Split-mouth trials are a design of randomized controlled trial in dentistry in which divisions of the mouth are the units of randomization. Since there is more than one tooth in each mouth division, the structure of the data is complex, which can create difficulties in the statistical analysis. The aim of this study was to determine what is the most appropriate method to analyze split-mouth trials with continuous outcomes, with regards to the treatment effect estimates, power, type-I error, confidence interval coverage and confidence interval width. A superiority split-mouth trial in the field of periodontology was simulated, using two mouth divisions and varying underlying study characteristics such as correlation among teeth, treatment effects and sample size. Twenty-four statistical methods were compared across 315 scenarios. The performance of the statistical methods depended mainly on the correlation among the data, and a paired t-test performed the best across the different scenarios.

Split-mouth trials are a design of randomized controlled trial in dentistry in which divisions of the mouth are the units of randomization. Since there is more than one tooth in each mouth division, the structure of the data is complex, which can create difficulties in the statistical analysis. The aim of this study was to determine what is the most appropriate method to analyze split-mouth trials with continuous outcomes, with regards to the treatment effect estimates, power, type-I error, confidence interval coverage and confidence interval width. A superiority split-mouth trial in the field of periodontology was simulated, using two mouth divisions and varying underlying study characteristics such as correlation among teeth, treatment effects and sample size. Twenty-four statistical methods were compared across 315 scenarios. The performance of the statistical methods depended mainly on the correlation among the data, and a paired t-test performed the best across the different scenarios.