We read the article “Lingual retainers bonded without liquid resin: A 5-year follow-up study” in the January 2013 issue of the AJO-DO with great interest (Tang ATH, Forsberg CM, Andlin-Sobocki A, Ekstrand J, Hägg U. Am J Orthod Dentofacial Orthop 2013;143:101-4). The authors are to be commended for their work to evaluate the effect of excluding the liquid resin component of a composite bonding product that is based on bisphenol A diglycidylmethacrylate when bonding lingual retainers. However, we have 2 concerns regarding this article.

First, why did the authors combine the mandibular and maxillary retainers in their research? In clinical work, we have noted that maxillary fixed retainers have a greater tendency to fall off, perhaps as a result of chewing movements, especially in patients with deep overbite. We believe that it would be better to divide the mandibular and maxillary retainers into 2 subgroups.

Table I showed 7 bonded maxillary retainers in the test group and 9 in the control group, 13 bonded mandibular retainers in the test group, and 11 in the control group. This means that 4 patients in the test group and 7 patients in the control group had only maxillary retainers. Although the difference is small, with the relatively small sample size, this small discrepancy could make a significant difference.

Our second concern is that there were 20 retainers in both groups, but the totals of tooth surfaces bonded with a metal retainer were 74 in the test group and 110 in the control group. How did such a great difference occur? Would it have some influence on the number of debonded tooth surfaces and the loosened retainers in the study period? And if the retainers in the control group had a long span, there could have been frequent bonding failures. We think that this should have been taken into account during the analysis and discussion of the results.