The crossover design to evaluate the efficacy of plaque removal in tooth-brushing studies

Objectives: To evaluate the crossover clinical trial design to assess plaque removal efficacy of the Sonicare Elite. Material and 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 2½ 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. 2½ 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. Conclusion: The crossover design is a valid model for assessing plaque removal efficacy in tooth‐brushing studies where no carry‐over effect is clinically plausible.