logo image

Tooth decay: main concepts and causes

author icon By Dr. George Ghidrai

Tooth decay, also known as dental caries or tooth cavity is a bacterial infection that causes demineralization and destruction of the hard tissues of the teeth.

Tooth decay and its complications represent the number one cause of tooth loss.

Dental decay is the most common pathological condition that occurs in humans. Dental pulp infections (pulpitis) are mainly caused by bacteria infections, which are a secondary development of tooth decays.

tooth decay
tooth decay

tooth decays

Dental caries can occur on any surface of a tooth that is exposed to the oral cavity, but not the structures that are retained within the bone.

Main causes

Three groups of factors will have to act for dental caries to form. These factors are also known as cariogenic factors.

  1. Infective factor

    The mouth contains a wide variety of oral bacteria, but only a few specific species of bacteria are believed to cause dental caries : Streptococcus mutans and Lactobacilli are among them.

    Bacteria collect around the teeth and gums and more likely in sites that provide microscopic retentions for dental plaqueDental plaque is a sticky, pale-yellow film of bacteria that forms on teeth. :

    • The grooves on the occlusal surfaces of molars and premolars

    • The areas between teeth also called interproximal sites

    tooth decay on the occlusal surface of a molar

    tooth decay inside the grooves on the occlusal surface of a molar

    teeth decays in the interproximal sites between two teeth

    decay in the interproximal site between two teeth

  2. Food factor

    The food factor is represented by the fermentable carbohydrates such as sucrose or table sugar. Bacteria from the mouth convert these carbohydrates into acids (such as lactic acid) through a process called fermentation.

    If left in contact with the tooth, these acids may cause demineralization, which is the dissolution of its mineral content. If demineralization continues over time, enough mineral content may be lost so that the soft organic material left behind disintegrates, forming a cavity or hole.

    Moreover, dental plaque develops particularly when foods containing carbohydrates are frequently left on the teeth.

    Basically, bacteria that live in the mouth thrive on these carbohydrates, producing acids that will progressively destroy tooth enamel and dentin, resulting in tooth decay.

  3. Tooth structure

    Tooth structure refers to the quality and hardness of dental tissues. There are certain diseases and disorders affecting teeth that may leave an individual at a greater risk for cavities.

    In these cases, teeth may be left more vulnerable to decay because the enamel is not able to protect the tooth.

    Although tooth structure is not the primary cause of dental caries, it is still an important factor.

    Dentin and cementum are more susceptible to caries than enamel because they have lower mineral content. Thus, when root surfaces of teeth are exposed from gingival recession or periodontal disease, caries can develop more readily.

    Moreover, the particular anatomy of each tooth may affect the likelihood of caries formation. Where the deep developmental grooves of teeth are more numerous and exaggerated, pit and fissure caries are more likely to develop. In addition, caries are more likely to develop when food is trapped between teeth.


  1. All dental decays occur from bacterial acid demineralization and acid demineralization occurs only where bacterial plaque is left on teeth.

  2. Decay most often occurs in sites that provide retention for dental plaque and are more difficult to clean :

    • deep groves, fissures or pits on the occlusal (or chewing) surface of molars and premolars
    • the areas between teeth also called interproximal sites
  3. Areas that are easily cleansed with a toothbrush, such as the front and back surfaces of teeth, develop fewer cavities.

  4. A tooth has to be exposed a certain period of time to cariogenic factors for a dental decay to form. Moreover, the frequency of which teeth are exposed to an acidic environment affects the likelihood of caries development.

  5. The caries process does not have an inevitable outcome, and different individuals will be susceptible to different degrees depending on various factors :

    • the shape of the teeth
    • oral hygiene habits
    • the buffering capacity of their saliva which can counterbalance the acidic environment created by bacterial fermentation
  6. Over the years, dental fillings can weaken, begin to break down or develop rough edges. This allows plaque to build up more easily and makes it harder to remove. Dental devices can also stop fitting well, allowing decay to begin underneath them.

    Cavities found on the margins or underneath fillings and other dental restorations are called recurrent caries or secondary caries.

Other risk factors

Reduced salivary flow rate is associated with increased caries since the buffering capability of saliva is not present to counterbalance the acidic environment created by acid fermentation.

As a result, medical conditions that reduce the amount of saliva produced by salivary glands (for example, Sjogren's syndrome, diabetes mellitus and others), medications, such as antihistamines and antidepressants, that can also impair salivary flow, or radiation therapy of the head and neck, may also increase the likelihood of dental decays.

Other risk factors may include the use of tobacco, intrauterine and neonatal lead exposure, extreme poverty etc.

Last review and update: August 2021

Top articles

Dental Implants, the Complete Patient's Guide

Today, dental implants are the state-of-the-art tooth replacement systems and are now more common than ever before. This comprehensive guide deals with all the important aspects of implant dentistry ...more

15 Common Tongue Diseases that Can Affect You

Because we use our tongue constantly, it can be frustrating and uncomfortable when we experience tongue problems. Learn about the different types of tongue problems, possible causes and how to deal with them ...more

Mouth Cancer. How to Deal with a Life-Threatening Disease

Mouth cancer is a serious condition that can be life threatening. The good news is that if oral cancer is caught early, there is a very high chance of curing it. Learn about the early signs of mouth cancer and what are the best ways to prevent or treat this disease ...more