We were pleased that our study has awoken your interest. We want to thank you cordially for your comments and for allowing us to clarify some of the issues raised.
It is correct that the type of ligature used may affect the dynamics of white spot lesion (WSL) formation, especially since elastomeric ligatures have a tendency to attract plaque at a greater rate. In most subjects treated with lingual appliances in our study, elastomeric O-rings were used as ligatures, especially during the stage of leveling and aligning. Elastomeric power chains were used for space closure, whereas steel ligatures were used mainly to selectively reduce friction when necessary. However, the type of ligatures used has rarely been reported in studies of WSL incidence (but more often in studies on treatment duration). Consequently, it would be difficult to draw a comparison between our study and existing reports on labial WSL incidences based on the type of ligature used. Moreover, our clinical experience in relation to archwire changes does not support your suggestion regarding a potential impact of the type of ligature on the speed of archwire replacement. Also, the information about complete treatment duration may be considered more meaningful in the context of WSL formation than would be the speed of archwire changes: complete mean treatment duration has been reported to be 19.02 ± 4.63 months (range, 7.67-29.47 months). Compared with reports about average treatment durations for labial multibracket appliances (20.7 ± 4.9 to 23.5 months for self-ligating brackets and 18.1 ± 5.3 to 23.5 ± 4.7 months for conventionally ligated brackets), the mean treatment duration in our lingual treatment sample seems to be on a par, or quite competitive, with those achieved with labial appliances. The rationale for this may be the use of individual setups to define and achieve treatment goals in a controlled and economic way, which is not very common in labial appliance treatment, as well as an improved 3-dimensional control with fully customized appliances, which are based on differences in the manufacturing process between the lingual brackets, used here, and conventional, noncustomized labial appliances. In addition, judging on the basis of systematic reviews and randomized controlled trials about treatment durations achieved with self-ligating compared with conventionally ligated appliances, one might conclude that the effects of ligature type are slightly overrated.
We agree with your objection that “the use of vestibular buttons for intra-arch and interarch elastics can facilitate the onset of labial WSLs” may, in theory, be a potential problem. However, we did not notice labial WSLs after the use of single vestibular buttons placed during lingual treatment, eg, on the canines. They may be considered to be an extremely rare finding, due to the good accessibility of these single buttons. On the other hand, you are correct insofar as labial WSLs were not within the scope of this study (as were not lingual decalcifications in studies of WSL incidence after labial appliances, including, in some instances, molar bands and lingual attachments).
The reason for the imbalance in the sample sizes between the preadolescent and adolescent subjects is simple. In this retrospective study, we excluded patients who were over 18 years of age to provide a comparison with the samples of previous studies on WSL formation in patients treated with conventional labial appliances, without creating a bias toward reduced formation of WSLs by including subjects who were potentially less susceptible to WSL formation because of their greater age. It was suggested that most of the patients in our sample were characterized by even more pronounced caries activity and susceptibility and a higher risk of WSLs because of their young age (mean, 14.35 years). Therefore, the incidence of postorthodontic lingual WSLs can be expected to be even more reduced in a sample with a higher mean age. Accordingly, we excluded older patients in an attempt to prevent the accusation of having intentionally reduced decalcification incidence by combining patients with low and high risks of caries activity. As a result, our sample provides a typical age distribution of under 18-year-old patients treated in an orthodontic office. We agree that a cutoff between 13 and 14 years would have led to better-balanced groups in terms of numbers of subjects. However, we considered it to be more meaningful to make a caesura at the age of 16 to separate the groups by higher or lower caries activity, which was reported to change at the transition to the late teen years, rather than at age 13. Based on available numbers of subjects, the secondary findings of comparisons of caries activity between the 2 age subgroups may therefore not be overemphasized here.
Further potential limitations to the findings of this first large study on lingual WSLs may exist in relation to the individual variations in the extent and quality of oral hygiene and nutritional habits. In view of the large sample size, however, the overall influence of minor individual variations in these factors was assumed not to be too substantial.
Since we are aware that more orthodontists are offering lingual appliances, we look forward to seeing large-scale research results of clinics offering both lingual and labial treatments. However, at present, we must content ourselves with the results we have. The results of the study by van der Veen et al are based on a small sample size, and this center does not treat enough fixed labial patients to provide a contrasting juxtaposition with the current lingual treatment sample.
The application of a thin extra layer of a fluoride-releasing bonding was discussed in the article; although the benefits of fluoride-releasing adhesives seem to be widely agreed on, systematic reviews warn against being too enthusiastic about potential benefits. Some additional reduction in WSL frequencies by an extra layer of fluoride-releasing bonding applied to the bracket base (and not to the bracket periphery) alone does not explain the large differences between our findings and labial WSL incidence assessed with or without the use of fluoride-releasing bonding.
Last but not least, the main reason why we are putting our “heart and soul” into proposing a consideration of the lingual technique as a treatment alternative to labial appliances is that it enables us to proactively address the concerns of increasing numbers of general dentists and pediatric dentists who may claim a high incidence of WSL as a counterargument to fixed orthodontic treatment, or even orthodontics in general. Considered as an extension or add-on to existing orthodontic therapeutic measures, the inclusion of lingual therapy in our therapeutic repertoire may be helpful for our specialty in general.