title: No statistically significant results for two removable orthodontic retainers.
abstract: METHODS
  Randomised controlled trial.
  
  
  METHODS
  Participants were randomly assigned to receive either a Hawley retainer (HR) or a clear overlay retainer (COR). The HR was composed of a 2 mm-thick acrylic resin base plate, one-arm clasps with 0.9 mm-diameter stainless steel wire on the first molars, and a Hawley bow with 0.7 mm stainless steel wire. The COR was made from a 0.75 mm-thick thermoplastic material with the buccal edge paralleling the gingival margin, the lingual portion extending 4 to 5 mm beyond the lingual gingival margin. Distally the second molars were covered. Both groups of patients were required to wear the retainers full-time, except during meals and were followed for one year.
  
  
  METHODS
  Retainer survival was the primary outcome. Small surface cracks were not considered as a breakage unless the retainers could not be worn because of crack expansion.
  
  
  RESULTS
  One hundred and twenty patients were randomised, 61 in the HR group, 59 in the COR group, nine patients (five in the HR group and four in the COR group) were lost to follow up. Fracture was the most often cited reason for breakage, followed by retainer loss. No significant differences were seen in survival times between the two groups. Both retainers tended to fracture, but the fracture locations were different.
  
  
  CONCLUSIONS
  This analysis suggests that the survival times of the HRs and CORs were not statistically significantly different. Therefore, clinicians could advise their patients to wear either of the two retainers without taking breakage into consideration.
authors.affiliation: NYU College of Dentistry, New York, USA.
authors.forename: Analia Veitz
authors.initials: AV
authors.lastname: Keenan