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Prosthodontics & Occlusion · single question

A patient with a metal frame RPD returns with allergic reaction a few days later. What is the most likely diagnosis?

  1. Cytotoxic reaction (Type II)
  2. Contact dermatitis (Type IV hypersensitivity)
  3. Serum sickness (Type III)
  4. Anaphylaxis (Type I hypersensitivity)
Show answer and explanation

Correct answer: B. Contact dermatitis (Type IV hypersensitivity)

  • A. Type II reactions involve antibody-mediated cytotoxicity — not the typical presentation of RPD metal allergy.
  • B. A patient who returns DAYS AFTER receiving an RPD with an allergic reaction is experiencing TYPE IV (DELAYED, CELL-MEDIATED) HYPERSENSITIVITY CONTACT DERMATITIS. Type IV reactions occur 24-72 hours after contact (delayed) and involve T-lymphocytes rather than antibodies. The metal alloy in the RPD framework (most commonly NICKEL) is the most common culprit.
  • C. Type III reactions involve immune complex deposition — not the typical pattern for RPD metal allergy.
  • D. Anaphylaxis is Type I (IgE-mediated, IMMEDIATE) — it occurs within minutes. A reaction appearing DAYS after RPD placement is NOT Type I.

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