Science / Medicine : A Dental Revolution : Our teeth have gotten better over the years as a result of fluoridation, regular brushing and better nutrition. Now, a dental revolution promises to make procedures far less complicated, painful and time-consuming.

Joseph Carey is an associate editor of U.S. News and World Report in Washington

Americans' teeth have improved markedly during the last three decades as a result of water fluoridation, regular brushing, better nutrition and the use of fluoride mouthwashes, dental floss and sealants. From 1980 to 1987, the proportion of U.S. children age 5 to 17 with no decay in their permanent teeth rose from 36.6% to 49.9%. Toothlessness among middle-aged adults declined from about about 8% 13 years ago to just 4% in 1985, according to the National Institute on Dental Research in Bethesda, Md.

Now, a second dental revolution--already under way--promises to build on these gains and make most procedures far less complicated, painful and time-consuming for the 133 million Americans who spend $33 billion annually on their teeth.

Scientists have identified the forms of bacteria in the mouth that cause decay and, using an array of new techniques, will be able to prevent major problems and treat those that occur much earlier than they do now. With new therapies, better materials and greater knowledge about controlling pain, dental care could become almost pleasant.

Since much preventive work will be simple and performed mostly by hygienists, general dentists will become "mouth physicians," said Dr. Harold Loe, the dental institute director. And while some contend that these new developments may put dentists out of work, others say there will be just as much work, only of a different type.

If preventive measures now on the drawing board work out, patients soon will be visiting the dentist less frequently for decay and more frequently for more serious conditions such as tumors and jaw-related problems.

One of the most promising approaches is under study at Boston's Forsyth Dental Center, where Jeffrey Hillman, a molecular geneticist, is developing a "good" strain of bacteria. He said this could eventually lead to a one-time mouthwash that would prevent cavities from ever developing.

Under normal conditions, certain strains of the bacterium Streptococcus mutans --believed to be the principal cause of tooth decay--sit on the surface of the tooth while sugar from food is metabolized to produce an acid that demineralizes the tooth surface and, over time, progresses into decay. Hillman's "good" strain of S. mutans would produce an antibiotic-like substance that attacks and kills off the "bad" strains and then establishes itself permanently in the mouth.

Hillman has found a strain that works for a relatively long time in animals but disappears after a month in humans. He is now using recombinant DNA technology to construct a strain that will permanently colonize the more complex system in humans and won't revert back to acid production and tooth decay.

Once completed, clinical trials involving many patients would begin. He said the recombinant has already shown some promise in animals but is probably five years from being ready for routine use in people.

When it's ready, a solution containing the bacteria would take five minutes to swab onto all tooth surfaces and probably cost less than $1. Said Hillman: "Ideally, it would be given once in a lifetime and patients would only have to go back to the dentist for cleaning."

A variation on this technique is also being developed to treat gum disease, which is responsible for bone loss in 77% of working adults between the ages of 18 and 64. Hillman admits that it has been difficult to find a strain that stays in the mouth for a long time, but believes he now has one that will be ready for human tests next year and on the market in five.

Dental researchers are also experimenting with novel ways to deliver fluoride and drugs to resist decay and gum problems. At the National Institute on Dental Research, chemist Dale Mirth has developed a pellet designed to be cemented to a tooth, slowly releasing fluoride for six months. The pellet actually consists of a fluoride solution packaged inside a permeable polymer membrane specially designed to release water-soluble drugs. Dental pellets have been constructed to release fluoride at a constant rate. Similar controlled-released systems have already been developed to treat glaucoma and as a contraceptive.

Such a system would be especially useful for handicapped people who can't brush regularly and those with braces, which prevent thorough cleanings. Studies show that the pellet can produce a 50% reduction in cavities in animals. Full-scale human tests could begin this fall and the pellet itself could be ready in five years at a cost of a few dollars apiece.

In addition, Forsyth scientists are working on a time-release plastic fiber impregnated with the antibiotic tetracycline to treat gum disease. The elastic-like thread is wrapped around the tooth and pushed into the adjacent disease-filled pocket, where it stays for 13 days and releases about 1,000 times more drug than could be delivered by a standard dose taken by mouth. It allows dentists to treat individual teeth instead of resorting to surgery, which is usually performed on sections of the mouth.

A recent study at five medical centers showed that 90% of 125 patients responded favorably, particularly those with severe disease. The fibers do not eliminate the need for scraping away the buildup of bacteria around the tooth, but could eliminate surgery in many cases, Forsyth pharmacologist J. Max Goodson said.

The new era promises that dental work will be accompanied by a new technology of pain killing. Three companies are marketing a new form of electronic anesthesia that within five years may replace Novocaine injections. Electronic dental anesthesia sends impulses to the brain through electrodes placed near the teeth and blocks the pain signals and the perception of pain. The patient controls the level of anesthesia through a small hand-held box. The electronic procedure produces a tingling sensation that ends when the device is turned off and leaves no other effects.

Tests of 500 patients conducted at the USC School of Dentistry show electronic dental anesthesia to be successful in about 35% of cases. Now used by about 2,000 dentists nationwide, the procedure can replace injections for fillings, crowns and bridge work, and non-surgical gum treatments at little or no cost to the patient, said Dr. Stanley Malamed, a USC professor of anesthesia and medicine.

No magic potion has been developed to wipe out painful drilling but a novel decay-removing method called Caridex may be the next best thing. Using a pen-like instrument, Dr. Bruce Baral of Long Beach squirts a solution onto a patient's tooth where it dissolves only decayed areas. About 20 minutes later, he scrapes it away leaving healthy areas intact. "It does the job, there's no pain whatsoever," said one of his patients, Beverly Hills lawyer Ronald Gart, who usually turns miserable at just the sound of a drill.

Decay is the breakdown of dentin--a semi-resilient shell beneath the enamel that makes up the core of the tooth surrounding the pulp and nerve--into decalcified collagen, which looks like cloth fabric, only with the fibers running parallel instead of at right angles. The active ingredient in Caridex, a sodium salt of a very simple chlorinated amino acid, attacks the electrochemical bonds between the fibers in the decalcified collagen, leaving healthy tissue alone.

About 3,000 dentists in the United States use Caridex, which was developed by dentists at Boston's Tufts University School of Dental Medicine. The technique doesn't completely eliminate the need for the drill--openings must still be made to shape a tooth for a filling or to gain access to decay. It is most useful for decay deep in the tooth near the nerve where a dentist could inadvertently overdrill and cause pain. At a cost to the dentist of about $1,200 for equipment and a few dollars per application, Caridex has done little or nothing to raise the price of a filling.

At the same time, when those old amalgams have to be replaced, there are many products on the horizon to improve their look, fit and longevity.

One is a superglue derived from mussels, first identified by biochemist J. Herbert Waite while at the University of Connecticut in 1981. Within about three years, this substance--which enables mussels to bond to rocks under water--could be available to glue fillings, attach caps and crowns, seal teeth to reduce cavities and even cement fractured teeth back together. It could also find use in medicine, such as bringing tissues together after surgery. Two firms--Genex Corp. of Gaithersburg, Md., which is producing genetically engineered versions, and Biopolymers Inc. of Plainville, Conn., which is developing chemically synthesized applications--say the adhesive should be available within a few years at a cost of about $50 to $100 per application.

Scientists are also working on better composite resins for crowns and restorations that look like natural teeth. These products have improved markedly during the last 15 years but still don't last as long as silver fillings, especially in the back teeth where grinding takes place. Most wear well during the first few years but then start deteriorating. Dozens of preparations are under study but probably won't be ready for another decade.

Better restorations will be possible, however, through quicker and more precise ways to produce them. In the next three to five years, four separate research teams are expected to come up with desk-top computer systems that can design and produce custom crowns and bridges in a single office visit. The technique would replace the impressions, molds, casting systems and the weeks to months now necessary to make crowns.

All four approaches involve designing a device to record the geometric information of the mouth. This data is processed by a computer, which produces an image of a model tooth on a screen that can be rotated, enlarged and viewed from several angles with complete accuracy. In a final stage, the computer generates a magnetic tape that directs a milling machine to cut a replica of the tooth from plastic or cement. "All of the tedium and inaccuracy of present restorations would be eliminated," said one developer, Paul Marinaccio of Foster-Miller Inc., a mechanical engineering firm in Waltham, Mass.

To improve and strengthen the bone and tissue that anchor teeth, roughly a dozen materials have been used during the last decade to rebuild tooth and jaw sections eaten away by gum disease. So far, it is unclear whether they can attach well to surrounding soft tissue and natural bone. But developers of a relatively new product, called HTR (hard tissue replacement) polymer, claim that their product does the job. "When injected into place, it actually regenerates bone," said Dr. Arthur Ashman of New York City.

HTR polymer encourages bone growth by creating a "microscopic scaffolding" into which new bone and tissue grow. If a tooth has been extracted, Ashman said, the dentist can go back and make a denture or implant because the patient has retained the jawbone; in the case of bone lost to periodontal disease, HTR polymer can support and anchor the remaining structures. One study, by U.S. Surgical Corp. in Norwalk, Conn., which makes HTR polymer, found a 98% success rate in 647 patients. Despite Ashman's enthusiasm, many researchers believe it is too soon to say that HTR polymer is superior. "It's no better or worse than other materials," said Dr. Roland Maffert, chairman of periodontics at Louisiana State University in New Orleans. "All have about a 60% success rate."

Since all of these developments portend an easier time for patients, will they at the same time put dentists out of business altogether? With less drilling to do, Forsyth director John Hein predicts that the ratio of dentists to population will shrink from about 1 per 1,600 in 1990 to 1 per 20,000 in 2010. The nation's 57 dental schools have already scaled back their first-year class size totals from 6,301 in 1978 to 4,370 in 1987; and three schools--Emory in Atlanta, Georgetown in Washington and Oral Roberts in Tulsa, Okla.--have closed permanently.

The American Dental Assn., however, insists that dentists will actually have more work as the population ages and people keep their teeth longer. And no matter how many breakthroughs occur, there will always be some people who just don't brush as often as they should or who can't shake a sweet tooth.

Attacking the Bacterium

The bacterium Streptococcus mutans is believed to be a principal cause of tooth decay. Scientists hope to develop a strain of reproduceable, parasitic bacterium that could kill off its rival and leave teeth less liable to decay. The approach has produced encouraging results in animal studies but is probably five years away for people.

Using the Time Factor

Scientists are working on an approach to treat diseased gums with a slow-release fluoride pellet (1) that could be cemented to a tooth. Others are developing a time-release plastic fiber (2) impregnated with an antibiotic: The elastic-like thread is wrapped around the tooth; over 13 days, it releases about 1,000 times more drug than could be delivered orally--to individual teeth.

Blocking Out Pain

Electronic anesthesia may replace Novocaine injections, scientists say. Electronic dental anesthesia (EDA) sends impulses to the brain through electrodes (3) placed near the teeth and blocks pain signals and the perception of pain. The patient controls the level of anesthesia through a small hand-held box. EDA produces a tingling sensation that ends when the device is turned off.

Sticking to Your Mouth

A superglue derived from the material that mussels use to bond to rocks under water could be available to glue fillings, attach caps and crowns, seal teeth and even cement fractured teeth together (4).

Computer Teeth

Scientists are looking to computers to help design and produce custom crowns and bridges in a single office visit. The technique would replace the impressions, molds, casting systems and delay now necessary to make crowns. Computer technology basically extends the ability to build the model of the tooth (5).

Hardening of the Mouth

To strengthen bone and tissue that anchor teeth, new materials are being sought to rebuild tooth and jaw sections eroded by gum disease. One claims to encourage bone growth by creating a "microscopic scaffolding" into which new bone and tissue grow (6).

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