edited by: MICHAELR. SLABAUGH
chern I~upplement
Weber State College Ogden, Utah 84408
Chemical Aspects of Dentistry Murry Helfman, D.D.S., F.A.G.D. 1299 Portland Avenue. Rochester, NY 14621 There are two diseases which are of major concern to the dental profession. These are dental caries (tooth decay) and periodontal (gum) disease. Both diseases are being treated and prevented hy procedures which utilize chemical expertise. This paper will describe some of these procedures and suggest how they might he incorporated into a high school chemistry curriculum. These ideas should be of personal interest to your students, since the average 15-year-old has ten decayed, missing, or filled teeth. Dental Caries The maior cause of tooth loss before age 35 is dental caries. This disease is characterized by the localized demineralization of tooth enamel and dentin hv urganic acids.'l'helie acids are formed by the action of specific bacteria on sugars and other fermentable carhohydrates. The more common acids involved are lactic, propion&, and acetic acids.
Acetic Acid
Propionic Acid
Lactic Acid
It is imnortant to realize that the nroduction of acids on the tooth suriace is a complex interaction between many types of bacteria which act upon different suhstrates. Streptococci, for example, produce lactic acid from carbohydrate suhstrates. Other hacteria, like veillonella have no enzyme systems with which to ferment sugars. These bacteria, however, are able to act upon lactic acid to produce vropionic and acetic acid. here are recorded cases of tooth decay where acids were introduced into the mouth from sources other than bacterial action. The usual source is citric acid from the pulp and rinds of citrus fruit. The victims often had habits of sucking on the fruits for abnormally long periods. Regardless of the source of acidity, a pH of 5.5 will result in the dissolution of tooth enamel, k h i i h is the hardest structure in the human body. One phenomenon which clinical dentists cope with daily is that regardless of diet or health habits, some people never get tooth decay. This is usually explained by a "triad theory" of dental caries. Briefly, there are three factors needed to produce.tooth decay: (1)diet, (2) microbial activity, (3) host suscevtibilitv. In order for dissolution of tooth enamel to occur; all three factors must he present. The following examples support this theory.
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Primitive peoples develuped uulth decay for the first time when they were exposed to the refined foodstuffsof Werttrn t i v i l i m tion. Animals raised in agerm-freeenvironmentwill not develop caries regardless of their diet. Whole communities became resistant to tooth decay because of trace elements in their food chain. Journal of Chemical Education
In each example, the control of one factor out of three interfered with the carious process. The prevention of tooth decav has occupied dental scientists for man\, sfears.The greatest sin& discovers is ~robablv the effect or the trace eiement fluoride in reducihg tooth decav. The caries rate of a communitv can be reduced hv 60% when I ppm ot fluoride ion is introduied into the w~ters"ppb.. Whrn the water s u o ~ l vis not fluoridated, thecaries rate can methods. he reduced by the &&wing
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Fluoride toothpastes and mouth rinses Topical applications by the dentist Dietary fluoride supplements in the vitamins given to young children These three techniques are good hut they do not achieve the level ot orotection achieved hs fluoride in the water SUDD~Y. ~ l u o r i d eprevents tooth decay by interacting with theapatite crystals which make up dental enamel. The general formula for apatites is Ca~o(PO~)d(z, where X is usually a hvdroxide ion (Xmay also be a halide). When the substitution o i fluoride for hydrbxide ions occurs, the reaction is not a complete converison of hvdroxyapatite to fluoroapatite. The resuitant crystals have p;operiies intermediate Getween the two. There are several theories as to how fluoride works to reduce tooth decay:
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Fluoride enhances apatite crystal growth, and thus affectscertain chemical and . rrhvsical vrooerties of the enamel (e.g., acid solu. . . bility). The ingestion of fluoride change8 the shape of tcoth cusps making them 1e. a..r.amecntihle to decav. ....-..... -. ~.-. ~ ~ ~ ~ * Fluoride inhibits the growth of bacteria. Fluoride increases the rate of mineralization of the tooth. The uptake of fluoride ion occurs in three stages. The initial stage occurs when the tooth minerals are crystallizing within the fetus sometime during the last trimester of pregnancy. During this process, there is a low level of uptake. The greatest fluoride uptake occurs after the teeth calcify hut before they are erupted. The final stage begins as the tooth is erupted and continues throughout the lifetime of that tooth. This last stage is the reason why adults and teenagers with high caries rates can benefit from fluoride treatments. In addition to fluorine. the trace elements boron. molvbdenum, and vanadium have also shown a tendency to redice tooth decav in humans. However, some trace elements have, on occasion, been shown to have negative effects. There is, for example, a significant increase in dental caries when substantial quantities of selenium are present in the food chain.
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Diet A second method of reducing tooth decay is diet control. There is an overwhelming amount of evidence to confirm the
theory that refined carbohydrates are a causative factor in tooth decay. During the Second World War when European countries were deprived of their normal supplies of sugar, the rate of tooth decay dropped to a level equal to that found in fluoridated communities. In animal studies, when sugar is removed from the diet, caries rates are also reduced. One must be aware that the term sugar is empirical. I t includes all fermentable carbohydrates. The fructose in an apple can be as cariogenic as thesucrose in a glass of soda pop. Several factors influence the relationship hetween refined carbohvdrates and the tooth decav rates of human beings. Most important is the retentiveness of the sugar source in the reeions of the teeth. Dried fruits like apricots or raisins have more caries potential than their fresh f;uit equivalents. There are fewer caries in southern states than in northern states even though more sugar is consumed in the South. The reason Droposed for this is that most of the sugar consumed there is in &e form of soda pop, which stays in-the mouth for a very short time. A second factor is the frequency of sugar consumption. In a widely accepted Scandinavian study, people who ate 70-Kg of sugar with meals and 15 Kg between meals developed more cavities than a control group which ate 94 Kg of sugar a t mealtimes only. If one wishes to eat sweets, he would be advised to do so at infrequent intervals in order to prevent tooth decay. Other Techniaues
A recent technique which has received much publicity in nreventine tooth decav is the use of bondinzs and sealants. Yhese materials when"applied look like colorless nail polish. They are polymeric materials which are made from glucidyl methacrylate (GMA) and bisphenol A (BIS). The polymerization is catalvzed bv Benzoin methvl-ether which is mixed with the react&. h i h e second type;the catalyst is activated by an ultraviolet light. Positive results for both methods have been published in the dental literature. The process of adhesion is similar to placing a dripping wet ice-cube tray into a freezer. In order for the material to adhere to the tooth surface, the enamel of the tooth must be decalcified. Both phosphoric and citric acid have heen used for this purpose. The BIS-GMA then penetrates the surface imperfections and adheres to the tooth upon setting. In some reports, the caries rate was reduced by 80% after two years. However, there is some question as to the cost effectiveness of the program. There have also been reports of the sealant actingHs i n adjunct to anaerobic bacteria, producing larger carious lesions than normally occur. The optimum way t,o prevent tooth decay would be via a single "magic bullet" treatment. There have been magic mouthwashes like chlorhexidine or dibasic calcium phosphate solutions. Chlorhexidine is an antiseptic that destroys the strentococcus mutans oreanism. It adheres to tooth surfaces and oral mucuous membranes for several hours. The chlorhexidine. however, tended to discolor the teeth. A solution containing phosphoric acid and dibasic calcium phosphate was intended for use by people who had lost the function of their salivary glands. Such a solution was used to modify tooth enamel. After this treatment, the amount of fluoride permanently incorporated into the enamel is doubled in these cases. The use of antimicrobials like penicillin has been discouraged, because the oral bacteria can become resistant after prolonged exposures to the drug. Antidecay vaccines against specific streptococcus organisms are currently being tested on human subjects. There is also some question as to the relative safety of these vaccines.
Silver Amalgan
The treatment of tooth decay consists of removing all weakened portions of the tooth and restoring its form and function. The type of restoration used varies with each situation. The chemistry of dental materials is vital to the quality of care we render to our patients. During the last ten years, one simnle chemical change in the silver amaleam has lead to vast imdrovements in c o n k o n dental restorkions. Prior to this discovery, a silver alloy was used which was composed of silver (65%),copper (6%),zinc (2%),and tin (25%),After a few years in the mouth. however. this amalaam would literallv expand out of the tooth and would thus Lave to be replacid. 1; was discovered that bv disuersina free copuer particles throughout this silver alluy, [he eipansl'on was&hstantially reducGd. As a result, the life expertanrv of the rrstorations made with this new silver amalga& is coisiderably longer. (Commerical advertisements for the material show comparison photographs after five years and ten years where the copper-enriched dloy does not exhibit any expansion changes while the conventional alloy does.) Periodontal Disease
After the age of 35, the leading cause of tooth loss is periodontal disease. This disease is characterized by inflammation of the soft tissue accompanied by the loss of supporting bone structure from the teeth. The causes of gum disease are multiple, and its progress is affected by host resistance. Studies with eerm-free animals confirm that bacteria are a factor in gum disease. When dental plaque is consistently removed once in a 24-hr time period, the disease process can be arrested. Factors like fluoride and diet also affect gum disease, and, consequentlv, the same preventative methods for tooth decay are applicable to gum &ease. The current method of treating periodontal disease is divided into the following phases:
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Dehridement of the teeth and their soft tissue attachments, Patient instruction in home-care techniques, Reevaluation of teeth and soft tissue attachments, and Surgery of the gum tissues in order to facilitate home care.
During the last few years, a chemical treatment has been developed a t the National Institute of Health to treat ~ e r i o dontaidisease without surgery. The technique involvis the use of various chemicals to treat the inflammed gum tissues. The initial debridement is accomplished by the dentist using a solution of chlorhexidine carried on suitable instruments. Depending upon the case, a two-week regimen of antibiotics may be prescribed. Finally, the patient is instructed to brush his teeth with a mixture of hydrogen peroxide, table salt, and sodium bicarhonate. At each recall visit, a sample is taken from the patient's gum tissues and examined under a phase microscope. When the technique works, specific microscopic changes are visible. With this technique, the dentist is free to select alternative chemicals as the situation requires. In the Classroom
I would like to recommend four ways that you can introduce dentistry into your chemistry classrooms: Design an analytical project I
