Comparison of retention and stability of two implant-retained overdentures based on implant location.

STATEMENT OF PROBLEM The location of dental implants and the choice of retentive attachments for implant-retained overdentures are selected based on clinician preference, expert opinion, or empirical information. Limited information is available regarding implant position and the effect on the retention and stability of 2-implant mandibular implant overdentures. PURPOSE The purpose of this investigation was to evaluate the effect of implant location on the in vitro retention and stability of a simulated 2-implant-supported overdenture and to examine the differences among different attachment systems. MATERIAL AND METHODS A model that simulates a mandibular edentulous ridge with dental implants in positions that approximate tooth positions, and a cobalt-chromium cast framework attached to a universal testing machine was used to measure the peak load (N) required to disconnect the attachments. Four different types of attachments (Ball/Cap, ERA, Locator, and O-Ring) were used in sequence in various positions on the model to evaluate the effect of implant location on the retention and stability of a simulated 2-implant-retained overdenture. Means were calculated, and differences among the systems, directions, and groups were identified by using a repeated measured ANOVA (α=.05). For differences observed between measurements, the Bonferroni post hoc method at the 5% level of significance was used to determine the location and magnitude of difference. RESULTS The interactions between the attachment system, direction of force, and implant location were statistically significant (P=.01). The vertical retention and horizontal stability of a simulated overdenture prosthesis increased with the distal implant location up to the second premolar, and the anteroposterior stability increased with distal implant location. The attachment type affected retention and stability differently by location. Ball attachments produced the highest levels of retention and stability, followed by Locator (pink), O-Ring, and ERA (orange). CONCLUSIONS The retention and stability of a 2-implant simulated overdenture prosthesis is significantly affected by implant location (P=.01) and abutment type (P=.01).