Root Resorption Following en Masse Retraction: A Prospective Assessment of Nickel-Titanium Closed-Coil Springs and Elastomeric Chains

Abstract

Introduction: Orthodontic en masse retraction, a technique used to close spaces in the dental arch, can sometimes cause external apical root resorption (EARR), an unintended side effect. This study investigates how different force delivery methods, specifically nickel-titanium (NiTi) closed-coil (CC) springs and elastomeric chains (E-chains), affect root length in the anterior and posterior teeth of the maxillary jaw. Root length changes were evaluated before and after retraction using cone-beam computed tomography (CBCT) imaging.

Methods: A prospective, in vivo, parallel-group comparative study was conducted on 24 patients (aged >18 years) requiring bilateral maxillary first premolar extractions. Patients were divided into two groups: Group 1 (n = 12) underwent en masse retraction using NiTi CC springs, and Group 2 (n = 12) used E-chains. Pre- and post-retraction CBCT scans were obtained to measure the root lengths of the maxillary incisors, canines, second premolars, and first molars. Standardized CBCT slice orientation and measurement protocols were used. Root length changes were measured as the distance from the cementoenamel junction to the root apex. Intra- and inter-examiner reliabilities were confirmed using intraclass correlation coefficients (ICC ≥ 0.90). Statistical analysis included paired and independent t-tests, with significance set at p < 0.05.

Results: Both groups demonstrated significant root resorption after retraction. The NiTi CC spring group showed statistically significant root length reduction across all teeth (p = 0.001-0.017), whereas the E-chain group exhibited non-significant changes in specific roots, including the right lateral incisor and distobuccal roots of the first molars. Intergroup comparisons revealed significantly higher root resorption in the NiTi CC spring group for the anterior teeth (p = 0.001). Posterior root resorption was not significantly different between groups (p = 0.466).

Conclusion: NiTi CC springs caused significantly greater root resorption in the anterior maxillary teeth than the E-chains. Clinicians should consider these effects when selecting retraction methods to minimize EARR, especially in cases that require en masse retraction of anterior teeth.

Keywords: microperforation; orthodontics; resorption; retraction; root.

Figure 1. Maxillary canine retraction using (A) nickel-titanium closed-coil spring and (B) elastomeric chain.

This figure represents study patients, included with appropriate informed consent.

Figure 2. Comparison of absolute root resorption in different teeth between study groups.

LCI: left central incisor, LLI: left lateral incisor, LC: left canine, LPM2: left second premolar, MB root of LM1: mesiobuccal root of left first molar, P root of LM1: palatal root of left first molar, DB root of LM1: distobuccal root of left first molar, RCI: right central incisor, RLI: right lateral incisor, RC: right canine, RPM2: right second premolar, MB root of RM1: mesiobuccal root of right first molar, P root of RM1: palatal root of right first molar, DB root of RM1: distobuccal root of right first molar, NiTi: nickel-titanium, E-chain: elastomeric chain This figure is derived from the data of the study.