What Causes Tooth Decay?

The main cause of tooth decay is usually the result of the destructive combination of three factors: dental plaque – sugars – acids.

Acids that cause tooth decay are produced by the bacteria of dental plaque when they consume/metabolise the sugars in our diet either in foods or drinks. With time the progressive breakdown of the enamel leads to the formation of dental cavities.

Several risk factors as nutrition habits, quality of oral hygiene, dry mouth problems, presence of fluoride in water or toothpaste, and heredity can play a significant role in how susceptible your teeth may be to tooth decay.

Causes of tooth decay – Dental plaque bacteria

Dentists consider dental plaque as the main cause of dental caries. Plaque is a soft film of bacterial colonies that builds on teeth’s surface and especially around the gum line, the edges of fillings and inside grooves and pit fissures. Bacteria start to accumulate on teeth minutes after each toothbrushing, using the sugars in our food as their own food source. When bacteria digest sugar they produce acids as a waste by-product of their metabolism, which start to decalcify the enamel.

Most of the acid (mainly lactic acid) produced by bacteria is dilluted and neutralized by the saliva in the mouth reducing its damage potential. But if bacterial plaque is not properly removed, it starts to harden creating dental tartar (calculus). When dental tartar has developed, the acids become trapped between tartar and teeth, making it difficult for saliva to reach and neutralize it. In this phase the demineralisation of the enamel accelerates and the risk of dental cavities increases significantly.

Not all dental bacteria have equal cariogenic potential of causing tooth decay. Streptococcus mutans is the most destructive bacterial strain in the mouth as it attaches easily to teeth and produces a lot of acid. Other common but less destructive acid-producing bacteria are lactobacillus and actinomyces. Some of these cariogenic bacteria can be transmitted from person to person, for example, from parents to children. Besides their catastrophic action on enamel, acids also provide a favorable environment for dental plaque to grow and multiply faster, producing even more acids.

Causes of tooth decay – Sugars

The main role of sugars in the cycle of events that causes tooth decay is to provide the food and energy for the bacteria to grow and produce acids. Bacteria utilize sugars like glucose, sucrose, fructose and lactose that are contained in the foods you consume. If we didn’t have sugar in our diet, plaque bacteria wouldn’t be able to cause much damage.

It is not always obvious which foods could provide the sugar that bacteria need to feed and produce acids. Foods that contain sugar, such as cookies, chocolates, cakes, soft drinks and candies are, as expected, the main energy sources that help bacteria to cause dental caries. However several other carbohydrate foods, such as bread, crackers, cereals or potato chips can be broken down to sugar in the mouth by enzymes found in saliva. Foods that break down into simple sugars (glucose, fructose, maltose and lactose) in the mouth are called fermentable carbohydrates. Sugary and starchy foods and beverages, such as raisins, cakes, candy, soda, honey, juice and milk, are the greatest contributors to the plaque that causes tooth decay.

Causes of tooth decay – Acids

Tooth enamel is the hardest structure of the human body. However its mineral structure makes it susceptible to acids that can easily destroy it. When the environment of the mouth becomes too acidic (the value of pH -that measures acidity- drops under 5.5-6.0), the acids start to dissolve the minerals (calcium and phosphate) that compose tooth enamel.

Any part of the tooth, from the crown down to any exposed area of the root is vulnerable to acid damage. What starts as a mild demineralization with the presence of a small white spot on the tooth surface, if left untreated, will develop to a hole in the tooth structure creating a dental cavity.

Consuming soft drinks that contain phosphoric and citric acids can create an acidic environment in the mouth that promotes enamel demineralization and tooth decay. However in other cases acids should only be considered as the ‘weapon’ used to destroy the tooth enamel. The acid-producing interaction of dental plaque bacteria with sugars in our diet is what actually causes tooth decay.

Tracing back to the causes of tooth decay we identified dental plaque and sugars as the main reasons for creating an acidic environment in the mouth. But neither dental plaque or sugars could cause problems in our mouth if we did not allow them to be there in the first place. The main reasons for that, and true cause of tooth decay, is poor oral hygiene combined with a diet rich in carbohydrates. If both these causes are eliminated, the risk of developing dental caries is minimized.

If teeth are brushed properly at least twice a day or even better after each time we eat, and flossed every day to clean between teeth, the bacteria will not have the time to form enough dental plaque to cause tooth decay. If our diet does not provide enough sugar for bacteria to feed, grow and metabolize to acids, teeth are safer even if our oral hygiene is not perfect. The frequency and timing of consuming foods and drinks that cause tooth decay is also important. Constantly snacking throughout the day keeps the mouth in acidic condition for more time enhancing the demineralization and the loss of enamel minerals.

By combining proper daily oral hygiene with a careful diet controlling the consumption of carbohydrates, we eliminate the main causes of tooth decay and provide a safer environment for our teeth. Except oral hygiene and diet, several other risk factors (either systemic or behavioral) may affect the mouth’s environment and increase the possibility of developing tooth decay.