In a multicentre randomised trial (German Research Association, grants DFG WA 831/2–1 to 2–6, WO 677/2–1.1 to 2–2.1.; controlled-trials.com ISRCTN97265367), patients with complete molar loss in one jaw received either a partial removable dental prosthesis (PRDP) with precision attachments or treatment according to the SDA concept aiming at pre-molar occlusion. The objective of this current analysis was to evaluate the influence of different treatments on periodontal health. Linear mixed regression models were fitted to quantify the differences between the treatment groups. The assessment at 5 years encompassed 59 patients (PRDP group) and 46 patients (SDA group). For the distal measuring sites of the posterior-most teeth of the study jaw, significant differences were found for the plaque index according to Silness and Löe, vertical clinical attachment loss (CAL-V), probing pocket depth (PPD) and bleeding on probing. These differences were small and showed a slightly more unfavourable course in the PRDP group. With CAL-V and PPD, significant differences were also found for the study jaw as a whole. For CAL-V, the estimated group differences over 5 years amounted to 0·27 mm (95% CI 0·05; 0·48;P= 0·016) for the study jaw and 0·25 mm (95% CI 0·05; 0·45;P= 0·014) for the distal sites of the posterior-most teeth. The respective values for PPD were 0·22 mm (95% CI 0·03; 0·41;P= 0·023) and 0·32 mm (95% CI 0·13; 0·5;P= 0·001). It can be concluded that even in a well-maintained patient group statistically significant although minor detrimental effects of PRDPs on periodontal health are measurable.