B y the time we reach middle age, most of us have had a few root canals -- or worse. Years of use make our teeth weaker and more vulnerable to decay and breakage.

Surprising statistic: At least two out of every 10 older Americans (about 20 million people) are toothless.

But strong, healthy teeth are important: If you have dental pain or denture problems, it can be difficult to eat fruits and vegetables, which are crucial for adequate nutrition. In addition, numerous studies have linked gum (periodontal) disease -- a primary cause of tooth problems -- to a variety of serious ailments, including heart disease, diabetes, dementia and some forms of cancer. How to optimize the health of your teeth...

Use sugarless candy or gum to stimulate saliva. Salivary flow decreases as we age, creating an ideal environment for mouth bacteria to flourish. Many heart drugs, antidepressants and other medications may further decrease saliva production.

To help lubricate your dry mouth, your doctor may have suggested that you suck on mints or other small candies. But the sugar in such candies -- including so-called breath mints -- feeds bacteria in the mouth, accelerating tooth decay you may not even see.

My advice: Switch to sugarless candies -- or chew sugarless gum. Also avoid "sticky" foods, such as dried fruit (including raisins and prunes), that tend to promote tooth decay.

Bite carefully. Our teeth become more fragile as we age, and any tooth that has had a root canal, crown or filling is more brittle than an intact tooth. A crown (a custom-made, thimble-like structure that fits over a trimmed-down tooth that has decayed) typically lasts for seven to 10 years, but the longevity of natural teeth, crowns and fillings may be shortened if you don’t take the right precautions.

My advice: If you have crowns, fillings and/or veneers (facings applied to the front of teeth to improve their shape and/or color) in the front of your mouth, biting into an apple, carrot or even a crusty piece of bread could shatter them. Instead, bite with your side teeth to shift the force on to them. Better yet, cut up apples, carrots or hard bread into bite-sized pieces so you can chew with the teeth in the back of your mouth (molars), which are usually the strongest.

Caution: Never chew ice -- even molars can be shattered with one good crunch. Also, don’t use your teeth as "tools" to do such things as open plastic packages, cut thread or crack nut shells.

Pamper your gums. Most people have some degree of gum recession (in which the gums have pulled back, exposing the roots of the teeth). It results from brushing too aggressively or from gum disease. Receding gums make teeth more susceptible to cavities at the roots and increase their sensitivity.

My advice: To minimize gum recession, most people know to use a "soft" or "ultrasoft" toothbrush, but it’s also important for these brushes to be replaced at least every three to four months. After that point, the bristles usually flare out and become less effective. When brushing, use light pressure. I recommend electric toothbrushes only if you have arthritis in your hands or some other condition that affects manual dexterity.

Smart idea: If you have receding gums and use sensitive toothpaste (such as Sensodyne or Colgate Sensitive), apply it with your finger to the sensitive area, count to 60 (to ensure good absorption), then brush.

Be vigilant about self-care. Up to 30% of the population is genetically predisposed to gum disease, which is a major cause of tooth loss. Even people who are not genetically primed for gum disease may wind up with bacterial infections in the tissues surrounding the teeth as a result of changing hormone levels, poor self-care or other health problems.

My advice: For adults with healthy teeth, twice-daily thorough brushing is fine. If you have gum disease or its precursor (gingivitis), which causes such symptoms as swollen gums, bad breath and gums that bleed easily when brushing or flossing, brush your teeth after every meal -- or, if that’s inconvenient, at least swish your mouth with water after you eat.

Important: Brush for a full two minutes with any fluoride toothpaste. When you floss (any type is fine), be sure to remove the plaque from the sides of every tooth.

Important: Since many people now drink bottled water instead of tap water, which is fluoridated in most municipalities, some experts fear that the incidence of tooth decay may increase. If you live in a community that does not have fluoridated water, look for bottled water brands that are fluoridated. Many companies, including Culligan and Natural Springs, produce fluoridated bottled water.

For a list of companies: Consult the International Bottled Water Association, 800-928-3711, www.bottledwater.org/public/fluorida.htm.

Opt for an implant. In the old days, when you lost a tooth, your dentist would crown the teeth adjacent to an empty space and create a "bridge" to hold a replacement tooth. An implant (a metal post and abutment that are surgically anchored into the jawbone to provide support for a crown) generally is a better option because its placement does not require cutting down adjacent teeth. However, the price of a bridge may be lower than implants initially, and some insurance companies balk at covering the cost of an implant.

My advice: If your dentist recommends a bridge, ask whether an implant can be used instead. If cost is an issue, work out a payment plan with your dentist.

Helpful: If your dental insurance does not cover implants, insist that your case be reviewed by a dentist. About half the time, such appeals result in at least partial reimbursement. Or ask the insurance company to pay you its standard reimbursement for a bridge and apply it to your implant.

If the cost is still too high: Go to a nearby dental school, where students are supervised by professors and the cost is about half of that charged at a private practice.