Five-year study of mandibular overdentures on stud abutments: Clinical outcome, patient satisfaction and prosthetic maintenance-Influence of bone resorption and implant position

Objectives: This prospective study analyses the 5-year clinical outcome, patient satisfaction and the technical outcome of a 2-implant overdenture on stud abutments. In addition, the influence of mandibular resorption and implant position on these outcomes was assessed.

Material and methods: Patients received two implants in a one-stage delayed protocol. Final prosthesis on stud abutments was finalized after 3 months. Implant survival, bone loss, plaque and sulcus bleeding index, OHIP-14, technical outcome and costs were assessed after 5 years. The Cawood-Howell classification defined the mandibular resorption. Inter-implant distances and angles (frontal, sagittal) were digitally measured. The significance level was p < .05.

Results: Fifty-six patients, 23 female and 33 males (mean age = 66.3, range 41-82), completed the follow-up. No implants were lost. Radiographical crestal bone loss was on average 1.25 mm (standard deviation SD 1.06), bleeding index was 0.75 (SD 0.73), and plaque index was 1.15 (SD 0.75) and higher for low mandibles (p = .001). The OHIP-14 reduction post-connection and after 5 years was significant (p < .001). Five-year maintenance required on average 6.7 (SD 4.8, range 0-25) interventions per patient. A larger inter-implant distance was associated with fewer replacement of retention inserts (p = .034) and less interventions (p = .006). Larger frontal (p = .023) and sagittal (p = .046) inter-implant angles (non-parallelism) required more inserts. The maintenance cost negatively influences the patient satisfaction (p = .004). 83% of the stud abutments showed wear.

Conclusion: The implant overdenture on cylindrical stud abutments is a good and stable solution, irrespective of the resorption profile of the mandible. OHIP-14 improved permanently up to 5 years but is negatively influenced by complication cost. A small inter-implant distance, more frontal, sagittal inter-implant divergence increased maintenance.