Original article
External apical root resorption and vectors of orthodontic tooth movement

https://doi.org/10.1016/j.ajodo.2019.10.017Get rights and content

Highlights

  • •

    Root movement causes resorption, and more movement causes more resorption.

  • •

    Directions of tooth movements incur different risks of apical root resorption.

  • •

    Intrusion is particularly deleterious, whereas extrusion is comparatively benign.

  • •

    Resorption may be inevitable until therapeutic prevention becomes available.

Introduction

External apical root resorption is nearly ubiquitous in people treated orthodontically. This study predicted the extent of external apical root resorption by the vector of the incisor movement.

Methods

Cone-beam computed tomography scans of 93 white American adolescents (45 boys, 48 girls) with a Class I malocclusion who received comprehensive orthodontics were analyzed. Half were treated with 4 first-premolar extractions, and the others were treated without extractions. An x, y, z coordinate system was registered on the maxillae, superimposing on foramina, to quantify vectors of maxillary incisor movements. Multiple linear regression identified significant predictors of resorption for each incisor.

Results

Strongly predictive models (R2 = 77%-86%) were obtained. All directions of incisor movement tested (anteroposterior, mediolateral, craniocaudal, torquing) increased the risk of resorption in a dose-response fashion. Intrusion was most damaging. The patient's sex, age, and duration of treatment were not predictive.

Conclusions

Root resorption is a very frequent consequence of tooth movement, especially intrusion and torquing, though no direction is harmless, and most corrections occur in combination. Incisor apical resorption was significantly greater in the extraction sample (ca 0.5 mm).

Section snippets

Material and methods

Subjects were white American adolescents who received comprehensive orthodontic treatment with fixed appliances. Institutional approval was granted before study initiation (IRB #17-05545-XP). Patients were free of disease or any discernible syndrome and were fully dentate (no hypodontia, ignoring third molars). No patient with open incisor apices or treated with palatal expanders was included. Cases in which canines resorbed adjacent teeth were excluded from the study. Incisors were free of

Results

Tooth movement accounted for most of the variation in root resorption. All 4 incisors had highly significant associations between vectors of OTM and millimeters of EARR (P <0.0001), with adjusted R2 ranging from 77% to 86% (Table I). Significant predictors were entered sequentially until the explainable variation was exhausted.27 The principal predictor of each incisor's EARR was intrusion measured at the tooth's apex and CEJ (Table II; Fig 4).

There was a potential issue with the craniocaudal

Discussion

There are several sorts of root resorption,40,41 but it is external apical resorption that most frequently concerns orthodontists because it permanently diminishes root volume, alters the center of resistance, and compromises support and anchorage. Severe cases of EARR are at risk of increased mobility or even tooth exfoliation, but resorption stops with the cessation of orthodontic forces.42,43 Patients generally are unaware of resorption, although discoloration or mobility can occur. Clinical

Conclusions

We quantified positional changes (x, y, z) of the maxillary permanent incisors during orthodontic treatment. We (1) described how tooth vectors affected EARR and (2) compared extraction (4-4/4-4) vs nonextraction outcomes in adolescent patients.

  • 1)

    Multiple linear regression accounted for most of the variability in EARR (∼80%) for each maxillary incisor.

  • 2)

    Intrusion was the strongest predictor of EARR, although all directions of the incisor movement elevated the risk and extent of periapical

Acknowledgments

The authors are pleased to recognize the courtesy of Dr Daniel Merwin in accessing his CBCT files and of Ms Miranda Sun (Anatomage) for help with programming.

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