A longitudinal study on mandibular implants supporting an overdenture: Theinfluence of retention mechanism and anatomic-prosthetic variables on periimplant parameters

Purpose: The aim of this 5-year longitudinal study was to investigate the i nfluence of the retention mechanism for overdenture fixation on the periimp lant parameters of mandibular implants. Materials and Methods: Ninety edent ulous patients, each with two interforaminal implants supporting an overden ture, participated in the study. They had received either a straight or sli ghtly bent round clip bar, a U-shaped rigid bar with or without distal exte nsions, or single-ball anchors. Anatomic-morphologic and prosthetic variabl es were assessed related to the implant position and the type of overdentur e retention. The degree of mandibular atrophy was determined using cephalom etric radiographs. The angle beta between the virtual axis connecting both implants and the mandibular hinge axis was measured on mounted casts. A sup porting surface was identified between bent clip bars and U-shaped extensio n bars. Clinical periimplant parameters were recorded, and changes of the p robing attachment level after 5 years were analyzed in 70 patients with res pect to the retention device and an atomic-morphologic and prosthetic varia bles. Results: A significant increase of the Plaque index was observed afte r 5 years. The mean clinical attachment loss after 5 years was about 0.2 mm . In more than 50%, beta was small, ie, less than or equal to 5 degrees. Fo r 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. Co nclusion: In view of the long observation period, it was concluded that the position and retention mechanism of mandibular implants supporting an over denture have little influence on the long-term stability of the clinical pa rameters.