We were very pleased by the interest of Drs Wang, Yi, and Bai in our article. We have carefully read their letter. We are grateful for the opportunity to offer some clarifications.
First, we did consider in our statistical analysis the differences between the groups concerning malocclusion severity, age, sex, socioeconomic class, and dental health; a multivariate analysis was performed through negative binomial regression (p. 753). In Table III, we reported the results of single and multiple regression analyses. We also explained that socioeconomic status was removed from the final model because its P value was greater than 0.20 (p. 755). Thus, we see no reason for any concern with respect to this matter. The unadjusted effect of social class was explained by other variables in the model.
Second, Dr Wang and colleagues asked about the average time of retention before the outcome assessment. This is reported on page 754: “In the treated group, the mean time after completion of treatment was 3.8 years.” We would like to add that, in the treated group, the duration of the retention period was not associated with oral health-related quality of life (OHRQoL) as measured by the oral health impact profile (short form) scores ( P = 0.80). Moreover, this variable could not be included in the multivariate analysis because half of the sample comprised subjects who were not treated. Therefore, it is reasonable to assume that the range of the retention period did not decrease the relevance of our results.
We agree that setting a specific time point to evaluate the impact of orthodontic treatment on OHRQoL could be an interesting idea for future research. Nevertheless, a longitudinal prospective study, with a proper follow-up period, would provide better insight into the long-term effects of orthodontic treatment on OHRQoL than a cross-sectional study with a prespecified point for outcome assessment (p. 757: “In the future, longitudinal research could provide a more accurate profile of the impact of orthodontic treatment on oral health-related quality of life.”). For example, the roles of residual treatment need or malocclusion relapse in the postretention phase of orthodontic treatment on OHRQoL, whether accompanied or not by worsened esthetics over time, are still open to debate.
Finally, we want to clarify that we recognize that, despite bringing new and relevant information about the relationship between OHRQoL and orthodontic treatment, our cross-sectional study has limitations. They were duly noted in the Discussion section (p. 756-7).