O-Ring Attachments on One-Piece Mini Dental Implants: In Vitro Analysis of Retention Force Reproducibility Using Different Pristine Matrix-O-Ring Combinations

Purpose: To analyze the influence of pristine matrix and O-ring dimensions on retention force and reproducibility in single one-piece mini dental implants (MDIs) with ball patrices under in vitro conditions.

Materials and methods: Three different matrix and O-ring combinations (MH1-MH3) were evaluated (n = 50 per group) on 1.8-mm-diameter implants. The matrices were manually mounted on the implants and were subsequently removed in a vertical linear manner using a metal pin with two strain gauges, recording the maximum force during disconnection. After five disconnections, the O-rings were exchanged, and the mean retention force was calculated, resulting in 50 values for each matrix and O-ring combination. Mean retention forces, SDs, and 95% CI were calculated. Analysis of variance was used to test the global differences, and post hoc pairwise comparisons were subsequently applied. The level of significance was set to P < .05.

Results: ANOVA (global P < .0001) and pairwise comparisons (all P < .0001) demonstrated statistically significant differences among the three different matrix and O-ring combinations, with mean values of 5.18 N (MH 1), 6.73 (MH 2), and 9.08 (MH 3). Within each combination, retention force variations of > 1 N could not be demonstrated; ie, by exchanging O-rings, a similar retention force can be reestablished.

Conclusion: Matrix and O-ring dimensions have a significant influence on retention forces in one-piece MDIs. Pristine O-rings demonstrated highly reproducible initial retention forces in all matrices.