"Back to the question: Do you brush to remove plaque or food? The equation for caries is "plaque bacteria plus a fermentable carbohydrate equals acid." We can break the equation by removing either the plaque or the carbohydrate. Removing the plaque thoroughly before introducing the carbohydrate prevents acid production. If you brush after eating to remove the food instead, it's after the fact and, therefore, not prevention. According to Dr. Martin Addy of Bristol, England, a long-time advocate of brushing before eating, brushing after the acid is produced is no longer preventive. Preventive means intervention before the event — in this case, prevention would occur before acid production, not after."