Biological definition of periodontal diseases: A historical review of host-response diagnostics and their implications for disease classification.

Understanding periodontal diseases through a biological lens has been a central aim in periodontal research. Visionary pioneers in the field established the foundations of our knowledge, providing invaluable insights into disease mechanisms and progression. This review highlights the evolving understanding of periodontal diseases, with particular focus on the transition from traditional diagnostic methods to molecular-based approaches. A narrative review was undertaken through a comprehensive literature search, synthesizing both historical perspectives and contemporary evidence. Over recent decades, fundamental discoveries have significantly advanced our knowledge of periodontal pathogenesis. Despite this, current diagnostic protocols and classification systems remain largely reliant on clinical phenotypes such as pocket depth, attachment loss, and radiographic changes. These measures, while valuable, lack the precision to capture the underlying biological processes. To address this gap, a variety of biological samples (such as saliva, blood, gingival tissue and gingival crevicular fluid) have been explored as potential sources of diagnostic information. Investigations have identified diverse biomarkers, ranging from specific bacterial species and their products to host-derived enzymes, immune mediators, and tissue degradation products originating from the periodontal tissues. These findings colectively underscore the promise of molecular-based strategies to enhance disease detection and monitoring. There is growing momentum toward the development of rapid, non-invasive, molecular diagnostic tools for periodontitis. Such approaches could not only enable earlier and more precise diagnosis within dentistry, but may also extend to applications in broader medical and non-dental settings.