Taking Care of Our Teeth

1. Taking Care of Our Teeth

2. General Objectives • What is tooth decay, how can it be prevented, and what are the key chemical ingredients in dental care preparations?

3. 4.1 Teeth, Tooth Decay, and Toothpastes: Clean and Healthy WHAT ARE TEETH?. The main part of a tooth (Figure 4.1) is a tough, bony substance called dentin. Covering the exposed outer portion of the dentin is material called enamel, the hardest substance in your body. Enamel can withstand all the mechanical stresses of biting and chewing. Only the heaviest of blows can cause it to crack or chip.

4. Both enamel and dentin consist of a crystalline lattice of calcium (Ca2+) ions, phosphate (PO43-) ions, and hydroxide (OH-) ions. This substance, called hydroxyapatite, has the formula Ca5(PO4)3OH. Fibrous protein fits in the spaces between the ions. This network of ions of hydroxyapatite makes teeth hard and rigid, whereas protein provides springiness and toughness.

5. Figure 4.1 Major parts of a tooth.

6. Teeth form by the process of mineralization—the deposit of calcium, phosphate, and hydroxide ions in the form of hydroxyapatite. Dissolving these ions in saliva is demineralization. The enamel on teeth is always dissolving to a tiny extent, forming ions in solution. At the same time, however, some of these ions are recombining to deposit enamel back on teeth. As long as mineralization and demineralization occur at the same rate, there is a state of dynamic equilibrium between these two opposing reactions, and no net loss of enamel results:

7. TOOTH DECAY AND GUM DETERIORAIION Tooth decay (dental caries) and gum deterioration (periodontal disease) result when demineralization exceeds the rate of mineralization. Severe tooth decay leads to such a large loss of enamel and dentin that the tooth either disintegrates or must be extracted. Decay is the leading cause of tooth loss before the age of thirty-five. After that age, tooth loss comes mostly from gum disease, which slowly destroys the gums, connective tissue, and bone that support teeth in their sockets.

8. Look again at the demineralization-mineralization equation. Anything that shifts the position of the dynamic equilibrium to the right results in a loss of enamel and (if allowed to proceed far enough) a loss in dentin. According to Le Châtelier's principle, any process (other than the reverse reaction) that removes calcium, phosphate, or hydroxide ions from the system causes the equilibrium position to shift toward the right.

9. This shift occurs when acids are present. An acid base reaction occurs when acid molecules provide hydronium (H3O+) ions that react with hydroxide (OH-) ions in hydroxyapatite: When this happens, OH- is removed to become H2O, and a new equilibrium position becomes established, with less enamel than before. Calcium and phosphate ions diffuse out of the enamel and are washed away by saliva. The missing enamel forms pits, or cavities, in your teeth, and you then suffer tooth decay.

10. Decay is a slow process, usually requiring months to occur, so only H3O+ ions having long and continuous contact with your teeth can begin to cause cavities. But your mouth, with its abundant moisture, warmth, and food in the form of sugars, is a paradise for acid-producing bacteria to stick to your teeth. Unless you clean you teeth throughly by brushing, flossing, and rinsing after eating, colonies of these bacteria can build up on your teeth in a matter of hours. This white or off-white deposits, consisting of about 70 percent bacteria, are plaque. The bacteria in plaque thrive on sugars, especially sucrose, and turn them into various carboxylic acid products. The normal pH of saliva is about 6.8, but plaque-produced acids can decrease the pH to 5.5 or less, causing a loss of enamel.

11. Wherever plaque persists, decay begins. Plaque flourishes in out-of-the-way cracks and crevices between your teeth and pear your gums. There the plaque can absorb minerals and harden into tartar, a tough crystalline substance consisting mainly of calcium phosphate, Ca3(PO4)2; calcium carbonate, CaCO3; and organic substances. Here hydronium ions get the uninterrupted time they need to dissolve enamel. Plaque and tartar also cause gums to deteriorate. Bacterial products inflame the gums, and the gums then produce a number of chemicals to destroy the bacteria. If present in sufficient quantities over a long enough period, these chemicals can also destroy the gum tissue and fibers that hold teeth in place. The gums then begin to shrink away from the teeth.

12. The chief culprit in both of these dental diseases is sugar, mostly in the form of sucrose. Eskimos living on their natural sucrose-free diet of animal fat and protein have almost no cavities; when they switch to a westernized diet, their incidence of tooth decay rises sharply. The length of exposure is important, too. For example, sugar in caramels, which cling to the teeth, causes more tooth decay than the same amount of sugar in soft drinks, which remain in the mouth only briefly. And people who eat sugary snacks between meals tend to develop more cavities than those who consume sugar only during meals.

13. USING FLUORIDES TO COMBAT TOOTH DECAY Limiting sucrose in your diet is an obvious way to combat tooth decay, but it is not the only one. Fluoride (F-) ions inhibit the klemmeralization of teeth by converting up to 30 percent of the hydroxyapatite in enamel into fluoroapatite:

14. Fluoride ions fit better in the apatite lattice than do the slightly larger hydroxide ions. This leads to a more stable crystal that is about 100 times less soluble in acids than is hydroxyapatite. When fluoridated enamel dissolves in saliva, few if any hydroxide ions are generated-just calcium, phosphate, and fluoride ions. Plaque-produced hydronium ions have little affinity for any of these ions, so little demineralization occurs.

15. Fluoride ions may also help prevent decay by inhibiting certain enzymes, found in plaque bacteria, that catalyze the conversion of sugars to organic acids in the first place. They may also inhibit the formation of sticky polysaccharides that promote the adhesion of bacteria to enamel surfaces. Fluoride even helps reverse decay in young children by increasing the mineralization of tooth enamel.

16. MOUTHWASH • R/ • CPCL 0.05% • Peppermint oil 0.10% • Alcohol 15.0% • Water to 100%

17. WHAT'S IN TOOTHPASTE? The main purpose of any toothpaste, gel, or powder is to help remove plaque from teeth. In addition, toothpastes can provide fluoride, help prevent the formation of tartar, and freshen breath. To accomplish their primary aim, all toothpastes contain cleaning and polishing agents known as abrasives. These give teeth their shine by scouring the enamel with a hard substance that has been finely powdered. More than half of the toothpastes use some form of silicon dioxide (SiO2) as their abrasive. Various calcium compounds—including chalk (CaCO3), calcium monohydrogen phosphate (CaHPO4), and calcium pyrophosphate (Ca2P2O7)—are also common. Each substance is hard enough to scratch off plaque deposits. But only calcium compounds are softer than and hence harmless to enamel; SiO2 has to be specially processed so that it does not mar the surface of teeth.

18. Toothpastes containing sodium pyrbphosphate (Na4P2O7) can prevent tartar from building up by interfering with the formation of crystalline solids (tartar) in plaque. But none of the abrasives can dislodge tartar once it has formed. Having a dentist or hygienist scrape it off is the only way to remove it. Another target for toothpastes is breath odor. Besides plaque, bacteria in your mouth can cause bad breath, so some toothpastes—particularly the gels-contain ingredients that kill these bacteria. Two such compounds are sodium N-lauroyl sarcosjnate (Figure 4.2) and sodium lauryl sulfate (see Figure 4.12). Compounds such as these also act as surfactants that help clean teeth and produce the foam we expect from a toothpaste.

19. Figure 4.2 Sodium N-lauroyl sarcosinate. About 80 percent of the toothpastes sold in the United States contain fluoride compounds at approximately the level of 0.1 percent fluoride. The most common forms are stannous or tin(II) fluoride, SnF2; sodium monofluorophosphate (MFP), Na2PO3F; and sodium fluoride, NaF.

20. Putting fluoride in toothpaste presents some technical problems, however. A typical tube of toothpaste sits on the shelf for six months or more before it is purchased. In that many months, the reactive fluoride can find a number of ways to become deactivated. One way is to form insoluble calcium fluoride (CaF2) by reacting with the abrasive. Therefore, not every toothpaste claiming to contain fluoride can provide it in its active F- ion form when you brush.

21. Current formulations that do deliver active fluoride contain sodium fluoride (NaF) with the SiO2 abrasive, stannous fluoride (SnF2) with the Ca2P2O7 abrasive, and sodium MFP (Na2PO3F) with just about any abrasive. The MFP ions release fluoride ions when they react with water in saliva: Each of these combinations has been clinically tested. People using them showed anywhere from 13 to 44 percent fewer cavities than did people using identical toothpastes without fluoride.

22. Toothpaste formula • Calcium phosphate 500 • SLS 25 • Glycerol 175 • PG 175 • Gum tragacanth 10 • Saccharin sod. 5 • Menthol, pepper oil 1,5 • Presrvative q.s

23. miswak • A few important benefits of Miswak • Kills Gum disease causing bacteria. • Fights plaque effectively. • Fights against caries. • Removes Bad breath and odor from mouth. • Creates a fragrance in the mouth. • Effectively clean between teeth due to its parallel bristles. • Increases salivation and hence inhibits dry mouth (Xerostomia)

24. Skin structure

25. ANTIPERSPIRANTS AND DEODORANTS We also use chemicals to mask or prevent unpleasant body odors and sweat. There are two kinds of sweat- eccrine and apocrine. Eccrine sweat, produced in eccrine sweat glands (see Figure 4.3) on almost all parts of the skin, is the cooling mechanism of your body. Whenever exercise or environment threatens to raise your temperature, eccrine sweat is exuded onto skin to evaporate. Evaporation, being endothermic, takes away excess heat energy so that your body temperature remains fairly constant. Besides water, eccrine sweat contains some organic compounds and salts but does not produce offensive odors.

26. Apocrine sweat, however, is a different story. Apocrine glands terminate in hair follicles (see Figure 4.3) at only a few places on your body-your underarms being one of those locations. Your nervous system activates these glands, which secrete liquid in proportion to the stress you feel. Although mostly water, about I percent of apocrine sweat consists of fat, cellular fragments, and bacteria. When exposed to the air, bacteria begin to flourish, producing smelly 'compounds and hence body odor.

27. There are five ways products can combat this body odor: • Inhibit the production of apocrine sweat • Prevent the sweat produced from reaching the open air on the skin • Kill offending bacteria in the exposed sweat • Decompose foul-smelling substances the bacteria create • Mask odors with more pleasant fragrances. Clearly, the most effective actions are at the top of the list. The federal government requires that manufacturers reveal the general action of their product. If it works by Methods 1 or 2 above, then it can be called an antiperspirant. If it works by any of the others, it must be called a deodorant. Some products with combinations of ingredients can claim to be both.

28. The active ingredient in most antiperspirants is one of the aluminum chlorohydrates, A12(OH)5Cl or A12(OH)4Cl2, or a zirconium-aluminum salt. These are water-soluble ionic compounds that produce A13+ ions in solution. Aluminum ions bind to the ducts of sweat glands, shrinking the openings and forming an aluminum-keratin complex that plugs up many ducts. The flow of perspiration is reduced or, for some glands, prevented altogether. In addition, aluminum chlorohydrates kill bacteria in the apocrine sweat that does reach the skin. This pore-clogging action cannot be used by everyone. Because sebum glands open up in the same places the apocrine glands do, both can get obstructed. For certain susceptible people, rashes (sort of an underarm acne) can develop.

29. Deodorants, which have ingredients to kill bacteria and absorb, decompose (by oxidation), or mask odors, are alternatives for people who are unable to use antiperspirants. Mouthwashes are essentially oral deodorants that work in a similar way. Besides providing a pleasing aroma, they include ingredients such as alcohols (which kill bacteria by dehydrating them) and various phenols (which kill bacteria by denaturing their proteins).

30. Antiprespirant /deodorant cream • Stearic acid 14.0 • Bees wax 2.0 • Liquid paraffin 1.0 • Tween 80 5.0 • Al-chlorhydrate 12.0 • Cetrimide 1.0 • Water to 100

31. Deodorant Stick • Stearic acid 3.4 • Sodium hydroxide 0.6 • D.water 1.0 • Glycerol 7.5 • Cetrimide 0.75 • Ethanol 75

32. 4.5 Hair-Care Products: Shampoos and Conditioners Most of your body systems are maintained automatically. Damage is repaired, chemical imbalances are corrected, and waste is removed with no conscious effort on your part. But your hair is not one of those systems. Made entirely of keratin, every strand of hair is dead. If any hair shaft becomes dry, cracks, or loses its softness or pliability, your body has no direct way of restoring it; deciding when and how to clean, style, or repair your hair is entirely up to you. The answers, however, come from some of the chemical principles you already know.

33. Shampoo is a hair care product used for the removal of oils, dirt, skin particles, dandruff, environmental pollutants and other contaminant particles that gradually build up in hair. The goal is to remove the unwanted build-up without stripping out so much as to make hair unmanageable

34. Shampoo, when lathered with water, is a surfactant, which, while cleaning the hair and scalp, can remove the natural oils (sebum) which lubricate the hair shaft. • Shampooing is frequently followed by conditioners which increase the ease of combing and styling.

35. SHAMPOOS Shampoos are more than just hair cleansers. If cleanliness were the only goal, any heavy-duty laundry detergent would do a superb job. But shampoos must also help keep hair healthy, soft, and shiny. These additional requirements call for a specialized product.

36. Your hair, being all keratin, has many of the same requirements as your skin. In particular, it needs sebum as an emollient to soften it and give it natural body and luster. Every hair follicle has its own sebaceous gland for this purpose (see Figure 4.3). But sebum needs to be present in the optimum amount. With too little sebum, your hair is dry and strawlike; with too much, it is greasy and matted. Therefore, shampoos must be able to wash away the greasiness without removing the shine. They do this with mild surfactants (Section 3.1) that have only limited cleaning ability. Sodium lauryl sulfate (Figure 4.12) is the most widely used surfactant in shampoos. It helps you keep that "Goldilocks" quantity of sebum on your hair: not too much, not too little, but just right.

37. Figure 4.12 Sodium lauryl sulfate. Harsh conditions can damage hair. Extremes in acidity or alkalinity can cause your hair's protein to denature and decompose. Hair needs a pH between 4 and 6—that is, slightly on the acid side of neutral—to achieve its maximum wet strength. Because most surfactant-water mixtures are strongly alkaline, typically with pH values of 10 or more, shampoos often contain acids to lower the pH. The most common are citric acid (the same compound that gives tartness to citrus fruits) and phosphoric acid, a mild acid often found in soft drinks (Figure 4.13). So many people are uneducated in chemistry that manufacturers advertise their products as "nonalkaline" or "pH-controlled" or even "acid-balanced," but they don't dare say that their shampoos are acidic.

38. Figure 4.13 Two acids used in shampoos.

39. The price of shampoo is higher than it needs to be because of those uneducated consumers. Each shampoo is filled with unnecessary ingredients including foaming agents (such as lauramide diethylamine; Figure 4.14) to make rich lathers, moderators to help the foaming agents work, and thickeners (such as lauramide diethylamine and sodium chloride) to give the runny liquids a richer texture. But the performance of the shampoo is not raised by any of these additives—only the price. • Figure 4.14 Lauramide diethylamine, a foaming agent and thickener.

40. Liquid Shampoo • R/ • Texapon 15 • Water 85

41. Shampoo paste • R/ • SLS 40 • Cetyl Alcohol 5 • Citric Acid 1 • Water 54

42. CONDITIONERS Besides cleanliness and shininess, a number of other qualities may be desirable in hair. If you are like most people, you appreciate hair that is easy to comb (no tangles), is free from damage (no split ends), and is never unruly (no fly-aways). Most of all, you probably like the fullness and manageability of hair with body. That is why conditioners are on the market.

43. Like other proteins, the molecules of hair are made of twenty different types of amino acids joined together. Some of these amino acids (aspartic acid and glutamic acid) have free carboxylic acid groups that tend to donate protons; others (for example, lysine) have free amino groups that are bases and tend to accept protons. Thus, hair has built-in acid-base properties. It has more acidic groups than basic ones, so at a pH higher (more alkaline) than 3.8 (a pH value between 4 and 6 is typical), hair has a net negative charge (Figure 4.15). This static charge causes strands of hair to repel one another, causing wild, fly-away hair that is difficult to style.

44. Figure 4.15 Part of a keratin molecule with aspartic acid (asp), lysine (lys), and glutamic acid (glu) in the ionic forms they assume at pH 4 to 6.

45. One function of a conditioner then is to supply positively charged ions to neutralize the negative charge. Most conditioners do this with ionic substances in which one or more amino groups is electrically positive: Your hair ceases to be charged once these amino compounds bind to it with ionic bonds.

46. Long-chain hydrocarbon groups in the conditioner also serve other functions: They replace the shine-producing coating removed by shampoos; they act as an oil-like lubricant between hair strands to minimize tangles; and they add thickness to the hair, contributing to its body. On the negative side, however, these molecules canbuild up on hair and make it limp.

47. Swimming, sunning, and styling take their toll on your hair. The outer layer of protein can get roughened or broken. The ends can become frayed, like a rope. In severe cases, whole strands of hair can split in two. And all this damage can detract from your appearance. This is the most difficult problem for a conditioner to handle because the damage is not uniform; each strand of hair can have its own unique defect. Fortunately, your hair's inner core has a different amino acid composition from that of its outer layer and tends to develop a greater negative charge. Thus, damage that exposes the inner core creates a site that attracts more conditioner. In other words, the positively charged amine compounds in a conditioner tend to flock toward places where they are needed the most.

48. Most conditioners also contain protein fragments to help repair damage. Derived from animal hides and hoofs, the protein is not quite the same as your own. However, like plaster on a wall, it serves to fill in the cracks and dents. The fragments are polar molecules that are attracted to the more negative (and damaged) parts of your hair. As these protein segments bind to the hair's own protein fibers, split ends recombine, rough spots smooth out, and hair gets extra body. Conditioners also may include oils (such as lanolin, glycol stearate, and wheat germ oil) to act as sebum substitutes, carbohydrates (such as honey, beer, and aloe) to act as humectants, and many other substances (such as vitamins and botanicals) that are generally of little consequence.

49. DANDRUFF Like any other part of your skin, the stratum corneum of the scalp is made of dead cells that have migrated to the surface (see Figure 4.3). It normally takes twenty to thirty days for this migration to occur, after which the cells slough off individually into your hair, almost imperceptibly. When a person has the abnormality called dandruff, however, the migration takes only seven to ten days and ends with cells being shed in large clumps or flakes.

50. This unsightly flaking can be controlled in two ways. The first method is to slow the runaway migration of skin cells. The most popular dandruff shampoos work in this way. Their active ingredients are either selenium sulfide (SeS2) or zinc pyrithione (Figure 4.16). The other antidandruff technique is to break up the flakes into insignificant pieces. Ingredients for this purpose include elemental sulfur (S) and salicylic acid. Because antidandruff materials aren't very soluble, shampoos containing them are opaque instead of clear.