Retention mechanisms and prosthetic complications of implant-supported mandibular overdentures: long-term results

Background: Although many studies report high survival rates of mandibular implants supporting an overdenture, complications with prostheses and the need for prosthetic maintenance are not so well documented. Purpose: The purpose of the present study was to analyze three categories of prosthetic complications in relation to the type of retention mechanism for overdenture connection to the implants (ie, rigid or resilient). Materials and Methods: One hundred nineteen patients with a total of 258 implants participated in the study. They had been monitored regularly during an observation period of 5 to 15 years (mean 9.3 yr). Seventy‐five patients had a resilient retention device (ball anchors or a round clip bar); 44 patients had a rigid bar with or without distal extensions. The incidence and rate of complications were calculated for the overall‐ and for the 2‐ and 5‐year observation periods. Comparisons were made between the three categories of maintenance and the two types of retention. A Kaplan‐Meier analysis was applied for calculations of changes of the retention mechanism. Results: The mean number of complications per overdenture during the entire observation period was 3.5; this did not differ statistically between the two retention groups. Some significant differences were found only for the 2‐ and 5‐ year period. Broken, loose, or lost female parts were more frequently observed with resilient devices, as were repairs and relining of the resin denture base, whereas tightening of bar retainers was more typical with rigid bars. A change from a resilient retention device to a rigid bar was performed more often than vice versa but not at a statistically significant level. Conclusion: Although these long‐term results do not indicate a significant difference between the retention groups, a slight superiority of the rigid bar is suggested.