To assess the prevalence of apical periodontitis in the Finnish population aged 30 years and older and relate it to the technical quality of root filling by the type of tooth.

As part of the Finnish nationwide Health 2000 study, panoramic radiographs were used of the dentate subjects (n = 5335) aged 30–95 years (mean 50.2 years) to assess the apical and endodontic status of their teeth (n = 120635). Apical periodontitis (AP) was recorded when the periodontal ligament space was more than double in width, or loss of lamina dura or a periapical radiolucent lesion was seen. Technically, adequate root fillings had a gap of 0–3 mm from the apex; all others were defined as inadequate. Statistical methods included chi-square tests and anova. Risk of AP was estimated as cross-product odds ratio and its 95% confidence interval.

Teeth with AP occurred in 27% of the dentate subjects being more prevalent in subjects with root filled teeth than in those without (39% vs. 9%; P < 0.001; OR = 6.3; 95% CI 5.3, 7.4). AP was more prevalent in men than in women (31% vs. 23%). At a tooth level, AP was most frequent in mandibular molars with inadequate root fillings. For all root filled teeth, an inadequate root filling doubled the risk of AP for both women (OR = 2.0; 95% CI 1.7, 2.4) and men (OR = 2.5; 95% CI 2.1, 2.9).

AP occurred principally in subjects and teeth with root fillings. Inadequate root fillings doubled the risk of AP. An improvement in the technical quality of root canal treatment is essential.