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 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.

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.