title: Retention force of plastic clips on implant bars: a randomized controlled trial.
abstract: OBJECTIVE
  Retention of overdentures is important for patients' satisfaction. The study tested whether the clinical performance of retentive clips made of poly-ether-ether-ketone (PEEK) is superior to those made of poly-oxy-methylene (POM).
  
  
  METHODS
  A total of 30 patients received complete dentures with round bars (SFI-Bar) on two implants in a chairside technique. Two types of clip matrices (PEEK/POM) were used in a split-mouth technique. Retention forces were measured separately for both materials at baseline when the dentures were inserted and after 1, 3 and 6 months. The measurement was performed extraorally and intraorally by using a measuring stylus equipped, respectively, with an opposing matrix or bar part. Simultaneously, at each point in time the patient and the dentist judged the retention either to be good, or to be too high or too low. Statistical analysis involved performance of global non-parametric testing of dependence of retention force on time and material was performed with Brunner-Langer model; non-parametric 95% confidence intervals (CIs) were calculated.
  
  
  RESULTS
  At baseline the median force for POM matrices was 6.89N (95% CI: 6.50-8.21) and for PEEK matrices 7.17N (95% CI: 6.97-7.93). After 6 months, the retention of POM decreased to 5.53N (95% CI: 4.81-7.00) and of PEEK to 6.42N (95% CI: 5.15-7.51). The retention force changed significantly over time (P = 0.004) without differences between POM and PEEK (P = 0.135). No significant alteration of the retention force over time was measured at the bar (P = 0.289). Retention was estimated to be good with 90% at baseline and with 80% after 6 months, equally by patients and dentist.
  
  
  CONCLUSIONS
  POM as well as PEEK material fulfills the requirements of retentive clips on round bars.
authors.affiliation: Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Bayer
authors.forename: Nathalie
authors.initials: N
authors.lastname: Komor
authors.forename: Annina
authors.initials: A
authors.lastname: Kramer
authors.forename: Dominic
authors.initials: D
authors.lastname: Albrecht
authors.forename: Regina
authors.initials: R
authors.lastname: Mericske-Stern
authors.forename: Norbert
authors.initials: N
authors.lastname: Enkling
mesh_terms: D000368:Aged; D001577:Benzophenones; D017267:Dental Prosthesis Design; D019094:Dental Prosthesis, Implant-Supported; D003799:Dental Stress Analysis; D003781:Denture Retention / Q000295:instrumentation*; D003828:Denture, Overlay; D005260:Female; D006801:Humans; D007659:Ketones; D008297:Male; D008875:Middle Aged; D010969:Plastics; D011092:Polyethylene Glycols; D011108:Polymers; D011446:Prospective Studies; D016037:Single-Blind Method; D016896:Treatment Outcome
chemical_list: D001577:Benzophenones; D007659:Ketones; D010969:Plastics; D011108:Polymers; C063834:polyetheretherketone; D011092:Polyethylene Glycols