DENTAL sealants, properly applied and periodically replenished, can eliminate decay in the chewing surfaces of teeth. Sealants, the plastic coatings applied to permanent molars, are second only to fluorides in preventing tooth decay over all and are more effective than fluorides in protecting the chewing surfaces of molars, where most cavities occur.
Yet fewer than 20 percent of American children and only a tiny fraction of adults who are prime candidates for tooth decay have had their teeth protected by sealants. The country is far from the goal established by the United States Public Health Service of sealing one or more teeth of half the children 8 to 14 years old by 2000.
The American Dental Association has been urging dentists for years to apply sealants to permanent molars as they emerge in children's mouths, and it wants adults to know that you don't have to be a child to seal out tooth decay. Anyone with healthy molars -- teeth that have not yet been drilled and filled -- can greatly increase the chance of keeping those teeth healthy for life by having sealants applied.
For all children and for adults at high risk for decay, studies have shown that it is well worth investing time and money now to protect those most vulnerable teeth, avoiding the pain and cost of dental repairs.
Dental sealants are coatings of plastic that are applied to the chewing surfaces of molars, where food tends to get lodged in pits and fissures that are difficult to clean thoroughly with a brush. Even saliva, which helps to clean food particles from other areas of the mouth, cannot clean the pits and fissures in permanent molars. Sealants work by filling in the cracks, preventing accumulations of food and keeping the bacteria that cause decay from getting to the enamel on the tooth surface.
The application of sealants starts with a thorough cleaning by the dentist or dental hygienist. Then the tooth surfaces are etched by acid for about 15 seconds so the nontoxic plastic material that is brushed on immediately afterward will stick more easily. Depending on the product, the plastic may then be ''cured'' with a chemical or light. For the sealants to adhere properly, saliva must be kept from contaminating the area until the plastic has hardened.
Sealing the eight first and second permanent molars in the back of the mouth takes about half an hour. Sealant may also be applied to wisdom teeth and the premolars, the molars closest to the front of the mouth. But the premolars are not usually treated because they are much less susceptible to decay than the larger molars behind them.
Sealants can be applied by a dentist or by a trained dental hygienist or dental auxiliary person. At each dental visit, teeth with sealants should be checked to be sure the treated areas are still adequately covered. When sealants wear down, they should be reapplied for continued protection.
According to a 1995 survey by the dental association, the cost of sealing each tooth averages $24, slightly less than half the typical cost of filling a cavity. Charges, of course, vary with location. Many private dental plans cover the cost. In 33 states, Medicaid provides some coverage, ranging from 100 percent to coverage for only the first permanent molars.
Currently, American Indians are more likely than the members of any other group in this country to get sealants because the public health service that cares for them offers them this benefit, said Dr. Richard J. Simonsen, a researcher in the dental products division of the Minnesota Mining and Manufacturing Company in St. Paul, Minn. He added that a number of small countries, including Finland, had much higher rates of sealant application than this country's.
In the early days of sealants, many dentists feared that coating tooth surfaces would lead to rampant dental disease if those teeth already had the beginnings of decay. But quite the opposite is true. Several studies have shown that an incipient cavity can be nipped in the bud and the health of the tooth restored by applying a sealant, because the plastic coating deprives the decay-causing bacteria of oxygen and food.
While sealants are best applied soon after the permanent molars erupt, it is never too late. Adolescents and college students, whose eating and dental hygiene habits may be less than ideal, are prime candidates for sealant protection. Having sealants applied would be a valuable parting gift for college-bound students. Many adults could also benefit.
Sealants are especially helpful for adults with deep fissures in their molars, especially those who grew up without access to fluoridated water and toothpaste with fluoride. Some adults are at high risk for decay because illness or injury makes it hard for them to clean their teeth properly. And some adults suffer from chronic xerostomia, or dry mouth. They may be on medications that reduce saliva formation, or they may have disorders that impair salivation, like Sjogren's syndrome, an autoimmune disease. When saliva is inadequate to cleanse the mouth, the risk of decay increases greatly.
Even with sealants, fluoride and proper oral hygiene remain critically important to lasting dental health, and there are many other teeth and tooth surfaces in need of protection. Teeth should be brushed with a fluoridated toothpaste at least twice a day, including just before bedtime. They should also be flossed each night. Regular dental checkups and semiannual cleanings remain vital to dental health, and so are dietary habits that do not leave the teeth chronically exposed to sweets and other carbohydrates that provide banquets for decay-causing bacteria.
Photos: Toothbrush bristles may not reach the bottom of fissures in an adult molar (cross section, above); sealant can protect the surface (left). (Dr. M. John Hicks/Baylor College of Medicine)