Oral health results from the interaction between oral microbiota, host tissues, saliva, diet, and behavioural and environmental factors. Dental plaque is a complex microbial biofilm that develops on oral surfaces and, under unfavourable ecological conditions, can contribute to the onset and progression of dental caries and periodontal diseases. Saliva is a key protective component of the oral environment, contributing to mechanical cleansing, acid neutralization, mineral homeostasis, lubrication, and microbial control. Major salivary parameters of interest include salivary pH, flow rate, buffering capacity, and molecular composition. In recent years, increased attention has also been paid to salivary biomarkers, such as proteins, enzymes, cytokines, immunoglobulins, and metabolites, as potential indicators of oral health status and disease-related changes. This review aims to summarize current knowledge regarding the role of dental plaque and salivary parameters in the assessment of oral health, with a particular focus on their relationship with dental caries and periodontal diseases.