A patient with bulimia nervosa asks how to reduce dental erosion. All of the following are appropriate recommendations EXCEPT:

Correct answer: A. Apply an acidulated phosphate fluoride (APF) gel

• A. CORRECT — this is the EXCEPTION. ACIDULATED PHOSPHATE FLUORIDE has a pH of roughly 3.5 and is itself erosive. It is contraindicated in patients with existing erosion, exposed dentine, or ceramic and composite restorations, all of which it etches and roughens. The correct choice is a NEUTRAL sodium fluoride preparation.
• B. Avoiding brushing for 30–60 minutes after an acid exposure IS correct advice. Softened, demineralised enamel abrades readily, so immediate brushing physically removes the softened surface layer.
• C. Rinsing with water — or better, a sodium bicarbonate rinse — after vomiting NEUTRALISES and dilutes the gastric acid and is an appropriate recommendation.
• D. Neutral sodium fluoride, whether as a 5000 ppm prescription paste or a neutral varnish, strengthens the remaining enamel without adding an acid challenge.

Note: Clinical signature of bulimia: PERIMOLYSIS — erosion of the palatal surfaces of the maxillary anterior teeth, often with amalgam restorations left standing proud of the dissolved surrounding tooth structure. It is frequently the first objective sign, and raising it requires care and a non-judgmental approach alongside referral for appropriate medical and psychological support.