Orthodontic Root Resorption — MFDS Part 1 MCQ

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ModerateOrthodontic PrinciplesOrthodontic Root ResorptionMFDS Part 1

Assuming comparable force magnitude and duration, which type of orthodontic tooth movement is most strongly associated with external apical root resorption?

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Correct answer: B — Intrusion

Intrusion is the single best answer. Intrusive loading concentrates compressive stress in a relatively small periodontal-ligament area near the root apex and is a recognised treatment-related risk factor for orthodontically induced external apical root resorption. Human comparative evidence has demonstrated substantially more resorption with intrusion than with an equivalent extrusive force. Extrusion generally produces less apical resorption. Tipping, rotation and bodily movement can all cause resorption, particularly when forces are excessive or prolonged, but they are not as consistently associated with the greatest apical risk. Risk also depends on individual susceptibility, root morphology, force magnitude and continuity, and treatment duration; therefore, intrusive mechanics should use carefully controlled light forces.

Reference: Currell SD, Liaw A, Grant PDB, Esterman A, Nimmo A. Orthodontic mechanotherapies and their influence on external root resorption: A systematic review. American Journal of Orthodontics and Dentofacial Orthopedics. 2019;155(3):313-329. https://pubmed.ncbi.nlm.nih.gov/30826034/