Transcript Dental prep

Taking Care of Our
Teeth
General Objectives
What is tooth decay, how can
it be prevented, and what are
the key chemical ingredients in
dental care preparations?
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.
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.
 Figure 4.1 Major parts of a tooth.
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:
demineralization
Ca5(PO4)3OH
mineralization
5Ca2+ +
3PO43- + OH-
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.
Look again at the demineralizationmineralization 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.
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:
H3O+
+ OH-
2H2O
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.
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.
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.
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.
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:
Ca5(PO4)3OH +
hydroxyapatite
F-
Ca5(PO4)3F
fluoroapatite
+ OH-
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.
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.
MOUTHWASH
R/
CPCL
Peppermint oil
Alcohol
Water to
0.05%
0.10%
15.0%
100%
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.
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.
Figure 4.2 Sodium N-lauroyl sarcosinate.
CH3
CH3
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
N
O
CH2
C
O-Na+
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.
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.
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:
PO3F2- +H2O
H2PO4- + F-
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.
Toothpaste formula
Calcium phosphate
SLS
Glycerol
PG
Gum tragacanth
Saccharin sod.
Menthol, pepper oil
Presrvative
500
25
175
175
10
5
1,5
q.s
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)
Skin structure
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.
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.
1.
2.
3.
4.
5.
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.
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.
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).
Antiprespirant /deodorant cream
Stearic acid
Bees wax
Liquid paraffin
Tween 80
Al-chlorhydrate
Cetrimide
Water to
14.0
2.0
1.0
5.0
12.0
1.0
100
Deodorant Stick
Stearic acid
Sodium hydroxide
D.water
Glycerol
Cetrimide
Ethanol
3.4
0.6
1.0
7.5
0.75
75
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.
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
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.
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.
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.
Figure 4.12 Sodium lauryl sulfate.
O
CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 O
S O- Na+
O acidity
Harsh conditions can damage hair. Extremes in
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.
Figure 4.13 Two acids used in shampoos.
O
HO
OH
CH2
C
O
C
C OH
O
CH2
C
citric acid
O
HO
P
OH
OH
OH
phosphoric acid
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 Ofoaming
CH
CH2 and
CH2 thickener.
CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 C N CH2CH3
agent
3
CH2CH3
Liquid Shampoo
R/
Texapon
Water
15
85
Shampoo paste
R/
SLS
40
Cetyl Alcohol 5
Citric Acid
1
Water
54
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.
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.
 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.
NH
(asp)
HC
C
O
(CH2)2
HC
C
H
(CH2)4
H
O
HC
C
+
N
H
O
NH
(glu)
O-
O
NH
(lys)
C
CH2
O
C
O-
 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:
CH3
(CH2)15
CH3
Cl-
N+
CH3
(CH2)15
CH3
Your hair ceases to be charged once these amino
compounds bind to it with ionic bonds.

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.
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.
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.
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.
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.
Hair care is up to you, and much of it consists of
applying chemical principles. Thus, chemistry really can
make you more attractive.
 Figure 4.16
Zinc pyrithione.
N
S
O
Zn
O
S
N
Summary
Demineralization of teeth produces decay. The process is
stimulated by acids and is inhibited by fluoride (F-) ions.
Toothpaste provides abrasives to clean teeth,
antibacterial agents, and usable forms of fluoride.
Skin cleansers may consist of surfactants, nonpolar
solvents, or absorbent solids. Emollients prevent water
evaporation from skin, whereas humectants attract water
to skin. Acne is treated with substances that irritate skin
and cause cells to slough off more rapidly. Sunscreen
products (and sunglasses) absorb harmful UV radiation
from the sun and thus protect skin (and eyes) from
damage.
Perfumes and colognes consist of compounds with
pleasing fragrances, a solvent, and a fixative. The aroma
depends on the ability of a substance to bind to the
appropriate receptor in the nose. Antiperspirants block
apocrine sweat from reaching the skin's surface,
whereas deodorants combat the odor resulting from
such sweat.
Hair shampoos contain mild surfactants (for cleaning)
and acids to neutralize alkalinity. Conditioners contain
ingredients that bind to hair to repair damage, minimize
tangling and fly-aways, and provide greater body.
Antidandruff agents slow the flaking rate from the scalp
or break the flakes into smaller pieces.
Terms for Review
After completing this chapter, you should know and
understand the meaning of the following terms:
apocrine sweat
demineralization
eccrine sweat
emollicnt
free radical
humectant
keratin
Melanin
Mineralization
plaque
sebaceous gland
stratum corneum
sunscreen
tartar
Topics for Discussion
 1. Do you favor tighter or looser government regulation
of personal products such as the ones in this chapter?
Why?
 2. An effective acne-treatment drug used on the skin was
found to increase the risk of birth defects in children born
to pregnant women who used the product. The federal
government allowed the drug to be used for treating
acne, but required warnings to potential users. Do you
favor this approach? Why?
 3. The Council of Dental Therapeutics of the ADA has
approved several brands of toothpaste. Are there valid
reasons for using other brands?
 4. What information do you need on a product's label?
Look at the labels of personal products (such as
toothpaste, soap, moisturizer, shampoo, deodorant,
and sunscreen) that you use. What are the functions of
the ingredients listed?
 5. Before toothpastes, baking soda (NaHCO3) was
widely used for cleaning teeth because it has good
abrasive properties. For much of that time, dental
science was not advanced enough to take into account
the effects of the bicarbonate (HCO3-) ions' acid-base
properties. Consult Chapter 6 to determine whether
bicarbonate acts as an acid or base in water and tell
what side effects that might have on teeth. Are they
beneficial or harmful?