A 5-year-old brushes unsupervised, has heavy plaque and carious primary molars, and complains of pain. Each of the following is a plausible cause of her pain EXCEPT one. Which is the EXCEPTION?

Correct answer: B. Periodontal disease

• A. This IS plausible. The permanent first molars erupt at around 6 years, and pericoronal soft-tissue inflammation during eruption is a well-recognised cause of pain — the eruption may begin shortly before the sixth birthday.
• B. CORRECT — this is the EXCEPTION. Destructive PERIODONTAL DISEASE is rare in a 5-year-old. Plaque-induced GINGIVITIS is common at this age and may cause tenderness on brushing, but true periodontitis with attachment loss is uncommon and, when present, signals a systemic problem — leukocyte adhesion deficiency, hypophosphatasia, Papillon-Lefèvre syndrome, neutropenia or leukaemia — and warrants medical investigation rather than being assumed as an everyday cause of pain.
• C. This IS plausible. Exfoliation of primary teeth with root resorption and mobility causes discomfort, though at 5 years this applies mainly to the incisors.
• D. This IS a plausible cause and, given heavy plaque and cavitated molars, the most likely one.

Note: The management point that follows: at 5 years the parent must still be brushing or at minimum supervising and re-brushing. Children generally lack the manual dexterity for effective independent brushing until around 8 years of age, so caregiver-delivered oral hygiene is the central preventive instruction.