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Orthodontics · patient case question

Tooth #8 is to be repositioned by ORTHODONTIC EXTRUSION. Which factor most needs to be taken into account?

Patient case: Trauma to the maxillary central incisors in a young adult

Patient: Male, 21 years old

Chief Complaint: “I hit my mouth on the edge of the pool and broke my front teeth.”

Background: Injury occurred four hours ago. No loss of consciousness, no nausea. Tetanus status current. Healthy, no medications.

Vital Signs: BP 126/78 mmHg · HR 88 bpm · T 98.4°F

Findings: Tooth #8: fracture through ENAMEL, DENTINE and with a visible PULP EXPOSURE of approximately 1 mm, bleeding, and exquisitely sensitive. Tooth #9: fracture through enamel and dentine only, NO pulp exposure. Separately, #8 is also INTRUDED approximately 3 mm into its socket. Radiographs show no root fracture and mature apices on both teeth.

  1. The curve of Spee
  2. The crown-to-root ratio
  3. The overbite
  4. The overjet
Show answer and explanation

Correct answer: B. The crown-to-root ratio

  • A. The curve of Spee is an arch-form consideration in comprehensive orthodontics, not the governing concern in extruding a single traumatised incisor.
  • B. CORRECT. Extrusion moves the tooth coronally, and the bone and attachment follow it only partially — so the clinical crown lengthens while the ROOT LENGTH SUPPORTED BY BONE shortens. Every millimetre of extrusion therefore worsens the CROWN-TO-ROOT RATIO, and in a traumatised tooth already at risk of external resorption from the intrusion injury, that margin matters. Assess the starting ratio, extrude slowly with light continuous force, and accept that a tooth with a short or resorbing root may not tolerate the movement.
  • C. Overbite will change as the incisor is extruded, and the occlusion must be checked — but it is a consequence to manage, not the limiting factor on whether the movement is feasible.
  • D. Overjet is the horizontal overlap of the incisors. Extrusion is a vertical movement and does not principally alter it.

Note: Two further points on the intrusion itself. Management depends on APEX MATURITY: an immature apex intruded less than 7 mm may be left to re-erupt spontaneously; a MATURE apex, as here, needs orthodontic or surgical repositioning, started early. And intrusion carries the WORST prognosis of all luxation injuries — pulp necrosis is near-universal in mature teeth, so plan endodontic treatment within two to three weeks, and watch for replacement and inflammatory resorption at every review.

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