Purpose: To investigate retention and stability characteristics of soft-liner and clip attachments used for bar/implant-assisted mandibular overdentures.

Materials and methods: Two implants were placed in an edentulous mandibular model. According to the type of bar, presence of cantilevers, and type of attachments, eight groups were tested: (1) Dolder bar with cantilevers and three titanium clips (DCC), (2) Dolder bar with cantilevers and resilient liner attachments (DLC), (3) Dolder bar without cantilevers and one titanium clip (DCWC), (4) Dolder bar without cantilevers and resilient liner attachments (DLWC), (5) Hader bar with cantilevers and three plastic clips (HCC), (6) Hader bar with cantilevers and resilient liner attachments (HLC), (7) Hader bar without cantilevers and one plastic clip (HCWC), and (8) Hader bar without cantilever and resilient liner (HLWC). Axial (retention) and nonaxial (stability during anterior, posterior, and lateral dislodging) forces were evaluated initially and after 540 times of prosthesis insertion and withdrawal.

Results: The highest retention and stability forces were observed with HCC, and the lowest forces were recorded with DLWC. The lowest retention and stability after wear was noted with DCWC and HCWC. For the majority of groups, the highest forces were noted with posterior dislodgment, and the lowest forces were observed with lateral dislodgment. The largest retention loss was recorded with DCC and HCC, and the lowest retention loss was noted with HLWC. DLC and HLC showed retention gain.

Conclusion: Hader bar with clips and cantilever extensions achieved the highest retention and stability forces after wear simulation, while bars without cantilevers and clips showed the lowest forces. For cantilevered Dolder and Hader bars, clip attachments showed increased retention loss, while soft-liner attachments showed retention gain.