Dental caries is decay of the teeth, which results in cavities, or holes in the teeth.

The term 'dental caries' refers to a dead tooth, or a tooth that is hollow or decayed

It is one of the most common diseases affecting humans, and occurs most often in children and young adults.

Bacteria in the mouth, eating refined carbohydrates, time and a susceptible tooth surface are all factors that act together to cause dental caries.

Symptoms of dental caries may include discoloured marks on the teeth and toothache.

Good oral hygiene can help prevent dental caries.

What is dental caries?

The word “caries” is Latin for “hollow”, and in Greek (“Ker”) it means “death”. The term “dental caries” thus refers to a dead tooth, or a tooth that is hollow or decayed.

Dental caries results in cavities, or holes in the teeth. It is an extremely destructive disease, and, second only to the common cold, is the most common disease found in humans. It occurs more often in children and young adults and is the most important cause of tooth loss in younger people. Root decay is common in geriatric patients who have kept their teeth throughout life but who have receding gums.

What causes dental caries?

There are four interrelated factors that cause dental caries: specific bacteria (found in plaque), sugar, time and a susceptible tooth surface.

Bacteria and Plaque

A pellicle, or coating on the teeth, starts to form as soon as you put down your toothbrush. The pellicle contains proteins from the saliva and “hosts” bacteria (Streptococcus mutans, Lactobacilli, and Actinomyces), which are normal inhabitants of the adult mouth and attach to the pellicle. This is the precursor to 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 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 five, 50% of children have the same bacteria as their mothers. By the age of four, 83% of children have already been infected with Streptococcus mutans.

Sugar

Sugar can be found in all carbohydrate foods, such as bread, potatoes, bananas and breakfast cereals, as these are broken down into simple sugars such as glucose, fructose, maltose and lactose as the carbohydrates are digested. The enzymes in the mouth start the digestion process. Of these sugars, glucose and fructose, such as found in honey and fruits, are more destructive than that of maltose found in grains.

Plaque + Sugar = Acid 

The bacteria in the plaque use the sugar as a source of energy – food. The bacteria digest the sugar, and by-products are excreted. These by-products are very sticky and acidic, and cause a fall in the mouth’s pH (acid/alkali value measured from 1 being very acid to 14 being very alkaline).

In a healthy mouth the pH is around 6.2-7.0. 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 starts to demineralise (lose calcium and other minerals from the enamel). As the enamel loses its minerals, it starts to break down. This is the start 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 amount of time these factors have to cause dental caries.

Anatomy of the tooth

The outer hard 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. The tooth enamel has no blood supply and can therefore also not heal itself once it has been damaged. It is literally a dead layer of cells.

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 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 canal, called the root canal, deep within the tooth. The root canal is literally a cavity in the root of every tooth. It contains not only the nerve but also the 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 very bottom end of the root there is a small opening and it is through this opening that the nerve and blood vessels in the tooth are connected to the nerve and blood vessels in the jaw.

Plaque + Sugar = Acid + tooth + time -> caries

Bacteria thrive on sugar and an acid 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 which creates an environment that becomes increasingly destructive with time.

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

Teeth with “nooks and crannies” will trap more food than those with smoother surfaces. This is one of the reasons why molars are more susceptible to caries that 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 dental caries, and who is at risk?

People susceptible to infections of S. mutans bacteria.

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, and 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 area that surrounds the tooth, the bone to which the tooth is attached, 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. Xerostomia refers to a dryness of the mouth 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 of dental caries

The first visible sign of trouble is a white spot on the tooth – the area of enamel being demineralised by the acid. If this area is now kept clean of plaque, and minerals such as fluoride are used, the spot can still remineralise, but if left untreated a cavity may still develop. This then shows as a dark spot on the tooth. Once the demineralisation has progressed to the inner part of the tooth (dentine), the damage is permanent, and a cavity can usually be seen provided it is not deep between the teeth. This cavity will deepen, until it eventually reaches the pulp and infects the nerve and blood vessels.

Toothache due to cavities may develop prior to actual infection of the pulp, on infection of the pulp, or at a later stage, although not all toothaches are due to cavities.

Visible pits or holes in the teeth.

Discolouration of teeth or fillings.

Filling which has broken or fallen out.

Some adults may also have a problem with Xerostomia.

If fillings are not placed properly or have broken, or crowns do not fit properly, it leaves a gap through which plaque bacteria and food particles can enter into the inner part of the tooth, causing destruction from inside the tooth. This form of destruction can usually only be seen on x-rays.

How is dental caries diagnosed?

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

When the dentist examines the surface of a tooth for possible caries, the surface should be clean (free of plaque and tartar) and dry. An explorer (a hand-held instrument with a thin sharp point) is used to gently probe the grooves, and if it becomes stuck, it usually means a cavity has formed.

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

Newer techniques such as the use of staining dye are helpful in detecting caries under old amalgam fillings when these are removed. The use of a white (tooth-coloured) filling in that cavity is problematic, since all the dye cannot always be removed, and will then be visible through the white filling. The strength of the bond of that filling to the surface of the tooth is also questionable.

Electronic caries detectors can be used to measure the amount of demineralisation in the fissures, but are very expensive instruments to purchase.

Can dental caries be prevented?

The following are ways to help prevent the development of dental caries:

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 soft because teeth are convex and the bristles must be able to fold around 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 cause of the acid, the plaque, must be removed before the tooth enamel has a chance to demineralise.

Fissure sealants

The sealing of the grooves on top of the premolars and molars as soon as their crowns erupt fully through the gum, prevents them from becoming clogged with food particles or plaque. Sealants are thin plastic-like coatings applied to the chewing surfaces of the molars. This coating prevents the accumulation of plaque on these vulnerable surfaces. 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

It has been demonstrated by studies in the United States that people who ingested fluoride in their drinking water had fewer dental cavities than the control group who had no fluoride in their drinking water. When these people 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 and protects 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.

It is possible to get too much fluoride and develop an unsightly mottling of the enamel called fluorosis. But this occurs only in areas where drinking water contains an excess of natural fluoride, and not 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 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, since the meal itself would generate an acidic environment. 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 acid in 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 gum, 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 are dental caries treated?

Fluoride treatment

If caries is detected early it can simply be treated 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, it will not be able to remineralise and will simply continue enlarging if it is not repaired, 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 the 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.

What is the outcome of dental caries?

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 the danger is 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 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.