Author’s response (Refers to: Ren J, Bai D. Mystery of apical root resorption. Am J Orthod Dentofacial Orthop 2012;141:132-3)

I thank Dr Bai for his interest in our article, but I want to express a few concerns regarding his assertions. As re- ported on page 121, the article focused specifically on “an unexpected problem encountered during the treatment of an unerupted maxillary permanent canine” and not generally on the treatment of an unerupted maxillary permanent canine. Not even the different “ways to treat impacted canines” was part of the topic of this article. The real message from this clinical report is that, when failure of a closed traction occurs, not only tooth ankylosis, but also osseointegration of the wire chain should be considered as possible causative factors. This clinical report made me wonder whether we ever had extracted canines with a healthy periodontal ligament that were not really ankylosed. It is well known that resorption of adjacent incisor roots occurs in nearly 50% of patients with ectopic canines. In this case report, it can be speculated that apical root resorption of the left lateral incisor was caused by the preexisting permanent canine position, because “the left canine was palatally displaced and inclined mesially, high in the alveolar process, with its crown overlapping the root of the adjacent lateral incisor,” as explicitly mentioned on page 122. Some apical root resorption of the lateral incisor was thus inevitable, and even treatment alternatives such as canine extraction followed by implant-prosthetic replacement or orthodontic therapy after compensatory extractions of 3 premolars would not have limited it. Increased buccal inclination of the 4 maxillary incisors rather than “moderate to severe” root resorption as mentioned by Dr Bai accounts for the difference between the panoramic radiographs in Figure 2, A and B. This proclination was initially pursued by the clinician to create enough space for the canine to erupt into the dental arch, but it was finally enhanced by the undesir- able intrusive effect from the osseointegration of the wire chain. It can be easily seen on the panoramic radiograph at the end of treatment (Fig 6) that apical root resorption was confined to the left lateral incisor. Proclination of the maxillary incisors also persisted as a dental compensation for the skeletal Class III tendency. It can be argued that occlusal finishing was not optimal, because of the excessive palatal root inclination of the lateral incisors at the end of treatment, but a longer treatment due to the unexpected problem should be taken into proper account. I believe that there is nothing more to say than what was written in the article. In addition, radiographs at the 2-year follow-up confirmed only a slight remodeling at the apical root of the maxillary incisors and moderate remodeling at the left lateral incisor.