Influence of case definitions on epidemiological estimates of periodontitis prevalence and its associations with smoking and OHRQoL

Objectives To compare periodontitis prevalence estimates obtained using the new classification system with those generated using other case definitions from the literature, examine the strength of the association between tobacco smoking and periodontitis (and that between periodontitis and its impact on oral‐health‐related quality of life; OHRQoL) using those definitions. Methods We conducted a secondary analysis of data from the 2009 New Zealand Oral Health Survey, a cross‐sectional dental examination survey of a representative sample of people aged 18 or over. We identified cases using 10 different periodontitis case definitions and then compared weighted prevalence estimates across those. The associations between smoking and periodontitis, and between periodontitis and short‐form Oral Health Impact Profile (OHIP‐14) scores, were then compared across the various case definitions. Results There was considerable variation in periodontitis prevalence estimates (range 3% to 59%). All definitions (but one) showed a higher prevalence of periodontitis in smokers than in non‐smokers. The new classification stage III definition showed the strongest association, with an adjusted prevalence ratio of 1.99 (95%CI: 1.35, 2.91). All case definitions (but one) had a higher mean OHIP‐14 score among people with periodontitis. Conclusions Periodontitis prevalence estimates are greatly influenced by case definition choice. The new classification system may be more accurate than any other used to date, but questions remain about its utility for periodontal epidemiology.