But let's do a checkup on four bad habits that can undo all your good work:

Ducking the dentist. At least 20% of Americans have one or more untreated cavities. Ignored, cavities can get larger, deeper and cause severe aches, infection or even tooth loss. Don't wait for pain to see the dentist; schedule regular checkups and cleanings once or twice a year. And be sure to tell your dentist about medicines you take: Dry mouth — a common cause of cavities in older adults — is a side effect in about 500 drugs, including those for allergies, asthma, blood pressure, cholesterol, pain and Alzheimer's disease. To relieve dry-mouth symptoms, drink more water or chew sugar-free gum.

Drinking sugar. Bacteria in your mouth that feed on the sugar in sodas and sweetened fruit drinks make acids that attack tooth enamel for up to 20 minutes after you're done drinking, says the American Dental Association. Repeated attacks weaken enamel, leading to cavities and sensitive teeth. Research also suggests that the high acidity of energy and sports drinks can erode enamel. The best tooth-friendly thirst-quencher is water — preferably with fluoride. This mineral occurs naturally in all water sources, and research shows it helps prevent cavities. Check bottled water labels for fluoride; if you use a filter for tap water, get one that doesn't remove fluoride.

Using old brushes. They're less effective at cleaning; plus the bristles may breed bacteria. Replace your brush every three to four months, sooner if it's frayed, and right after you've had a cold, flu, mouth infection or sore throat. More tips: Choose a soft-bristled brush with a small head to get at hard-to-reach spots; brush in circular motions with fluoride toothpaste.

Biting things open. You know you've done it — with a bag of chips, a piece of tape or even a price tag on new clothes. Not a good idea: Your tooth could crack, which hurts; if the nerve in a cracked tooth gets damaged or infected, you might need a root canal.