Dental Health International Nederland
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Chapter 1 - Mouth, teeth and dental caries
This chapter presents a brief description of the mouth, the teeth and dental caries, the disease that causes tooth decay and cavities in teeth.
It provides the basic knowledge needed for using the Atraumatic Restorative Treatment of dental caries described in the following chapters.
The Mouth
With our mouth and teeth we are able to talk, to smile, to express emotions and to enjoy eating. The lips are the entrance to the oral cavity. The oral cavity is bordered by the lips, the cheeks, the floor of the mouth and the tongue, and by the soft and hard palate, also called the roof of the mouth.
The inside of the oral cavity is covered by a slippery mucous membrane. That is because there is always saliva in the mouth. Saliva contains substances that help digestion. It also contains minerals and proteins that protect the teeth. We produce a lot of saliva when we chew coarse foods. We produce only a little saliva when we sleep. As the flow of saliva needs to be controlled when carrying out restorative procedures in the mouth, it is useful to know where it comes from:
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 through little openings in the mucous membrane of the cheek, close to the left and right upper molarsthrough openings in the floor of the mouth, just behind the lower front teeth. |
The tongue has a very important function, that of taste. It enables us to tell the difference between sweet, salty, sour and bitter foods. When we eat, the tongue, lips and cheeks place pieces of food between the teeth so they can be chewed and mixed with saliva. They can then be swallowed and digested. The tongue is a very active muscle. When giving oral treatment such as ART, you often need to control the tongue, so that the treatment area remains dry.
The Teeth
The teeth are arranged in two arches in the upper and lower jaws. They are surrounded by the lips, cheeks and tongue. Each tooth consists of a crown and a root, which join at the slightly thinner part, called the neck. The crown is that part visible in the mouth. The root is inside the jaw and holds the tooth in place
(Fig 1.1). Teeth are of different shapes and sizes depending on their functions.
Figure 1.1
Teeth are attached to
the jaw by their roots:
a cross-sectional view
of an incisor and a
molar tooth.
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The crown of a tooth is covered with enamel. This is the hardest tissue in the body. Under the enamel lies the dentine. This is hard also and makes up the main part of the tooth. However, it is not as hard as enamel. It is a living tissue and can become painful and sensitive under certain circumstances.
In the middle of the tooth is the pulp. It contains nerves and blood vessels, which enter the tooth through a very fine hole in the tip of the root. The pulp connects the tooth to the rest of the body and is the source of all nutrition to the tooth as well as all pain sensation.
The tissue that surrounds a tooth and covers the jawbone is called the gum or gingiva(Fig. 1.1). Healthy gingival tissue fits closely around the tooth and feels firm to the touch and does not bleed if you press on it gently. Bleeding gingiva indicates gum disease and the need for better cleaning of teeth.
During our growing period we get two sets of teeth. The primary teeth develop during the first two years. These then are gradually replaced by the permanent teeth between the age of 6-12 years.
Primary Teeth
There are 20 primary teeth, 10 in each jaw (Fig. 1.2). In each jaw there are:
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- four front teeth: the incisors,
- two canines,
- four molars.
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The primary teeth are much smaller, more round and whiter than the permanent teeth.
Figure 1.2
The primary teeth;
looking at the chewing sufaces
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Permanent Teeth
Adults usually have 32 permanent teeth, 16 in each jaw (Fig. 1.3).
In each jaw there are:
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- Four front teeth (incisors). These are shaped like a shovel with a wide edge for biting;
they have one root. The upper incisors are bigger than the lower ones.
- Two canines which are similar in the upper and lower jaws. They are the strong, pointed
teeth at the corners of the mouth. They have only one root.
- Four premolars which look like small molars. The crowns are round rather like the shape of
a tin can; they have two cusps, one next to the cheek and one next to the tongue.
Most pre- molars have one, some have two roots.
- Six molars. These are the large teeth at the back of the mouth used for grinding food.
All molars have square crowns, like building blocks. They may have three, four or five cusps.
The molars in the upper jaw have three and those in the lower jaw two roots.
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Figure 1.3
a. looking at the front of the mouth
b. looking at the chewing surfaces
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The following names are used for the surfaces of the teeth (Fig. 1.4):
1. Occlusal surface
2. Mesial surface
3. Lingual surface
4. Distal surface
5. Buccal surface
6. Incisal edge
7. Proximal surfaces
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- the chewing surface of molars and premolars.
- the surface nearest the midline of the body.
- the surface nearest to the tongue in the lower jaw; it is called the palatal surface in the upper jaw.
- the surface furthest from the midline.
- the surface nearest to the lips and cheek.
- the incisors and canines have a cutting edge instead of an occlusal surface.
- surfaces that are close together, i.e.; the mesial surface of one tooth may touch the distal surface of the next tooth. The two surfaces are described as proximal surfaces.
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Figure 1.4
The permanent teeth: the names of the tooth surfaces
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Dental Plaque and Calculus
In the mouth there are billions of living bacteria. Most of these bacteria are harmless. Some of them help in the digestion of our food. Dental plaque is the soft, white or yellow layer that sticks to the teeth. Plaque is made up mainly of bacteria. It also contains remains of saliva, various blood cells and particles from food.
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Plaque builds up:
- where the gum meets the neck of the tooth,
- in the grooves (fissures) of the chewing (occlusal) surfaces of the teeth,
- in the narrow areas between the teeth (proximal surfaces).
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Since plaque is the cause of both tooth decay and gum disease, these are the places where these oral diseases generally start. Plaque is found on teeth in everybody’s mouth. But some people have much more than others do. These people are more likely to develop gum disease and tooth decay.
Formation of Plaque
Immediately after the teeth have been cleaned, new plaque begins to grow on the tooth surfaces. A very thin layer of saliva components forms on all oral surfaces. Bacteria settle on this saliva layer and start to multiply until they form an unbroken layer of plaque.
If the bacteria are supplied with sugar they produce sticky substances that allow the plaque to grow quickly. If plaque is not removed each day its composition changes and it becomes more harmful to the teeth and gums.
Dental Calculus
When plaque stays on the teeth for long periods it becomes very hard. This is because calcium and other minerals from saliva and some foods settle in the plaque. This new substance is called calculus. Some facts about calculus are mentioned below.
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- Young calculus is light yellow, and has a rough surface that is easily stained dark by foods, tea and tobacco.
- The surface is always covered with soft, bacterial plaque.
- Calculus can be found on any surface of all teeth,
- Most frequently, larger amounts of calculus are found close to the openings through which saliva comes into the mouth.
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Dental Caries
The most common oral disease is dental caries. This is the disease that destroys the enamel and the dentine of the tooth. It starts with loss of minerals from the enamel surface. At this early stage the process can be reversed. If the caries is not stopped, a cavity will form in the dentine. The process is progressive and may end with total destruction of the entire tooth crown.
Caries may progress slowly or rapidly. This depends on many factors like diet, saliva composition, number of bacteria, oral hygiene and other habits. Caries progression, therefore, may vary from person to person and from population to population. It may take years for caries to create a large cavity if progression is slow. But the same process may need only a few months, if progression is fast. When caries has reached the dentine, the tooth can become sensitive and the person may feel this as tooth-ache. The patient may complain of pain when eating sweets, something hot or cold, or when biting on something hard. This is because the pulp is either inflamed or infected by bacteria.
Recognizing Dental Caries
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The signs of dental caries are:
a break in the enamel or a cavity in the tooth,the dentine in the cavity is softer than the surrounding dentine,an area in the enamel that has a different color from the surrounding enamel |
Color can thus be a sign of the presence of caries.
Caries that is progressing rapidly is usually rather light in color whilst slowly progressing caries is usually darker. Sometimes, however, pits and fissures are dark colored not because of dental caries, but because of staining due to some foods.
The Causes of Dental Caries
Some of the bacteria which accumulate in plaque can digest sugar and turn it into acid. If left on the tooth, acid will attack the enamel and dissolve it.
Bacteria + food and drink containing sugar
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V
Acid
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V
Caries
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Sugar is easily digested by bacteria and acid is produced rapidly. Plaque becomes acidic very quickly. This means that sugary foods are dangerous for teeth particularly if they are eaten often. Other foods like rice, flour, potatoes and maize contain starch, which is another form of sugar. Starch is digested and converted to acid much more slowly than sugar. So, starchy foods are less dangerous for teeth.
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The places on the teeth where caries begins most often are:
- pits and fissures on the occlusal surfaces,
- pits and fissures on buccal and lingual surfaces,
- the areas where teeth touch each other, the proximal surfaces,
- around the neck of the teeth near the gingiva.
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The Development of Dental Caries
Caries begins on the enamel of the tooth (Fig 1.5a). In the early stages there are no symptoms. The first sign that can be seen is a change in the color of the enamel; it turns whitish. This change is because the acid produced by the bacteria in the plaque has dissolved some of the minerals in the enamel (mainly calcium phosphate). But there is no hole, because a lot of the minerals remain. At this stage, the decay can be arrested and the enamel made sound again by the minerals in the saliva and plaque. But for this to occur, the tooth must be kept clean, so that there are few acid attacks. Fluoride, as found in toothpaste, can also help in the healing of early caries.
If efforts to arrest the decay are not made, the dentine is then attacked. It becomes soft, spongy and yellow and the enamel becomes undermined (Fig 1.5b). The decay then spreads through the dentine towards the pulp. At this stage the tooth may be painful when cold, hot or sweet foods are eaten, or after biting on hard things. This is because the pulp is inflamed.
If a cavity is not treated with a restoration, the caries will continue to destroy the tooth; the hole will become bigger and the caries will reach the pulp. The patient may then complain of toothache.
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The pain may be:
- continuous and intense,
- throbbing like the pulse or
- a shooting pain like a stabbing knife.
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The destruction of the tooth crown can produce sharp enamel edges that hurt the tongue, cheeks or lips. The caries may destroy the tooth completely and it may have to be extracted (Fig 1.5c). Teeth are most likely to decay during childhood and adolescence when they are new in the mouth. Often the first molars, which enter the mouth at six years, are the first permanent teeth to decay.
However, not all decay in dentine spreads further. There are ways to arrest decay. Arrested decay is dark in color and is hard. However, the affected tooth may still need to be restored to prevent the tongue or lips or cheeks from being cut on the sharp edges of the enamel.
Complications
When the caries reaches the pulp, it can result in several complications:(Fig. 1.5d)
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the pulp will die after some time,an abscess or cyst may form in the bone around the end of the root,the abscess may grow into a tender swelling in the mouth. |
These conditions are often extremely painful. The tooth may be tender to bite on and if you tap the tooth vertically on the occlusal surface there will be sharp pain. However, pain may disappear after a while. But that does not mean that the caries has disappeared also.
Figure 1.5
The development stages of dental caries
a. Enamel caries: No pain
b. Dentine caries:maybe sensitive to hot, cold and sweet
foods/drinks and eating hard things; there may be pain
c. Pulp involved: severe continuous or throbbing pain
d. Abscess: deep acute pain which may disappear
after a while.
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Progression and Complications in the Primary Dentition
The progression of caries in primary teeth is very similar to its development in permanent teeth. However, the primary teeth are much smaller than permanent teeth and the layers of enamel and dentine are thinner. Caries in primary teeth, therefore, progresses much faster into dentine and thereafter the pulp than in permanent teeth. While some people consider that decayed primary teeth do not matter because they are replaced by permanent teeth, it must be remembered that:
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- decay in primary teeth can be very painful,
- the experience of an extraction is very threatening for a small child,
- the developing permanent teeth can be damaged by abscesses around the roots of primary teeth, and
- the eventual position of the permanent teeth can be disturbed if the primary teeth are extracted early.
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Thus, caries in primary teeth needs to be prevented and treated.
Preventing and Controlling Dental Caries
Caries can be prevented by the following 3 activities together:
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by removing plaque completely, carefully and effectively at least once a day,by restricting the frequency of eating and drinking sugary foods and drinks,by increasing the defense of the enamel, for example by using fluorides in toothpastes or mouthrinses. |
Control of Caries
Very early caries in the enamel can be stopped or even reversed by keeping the teeth clean from plaque and by applying a fluoride mouthrinse or by using a fluoride containing toothpaste. If the fissures are deep, a fissure sealant to close over and protect the area can be applied (Chapter 6). However, once the caries has reached the dentine and a cavity has formed, it is necessary to remove the decayed dentine and repair the cavity to stop the caries.
A good way to do this is by placing an adhesive restorative material, such as glass-ionomer, into the cavity. This material will stick closely to the tooth and form a seal between the restoration and the tooth. It so prevents any more bacteria getting into the cavity. Glass-ionomers also release fluoride into the surrounding tooth structures and make them stronger against further attack from bacterial acid.