Oral diseases remain widespread, while concerns about antimicrobial resistance, microbiome disruption, and adverse effects from prolonged antiseptic use encourage interest in plant-based approaches. This structured narrative review synthesises literature published predominantly from 2010 to 2026, including mechanistic, in vitro, biofilm, preclinical, clinical, and formulation studies addressing medicinal plants, isolated phytochemicals, and plant-derived oral healthcare products. We examine how these interventions may influence oral health through mechanisms extending beyond direct bacterial killing. We synthesise evidence on major phytochemical classes, including polyphenols, terpenoids, alkaloids, sulfur compounds, and glycosides, together with their effects on biofilms, quorum sensing, inflammation, oxidative stress, and tissue repair. We also assess clinical evidence for botanical formulations and emerging delivery systems designed to improve stability and local retention. Current evidence indicates that several plant-derived compounds can inhibit biofilm formation, interfere with bacterial virulence, modulate inflammatory signalling, and support tissue recovery. Green tea, pomegranate, cranberry, turmeric, neem, aloe vera, mangosteen, and propolis show promising clinical or experimental activity, although evidence strength varies considerably among plants and formulations. Nanoemulsions, lipid-based carriers, and mucoadhesive systems may improve phytochemical stability and local exposure, but clinical validation remains limited. Overall, phytotherapy appears most useful as an adjunct to established oral hygiene rather than a replacement for conventional care. Standardized extracts, well-characterized formulations, microbiome-based outcomes, long-term clinical trials, and clearer regulatory pathways remain essential before wider clinical adoption.