Die Bedeutung der Kjaer-Merkmale bei der Risikoeinschätzung externer Wurzelresorptionen vor einer kieferorthopädischen Therapie - eine retrospektive Analyse

Objektive: External root resorption can occur in the course of orthodontic therapy on single or multiple teeth. The risk of root resorption varies greatly from individual to individual, and approximate risk assessment prior to the start of treatment is based, among other things, on radiographically depictable dental, resorption-specific features. Aim of the study: The aim of this retrospective study was to assess the relevance of the dental characteristics (Kjaer characteristics) established by Inger Kjaer [1995], which have been associated with an increased incidence of external root resorption during orthodontic treatment. In addition, patient-specific characteristics, such as age, general disease, oral dysfunction, dental trauma, and orthodontic treatment factors that have been described in a context of root resorptions were collected. In this way, an adequate risk assessment of patients for root resorptions before orthodontic therapy should be performed. Material and methods: The treatment records and panoramic radiographs of 1156 patients were retrospectively analyzed. Patients were between ten and eighteen years of age and were treated in the Department of Orthodontics at the Center for Dental, Oral and Maxillofacial Medicine, Philipps University Marburg, Germany, from 2000 to 2019. Data were collected anonymously and radiographs were examined for present Kjaer features and external apical root resorption. The severity of the root resorptions was documented in three different degrees of tooth-related severity. Bivariate and multivariate analyses were then performed, with α = 0.05 defined as the significance level. Results: The majority of the patients included had at least one Kjaer feature, and only 2.2 % of the patients did not have any of the morphological characteristics investigated. During the course of orthodontic therapy, mild root resorption of individual teeth occurred in patients with and without Kjaer features (72.9 %). On average 3.22 ± 3.24 teeth were affected by blunting. Root resorption grade two was present in 15.5 % of patients. Severe root resorptions were comparatively rare at 2 %. Multivariate analysis confirmed a correlation of root resorptions with the presence of the Kjaer characteristics short tooth roots (p < 0.001), narrow tooth roots (p = 0.006), and aplasia (p < 0.001). Furthermore, the studied parameters dentition phase at the end of treatment (p < 0.001), orthodontic appliance used (removable: p < 0.001; combined removable and fixed: p = 0.008), and orthodontic treatment duration (p < 0.001) had a statistically significant effect for the occurrence of external root resorption. In contrast, no correlation could be found between root resorptions and extraction therapies (p = 0.154), and the Kjaer trait atypical deciduous tooth resorptions (p = 0.087) was irrelevant for the occurrence of resorptions. Conclusion: Based on the data of the present study, the pathogenesis of external apical root resorption is complex and a simple risk assessment based on radiographs alone is very limited or even impossible. In the initial diagnosis, panoramic radiographs should be used to detect narrow and short tooth roots, among other things, and patients should be informed about any root resorption of these teeth. Affected teeth should be moved orthodontically as gently as possible and examined clinically and radiographically for resorptions at regular intervals. Orthodontically controllable factors, such as the appliances used and the duration of treatment, should generally be applied in such a way that the risk of tooth structure loss is avoided as far as possible and is at best minimal. Further investigation of other influencing factors, such as genetic predispositions and composition of the gingival sulcus fluid, is needed to predict an individual risk of root resorption during orthodontic tooth movement.