Data on implant failures will show different results depending on how patients are compiled and analyzed: A retrospective study on 3902 individual patients treated either with one single implant or implants in the edentulous upper jaw.

Edentulous patients present a significantly and substantially higher risk of implant failures than patients provided with a single implant. When patients with different clinical conditions are pooled into the same group, patients with the most common condition in the total group have greatest impact on the result of the total group. Based on the present observations, risk patterns for a certain oral condition are not necessarily comparable with the implant treatment received by other patients, and the external validity may be limited in small, homogeneous groups of patients.