In this review, we critically evaluate the case–control studies examining the relationship between rheumatoid arthritis (RA) and periodontitis, two common chronic inflammatory diseases with a similar host-mediated pathogenesis. We review the “two-hit” periodontitis model that our group previously proposed, in which we elucidate how a systemic disease such as RA can potentially exacerbate or initiate periodontitis. Furthermore, we discuss adjunctive host modulation therapy, originally developed for periodontitis (i.e., subantimicrobial-dose doxycycline alone or in combination with an anti-inflammatory agent), to simultaneously mitigate RA and periodontitis. Finally, we review studies describing periodontal treatment effects on both RA disease activity measures and systemic inflammation. Current evidence suggests that an association exists between periodontitis and RA. Well-designed multicenter longitudinal clinical trials and studies with sufficient sample sizes are needed to ascertain the temporal relationship between these two diseases and whether periodontal treatment can reduce the severity of RA or prevent its onset.