Comparison of Retention and Strain Energies of Stud Attachments for Implant Overdentures

Purpose: The retentive forces and the strain energies absorbed during dislodging of implant overdenture stud attachments are useful parameters to consider in the selection of attachments. The purpose of this study was to compare the retentive forces and strain energies of the Nobel Biocare standard ball, Nobel Biocare newer generation ball (Yorba Linda, CA), Zest Anchor, Zest Anchor Advanced Generation (Escondido, CA), Sterngold-Implamed ERA white, and Sterngold-Implamed orange attachments (Attleboro, MA) on an implant-retained in vitro overdenture model. Materials and Methods: The attachments were tested using two permanently placed Branemark system implants on a test model attached to an Instron machine. Each attachment had one part embedded in a denture-like housing, and the other part screwed into the implants. Dislodging tensile forces were applied to the housings in two directions simulating function: vertical and oblique. Eight tests were done in two directions with six specimens of each attachment. Retentive forces generated and strain energies absorbed during displacement were determined. A I-way ANOVA followed by the Tukey studentized range test was used to determine groups that were significantly different at the p < 0.05 level. Results: The Zest Anchor Advanced Generation attachment had significantly the highest retentive vertical and oblique forces [37.2 (5.5) N and 25.9 (3.2) N, respectively]. The Zest Anchor had the lowest vertical force [10.8 (4.2) N], and Nobel Biocare Standard had the lowest oblique retentive force [10.6 (3.0) N]. The Nobel Biocare Standard Ball attachment had the highest strain energies [29.7 x 10(-3) (11.9 x 10(-3)) J, 30.3 x 10(-3) (14.3 x 10(-3)) J, respectively, in the vertical and oblique directions]. The Sterngold-Implamed ERA White and Zest Anchor had the lowest strain energies [5.3 x 10(-3) (3.2 x 10(-3)) J and 4.5 x 10(-3) (1.1 x 10(-3)) J, respectively, in the vertical and oblique directions]. Conclusion: The retentive forces and strain energies of implant overdenture stud attachments are different and should be considered during prosthesis selection.