Time dependent failure rate and marginal bone loss of implant supported prostheses: a 15-year follow-up study.

This study deals with 4971 implants (Brånemark system) installed in 1315 patients, either fully or partially edentulous, and followed from implant installation up to the last control. A predominance of female patients (61%) and a nearly equal number of upper and lower jaws characterised the study group. Patients were scheduled each 6-12 months for recall. The observation time varied from 0.5 to 15 years (mean 5.1). The whole cohort was split up into compromised (n = 59) and non-compromised (n = 1256) patients. The former are defined as grafted (autologous bone) and patients irradiated in the head and neck area. In the compromised patients 24 out of 59 patients (40.6%) showed failures, in whom 59 out of 310 (19%) implants failed. In the non-compromised patients, implant failures were observed in 11.6% of the patients, which corresponds to 5.9% of the installed implants, excluding iatrogenic failures. Failures were further divided chronologically into early (up to 1 year after abutment connection) and late failures. There were early implant failures in 12.5% of the compromised patients and in 3.4% of the others. Late implant failures occurred in 7.4 and 2% of the two patients groups, respectively. While gender did not affect the failure rate, implant lengths, corresponding to the available bone height did, since a 21.5% failure rate for the 7-mm implants contrasts with 4.1 and 3.8% for 13- and 15-mm implants, respectively. Early as well as annual late failures are more frequently found in the maxilla. Implant fractures only occurred in the fixed (both partial and full) prosthesis group but never surpassed the 0.2% annual level. Marginal bone loss, exceeding the third screw thread occurred in 1.8% of the implants at the last control. It appears that this type of implant configuration offers a high long-term predictability. Failures occur before, at or during the first year after abutment connection and in very short implants. Marginal bone as a whole is very stable over the years.