Effect of Dislodging Forces on Mandibular Implant Attachment-Retained Overdenture

Objectives: The goal of this in vitro study was to evaluate stress patterns and retention of ball and socket and 2 telescopic attachments of different convergence angles retaining an implant-supported overdenture prosthesis. Materials and Methods: This study was carried out on an edentulous mandibular acrylic resin educational model. Four dummy implants, 3.5 mm in diameter and 11 mm in length, were installed in the interforaminal area. The framework of the overdenture was cast. Eight strain gauges were attached to the buccal and distal surfaces of all implants. The experiment was divided into 3 phases: 1 with the ball and socket attachment and the other with the angle 4 degrees followed by angle 6 degrees telescopic retainers. Once retention and stress analysis studies were completed for the ball attachments, they were replaced by the telescopic retainers. The universal testing machine was used to measure the retentive forces of the studied attachments. A 4-channel strain-meter was used to record the microstrains transmitted to each strain gauge while the machine was adjusted to move in a tensile mode. Results: Statistical analysis showed the highest significant retention values for the ball and socket followed by telescope angle 4 degrees and finally angle 6 degrees. The same ranking was found on comparing the mean strains developed at the implants. Conclusion: This study has demonstrated that implant overdenture attachment design and dislodging forces may significantly influence stress/strain magnitude around implants; the higher the retention (resistance to dislodging forces) of the attachments the more the transferred stresses. (Implant Dent 2011;20:246-254)