Treponema denticola is an important pathogenic Treponema pathogen in the human oral cavity. Early studies have found that Treponema denticola is closely related to the occurrence and development of periodontal diseases. With the development of technical methods in recent years, many studies have shown that Treponema denticola not only can participate in periodontal diseases through a variety of mechanisms but also can play an important role in the development of various oral diseases. Treponema denticola is detected in high concentrations in peri-apical diseases and peri-implant diseases, and its surface protein is also prevalent in oral tumor samples. This paper reviews the research progress of Treponema denticola in periodontal diseases, pulp peri-apical diseases, peri-implant diseases and oral tumors, and summarizes the relevant mechanisms. For example, Treponema denticola can cause immune regulation disorder, destroy the epithelial barrier, induce bone absorption, promote the occurrence and development of inflammation through a variety of surface proteins, including chymotrypsin-like protease complex (CTLP), major outer sheath protein (Mosp), Td92, and LOS. It can also escape complement-mediated killing effects through surface FhbB lipoproteins and promote the occurrence and development of oral tumors by regulating the tumor microenvironment. These theories provide a theoretical basis for further understanding the development of oral diseases, controlling the infection of Treponema denticola, and exploring more effective treatment strategies.

Salivary exosomes are extracellular vesicles with a diameter of 30-50 nm in saliva. With the development of technology in recent years, many studies have revealed that salivary exosomes play an important role in the occurrence and development of various oral diseases. For example, salivary exosomal CD9 and CD81 promote tumor cell metastasis by regulating the cell adhesion and movement, salivary exosomal miR-24-3p promotes the tumor cell proliferation by acting on PER1, and salivary exosomal programmed cell death-ligand 1 (PD-L1) mRNA inhibits the destruction of inflammatory tissue, which can be biomarkers for the diagnosis of oral cancer, periodontitis and other oral diseases. Therefore, salivary exosomes can be used as potential prognostic and diagnostic markers for oral diseases. In addition to oral diseases, such as oral cancer, periodontitis, oral lichen planus, Sjogren's syndrome, etc., salivary exosomes are closely related to distant tumors, such as pancreatic cancer, lung cancer, and systemic diseases, such as Parkinson's disease, inflammatory bowel disease, etc. It is of great significance to study the role of salivary exosomes in the diagnosis and treatment of oral and systemic diseases and to develop the potential of salivary exosomes as biomarkers for disease diagnosis.