Both xylitol and arginine have anticariogenic properties. Which statement is TRUE?

Correct answer: A. Xylitol inhibits S. mutans; arginine raises plaque pH via ammonia production

• A. Correct. Xylitol is a non-fermentable sugar alcohol that inhibits S. mutans metabolism/growth, while arginine is metabolized to ammonia, raising/buffering plaque pH — two distinct anticariogenic mechanisms.
• B. Arginine is NOT fermentable into acid and does not lower pH — it raises pH via ammonia production, the opposite of this statement.
• C. This swaps the mechanisms — xylitol does not work via ammonia production, and arginine is not simply a 'sugar substitute' in the way xylitol is.
• D. Neither is a fermentable sugar in the cariogenic sense — xylitol is non-fermentable by cariogenic bacteria, and arginine is an amino acid, not a sugar.

Note: Memory trick: 'Arginine = Alkaline' | 'Xylitol = eXterminates mutans.'