Biomechanical retention and stability of mandibular implant-retained overdentures

Objectives: The aim of this in vitro study was to compare the biomechanical retention and stability of implant-retained mandibular overdenture with different attachment systems. Methods: An edentulous mandibular model was selected from a clinical case. 2 implants were placed in the canine region of the model and a complete overdenture was fabricated. The overdenture was modified to house different retention mechanisms, including one soft lining material with different consistencies and 4 prefabricated attachment systems (Snap Cap, O-ring, Dal-Ro, and Locator). Pull off tests under vertical and oblique forces were performed through an Instron machine. Maximum dislodging forces and the force-versus-displacement stability were analyzed. Results: Different attachment systems showed significant differences in the amount of maximum dislodging force under the test setting. The Locator and O-ring attachments demonstrated the highest magnitude in maximum dislodging force under vertical and oblique load. The soft liner with different consistencies provided significantly lower maximum dislodging force than prefabricated attachment systems. However, most of the attachment systems tested showed no significant difference in the biomechanical force-versus-displacement stability. The Snap Cap attachment provided the most and the O-ring attachment the least in general. Conclusions: Different attachment systems provided significant different biomechanical retention; however, no significant differences were found for biomechanical force-versus-displacement stability among most of the attachment systems tested.