, at the center in 35.2%, and at the apical one-third in 56.0%. Thereafter the subjects were divided into groups by age, namely, younger than 30 years, 30 to 50 years, and over 50 years old, and it was revealed that the ratio of the two-canal type increased with age. In regard to tooth morphology, it was confirmed that the two-canal type shows more frequent occurrence with aging in maxillary first premolar. Based on our findings, we consider that CBCT can be useful for determining the root canal morphology with complicated shapes.

The root canal morphology undergoes aging-related changes, and relevant quantitative analyses have not yet been reported. We compared the cone beam computed tomography (CBCT) and micro-computed tomography (microCT) scans of extracted mandibular incisors to check the accuracy of morphological measurements. Thereafter, the root canal morphology and aging-related changes in the mandibular incisors of Japanese individuals were assessed using CBCT.Six extracted teeth were fixed in a phantom head and imaged using CBCT and micro-CT. The correlation between the findings of the two imaging modalities was examined. Further, CBCT reconstructed images of the mandibular incisors of 81 individuals were observed. Age-related changes of the root canals were compared between participants aged <30 years and those aged ≥30 years. The CBCT and micro-CT findings regarding the root canals of the extracted teeth coincided in 94.4% of the cases. Mandibular incisors exhibiting two root canals in either cross-section accounted for 9.9% of central incisors and 12.4% of lateral incisors. Mandibular central incisors with two root canals were observed in two (6.3%) individuals aged <30 years and six (12.2%) aged ≥30 years. Mandibular lateral incisors with two root canals were observed in one (3.1%) individual aged <30 years and nine (18.4%) aged ≥30 years. CBCT allows accurate evaluation of complex root canal morphologies and is useful for endodontic preoperative assessment. Mandibular incisors have more frequent occurrence of two root canals with aging.