The 2018 periodontal classification: what actually changes chairside

Why a new classification

For nearly 20 years, periodontal diagnosis relied on the 1999 classification, which notably distinguished between "chronic" and "aggressive" periodontitis. The problem: that boundary proved hard to apply consistently from one clinician to another, and it didn't reliably reflect actual severity or risk of progression. In 2017, the American Academy of Periodontology and the European Federation of Periodontology held a joint World Workshop to overhaul it entirely; the result, published in 2018, is the classification in use today.

The principle: stage and grade

Periodontitis is now described along two independent axes rather than a single label.

Stage (I to IV) reflects severity and complexity at the time of examination: maximum interdental attachment loss, radiographic bone loss, teeth lost to periodontal disease, and complexity factors such as probing depth, furcation involvement, and ridge defects. It's determined by the worst affected site in the mouth, not an average.

Grade (A, B, or C) reflects the estimated rate of progression and level of risk: direct evidence when earlier radiographs allow comparison over time, or indirect evidence via the percentage of bone loss divided by the patient's age, adjusted for risk factors such as smoking or poorly controlled diabetes.

What actually changes in charting

In practice, two things stand out. First, diagnosis is no longer a single label: stage and grade now need to be recorded separately, which carries more prognostic value but requires information that isn't always available at the first visit (older radiographs, in particular). Second, in the absence of longitudinal data, grade B is the recommended default starting point, to be reassessed later based on clinical evolution and identified risk factors.

Limitations and caveats

The classification has clearly improved the consistency of periodontal diagnosis, but it isn't without limitations: grade remains hard to estimate precisely without radiographic history, and several studies have documented meaningful inter-clinician variability when assigning it without prior records. Treating the diagnosis as evolving — reassessed at each recall rather than fixed at the first exam — remains the best safeguard for reliability.

Conclusion

Beyond the change in vocabulary, this classification marks a shift in perspective: periodontitis is no longer seen as two distinct diseases (chronic and aggressive), but as a single disease whose severity and risk vary along a continuum. For everyday practice, it's less an administrative burden than a more precise tool for communicating a patient's actual prognosis.