We read with interest the article in the November 2010 issue on tooth color after orthodontic treatment (Karamouzos A, Athanasiou AE, Papadopoulos MA, Kolokithas G. Tooth-color assessment after orthodontic treatment: a prospective clinical trial. Am J Orthod Dentofacial Orthop 2010;138:537.e1-8). The authors are to be commended for their aim to conduct a randomized trial to prospectively assess in-vivo color alterations of natural teeth associated with fixed orthodontic treatment. Even if the statistical tests used are correct, there seemed to be a study design issue. Our main concern was that it does not seem that the authors had performed any sort of pre-hoc sample size calculation before enrolling patients and undertaking this experimental study. In a prospective randomized study, if statistical tests are used, their power should be determined a priori. And, for a particular experimental result to be claimed as significant or not significant, sufficient statistical power must be obtained, and the sample size for each group should be calculated a priori. Did the authors perform a pre-hoc sample size calculation? Since we don’t know whether this study was sufficiently powered, we don’t know whether these findings are statistically correct and sufficiently powered.

The authors claimed that their study clearly indicated that the color of natural teeth after comprehensive orthodontic treatment with fixed appliances changes in various ways. In fact, we don’t know whether these results are statistically significant. Although this study is innovative and important, an accurate experimental design is the only way to draw adequate conclusions about experimental findings, transforming good hypotheses into statistically correct and evidence-based scientific conclusions. We hope our suggestions will be useful to other investigators who will be involved in similar studies in the future.