Formation of carious lesions in the teeth; decay

What is the structure of a tooth?

A tooth comprises of enamel, dentin and pulp. Enamel is the hardest substance of the body. Under the enamel is the dentin, which has a softer composition. The pulp houses the blood vessels that supply the teeth, and nerves that are responsible for the tooth's sense of touch and pain. The tooth is connected to the surrounding bone through ligaments. After childhood, the ”milk teeth” are replaced by permanent teeth. Normally, there are 20 milk teeth and 32 permanent teeth including the wisdom teeth.

What causes dental decay? Which factors influence dental decay?

Even though dental enamel is the hardest substance in the body, it can be damaged. Dental decay, or caries, means the decay of the tooth's hard tissues, i.e. enamel and pulp. Tooth decay is a sum of several factors.


There are many types of bacteria living in the mouth even normally. Mutans Streptococci bacteria in particular cause dental decay. Some people have more mutans streptococci bacteria in their mouths than others. In order to live in the mouth, bacteria need sugar. When bacteria feed off sugar, acidic substances are produced as their metabolites. These acids corrode the surface of the enamel, breaking down its components. From the enamel, dental decay can advance to the dentin and all the way to the pulp. As dentin is softer than enamel, dental decay advances more rapidly in it.


Diet is another significant factor in dental decay. Cavities form in the teeth when bacteria have regularly access to sugar. The quality of food and in particular how often one eats have an impact on dental decay. Each snack or meal causes an acid attack in which acidic substances erode the surface of the teeth for up to half an hour. Frequent sweet snacks and acidic drinks in particular are very detrimental to teeth.


Saliva rinses the mouth, decreasing the amount of bacteria on dental surfaces. In addition, saliva contains minerals that strengthen the surface of the enamel. The effect of saliva is the third significant factor in the formation of cavities. Dry mouth and decreased flow of saliva radically predispose to dental decay.


Fluoride strengthens the components of the enamel. Using fluoride may even stop early-stage damage on the surface of the enamel. Sources of fluoride include fluoride-containing toothpastes, fluoride tablets and fluoride varnish used by a dentist.

How can I recognize a decayed tooth?

The chewing surfaces of molars, surfaces between the teeth and gum lines are the most likely to decay. These areas is often more difficult to clean. A cavity in its early stage commonly causes twinge and sensitivity to cold in the tooth. When it advances, the symptoms of caries include sensitivity to touch and heat. Toothache may also suggest advanced caries. Once caries reaches the pulp, the result is pulpitis, an inflammation of the pulp. In this case, the tooth requires root canal therapy. A deep caries does not necessarily cause any symptoms, and this way it can sometimes advance insidiously. Even symptomless teeth should be checked by a dentist regularly.

How can I prevent dental decay?

The Mutans Streptococci is often transmitted at childhood, typically from the mother. The bacteria may be passed through saliva, e.g. by eating with the same spoon or licking the child’s pacifier. The younger a child is at the time of acquisition, the more likely the bacterium is to be transmitted. Salivary contact with the child should be avoided, and mothers should also take care of their own oral hygiene. Avoiding Mutans Streptococci alone does not protect the child from dental caries. A child does not know to crave for sweets before he or she is taught this habit. The later the child becomes interested in sweets, the better he or she is spared from caries for the rest of his/her life.

In order to keep the number of acid attacks at a minimum, meals should be had at regular intervals. Snacking, sweet and acidic drinks and unnecessary snacks should be avoided. Even sugared coffee causes a detrimental acid attack. Sweet treats should be had with meals.

The use of xylitol products after meals is recommended. Instead of ordinary sweets, ones sweetened with xylitol should be preferred. Oral bacteria are not able to feed off xylitol, and as a result there is no acid attack. In addition, chewing xylitol chewing gum increases the flow of saliva, which rinses off the bacteria and dilutes their acidic metabolites.

The best way to avoid dental decay is taking care of good oral hygiene. Thorough brushing of teeth in the morning and evening with a fluoride toothpaste is the most important thing. Mechanical brushing removes bacteria from dental surfaces. The fluoride contained in the toothpaste hardens the enamel even more and can even repair and stop damage in the enamel. Contact points between teeth should be cleaned using dental floss or toothpicks as they cannot be reached by a toothbrush.

How are teeth filled?

A cavity that extends to the pulp must be filled. The dentist removes the decayed dental tissue by drilling. The removed tissue is replaced by a filling material, e.g. plastic, ceramic or amalgam. A badly decayed tooth may also be crowned. If the cavity has extended all the way into the pulp, root canal therapy is necessary before filling.





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