Technical Advances
In 1907, William Taggert first cast gold inlays, and since then the casting process has been perfected to allow for the shrinkage of the gold as it sets. In 1924 synthetic resins began to replace vulcanite as a material for denture bases. These new materials appear more lifelike than vulcanite and more closely resemble natural gum tissue. In 1925 the use of flexible materials for making impressions of the teeth started to replace the use of plaster, which was difficult to manipulate in the mouth.
After the introduction of ether and other general anesthetics in the mid-1800s, scientists began searching for drugs that would act as local anesthetic agents. Cocaine was used as a local anesthetic in the 1880s, but it was not very satisfactory because of the toxicity and narcotic nature of the drug. In 1905 the American physician Albert Einhorn synthesized procaine (Novocain), and it soon became the most widely used dental anesthetic. Injected directly into the gum tissue, it temporarily numbs the area so that a tooth can be painlessly drilled or extracted.
New drilling instruments were also introduced in the 20th century. The use of diamond bits and carbide burs began around 1925, and the modern high-speed and ultra high-speed dental drills came into use around 1957. These new drills revolve at speeds ranging from 300 to 400 thousand revolutions per minute and do not produce an annoying whirring sound.
Oral Hygiene
The value of proper oral hygiene was also a subject of much research in the early 1900s. Sir William Hunter, in 1910, published an article entitled "The Role of Sepsis and Antisepsis in Medicine," in which he pointed out that general health may be affected by infections around the teeth. Hunter's work, together with that of Edward C. Rosenow and others, added further impetus to the teaching of medical subjects to dental students. It also affected members of the medical profession, who began to consider more seriously the claims of dentists that oral infections may be an important cause of systemic disease, including cardiac ailments. Between the years 1909 and 1912, W. G. Ebersole, then the chairman of the Oral Hygiene Committee of the National Dental Association, actively campaigned to impress upon his fellow dentists the value of proper oral hygiene. He also introduced the teaching of oral hygiene to school children.
Preventive Dentistry
The field of preventive dentistry advanced greatly with the discovery of the decay-preventing action of fluorides. In 1908, Frederick Sumter McKay, a dentist in Colorado, noticed that many of his patients, while having few cavities, had mottled tooth enamel. It was soon found that the mottling of the teeth, as well as the apparent resistance to tooth decay, were related to substances in the drinking water, and in 1931 it was found that the particular substance was a fluoride. In 1938 the U.S. Public Health Service conducted detailed studies in two communities in Illinois, Galesburg and Quincy. In Galesburg the water supply was known to have a relatively high fluoride content while that of the Quincy water supply was free of fluorides. The results of these studies showed that the chil dren of Galesburg had many fewer cavities than did the children of Quincy. Through studies in other communities it was found that a fluoride content of 1 part per million (ppm) was high enough to help prevent dental cavities in children but was still low enough to keep the teeth from becoming mottled.
In 1942 David B. Ast, then the director of the New York State Bureau of Dental Health, suggested the artificial fluoridation of water in communities with fluoride-deficient water. In 1944 the water supply of Newburgh, N.Y., was artificially fluoridated to bring its fluoride content up to 1 ppm while the neighboring city of Kingston, which had no fluorides in its water supply, was used as a control. As a result of this and similar experiments, it was found that fluoridation of water supplies can reduce dental decay in children by as much as 60%. About 145 million people in the United States are currently supplied with fluoridated water. Fluoridation has also become widespread in other parts of the world, including in the United Kingdom, Canada, and Australia.
Dental Education
One of the most important contributions to modern dental education was the report of a survey conducted by the Carnegie Foundation in 1921. The survey, headed by William J. Gies, one of the founders of the Columbia University School of Dental and Oral Surgery, obtained information concerning dental education from state dental board examiners, practitioners, teachers, dental schools, and professional educators. The results of the survey brought about great advances in the quality of dental education and led to improvements in the facilities of dental schools. It also created a public awareness of the value of dental education and research.
Until 1869 a dental course in the United States consisted of one academic year (16 weeks) of training with no pre-dental requirements. In 1870 the program was increased to two academic years (16 to 20 weeks each), and in 1891 it was lengthened to three (28 to 32 weeks each). In 1917 the dental course was increased to four years of 32 weeks each. Between 1899 and 1902 the academic requirement for entrance to dental school was one year of high school. From 1902 to 1907 it was two years of high school, and from 1907 to 1910 it was increased to three years of high school. In 1910 high school graduation was required, and in 1921 a minimum of two years of college training was set as the requirement. Today, entry preference is given to college graduates, although acceptance to dental school is possible following a minimum of three years of undergraduate course work. Pre-dental college requirements include courses in physics, chemistry, and biology.
Current Research
Present-day dental research is primarily aimed at finding the causes, cures, and prevention of oral diseases, especially dental caries, gum diseases, and tooth irregularities. Current studies include research into the use of a vaccine to guard against the development of colonies of Streptococcus mutans that normally exist in the mouth. A bacterium, S. mutans encourages tooth decay by converting sugar to lactic acid, which destroys tooth enamel. Other research may lead to the development of a harmless, genetically modified strain of S. mutans to colonize the mouth in place of the naturally occurring microbe.
The molecular biology of dental disease also is under investigation. For example, researchers have decoded the genetic sequence of both S. mutans and the bacterium Porphyromonas gingivalis, which is thought to play an important part in the development of periodontitis (gum disease). Research is also under way to develop new, more durable compounds that can be used in place of current composite materials (resin-based compounds that, because they resemble natural tooth material, have become popular as fillings).
Future improvements also are expected in dental implantation, in which lost teeth are replaced by a metal post that has been secured to the jawbone and topped with a crown, bridge, or denture. Advanced imaging technology and greater knowledge regarding post-implant healing should ultimately permit greater success in providing stable attachments between the post and jaw.
Genetic engineering may one day provide a means of natural tooth restoration. Researchers have discovered stem cells (unspecialized cells that have not yet differentiated into specific types of tissue cells) in children's primary dentition (commonly called baby teeth). The investigators have found that these stem cells, harvested after falling naturally from a child's mouth, can be induced to form dentin, the tissue that makes up the bulk of a tooth, and so may eventually prove useful in tooth repair.
