Context Removable partial dentures used to restore the shortened lower dental arch may adversely affect the remaining natural teeth and are associated with a low prevalence of use. Objective: To report the findings for caries incidence 2 years after restoration of lower shortened arches with bilateral cantilever resin-bonded bridges (RBBs) and conventional partial dentures (RPDs). Design: Randomised controlled trial. Setting: Secondary care Patients: 25 male and 35 female subjects of median age 67 years were randomly allocated to 'bridge' and 'denture' treatment groups of 30 patients each matched for age and sex. Caries incidence was recorded during dental examinations 3 months, 1 and 2 years after insertion of new lower prostheses. Interventions: Cantilever RBBs and conventional RPDs with cast metal frameworks. Results: There was a highly significant difference in the frequency of new caries lesions, 11 and 51 in the bridge and denture groups respectively (P < 0.01). 20 out of 27 bridge patients and 9 of 23 denture patients had no caries experience. Multivariate modeling identified treatment group as the only significant predictor of caries occurrence. Conclusions: Two years after restoration of lower shortened arches for an elderly sample of patients, there was a significantly greater incidence of new and recurrent caries lesions in subjects restored with RPDs compared with cantilever RBBs.