Early next year, 30 college students in Boston will add an unusual test to their curriculum. From January through March, they will travel to the Forsyth Dental Clinic to drink a liquid protein produced by the bacteria that cause tooth decay. Then they will have their blood and saliva tested for the presence of special antibodies that ultimately fight tooth decay.
If the results are positive, a vaccine against cavities may be available within the next decade to be given routinely alongside vaccines for diphtheria, measles, mumps, tetanus and whooping cough.
Tooth decay afflicts about 95% of the population, costs billions of dollars to treat annually and is the leading cause of tooth loss in adults 35 years and younger.
Two advances--fluoridation and dental sealants--are capable of temporary protection against tooth decay. But the real breakthrough, a vaccine that could immunize people against dental cavities, has remained elusive.
Promising Leads There are two promising leads. Some researchers, like immunologist Daniel Smith of Forsyth Dental Clinic, are concentrating on the protein produced by the bacteria that cause tooth decay. Others, including biologist Roy Curtiss III of Washington University's School of Dental Medicine, are attempting to control the bacterium itself.
Known as streptococcus mutans--or s. mutans--the bacteria that produce cavities gradually colonize the mouth during tooth development. Infants "don't seem to have the bacteria in their mouths until they develop teeth," Curtiss said. "Studies suggest very strongly that infants acquire the bacteria from other family members."
Once the bacteria take hold in the mouth they reproduce slowly but persistently. "Only 50% of 3-year-olds have detectable levels of s. mutans in their mouths," Smith said. But "s. mutans grows in the mouths of some 95% of teen-agers.
"If we could devise a scheme where we could immunize kids before they have s. mutans and then keep antibodies high against the bacteria during the cavity-prone years, we think we could have a more complete system for protection from tooth decay."
Three-Step Process S. mutans is one of the more benign members of the large bacterial family that causes strep throat and rheumatic fever. This germ erodes teeth in a three-step process, Curtiss explained.
First, it attaches to a thin layer of saliva that bathes the teeth with a filmy protein.
Next, s. mutans takes advantage of sugar in the diet. The bacteria break down sugar for their own energy use and also to produce a gluey substance that enables them to stick to the tooth and to other bacteria. This buildup is known as dental plaque and can be removed only by professional dental cleaning, Curtiss said.
Finally, cavities develop as s. mutans produces lactic acid, which gradually eats away tooth enamel.