Retentive Characteristics of Narrow-Diameter Implant-Retained Overdentures after Fatigue Loading

Objectives: To compare retentive and morphological changes of five stud attachment systems for implant-retained overdentures after repeated insertion (7,200 cycles) and 78N loading in vitro onto implant abutments.

Methods: Five mechanical (Pink Liner, Zest Locator; Metal Housing and Micro Metal Housing, 3M IMTEC; Micro Metal Housing, Intra-Lock; and Silicone Liner, Dentatus USA) attachments were embedded in overdenture base (n=10).  Overdentures with Locator attachments were tested on acrylic models with two parallel Endure implants (4.3×9mm). The O-ring attachments and silicone liner were tested on models with four parallel narrow-diameter implants. Specimens were loaded sinusoidally from zero to 78N in a coil cycler fatigue machine (Proto-Tech, Portland, OR) at 2Hz for 7,200 cycles in a 37°C water bath.  Vertical tensile dislodging forces were recorded at a cross-head speed of 50 mm/min after repeated insertions (baseline, 50, 500, 900, 1,800, 3,600, 5,400, and 7,200 cycles). Statistical analysis: ANOVA and Tukey HSD post-hoc tests at the 95% confidence level.

Results: The peak load-to-dislodgement force ranged from 6.4 (0.5) N to 19.0 (2.9) N after 7,200 cycles of repeated insertion.  The retention values of the MDI Micro Metal Housing and Locator Pink Liner attachments were significantly higher than other groups after 7,200 cycles (P<.01). The Locator Pink Liner group, Silicone Liner group, and MDI Micro Metal Housing with O-ring attachment showed changes in retentive force values of 82.8%, 31.5%, and 18.1% respectively after 7,200 cycles fatigue loading. Microscopic examination of the specimens revealed wear and degradation consistent with the loss of retention.

Conclusions: The retention force values of O-ring attachments with four narrow-diameter implant systems were equivalent to the Locator Pink Liner with two regular implants after 7,200 cycles fatigue loading.