A series of 156 consecutive fully edentulous patients were rehabilitated by means of fixed prostheses on either 4 or 6 screw-shaped titanium implants. This retrospective study calculated survival rates for both prostheses and individual implants. Only patients with a 10-year follow-up were considered. The implant lengths were 10 (90%) or 7 mm. They were all inserted after pretapping. In the mandible 13 and 59 prostheses were installed on respectively 4 and 6 implants. In the upper jaw the respective numbers were 14 and 70. Both groups (4 versus 6 implants) were age- and gender-matched. A reduced jaw bone volume was the major reason for limiting the number of implants to 4. Although a tendency existed for an increased failure rate in patients with only 4 implants, the survival rate for both individual implants and prostheses was the same in both groups at the end of the 10-year observation period. The present tendency of some clinicians to install as many implants as possible in full edentulism should be seriously questioned.
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Brånemark et al. (1995) studied this question.