Cavities (dental caries)

Woman with dental caries
Woman with dental caries

Dental caries is a destructive disease which results in cavities, or holes, in the teeth. It is one of the most common diseases affecting humans.

The word "caries" is Latin for "hollow", and in Greek ("ker"), meaning "death". The term "dental caries" thus refers to a tooth hollowed out by decay, which may progress to result in the death of the tooth.

It's extremely destructive, and, second only to the common cold, is the disease most frequently suffered by humans. Caries is the most important cause of tooth loss in younger people. Decay attacking exposed roots is common in geriatric patients who have kept their teeth throughout life but who have receding gums.


Caries is a multifactorial disease with four interrelated factors together causing dental decay. These are specific bacteria found in plaque, refined carbohydrates, a susceptible tooth surface and time.

Bacteria and plaque: Plaque is a pellicle, or coating, which starts to form on your teeth as soon as you put down your toothbrush. The pellicle contains proteins from the saliva and harbours a host of bacteria (Streptococcus mutans, Lactobacilli and Actinomyces), which are normal inhabitants of the adult mouth and attach to the pellicle. This is the precursor to dental plaque.

New-born babies have none of these plaque-forming bacteria. In fact, it is the mother who transmits her plaque-forming bacteria to her child by kissing the baby on its mouth, by first putting the spoonful of food into her own mouth and then into the baby's mouth, and even by blowing on the food and then feeding the baby that food.

By the age of four, 83% of children have already been infected with Streptococcus mutans, while 50% of five year old children have the same oral bacteria as their mothers.

Sugar: Carbohydrates in foods such as bread, potatoes, bananas and breakfast cereals, are broken down by digestion into simple sugars such as glucose, fructose, maltose and lactose. The enzymes in the mouth start the digestive process. Bacterial activity on these sugars results in destructive acids, especially in the case of glucose and fructose, such as found in honey and fruits. Maltose, a sugar found in grains, produces less aggressive acids.

Plaque + sugar = acid: The bacteria in the plaque use the sugar as a food and source of energy. The digestive process results in the excretion of by-products which are very sticky and acidic, causing a fall in the pH value of the mouth (acid/alkali balance measured from 1 being very acid to 14 being very alkaline).

In a healthy mouth the pH is around 6.2 to 7.0. A pH of 7 is neutral (neither acid nor alkaline). Thus a mouth with a pH of 6.2 - 7.0 is near neutral, and no damage is being done to the teeth. The problem starts when the pH is less than 5.5.

The tooth is now in an acid environment, and demineralisation may occur (the loss of calcium and other minerals from the enamel). As the enamel loses its minerals, it starts to break down. This is the beginning of a cavity.

Time: All the above factors can be present, but if the plaque is not allowed to lie on the tooth surfaces for any length of time, no decay will result. Thus cleaning your teeth soon after eating will decrease the chances of your suffering dental caries.

Anatomy of the tooth

The outer layer of the tooth (enamel) contains large amounts of calcium and is very hard. In fact, it is the hardest structure that can be formed by the body. Enamel has no blood supply and can therefore not heal itself once it has been damaged. It is a mineralised tissue on a protein matrix.

Certain parts of the tooth contain very little enamel, for instance in the grooves (fissures) on top of the molars. Therefore, the protective layer of the tooth is very thin here. To add to the problem, it is difficult to keep the grooves clean, and plaque and bits of food quickly gather in the grooves. That is why it is important that these grooves should be protectively sealed with a layer of resin, called a fissure sealant, soon after the tooth appears.

The enamel protects the inner, somewhat softer, more porous inner layer of the tooth, called dentine. The dentine is the living part of the tooth and is directly linked to the nerve inside the tooth. The nerve runs in a channel, called the root canal, deep within the tooth.
It contains not only the nerve, but also blood vessels, which provide the dentine with nutrients and oxygen and keep it alive.

Thus the root canal is surrounded by the dentine, which is protected by the tooth enamel on the outside. At the end of the root there is a small opening, through which the nerves and blood vessels in the tooth emerge to link with nerves and blood vessels in the jaw.

Plaque + sugar = acid + tooth + time -> caries

Bacteria thrive on sugar and an acidic environment – the more sugar you have, the more acid is formed, and the more the bacteria thrive and multiply. And the more bacteria present, the more acid is produced. In other words, it is a vicious circle, creating an environment that becomes increasingly destructive with time.

The sticky acid excreted by the bacteria is deposited right against the surface of the tooth, and immediately starts attacking, or demineralising, the enamel. Saliva has the ability to neutralise the acid, but requires 20 minutes to achieve this.

Teeth with "nooks and crannies" will trap more food than will those with smoother surfaces. This is one of the reasons why molars are more susceptible to caries than front teeth.

Teeth that have just emerged, such as those of children and young adults, have enamel that is not yet very strong, and are thus highly susceptible to acid attack. Acute caries is common in these cases, and the progression of the caries is so quick that a large cavity can be formed in a matter of months.

Who gets it and who is at risk?

  • It occurs more often in children and young adults and is the most important cause of tooth loss in younger people, although there has been a definite decrease in the number of cavities in children. Dental caries is not only a childhood disease, however, as it can attack at any age.
  • Caries on the roots of teeth in adults is a major problem, since older people are more susceptible to recession of the gums. This is due to incorrect brushing techniques or periodontal problems. (“Periodontal" refers to the gum and bone that surround the root and the ligament which attaches the tooth to the bone). The area of the root now exposed is not protected by enamel, and caries can start and spread rapidly in those areas.
  • People taking medications that can cause Xerostomia (dry mouth) or who naturally have a problem with Xerostomia.  The dryness of the mouth is due to a decreased function of the glands that produce saliva.
  • Paraplegics, quadriplegics and any other people who might have problems with co-ordination of hand movements, thus preventing them from maintaining good oral care at home.
  • People who suffer from diseases such as arthritis where arm and hand movements are restricted, thus preventing them from maintaining good oral care at home.
  • People who like snacking during the day, drink a lot of sugared beverages, or eat mints to combat a problem with bad breath or smoking, will have their teeth exposed to acid for far longer than normal, and are thus at much greater risk of developing caries.

Symptoms and signs

Some adults may also have a problem with xerostomia.

If fillings are not placed properly or have broken, or crowns do not fit accurately, gaps are left through which plaque bacteria and food particles can enter into the inner part of the tooth. This causes destruction beneath the restoration, which can usually only be seen on


It is easy to see the first sign of caries on the visible surface of the tooth, but it is more difficult when caries develop on surfaces in contact with adjacent teeth, on the part of the tooth surface that is covered by gum, or in the grooves and fissures of a tooth.

When the dentist examines a tooth for possible caries, the surface should be dry and clean (free of plaque and tartar).

An explorer (a hand-held instrument with a thin sharp point) is used to gently probe the grooves. If it becomes stuck, it usually because caries has started.

The tooth surface may display some discolouration (white or brown-black), which can be due to caries, but intra-oral radiographs must be taken to rule out staining or tartar build-up. Intra-oral radiographs are also used to locate caries on adjacent surfaces between teeth, on the tooth surface covered by gum and to determine the extent of the cavity.

Newer techniques include the use of staining dye. This is helpful in detecting caries, for example, under old amalgam fillings when these are removed. The subsequent use of a white (tooth-coloured) filling may be problematic, since it may not be possible to remove all the dye, and remnants will then be visible through the white filling. Sophisticated (and expensive) electronic caries detectors can be used to measure the amount of demineralisation in the fissures.


Dental caries can be prevented!

Good oral hygiene: It is important that the plaque should be effectively removed. Even brushing two to three times per day is not good enough if you do not use the correct technique.

Flossing is also essential in the removal of plaque: it is the only effective way of cleaning between teeth. The bristles of the toothbrush must also be sufficiently flexible to be able to fold around the convex surfaces of the teeth. Plaque is very soft and easily removed once you are able to reach it. It can even be wiped off children's teeth with a piece of cloth.

If your teeth do not feel clean after you have brushed or feel coated with plaque soon after brushing, your technique is wrong.

The secret is that the origin of the acid, the plaque, must be removed before the tooth enamel starts to demineralise.

Fissure sealants: Sealants are thin plastic-like coatings applied to the chewing surfaces of the molars. Sealing the grooves on top of the premolars and molars as soon as their crowns erupt fully through the gum prevents these vulnerable surfaces becoming clogged with food particles or plaque.   Older people may also benefit from the use of fissure sealants.

Fluoride: Fluoride, a natural mineral, is often recommended to protect teeth against dental caries.

Systemic fluoride: Studies in the United States have demonstrated that people who ingested fluoride in their drinking water had fewer dental cavities than control groups who had no fluoride in their drinking water. When people from the first group moved to areas where no fluoride was present in the water, their incidence of caries increased significantly.

Fluoride that is ingested when the teeth are developing, as in the case of young children, is incorporated into the structure of the enamel, protecting it against the action of acids. It is necessary to give children fluoride supplements if the water does not naturally contain sufficient amounts of the mineral. Speak to your local dentist to find out whether the water in your area contains enough fluoride.

In areas where drinking water naturally contains an excess of natural fluoride, it is possible that teeth develop an unsightly mottling of the enamel called fluorosis. This will not occur in water systems that are artificially fluoridated and thus contain the correct amount of fluoride.

Topical fluoride: Topical fluoride is recommended to protect the surface layers of teeth. Topical fluoride can be found in toothpastes and mouthwash. It can also be applied professionally, and certain contemporary fillings now release fluoride over a period of months, thus protecting the tooth from inside the sealed cavity.

Diet: Chewy, sticky foods (such as dried fruit or sweets) are best eaten as part of a meal rather than as a snack. If possible, brush the teeth or rinse the mouth with water after eating these foods.

Minimise snacking, which creates a constant supply of sugar, and thus introduces acid into the mouth. Avoid constant sipping of sugary drinks or frequent sucking on candy and mints.

Eating nutritious meals and limiting the number of sugary snacks you eat between brushings is also an important part of a sound oral health routine, as is drinking plenty of water. Water keeps saliva flowing, which neutralises the acid created by plaque.

Some mouthwashes kill bacteria in the mouth, but can only be used for a limited time, and under supervision of your dentist. Using sugarless chewing gums, especially those with xylitol increases the flow of saliva, and thus helps prevent decay.

When children have to take antibiotics provided in a sugary, sticky syrup, have them rinse their mouths, brush their teeth or eat some cheese after each dose.

How is dental caries treated?

Fluoride treatment: If caries is detected early it can be treated simply with high concentrations of fluoride, resulting in the arrest of the caries and remineralisation of the tooth enamel. This fluoride is applied in the consulting room during the six-monthly check-up. If a cavity has however, already progressed into the dentine of the tooth, remineralisation is not possible. The defect will simply continue enlarging if it is not repaired, and will progress until the whole crown of the tooth is eaten away.

Fillings: Fillings can be used to repair the damage caused by caries. Different types of filling materials are available.

Crowns: Crowns are used if decay is extensive since most fillings only "plug" the hole created by the caries, and do not significantly increase the strength of the remaining poor tooth structure.

Root canal treatment: The removal of the contents of the pulp chamber and canal in the roots may be necessary if infection has reached the pulp.

Removing "hopeless" teeth: In cases where the destruction caused by the caries is so advanced that the tooth cannot be saved, the tooth is removed and an implant, denture or bridge can be put in place.

Home treatment for toothache

If you suffer from occasional mild toothache, try the following:

  • If you have sensitivity to cold drinks, try using toothpaste made for sensitive teeth. If your gums have receded (pulled away from the teeth), you may have exposed root surfaces. Toothpaste for sensitive teeth can help protect these areas.
  • You also should avoid "swishing" any alcoholic beverages, such as wine, which can dry out the roots and make the sensitivity worse. If there's no change after routinely using toothpaste for sensitive teeth, see your dentist.
  • The other condition you can attempt to treat at home is dull ache and pressure in your upper teeth and jaw. This can signal a sinus headache, so try an over-the-counter sinus medication. If the pain persists, tell your dentist or doctor.


If left untreated, dental caries slowly eats into the tooth, destroying dentine and weakening the tooth.

As the caries progresses and destroys the dentine, which forms the underlying support for the enamel, the enamel is also endangered. Eventually the dentine support is so weak that the enamel breaks away – and you become aware of a problem due to a broken tooth. If there is a filling next to the area of decay, the filling itself might break, or even fall out.

The deeper the caries progresses into the dentine, the greater is the danger of the nerve and blood vessels becoming infected with the bacteria causing the caries. Often this is accompanied by toothache (or hot and cold sensitivity), which disappears after a day or two. However, easing of these symptoms does not indicate that the problem has resolved. Once the pulp is infected, the pain invariably returns, has a greater intensity and stays, and the only way to save the abscessed tooth is to perform root canal treatment.

When to call the dentist

Most types of toothache require a trip to the dentist. See your dentist if you experience any of the following:

  • Sharp pain when you bite down on food.
  • Lingering pain after you eat hot or cold foods.
  • Constant and severe pain.
  • Chronic pain in your head, neck or ear.

Revised and reviewed by Professor Bill Evans, BDS Dip Orth(Witwatersrand). Orthodontist: South African Dental Association and Senior Specialist, Department of Orthodontics, University of the Witwatersrand, Johannesburg. February 2015.

Read more:

- Fillings

- Root canal treatment

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