Retention Of Overdentures Supported By Two Different Implant Systems

"Background:" The retention of implant-supported mandibular overdentures is usually achieved using conventional dental implants with ball attachments. It has been suggested that mini-implants can be used as well, but there is no scientific evidence about its retention.

"Objectives: " To compare the retentive force of three overdenture designs supported by ball attachments, using either conventional dental implant or mini-implant systems.

"Methods: " Eighteen implants were placed in six acrylic resin models. Models were fabricated based on the diameter (3.5mm or 1.8mm) and number (Two, three or four) of conventional dental implants (SIS-SIH, Space Implant System, Bogotá, Colombia) or mini-implants (MDI Sendax, 3M ESPE, St. Paul, MN, USA) inserted. Six mandibular ball retained overdentures were fabricated and five hooks were placed at each one on the anterior (1), medial (2) and posterior (2) occlusal surfaces of the prostheses. Retention was assessed by pulling anchored chains attached to the universal testing machine (Instron 1011, Instron Corp, Norwood, MA, USA). Chains were attached to the hooks by separate (One hook) and together (Five hooks). A total of 720 insertion and dislodging cycles (crosshead speed of 50 mm/min) were performed (120 each overdenture). Statistical analysis was performed using a non parametric Wilcoxon signed-rank test.

"Results: " There is a statistical significant difference in the retentive force between the two implant systems, being higher the retention with the SIS-SIH system compared to the MDI SENDAX system (8.6 N vs. 1.9 N for 2 implants, 13.2 N vs. 3.1 N for 3 implants and 16.6 N vs. 3.8 N for 4 implants, respectively).

"Conclusions: " Overdentures supported by mini-implant systems demand a higher number of implants to achieve a satisfactory clinical retention. A considerable loss of retention is observed at the plastic rings after 60 insertion and dislodging cycles, when any of the two implant systems tested are used.