Background
Impacted canines are clinically common, with an incidence of approximately 1%-3%, and the incidence of palatal interruptions is higher than that of labial interruptions [
1‐
3]. Impacted canines affect the patient's dental function, aesthetics, and psychological health. Root resorption of adjacent teeth is more common among patients with its associated conditions. The rate of root resorption of adjacent lateral incisors is approximately 44.5%, the rate of root resorption of nonadjacent lateral incisors is approximately 7.35% [
4,
5], and there are more Asians who experience severe root resorption [
6]. The causes of root resorption of adjacent incisors in patients with impacted canines remain unclear and may involve factors such as sex, inflammation, location of interrupted cuspids, and mechanical pressure [
7,
8].
However, diagnosing incisor root resorption is challenging due to the absence of symptoms, especially when the crown of a canine overlaps the root of a neighboring toot on panoramic radiographs, and delaying patient consultation often leads to severe root resorption, increasing the time and cost of treatment. Identifying and diagnosing impacted canines early is critical [
9].
When treating resorbed lateral incisors, various factors, such as age, complaints, and severity of resorption, need to be considered. Due to the low long-term retention rate and the time and cost of treatment, it is often recommended to extract more severely resorbed incisors and restore them through cuspid reshaping or implantation [
10‐
12]. There are few reports in the literature on long-term follow-up after orthodontic treatment of severe root resorption of lateral incisors due to impacted canines, and analysis of long-term outcomes can guide to support orthodontic therapy planning.
Discussion
The diagnosis of adjacent lateral incisor root resorption due to canine obstruction is often delayed in the early stages, and even when resorption reaches the pulp, symptoms are often not obvious. The rate of accurate diagnosis of adjacent root resorption on radiographs is only 30% to 50% and up to 70% on CBCT [
13‐
16]. Misdiagnosis on radiographs is often one of the medical causes of root resorption of adjacent teeth in patients with impacted canines. CBCT provides the specific location of the impacted canines and provides the precise location for surgical exposure and orthodontic traction direction [
17], thereby preventing medical root resorption caused by orthodontic therapy.
In patients with severe root resorption of the lateral incisors due to impacted canines, extraction of the lateral incisors followed by replacement of the canine and subsequent restorative reshaping is often chosen for long-term preservation [
12,
18]. However, canine restorative reshaping requires removing a large amount of normal dental tissue, even requiring root canal treatment, and is not permanent, thereby increasing the burden on the patient. The two patients described in this article were young; if their lateral incisors were extracted, they would need implants in adulthood, but the lack of bone in the anterior region may lead to implant failure, as well as aesthetic and psychological consequences. There is a risk of treatment failure for impacted canines. Therefore, a non-extraction-retained lateral incisor design was used to maintain patient aesthetics and to preserve the missing tooth space for restoration in adulthood, as both patients were straight-faced, and the orthodontic design did not require extraction to orthodontically retract the anterior teeth.
With an increased risk of root resorption of the lateral incisors, impacted canines in permanent dentition often require surgical exposure combined with orthodontic treatment [
19]. Rational biomechanical and directional design of traction of the impacted canines is essential to prevent root resorption of the lateral incisors [
20]. The earlier an impacted canine is detected, the simpler the treatment modality. The treatment principles for both cases included a rational anchorage design, three-dimensional directional control, sufficient eruption space for the canines, and the application of light force to the lateral incisors. In these two cases, molars were used as anchorage and to prevent further root resorption caused by neighboring teeth. The impacted canines were initially designed to move palatally and distally medially, followed by labial movement after the canine crowns moved away from the roots of the lateral incisors, similar to the direction of movement reported by Herav et al. [
21]. The lateral incisor brackets were then bonded after the canines were aligned to avoid any unnecessary movement of the lateral incisors. Light force was applied to align the lateral incisors. With a proper mechanical design, medical secondary resorption of the roots of the adjacent teeth of the mobile teeth can be effectively avoided.
Long-term follow-up reports of the retention of severely resorbed roots are rare. In this paper, in two cases, severely root-resorbed lateral incisors with normal orthodontic tooth movement were shown to have good long-term stability after treatment. It is possible that orthodontic treatment changed the long-term pressure of the impacted canines on the adjacent teeth, modified the periodontal tissues around the resorbed roots, and ensured the long-term stability of the occlusion. Becker et al. [
22] conducted a long-term follow-up study, and orthodontic movement did not aggravate the loosening or discoloration of adjacent teeth with severe root resorption due to impacted canines, and splinting was not required after the treatment. Moreover, orthodontic movement did not increase the risk of secondary root resorption. Furthermore, Falahat et al. [
23] reported that severely resorbed incisors were stable long-term, with normal long-term pulp vitality, and required no root canal treatment. The long-term observations reported in two cases suggest that a conservative, non-extraction treatment option is available for patients with severe root resorption due to impacted canines.
In this study, two patients with severe lateral incisor root resorption due to impacted canines were followed over a long period and showed good stability and normal pulp vitality 5–10 years after orthodontic treatment. For patients with high aesthetic demands for their anterior teeth, neither prosthetics nor nonextraction treatment is recommended for adolescents. Patients with severe root resorption of adjacent teeth due to impacted canines can try to retain them, but orthodontic treatment with light and intermittent force should be applied. Long-term follow-up after treatment is required to ensure success.
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit
http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (
http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.