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A longitudinal study on mandibular implants supporting an overdenture: the influence of retention mechanism and
M Oetterli1, P Kiener, R Mericske-Stern
1Department of Prosthodontics, University of Berne, Switzerland.
Purpose:
The aim of this 5-year longitudinal study was to investigate the influence of the retention mechanism for overdenture fixation on the periimplant parameters of mandibular implants.
Materials And Methods:
Ninety edentulous patients, each with two interforaminal implants supporting an overdenture, participated in the study. They had received either a straight or slightly bent round clip bar, a U-shaped rigid bar with or without distal extensions, or single-ball anchors. Anatomic-morphologic and prosthetic variables were assessed related to the implant position and the type of overdenture retention. The degree of mandibular atrophy was determined using cephalometric radiographs. The angle beta between the virtual axis connecting both implants and the mandibular hinge axis was measured on mounted casts. A supporting surface was identified between bent clip bars and U-shaped extension bars. Clinical periimplant parameters were recorded, and changes of the probing attachment level after 5 years were analyzed in 70 patients with respect to the retention device and anatomic-morphologic and prosthetic variables.
Results:
A significant increase of the Plaque Index was observed after 5 years. The mean clinical attachment loss after 5 years was about 0.2 mm. In more than 50%, beta was small, i.e., < or = 5 degrees. For these implants, loss of clinical attachment was significantly lower. The correlation between attachment loss and beta was weak, while no significant correlation was found with regard to the degree of atrophy and surface.
Conclusion:
In view of the long observation period, it was concluded that the position and retention mechanism of mandibular implants supporting an overdenture have little influence on the long-term stability of the clinical parameters.