title: The crossover design to evaluate the efficacy of plaque removal in tooth-brushing studies.
abstract: OBJECTIVE
  To evaluate the crossover clinical trial design to assess plaque removal efficacy of the Sonicare Elite.
  
  
  METHODS
  A single-cohort, 12-week, two-treatment, single-blind, crossover clinical trial recruited 45 subjects. Plaque was recorded using the modified Quigley and Hein index plaque index (PI). After screening, subjects used the toothbrush for 2 weeks and were reminded to abstain from tooth cleaning 12-18 h prior to appointments. At visit two, subjects were randomized to 2 or 2(1/2) min. brushing time. PIs was recorded pre- and post-brushing. Subjects brushed for the allocated time for a further 2 weeks. At visit 3, PIs were recorded pre- and post-brushing. Two weeks later, at visit 4, the subjects crossed over and the protocol was repeated.
  
  
  RESULTS
  There was no evidence of a learning effect within each arm of the crossover. A significant period effect was detected; however, no significant treatment by period effect was found. 2(1/2) min. brushing removed more plaque at full mouth (p=0.037), smooth (p=0.012) and lingual (p=0.002) sites compared with 2 min.
  
  
  CONCLUSIONS
  The crossover design is a valid model for assessing plaque removal efficacy in tooth-brushing studies where no carry-over effect is clinically plausible.
authors.affiliation: School of Dental Sciences, University of Newcastle upon Tyne, Newcastle upon Tyne, UK. g.i.mccracken@newcastle.ac.uk
authors.forename: G I
authors.initials: GI
authors.lastname: McCracken
authors.forename: N
authors.initials: N
authors.lastname: Steen
authors.forename: P M
authors.initials: PM
authors.lastname: Preshaw
authors.forename: L
authors.initials: L
authors.lastname: Heasman
authors.forename: F
authors.initials: F
authors.lastname: Stacey
authors.forename: P A
authors.initials: PA
authors.lastname: Heasman
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D018592:Cross-Over Studies; D003773:Dental Plaque / Q000628:therapy*; D003774:Dental Plaque Index; D006801:Humans; D008875:Middle Aged; D016037:Single-Blind Method; D013997:Time Factors; D014099:Toothbrushing / Q000379:methods*