The aim of this study was to evaluate some effects of treatment first with optimised complete dentures and then with mandibular fixed tissue-integrated prostheses (TIPs). The most important functional variables studied were bite force, chewing efficiency and chewing ability. Other variables were changes in dietary selection and habits, psychological reactions, bone loss around the titanium fixtures in the long-term perspective and technical failures of the prosthetic and titanium components. The group of subjects studied comprised 64 dissatisfied complete denture wearers. They were divided and match-paired into 2 groups and, after initially being treated with optimised complete dentures, they were followed-up 6 and 4 years respectively after insertion of a mandibular fixed TIP. Treatment with optimised complete dentures produced small if any changes in functional, psychological or dietary variables compared with initial status. After treatment with a mandibular TIP, a dramatic improvement of the patients' assessment of their chewing ability and of the results of the chewing efficiency test and bite force measurements was recorded. The psychological reactions were also positive. However, the patients' dietary selection and habits did not change markedly compared to the original denture situation. Bone resorption around the titanium fixtures was in both groups 0.40-0.45 mm the first year after insertion of the TIP and then on average 0.06-0.08 mm annually. More bone loss was found around the mesially located fixtures than the distal ones. Oral hygiene was shown to influence the rate of bone loss. Technical failures of the TIPs were uncommon and none of the 270 fixtures was lost after insertion of the mandibular TIP in both groups during the follow-up period. In conclusion, the results given in Papers I-VI show that although the TIP method is demanding and expensive in its initial stages, the clinical and economic investments made are obviously sound in the long-term perspective. Especially when the psychosocial benefits are considered, the overall cost-benefit ratio of treatment with tissue-integrated prostheses therefore seems to be very favourable.