Aim: This review aims to analyze the microbiology, pathogenesis, and current therapeutic strategies of dental caries and periodontal diseases, with a focus on the role of polymicrobial biofilms, host–microbe interactions, and the major pathogenic species involved in disease progression. Materials and Methods:A comprehensive literature review was conducted using major scientific databases, including PubMed, Scopus, Web of Science, and Google Scholar. Studies published between 2000 and 2025 were included. Relevant experimental, clinical, and review articles addressing the etiology, microbial composition, virulence mechanisms, host immune responses, and therapeutic approaches for dental caries and periodontal disease were analyzed. Results:The oral cavity contains more than 700–800 bacterial species, with Streptococcus mutans serving as the primary cariogenic pathogen and Porphyromonas gingivalis identified as a key driver of periodontal disease. Dental caries progression is primarily attributed to acid production and enamel demineralization, while periodontal disease results from a dysbiotic shift in the subgingival microbiome accompanied by destructive host inflammatory responses. The “red complex” (P. gingivalis, Treponema denticola, and Tannerella forsythia) exhibits strong synergistic virulence in advanced periodontitis. Biofilm formation, extracellular polysaccharide (EPS) matrix production, quorum sensing, and immune components such as neutrophils, macrophages, and matrix metalloproteinases (MMPs) all contribute to disease development Conclusions:Dental caries and periodontal diseases result from complex interactions between polymicrobial biofilms and host immune responses. A deeper understanding of microbial ecology, virulence pathways, and host–pathogen interactions is essential for improving prevention and treatment. Advances in targeted antimicrobial therapies and innovative therapeutic approaches hold promise for enhancing global oral health outcomes.