Purpose: To investigate the chewing efficiency of edentulous patients wearing complete dentures, treated with a single implant in the mandible, placed underneath the existing mandibular dentures, using two different loading protocols (immediate loading or conventional loading), over an observation period of 5 years. Methods: One-hundred and fifty-eight (158) edentulous seniors aged 60-89 years received an implant in the midline of the lower jaw and were randomized either to the immediate loaded group A (n=81) or the conventional loaded group B (n=77). Chewing efficiency was obtained before treatment, one month after implant placement during the submerged healing phase (only group B) and 1, 4, 12, 24 and 60 months after implant loading. Results: After 5 years, chewing tests from 89 patients (45 in the immediate loading group and 44 in the conventional loading group) were available for every recall visit and thus statistically analyzed. The chewing efficiency increased over time in both groups. A significant increase was observed up to 4 months after loading (p≤0.05). Later, chewing efficiency further increased, but not significantly. Between the two loading protocols, chewing efficiency did not differ significantly (p>0.05) at any follow-up investigation. Conclusion: A single mandibular implant placed underneath existing mandibular dentures improves chewing efficiency of edentulous patients significantly over an observation period of 5 years, irrespective of the loading protocol.