We thank Dr R. C. Solem for his valuable comments on our article (Alqerban A, Jacobs R, Fieuws S, Willems G. Radiographic predictors for maxillary canine impaction. Am J Orthod Dentofacial Orthop 2015;147:345-54). We are indeed aware of the limitations of cross-sectional studies. Our inclusion criterion was primary eruption failure of the maxillary canine, as diagnosed radiologically by an unchanged position in the maxillary arch during a 1-year interval. After that period, positional follow-up of the canine ceased for ethical reasons and to prevent further complications as a consequence of delaying orthodontic intervention.
We fully agree that more information from earlier time points might help to clarify factors that cause canine impaction. However, ethical concerns arise when exposing even younger children to ionizing radiation for the purpose of predicting possible canine impaction.