The pathogenesis of periodontitis and of rheumatoid arthritis show remarkable similarities. There is a distinct degree of co-existence between the 2 diseases. The prevalence of periodontitis is more pronounced in rheumatoid arthritis patients and the prevalence of rheumatoid arthritis is more pronounced in periodontitis patients. At present, a positive influence of periodontal treatment on the rheumatoid arthritis disease activity or of rheumatoid arthritis drug treatment on periodontitis is not sufficiently supported by clinical research. Periodontitis may play a role in unsatisfactory therapy response in some rheumatoid arthritis patients.