There is little or no information about the distribution of elastic fibers in the human fetal head. We examined this issue in 15 late-stage fetuses (crown-rump length, 220-320 mm) using aldehyde-fuchsin and elastica-Masson staining, and we used the arterial wall elastic laminae and external ear cartilages as positive staining controls. The posterior pharyngeal wall, as well as the ligaments connecting the laryngeal cartilages, contained abundant elastic fibers. In contrast with the sphenomandibular ligament and the temporomandibular joint disk, in which elastic fibers were partly present, the discomalleolar ligament and the fascial structures around the pterygoid muscles did not have any elastic fibers. In addition, the posterior marginal fascia of the prestyloid space did contain such fibers. Notably, in the middle ear, elastic fibers accumulated along the tendons of the tensor tympani and stapedius muscles and in the joint capsules of the ear ossicle articulations. Elastic fibers were not seen in any other muscle tendons or vertebral facet capsules in the head and neck. Despite being composed of smooth muscle, the orbitalis muscle did not contain any elastic fibers. The elastic fibers in the sphenomandibular ligament seemed to correspond to an intermediate step of development between Meckel's cartilage and the final ligament. Overall, there seemed to be a mini-version of elastic fiber distribution compared to that in adults and a different specific developmental pattern of connective tissues. The latter morphology might be a result of an adaptation to hypoxic conditions during development.

To provide a better understanding of the local immune system in the face and external genitalia, i.e., the oral floor, lower lip, palpebral conjunctiva, anus and penis, we examined the distribution and density of CD1a-positve Langerhans cells, CD8-positive suppressor T lymphocytes and CD68-positive macrophages using specimens from 8 male elderly cadavers. The density of Langerhans cells showed an individual difference of more than (or almost) 10-fold in the lip (oral floor). In the oral floor, Langerhans cells were often spherical. Submucosal or subcutaneous suppressor lymphocytes, especially rich in the oral floor and penile skin, migrated into the epithelium at 4 sites, except for the anus. In the conjunctiva, macrophage migration into the epithelium was seen in all 8 specimens. The density of suppressor lymphocytes showed a significant correlation between the oral floor and the lip (r=0.78). In contrast, the anal and penile skins showed no positive correlation in the density of all three types of immunoreactive cells examined. Overall, irrespective of the wide individual differences, the oral floor and conjunctiva seemed to be characterized by a rich content of all three cell types, whereas the penile skin was characterized by an abundance of suppressor lymphocytes. Based on the tables, as mean value, the relative abundance of three different cell types were as follows; CD1a-positive Langerhans cells (anus), CD8-positive lymphocytes (penis), and CD68-positive macrophages (lip). The present observations suggest that the local immune response is highly site-dependent, with a tendency for tolerance rather than rejection.

In maxillary molar region implant therapy, support is sometimes obtained from trabecular bone comprising the maxillary tuberosity, pterygoid process of the sphenoid bone, and pyramidal process of the palatine bone. Great care is necessary in such cases due to the presence of the greater palatine canal, which forms a passageway for the greater palatine artery, vein, and nerve. However, clinical anatomical reports envisioning embedding of pterygomaxillary implants in this trabecular bone region have been limited in number. In this study, the 3-D morphology of the greater palatine canal region, including the maxillary tuberosity region and points requiring particular care in pterygomaxillary implantation, were therefore investigated. Micro-CT was used to image 20 dentulous jaws (40 sides) harvested from the dry skulls of Japanese individuals with a mean age of 28.2 years at time of death. The skulls were obtained from the Jikei University School of Medicine cadaver repository. Three-dimensional reconstruction of the trabecular bone region, including the greater palatine canal, was performed using software for 3-D measurement of trabecular bone structure. Trabecular bone region morphometry was performed with the hamular notch-incisive papilla (HIP) plane as the reference plane. The results showed a truncated-cone structure with the greater palatine foramen as the base extending to the pterygopalatine fossa. This indicates the need for care with respect to proximity of the dental implant body to the greater palatine canal and the risk of perforation if it is embedded in the maxillary tuberosity region at an inclination of 60° toward the lingual side. Moreover, caution must be exercised to avoid possible damage to the medial wall of the maxillary sinus if the inclination of the embedded dental implant body is almost perpendicular to the HIP plane.