Saliva as a diagnostic medium for certain diseases

Saliva is a complex biological fluid with a variety of biomolecules, such as DNA, RNA, proteins, metabolites and microbiota, which can be used for the screening and diagnosis of many diseases. In addition, saliva has the characteristics of simple collection, non-invasive and convenient storage, which gives it the potential to replace blood as a new main body of fluid biopsy, and it is an excellent biological diagnostic fluid. In this review, we review research related to saliva diagnostics, including saliva content, techniques and processes related to saliva detection samples, and saliva detection studies in various diseases. The densities of Streptococcus mutans and Lactobacillus in people with high caries activity were much higher than those with low caries. Porphyromonas gingivalis has been confirmed to be closely associated with periodontitis. Currently, an ELISA kit has been developed to specifically detect P. gingivalis in saliva. Compared with qPCR, its detection rate is higher, and the sensitivity and specificity are as high as 92 - 96%, respectively. Therefore, it is expected to become an easy and rapid diagnostic tool for the detection of P. gingivalis and has great potential for rapid screening of periodontitis. Saliva contains various biological components, including DNA, RNA, proteins, microorganisms and metabolites, which are potential biomarkers. Biomarkers can reflect the physiological and pathological state of the body, which is an important basis for personalized medicine. Therefore, comprehensive analysis and identification of various components in human saliva will greatly help us to develop biomarkers related to human health and disease status, early identification of diseases, assessment of prognosis and disease risk, and monitoring the effect of treatment. Currently, more than 100 metabolites have been reported to be altered with the malignant progression of OSCC, such as lactate, choline, glutamate, histidine, sialic acid, and trimethylamine N oxide. Oral microorganisms play an important role in host health and disease. In recent years, some studies have shown that the change of oral microflora will destroy the balance between microorganisms and the human body, together with the influence of risk factors, leading to the occurrence of OSCC. Oral microorganisms, epithelial barrier, immune system, and chronic inflammation constitute the four important factors leading to oral cancer. Therefore, oral microorganisms are potential biomarkers for the early diagnosis of OSCC. The results show that the accuracy of the model is 95.70% and the sensitivity is 100%.This review integrates recent studies and summarizes the research contents of the research progress of saliva in early diagnosis of oral and systemic diseases. This review aims to explore the value and prospect of saliva diagnosis in clinical application. Keywords: biomarkers, oral diseases, salivary diagnosis, systemic diseases