PRTN3 and rheumatoid arthritis: Our aim was therefore to investigate the prevalence of periodontitis amongst patients with RA, with special focus on seropositivity, both ACPA and rheumatoid factor (RF), in the Swedish population-based Epidemiological Investigation of Rheumatoid Arthritis (EIRA) case-control study, by linking EIRA with the National Dental Health Registry (DHR).