Comparative Study of Morphology and Distribution of Valves in Human Retromandibular Vein.

The objective of this study was to analyze the distribution and morphology of the valves in the human retromandibular vein. The retromandibular, internal thoracic, azygos, femoral, and brachial veins were harvested from 46 cadavers donated to the Department of Anatomy at Tokyo Dental College for dissection. The frequency of the valves in each vein, the length of the cusps, and the thickness of the vein itself were measured. Valves were present at high frequency (92.1%) in the veins of the limbs and had cusps at least twice as long as the internal diameter of the vein. Veins in the trunk contained a lower frequency of valves, with cusps that tended to be shorter (1.60±0.77) than those of the venous valves in the limbs (2.12±0.60). The valves of the retromandibular vein tended to resemble venous valves in the trunk in terms of both frequency and morphology. The main function of venous valves in the limbs is to prevent retrograde flow. Conversely, valves in the veins of the trunk and retromandibular vein play a role in retaining blood in the veins, and their relationship to other veins means that they can cause major hemorrhage.

Structural analysis of the mylohyoid muscle as a septum dividing the floor of the oral cavity for the purposes of dental implant surgery: variety of muscle attachment positions and ranges of distribution.

OBJECTIVES: The objective was to investigate the details of the attachments of the mylohyoid muscle to the mandible anterior to the hyoid and mylohyoid lines to understand the positional relationship between the sublingual space and the mylohyoid, knowledge that is essential for dental implant surgery in the incisal region, as well as the routes of communication between the sublingual space and other spaces. METHODS: While evaluating the presence or absence of an anterior mylohyoid muscle fiber attachment to the mandible, sublingual gland herniation, spaces between muscle fascicles were also recorded as sites of penetration. The mean muscle thickness in each of these areas was also calculated. RESULTS: In all specimens, the mylohyoid originated not only from the mylohyoid line but also from the lingual surface of the center of the mandibular body (the mandibular symphysis) below the mental spines. The mylohyoid muscle fascicles were thickest in the posterior region, and further anterior to this, they tended to become thinner. Sublingual gland herniations passing through the mylohyoid were noted in the anterior and central regions, but not in the posterior region. Penetration between the muscle fascicles was most common in the central region, and no such penetration was evident in the posterior region. CONCLUSIONS: These results suggest that the mylohyoid functions only incompletely as a septum, and that routes of communication from the sublingual space to the submandibular space may be present in both the anterior and central muscle fascicles of the mylohyoid. Therefore, bleeding complications during dental implant placement in the anterior mandible can be serious issues. There is a potential for sublingual hematoma that could compromise the airway by pressing the tongue against the soft palate into the pharynx.

Subset of the periodontal ligament expressed leptin receptor contributes to part of hard tissue-forming cells.

The lineage of periodontal ligament (PDL) stem cells contributes to alveolar bone (AB) and cementum formation, which are essential for tooth-jawbone attachment. Leptin receptor (LepR), a skeletal stem cell marker, is expressed in PDL; however, the stem cell capacity of LepR+ PDL cells remains unclear. We used a Cre/LoxP-based approach and detected LepR-cre-labeled cells in the perivascular around the root apex; their number increased with age. In the juvenile stage, LepR+ PDL cells differentiated into AB-embedded osteocytes rather than cementocytes, but their contribution to both increased with age. The frequency of LepR+ PDL cell-derived lineages in hard tissue was < 20% per total cells at 1-year-old. Similarly, LepR+ PDL cells differentiated into osteocytes following tooth extraction, but their frequency was < 9%. Additionally, both LepR+ and LepR- PDL cells demonstrated spheroid-forming capacity, which is an indicator of self-renewal. These results indicate that both LepR+ and LepR- PDL populations contributed to hard tissue formation. LepR- PDL cells increased the expression of LepR during spheroid formation, suggesting that the LepR- PDL cells may hierarchically sit upstream of LepR+ PDL cells. Collectively, the origin of hard tissue-forming cells in the PDL is heterogeneous, some of which express LepR.

Retromandibular vein position and course patterns in relation to mandible: anatomical morphologies requiring particular vigilance during sagittal split ramus osteotomy.

Major bleeding associated with sagittal split ramus osteotomy (SSRO) involves vessels such as the inferior alveolar, facial, and maxillary arteries and veins, and the retromandibular vein (RMV). The present study aimed to clarify and classify the three-dimensional variations in RMV position and course direction in relation to the mandible. Specimens comprised a total of 15 scientific cadavers, and the relationship between RMV and the mandible lateral and posterior views was observed. We identified 3 patterns on the lateral view, the mean distance between the RMV and the posterior border of the ramus was 3.9 mm at the height of the lingula. A total of five course patterns were identified on the posterior view. In no course pattern, the RMV inferior to the lingula was lateral to its position superior to the lingual. The present findings suggest that it may be possible to predict correlations with intraoperative bleeding risk. Further study is planned using contrast computed tomography in patients with jaw deformity for skeletal classification.