Kuala Lampur, July 29 -- JULY 29 - We've all had days like this. Perhaps you're fasting. Perhaps you've been feeling unwell. Or maybe work has simply been so hectic that you've barely had time to eat. As bedtime approaches, a familiar thought crosses your mind.

"I hardly ate anything today. Surely I can skip brushing my teeth just this once."

It sounds perfectly reasonable. After all, if there is little or no food left in your mouth, what exactly is there to clean?

Surprisingly, the answer has very little to do with food. Many people think brushing is simply about removing leftovers from a meal. In reality, your mouth remains active every minute of the day, whether you are eating or not. Saliva continues to flow, the lining inside your...