Xuemin Yin

BACKGROUND: Retromolar canal (RMC) arises from the mandibular canal (MC) behind the second or third molar and travels anterosuperiorly to a retromolar foramen (RMF). RMCs and RMFs have generally been ignored in anatomical textbooks and have rarely been reviewed or studied in the anatomical and dental literature until the last decades. OBJECTIVE: This study aimed to characterize RMF in a Chinese population concerning its incidence, origin, and classification via anatomical study and periapical radiography. METHODS: 123 dry adult Chinese mandibles were collected to observe the incidence of RMFs. RMFs were determined using a steel wire 0.5 mm in diameter. The passways or origins of the retromolar canal (RMC) were determined and classified via periapical radiography. For each RMF, two dentists independently measured the diameter and its distances to the lingual cortex, the buccal cortex, and the distal edge of the last tooth (or the alveolar fossa) using a vernier caliper. RESULTS: The incidence of RMFs was 31.71%. The average RMF diameter was 0.78 ± 0.27 mm. From RMF, the distance was 4.27 ± 1.87 mm to the lingual cortex, 8.61 ± 2.23 mm to the buccal cortex, and 7.84 ± 3.87 mm to the distal edge of the last tooth (or the alveolar fossa). RMCs were classified into MC type originating from the mandibular canal and AF type originating from the alveolar fossa. The diameters of MC ones were more significant than those of AF ones. There was no apparent correlation between the existence of the third molar and the presence of an RMF. CONCLUSION: The incidence of RMFs in Chinese may be about one-third, which is a potential factor in the onset of surgery accidents. RMCs can be classified into two types by their origins. One of them is MC, which originates from the mandibular canal, and the other is AF, which originates from the alveolar fossa.

Adenoid cystic carcinoma of the salivary gland (SACC) is a rare malignant tumors of the head and neck region, but it is one of the most common malignant tumors that are prone to perineural invasion (PNI) of the head and neck. The prognosis of patients with SACC is strongly associated with the presence of perineural spread (PNS). Although many contributing factors have been reported, the mechanisms underlying the preferential destruction of the blood-nerve barrier (BNB) by tumors and the infiltration of the tumor microenvironment by nerve fibers in SACC, have received little research attention. This review summarizes the current knowledge concerning the characteristics of SACC in relation to the PNI, and then highlights the interplay between components of the tumor microenvironment and perineural niche, as well as their contributions to the PNI. Finally, we provide new insights into the possible mechanisms underlying the pathogenesis of PNI, with particular emphasis on the role of extracellular vesicles that may serve as an attractive entry point in future studies.

Extracellular vesicles (EVs, including exosomes) are a group of heterogeneous nanometer‐sized vesicles that are released by all types of cells and serve as functional mediators of cell‐to‐cell communication. This ability is primarily due to their capacity to package and transport various proteins, lipids, and nucleic acids—namely DNA and messenger RNA (mRNA), but also microRNAs (miRNAs) and long non‐coding RNAs (lncRNAs). These contents can influence the function and fate of both recipient and donor cells. More and more studies have shown that EVs are involved in every phase of cancer development, mediating bidirectional cross talk between cancer cells and their tissue microenvironment. More specifically, EVs can promote tumor progression by modifying vesicular contents and establishing a distant premetastatic niche with molecules that favor cancer cell proliferation, migration, invasion, metastasis, angiogenesis, and even drug resistance. Given that the packaging of these molecules is known to be tissue‐specific, EVs can not only serve as novel prognostic and diagnostic markers but also be used as potential therapeutic targets and vehicles for drug delivery. The present review discusses the current understanding of the multifaceted roles of EVs in the progression of oral and salivary gland cancers, as well as their potential use in clinical applications.

Objectives: Tumor‐derived exosomes (TDE) have been shown to participate in different steps of the dissemination of cancer cells. However, the role of salivary adenoid cystic carcinoma‐derived (SACC‐derived) exosomes had not been documented in SACC. The study aims to explore the functions of SACC‐derived TDE in SACC progression and investigate potential mechanisms.Methods: Salivary adenoid cystic carcinoma cell line SACC‐83 was used to generate TDE. Afterward, SACC‐83 or HUVECs were cocultured with or without TDE. Tumor migration, tumor invasion, and endothelial permeability were examined by wound healing assay, tumor invasion assay, endothelial permeability assay, and tumor cell transendothelial migration assay, respectively. Moreover, the expression levels of cell junction‐related proteins were examined by qRT‐PCR and Western blot.Results: Salivary adenoid cystic carcinoma ‐83‐derived exosomes were taken up by their host cells. Meanwhile, TDE increased migration and invasion capacity of SACC‐83 cells and enhanced endothelial cell permeability. Furthermore, we demonstrated that the expression of cell junction‐related proteins (Claudins and ZO‐1) was downregulated, which is presumably involved in the TDE‐mediated promotion of migration, invasion, and metastasis.Conclusion: The results suggested that SACC cell‐derived exosomes were loaded with individual components that could enhance invasiveness and induce microenvironment changes, thus promoting SACC aggression.