Tooth Decay

Tooth decay (dental caries) is an unpleasant fact of life. Aging, diet, and

improper dental hygiene lead to breakdown of critical building block of

teeth, hydroxyapatite, Ca5(PO4)3OH. The hydroxyapatite forms a three-

dimensional crystalline structure, and this structural unit is the principal

component in the exterior, the enamel part of the tooth. Hydroxyapatite

is also a major component in the dentin, is directly underneath the

enamel.

Hydroxyapatite breakdown causes the super-strong enamel

to become porous and weak. The pores created are ideal

hiding places for bacteria that form acids from foods

(especially sugars) that hasten the decay of the tooth.

Saliva is teeming with bacteria in concentration up to 100 million per

millilitre of saliva! Within minutes after you brush your teeth, sticky

glycoproteins in saliva adhere to tooth surface. Then millions of oral

bacteria immediately bind to this surface. Although all oral bacteria

adhere to the tooth surface, only Streptococcus mutans causes dental

caries, or cavities.

Dental Caries: A Bacterial Infection

There are two specific groups of bacteria found in

the mouth that are responsible for dental caries:

Mutans streptococci (Streptococcus mutans)

Lactobacilli

They are found in relatively large numbers

in the dental plaque.

The presence of lactobacilli in the mouth

indicates a high sugar intake.

Dental Caries

The Caries Process

For caries to develop, three factors must occur at the

same time:

A susceptible tooth

Diet rich in fermentable carbohydrates

Specific bacteria (regardless of other factors, caries cannot occur

without bacteria)

The Role of Saliva

Physical protection provides a cleansing effect. Thick, or viscous,

saliva is less effective than a more watery saliva in clearing

carbohydrates.

Chemical protection contains calcium, phosphate, and fluoride. It

keeps calcium there ready to be used during remineralization. It

includes buffers, bicarbonate, phosphate, and small proteins that

neutralize the acids after we ingest fermentable carbohydrates.

Antibacterial substances in saliva work against the bacteria.

If salivary function is reduced for any reason, such as from illness or

medications or due to radiation therapy, the teeth are at increased

risk for decay.

Why does S. mutans cause dental

caries while others do not?

The answer lies in the special enzyme called

glucosyl transferase that is found on the surface

of S. mutans cells. Glycosyl transferase is a very

specific enzyme.

It can act only on the disaccharide sucrose, which

it breaks down into glucose and fructose.

The enzyme then adds the glucose to a growing

polysaccharide chain called dextran that adheres

tightly to both the tooth enamel and the bacteria.

Plaque is made up of huge masses of bacteria, embedded

in dextran, adhering to the tooth surface.

This sticky mixture accumulates on teeth within 20

minutes after eating.

Plague that remains on the teeth forms tartar. Both

plaque and tartar irritate the gums resulting in gingivitis

and ultimately, periodontitis.

This is just the first stage of cavity formation. The

fructose released by the cleavage of sucrose is utilized by

the bacteria in the energy-harvesting pathways of

glycolysis and lactic acid fermentation. Production of

lactic acid decreases the pH on the tooth surface and

begins to dissolve calcium from the tooth enamel.

Why is the acid not washed away from

the tooth surface?

After all, we produce about one litre of saliva each day,

which should dilute the acid and remove it from the tooth

surface. The problem is the dextran plaque; it is not

permeable to saliva, and thus plaque keeps the bacteria

and the lactic acid localized on the enamel.

What measures can we take to prevent

tooth decay?

The number one strategy for keeping teeth healthy is

good dental hygiene, including frequent brushing and

flossing and use of fluoride products regularly to reduce

plaque build-up.

Methods of Caries Intervention

Fluoride: A variety of types are available to strengthen the

tooth against solubility to acid.

Antibacterial therapy: Products such as chlorhexidine

rinses are effective.

Fermentable carbohydrates: Reduce the amount and

frequency of ingestion.

Salivary flow can be increased by chewing sugarless gum,

for example, those with a non-sugar sweetener such as

xylitol.

Preventive measures against caries.

A, Fluoride rinse. B, Chlorhexidine rinse. C,

Xylitol gum

Food choice is also a strategy for keeping teeth healthy.

Diets that build strong teeth and enamel are critical to

teeth resistant to dental caries. Calcium rich diets help

build strong enamel. While some experimental and animal

studies suggest that fruits and some starchy stables are

cariogenic, several studies show that high intakes of

starchy staple foods are associated with low levels of

dental caries.

Include many complex carbohydrates in the diet; these

cannot be used by glycosyl transferase and will not lead to

the formation of acid. Further, the complex carbohydrates

from fruits and vegetables help prevent tooth decay by

mechanically removing plaque from tooth surfaces.

Raisin (dried sweet grape, generally called currant- a

misnomer), used in cakes, bread etc. and other

antioxidants help prevent the production of acid by mouth

bacteria.

Other researches have indicated polyphenolic compounds in raisin

such as catechins, epicatechins and flavonols, have anticariogenic,

bactericidal effect against S. mutans and S. sobrinus and prevent

adherence of bacteria to teeth. Further, they inhibit the enzyme

glycosyl tranferase that causes dental caries. Catechins quell

reactive oxygen species that are the cause of inflammation in

gingivitis.

Researchers have developed a vaccine that prevents tooth decay in

rats. Such a vaccine may one day be available for humans!

GO FOR A DENTAL CHECKUP!!