Bodily Tooth Movement — MFDS Part 1 MCQ

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ModerateAnatomy (Head & Neck)Bodily Tooth MovementMFDS Part 1

During orthodontic retraction of a maxillary central incisor, superimposed records show that the incisal edge and root apex have moved palatally by the same distance. There is no change in the inclination of the tooth's long axis or in its vertical position. Which type of tooth movement has occurred?

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Correct answer: E — Translation

Translation, or bodily movement, is correct because the crown and root apex move by the same distance in the same direction while the long-axis inclination remains unchanged. A force acting through the tooth's centre of resistance produces translation. When force is applied at a bracket away from that point, an appropriate force-couple system can provide the moment-to-force ratio required for bodily movement; a couple alone would produce rotation rather than translation. Tipping causes unequal crown and root movement with a change in inclination. Rotation turns the tooth around its long axis. Intrusion and extrusion are vertical movements towards or away from the apical tissues, respectively, and are excluded by the absence of vertical displacement.

Reference: Kuruthukulam RM, Patil AS. The center of resistance of a tooth: a review of the literature. Biophysical Reviews. 2023;15:35-41. https://pubmed.ncbi.nlm.nih.gov/36909954/