With interest, we read the article entitled “How does orthodontic treatment affect young adults’ oral health-related quality of life?” by Palomares et al in the June 2012 issue of the AJO-DO . First, we would like to congratulate the authors on their work and for being the first in Brazil to investigate the effects of orthodontic treatment on the oral health-related quality of life of young adults who had completed treatment. However, we have 2 major concerns about this study.
First, in Table I, the chi-square test showed a significant difference between treated and nontreated groups in their baseline socioeconomic classes ( P <0.01). It has been reported that socioeconomic status would affect not only the index of orthodontic treatment need, but also the level of oral health-related quality of life. So, in our opinion, it is possible that this imbalanced baseline could lead to a false-positive result. The same problem also existed in the subjects’ baseline ages, which also lacked balance ( P <0.01). To eliminate this discrepancy, proper statistical methods such as readjusting the sample composition should be performed.
Our second concern is that the participants were young adults who had completed treatment between 6 months and 10 years previously. It is reported that the index of orthodontic treatment need grades at the end of orthodontic treatment and at 6.5 years postretention are different. So we can assume that, even for the same person, the index of orthodontic treatment need value would change during such a long span of time (6 months-10 years). What is the average time of retention before the assessment? We advise setting a unified time point for the measurement, if possible. If not, in our opinion, using a regression model to discuss the impact of the time factor might be necessary.