The landmark study behind the plaque-gingivitis link (Löe, 1965)

Löe H, Theilade E, Jensen SB. "Experimental Gingivitis in Man." Journal of Periodontology, 1965; 36(3):177-187.

Description

This is one of the most cited studies in all of periodontology. Before it, the causal link between dental plaque and gingivitis had never been demonstrated experimentally in humans — only observed through correlation. Löe and colleagues designed a simple protocol to settle the question: induce gingivitis in a lab setting, in healthy subjects, by deliberately withdrawing oral hygiene.

Method

Twelve dental students, selected for their excellent oral hygiene and clinically healthy gums at baseline, stopped all brushing and interdental cleaning for 9 to 21 days. The authors measured the Plaque Index (PI) and Gingival Index (GI) at regular intervals — two indices Löe himself had helped develop a few years earlier. At the end of the observation period, oral hygiene was resumed to observe whether the lesions were reversible.

Results

All 12 subjects developed visible plaque accumulation and generalized (mild to moderate) gingivitis within a few weeks, without exception. The severity of gingival inflammation closely tracked plaque accumulation. Once brushing resumed, gingivitis regressed in every subject, confirming that inflammation is reversible at this early stage.

Analysis

The sample is small (12 subjects) and not randomized in the modern sense — expected for a 1965 experimental study. Its strength doesn't come from statistical power, but from its design: by removing hygiene and then reintroducing it in the same subjects, the study establishes a direct causal link (and its reversibility), where earlier observational studies could only suggest an association. This design became a model reused in hundreds of later studies (the "experimental gingivitis model"), still used today to test new oral hygiene products.

Conclusion

This study established dental plaque as a direct and sufficient cause of gingivitis, and demonstrated that gingival inflammation is reversible through plaque control alone — a principle that remains foundational to periodontal prevention six decades later, including the clinical value of tight control over at-risk sites during recall visits.