Updated on February 9, 2024
7 min read

What is Tooth Decay?

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What is Tooth Decay?

Tooth decay, also known as cavities, is a common oral health problem.

3D illustration of a severe tooth decay

Tooth decay is caused by acid-producing bacteria, especially Streptococcus mutans (S. mutans). The bacteria in the mouth break down the enamel and dentin of the teeth, leading to cavities and other damage. 

On average, one in five people in the United States has untreated tooth decay. More than 80% of people will have had at least one cavity before the age of 34.

Tooth decay can cause pain, sensitivity, and even tooth loss if left untreated. Learning about the symptoms will help you treat the problem before it becomes more serious.

Symptoms of Tooth Decay 

The common signs of tooth decay include:

  • Bad breath
  • Toothache or tooth pain
  • Increased tooth sensitivity to sweets or hot or cold temperatures
  • Swollen or bleeding gums
  • White or discolored stains on tooth surfaces
  • Visible holes or pits in teeth
  • A dental abscess (which can cause fever, pain, and facial swelling)
  • Teeth that chip or fracture easily from weakened enamel

What Happens if Tooth Decay is Left Untreated?

Untreated tooth decay can lead to many uncomfortable physical consequences, including:

These physical symptoms negatively impact lifestyle and cause problems with speaking, eating, working, and playing. In extreme cases, tooth decay may lead to death when an infection travels from the tooth to the brain, heart, or bloodstream.

How to Prevent Tooth Decay

Tooth decay can be easily prevented and reversed if caught in the earliest stages. To prevent tooth decay, follow these best practices:

  • Use an electric toothbrush to brush your teeth thoroughly at least 30 minutes after eating 
  • Use enough fluoride by brushing twice a day with an ADA-accredited fluoridated toothpaste, drinking tap water with fluoride, and using a fluoridated mouth rinse
  • Drink enough water to prevent dry mouth
  • Always brush before bedtime
  • Floss daily to remove plaque
  • Limit sugary foods, carbohydrates, and snacking
  • Eat calcium-rich foods
  • Avoid tobacco products

Scheduling dental office visits twice yearly for regular check-ups and professional cleanings is one of the best ways to prevent tooth decay. 

Dentists can place dental sealants or plastic coatings to prevent cavities on the chewing surfaces of back teeth. They can also apply fluoride varnishes to help remineralize teeth. 

What Does a Cavity Look Like?

When a cavity is just forming, it might be impossible to detect visually. However, dentists can pick up minimal tooth decay on an X-ray between the teeth.

progression of a cavity

Cavities usually appear as a darker shadow or hole. When a cavity grows, it will become a darker, larger shadow on the X-ray. 

The cavity will typically appear as a little white spot on the tooth in its initial stages. This indicates the tooth is losing essential minerals that keep it strong and healthy (a process referred to as demineralization).

As the cavity progresses, a discolored or dark spot will form on the tooth. Cavities come in different colors and shades, from white to gray to black and even yellow. They may also appear as a visible pit or hole in the tooth.

What Causes Tooth Decay?

Tooth decay happens when bacteria in the mouth break down enamel and dentin. A combination of factors can cause tooth decay, including:

Poor Oral Hygiene

Poor oral hygiene allows bacteria to build up on the teeth, leading to plaque formation. Plaque is a sticky film containing bacteria that can cause tooth decay if not removed regularly.

Sugary and Acidic Foods and Drinks

Sugary and acidic foods and drinks can also contribute to tooth decay. Dental caries may develop when these foods and drinks are consumed frequently, as the bacteria in the mouth feed on sugars and acids. These acids break down the enamel and dentin of the teeth.

On the other hand, acidic foods and drinks can wear down and weaken enamel. Over time, this will make your teeth more sensitive and cause enamel erosion.

Certain Medical Conditions

Certain medical conditions, such as diabetes and dry mouth, can increase the risk of tooth decay. These conditions affect saliva production, a natural defense against decay.

Eating disorders like bulimia can also increase the risk of tooth decay. This is because the body doesn’t receive the nutrients needed to maintain healthy teeth, and the enamel can be damaged from frequent vomiting.

Limited Fluoride

Fluoride is a mineral that helps strengthen enamel and protects against tooth decay. One study shows that a 6-month treatment with 5% NaF improved oral health.11

Fluoride can be found in toothpaste, mouthwash, drinking water (in most communities), and other dental products. If you don’t use products with fluoride, you may be at a higher risk of tooth decay.

6 Stages of Tooth Decay

There are six distinct stages of tooth decay, each more dangerous than the next. 

1. Demineralization

Demineralization is when the minerals in the tooth enamel, primarily calcium, decrease. This occurs when acids produced by bacteria eat at the minerals in the outermost layers of teeth.

Demineralization may cause white spots to appear on the teeth. You may be able to reverse demineralization at home by brushing with fluoride toothpaste and flossing.

Stages of Tooth Decay Illustration

2. Enamel Decay

When demineralization and remineralization stop, enamel decay will occur. This creates a hole or sticky spot in the tooth.

When this happens, white spots darken to a brownish or yellowish color, sensitivity increases, and cavities form. A dentist must treat the cavities at this stage to prevent further complications.

3. Dentin Decay

When tooth decay progresses past enamel decay, it reaches the dentin, the tissue that lies under the enamel.

Dentin contains tubes that lead to the tooth’s nerves, making it more sensitive to acid damage. Because dentin is much softer than enamel, decay advances much quicker when it reaches this stage. At this point, you may start developing symptoms like sensitivity to certain foods and drinks. 

4. Pulp Damage

At this stage in the decay process, the bacteria reach the pulp, the tooth’s innermost level that contains nerves and blood vessels. At this stage, tooth decay can cause extreme tooth pain.

If untreated, the bacterial infection may cause a dental abscess.

5. Dental Abscess

When tooth decay advances into the pulp, bacteria invade and cause an infection. The infection causes inflammation that creates an abscess or a pocket of pus at the bottom of the tooth.

A dental abscess causes:

  • Severe pain that can radiate into the jaw
  • Swelling of the gums, face, or jaw
  • Fever
  • Difficulty breathing, swallowing, or opening the mouth 

An abscess requires immediate treatment to prevent the infection from spreading to the jaw, head, and neck.

6. Tooth Loss

If the tooth becomes too compromised from decay and infection, tooth extraction is the only option to prevent further damage.

Tooth Decay Treatment

Here are the standard methods dentists use to treat tooth decay:

Silver Diamine Fluoride

This antibacterial varnish contains a higher level of fluoride than traditional treatments. Dentists can use it for very small cavities to help prevent them from growing. It’s recommended for people who may not be eligible for a traditional filling. 

Dental Fillings

temporary filling

Fillings are used to treat typical cavities. A dentist removes the decayed tooth tissue and restores the tooth by filling it with artificial material.

Dental Crown

A crown is a cap made of gold, porcelain, or metal that repairs and replaces decayed or weakened areas of teeth. It covers the entire tooth and provides more stability and support for teeth that have more severe tooth decay.

Root Canal

Root canal treatment

Root canal treatment is used when the nerve in a tooth dies from decay or injury. The pulp and decaying portions of the tooth are removed, and the roots are filled with sealing material. 

Tooth Extraction

The dentist may have to pull your tooth if they can’t fix the damage to the tooth. 

When to See a Dentist 

The earliest stage of tooth decay, demineralization, can be reversed before permanent damage occurs. However, the decay can progress if left untreated and cause worse problems.

You should see a dentist if you experience any tooth decay symptoms mentioned here. Treatment for tooth decay depends on its severity. If caught early, you can reverse demineralization with proper oral hygiene and fluoride treatment.


Tooth decay is a common dental issue that can be prevented and reversed if caught in the earliest stages. To prevent tooth decay, it’s important to maintain good oral hygiene. As mentioned above, see a dentist immediately if you experience concerning symptoms.

Last updated on February 9, 2024
11 Sources Cited
Last updated on February 9, 2024
All NewMouth content is medically reviewed and fact-checked by a licensed dentist or orthodontist to ensure the information is factual, current, and relevant.

We have strict sourcing guidelines and only cite from current scientific research, such as scholarly articles, dentistry textbooks, government agencies, and medical journals. This also includes information provided by the American Dental Association (ADA), the American Association of Orthodontics (AAO), and the American Academy of Pediatrics (AAP).
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  3. Forssten SD, Björklund M, Ouwehand AC. “Streptococcus mutans, caries and simulation models.” Nutrients, 2010.
  4. “Hidden Dental Dangers That May Threaten Your Whole Body.” Harvard Health, Harvard Medical School.
  5. Heng C. “Tooth Decay Is the Most Prevalent Disease.” Fed Pract, 2016.
  6. “Hygiene-Related Diseases.” Centers for Disease Control and Prevention, 2016.
  7. “Oral Health Conditions.” Centers for Disease Control and Prevention, 2020.
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  10. “Tooth Decay.” Medline Plus., U.S. National Library of Medicine, 2020.
  11. Medjedovic E, Medjedovic S, Deljo D, Sukalo A. “IMPACT OF FLUORIDE ON DENTAL HEALTH QUALITY.” Mater Sociomed, 2015.
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