Retention of implant-supported overdentures at different implant angulations: comparing Locator and ball attachments.

OBJECTIVES: To assess the effect of implant angulation on the retention of two different attachment systems for implant-supported overdentures after a simulated fatigue period of 5.5 years. MATERIAL AND METHODS: Two test set-ups were constructed. A two-implant mandibular implant-supported overdenture design was simulated using acrylic resin blocks to support implant replicas (Model 1 and Model 2). The replicas were set up in the canine regions (22-mm inter-implant distance). In Model 1, the implants were parallel (0° to the vertical axis) and in Model 2 they were divergent (20° to the vertical axis). The Locator and the ball attachment systems were tested at both set-ups. A simulated fatigue period of 5.5 years that equated to 10,000 cycles of insertion and removal of the denture was used. Retention values for each attachment system at each angulation set-up were measured at baseline, every 500 cycles until 4000 cycles and then every 1000 cycles. RESULTS: After simulated fatigue, the retention for both systems at both set-ups reduced. The Locator system reduced from 108.9 to 20.2 N in the parallel set-up and from 82.3 to 17.3 N in the divergent set-up. For the ball system, the retention reduced from 56.2 to 46 N when parallel and from 45.7 to 40.7 N when divergent. CONCLUSION: Both attachment systems showed a significant reduction in retention after simulated fatigue at both parallel and divergent set-ups. The change in implant angulation caused a significant reduction in retention for the ball attachment system only, although this was still higher at the end of testing than the Locator attachment system. The Locators also had a significantly faster rate of loss of retention at both set-ups. Clinically, this may indicate that the ball attachments may perform better with divergent implants.

The effects of simulated bone loss on the implant-abutment assembly and likelihood of fracture: an in vitro study.

PURPOSE: The crestal bone level around a dental implant may influence its strength characteristics by offering protection against mechanical failures. Therefore, the present study investigated the effect of simulated bone loss on modes, loads, and cycles to failure in an in vitro model. MATERIALS AND METHODS: Different amounts of bone loss were simulated: 0, 1.5, 3.0, and 4.5 mm from the implant head. Forty narrow-diameter (3.0-mm) implant-abutment assemblies were tested using compressive bending and cyclic fatigue testing. Weibull and accelerated life testing analysis were used to assess reliability and functional life. Statistical analyses were performed using the Fisher-Exact test and the Spearman ranked correlation. RESULTS: Compressive bending tests showed that the level of bone loss influenced the load-bearing capacity of implant-abutment assemblies. Fatigue testing showed that the modes, loads, and cycles to failure had a statistically significant relationship with the level of bone loss. All 16 samples with bone loss of 3.0 mm or more experienced horizontal implant body fractures. In contrast, 14 of 16 samples with 0 and 1.5 mm of bone loss showed abutment and screw fractures. Weibull and accelerated life testing analysis indicated a two-group distribution: the 0- and 1.5-mm bone loss samples had better functional life and reliability than the 3.0- and 4.5-mm samples. CONCLUSION: Progressive bone loss had a significant effect on modes, loads, and cycles to failure. In addition, bone loss influenced the functional life and reliability of the implant-abutment assemblies. Maintaining crestal bone levels is important in ensuring biomechanical sustainability and predictable long-term function of dental implant assemblies.