Abstract:
The purpose of this experimental study was to evaluate wear characteristics and retention force of the RetenDent mini-implant overdenture system (Chulalongkorn product) after the insertion-removal fatigue test. One-piece mini-implants attachment system for overdenture, Osstem MS denture® type implant (OSSTEM, Germany GmbH), and RetenDent mini-implant were tested. All samples were subjected to repeated insertion and removal fatigue cycles by the universal testing machine (E1000, INSTRON Instrument, England). Subjected fatigue cycles were 5500 with 1.00Hz frequency to mimic a 5-year insertion and removal three times per day. The retention force was measured by separating the O-ring from the abutment and recorded with the universal tester (EZ-SX, SHIMADZU, Japan). The retention force was measured six times, at baseline and the end of 1100, 2200, 3300, 4400, and 5500 cycles. These represent each year of use. After fatiguing, the O-rings and mini-implant ball abutments were examined with a stereomicroscope (SZ61 OLYMPUS, Japan) and compared to baseline. The result showed a mean retention force of 6.65N for the RetenDent group and 6.84N for the Osstem group, which were not statistically different. The two attachment systems had no significant effect on retention force. However, the fatigue cycles alone and the interaction between the attachment system and fatigue cycles had significant effects on retention force. The RetenDent group’s retention was significantly higher at baseline (10.96N) and after 1,100 cycles (8.73N) compared to the Osstem group (6.50N and 6.66N). There was no statistical difference at 2200 cycles. The Osstem group’s retention became significantly higher after 3300, 4400, and 5500 cycles (6.86N, 7.06N, 6.997N) compared to the RetenDent group (5.04N, 4.49N, 3.88N). In conclusion, the RetenDent and the MS denture® mini-implant attachment system provided a similar 5-year average retention force at higher than the minimum recommended for overdenture. The RetenDent group had significantly higher retention forces at the first two-point of measure. There was no wear on the ball abutment of both groups under the stereomicroscope after 5,500 fatigue cycles.
