Tooth Decay

Tooth decay is people's top dental concern.

Find out the causes and risk factors of dental decay, and how fast it happens.

Already have it? Read about treatments.

So far, no tooth decay? Great - do review how to keep preventing it.

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Causes of tooth decay

Acids & bacteria

To appreciate the causes of tooth decay, it helps to know what it is. Tooth decay is the result of acid washing and dissolving the tooth. A dental cavity (hole) is simply localized tooth decay.

Now, the acids causing tooth decay arise in two ways. Chiefly, acids arise from the mouth's bacteria, which naturally convert food (sugars and starches) into acid. Acids also arise from acidic drinks (orange or lemon juice, soda) and foods (kiwis, strawberries).

Risk factors

Triggers of causes

Factors in tooth decay are things, habits, or conditions that help oral bacteria put out acids. Factors include:

  • Plaque - Plaque is a major factor in tooth decay. Since plaque on teeth contains bacteria, all their acid washes the teeth.
  • Foods and drinks with sugars, starches, or acids - Sugars and starches are what oral bacteria convert to acid. These foods vary in cariogenicity, i.e. how badly their acid decays teeth. Worst are starches that are refined and cooked (cookies, pastries, cereals) and sucrose sugar (table sugar, hard candies). Sugars in milk, raw starches, and fruits are less cariogenic. Sticky foods are more cariogenic than non-sticky foods, because stickiness to teeth implies acids concentrate on teeth.
  • Frequent snacking or lengthy sipping - Snacking frequently is also a factor in tooth decay. With each snack, a new bacteria-induced acid attack on teeth ensues. Sipping sugary drinks for long contributes to tooth decay, among them coffee, tea, and soda. The prime example among babies is falling asleep while sipping bottled milk.
  • Insufficient saliva - Insufficient saliva speeds up tooth decay, because saliva counters tooth decay. It washes away food debris, starving bacteria of the input for their tooth-decaying acids. Plus, it contains calcium and phosphorus minerals that reverse tooth decay, a process known as remineralization.
  • Cracked or loose fillings - Fillings that are cracked or loose invite draw food and bacteria inside, setting off tooth decay.


How fast?

It takes several years in an adult for tooth decay to pass from the tooth's surface to the root, the stage where cavities are most damaging.

Tooth decay need not be permanent; small cavities can reverse and heal, or stabilize for years. So, upon detecting a small cavity, your dentist may note it, but not target it, and instead check it again at your next dental cleaning.

Root cavities do decay fast, and immediate action is ideal. However, being inside the tooth, root cavities are not apparent and often discovered only too late, making a root canal inevitable.

Prevent tooth decay

Keep good habits

Prevention of tooth decay is about fighting the tooth-decaying acids, and about promoting saliva.

Eat well

To promote saliva, hydrate yourself, chew sugar-free gum, and address any causes of dry mouth.

Limit snacking between meals; avoid sipping sugary drinks for long (using a straw helps).

Mind sticky, sugary, starchy foods. End meals with cheese or yogurt, rich in calcium for teeth. Consume enough vitamin D, which strengthens bones and teeth and helps absorption of calcium.

If you do consume sweets and soda, know that it is worse for teeth to do so in frequent bits than to do so in one splurge.

Fight plaque

To combat plaque, practice good oral hygiene. Brush teeth twice per day to remove plaque from exposed surfaces, and floss once per day to remove plaque between teeth and under the gum line. Seek regular dental cleanings to remove plaque and tartar that brushing and flossing cannot, especially in back teeth and fillings. A fluoridated toothpaste strengthens dental enamel against acids. After nightly oral hygiene, do not eat, because during sleep there is less protective saliva.

Seal molars

A sealant is a plastic film applied to the chewing surfaces of the back teeth. It keeps plaque away from the pits and fissures there, where most cavities occur because flossing and brushing cannot reach.

Many studies have shown that caries protection is 100% in pits and fissures that remain completely sealed. Sealants can and do come off - after 5 years, about 50% of sealants are inadequate. You can have them restored during a dental cleaning.

Children should get sealants on their permanent molars right after they erupt, around the ages of 6 and 12.

How to treat cavities


With fillings, the dentist drills away the decayed portion, then fills it with a material, which could be silver alloy, gold, or tooth-colored resin/porcelain.

The choice of material depends on the tooth's location and decay, and the patient's aesthetic and price preferences.

With dental crowns, too much decay has occurred to recommend fillings, which would leave the tooth prone to breaking. The dentist repairs the decayed portion and encases the weakened tooth with a cap, or dental crown, which resembles a real tooth and protects your real tooth underneath.

A root canal is in order if the decay has exposed the tooth's root, which is easily infected. An infected tooth, even lacking symptoms, eventually will cause pain and die.

Incidence of caries

A story of sugars

Dental cavities have existed for over one million years, since at least the Australopithecus hominid.

The incidence of caries in the European population remained low until about 1000 AD (2-10 decayed teeth out of 100), when it rose sharply with the arrival of sugar cane (24 decayed teeth out of 100). Around 1850, incidence spiked again, likely owing to greater availability of refined flour, bread, and sweetened tea. Since 1950s, when the practice of brushing teeth became widely adopted, incidence has dropped dramatically.

Journal of Dental Research - Carbonated soft drinks and dental caries in the primary dentition
PubMed Health - Dental cavities
Wikipedia - Dental caries - Production of oral bacterial acid - Diet and dental caries
Colgate Education - Not All Early Tooth Decay Needs A Filling
National Institutes of Health - Seal Out Tooth Decay
National Institutes of Health - Dental sealants in the prevention of tooth decay: Consensus
University Of Illinois - Chicago - Epidemiology of dental disease
Newswise - ADA report on the importance of dental sealant use