title: A randomized clinical trial comparing two mandibular implant overdenture designs: 3-year prosthetic outcomes using a six-field protocol.
abstract: OBJECTIVE
  This clinical trial tested the null hypothesis that there would be no difference in prosthetic maintenance for two-implant mandibular overdentures retained by either a bar-clip mechanism or ball attachments. Prosthetic outcomes are reported over 3 years using a six-field protocol.
  
  
  METHODS
  One hundred edentulous participants received new maxillary complete dentures and a mandibular two-implant overdenture (IOD), with random assignment to either a bar and metal clip or two ball attachments (titanium alloy matrix and spring) for retention. Eighty-seven subjects were available for follow-up after 3 years.
  
  
  RESULTS
  Almost three times as many bar-clip dentures (63%) were rated successful compared to the ball attachment design. Two percent of the participants in each group died over the course of the study, while 15% of the bar-clip and 8% of the ball IOD subjects were lost to follow-up. More than three times as many ball attachment IODs (60%) required retreatment in the form of excessive repairs, and twice as many of the ball attachment design (8%) required replacement. The ball attachment IOD was significantly more likely to require patrix tightening or matrix replacement, while the bar-clip design was more likely to require activation of the matrix.
  
  
  CONCLUSIONS
  Using the criteria of a six-field protocol for implant overdenture outcomes, the bar-clip IOD was a significantly more successful prosthesis, requiring less maintenance than the titanium alloy matrix and spring ball attachment IOD employed in this study. The null hypothesis was therefore defeated.
authors.affiliation: Department of Oral Health Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, Canada. jnwalton@interchange.ubc.ca
authors.forename: Joanne N
authors.initials: JN
authors.lastname: Walton
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016734:Dental Clasps; D019094:Dental Prosthesis, Implant-Supported; D019232:Dental Restoration Failure; D003779:Denture Design; D003834:Denture Precision Attachment; D003780:Denture Repair; D003781:Denture Retention / Q000295:instrumentation*; D003826:Denture, Complete, Lower; D003828:Denture, Overlay; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D019233:Retreatment