title: Retention of implant-supported overdentures at different implant angulations: comparing Locator and ball attachments.
abstract: OBJECTIVE
  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.
  
  
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: King's College London, Dental Institute, London, UK.
authors.forename: Nazia
authors.initials: N
authors.lastname: Sultana
authors.affiliation: King's College London, Dental Institute, London, UK.
authors.forename: David W
authors.initials: DW
authors.lastname: Bartlett
authors.affiliation: Guy's and St Thomas' Hospitals Foundation Trust, London, UK.
authors.forename: Mahmood
authors.initials: M
authors.lastname: Suleiman
mesh_terms: D019094:Dental Prosthesis, Implant-Supported; D019232:Dental Restoration Failure; D003781:Denture Retention / Q000295:instrumentation / Q000379:methods*; D003828:Denture, Overlay; D006801:Humans
keywords: Biomechanics; finite elemente analysis; material sciences; prosthodontics