What causes tooth decay?

Although its rates have declined, particularly among some young children, tooth decay remains a problem for some teens and adults. That's because plaque, a sticky film of bacteria, constantly forms on our teeth. When we eat foods or drink beverages that contain sugar or starch, the bacteria produce acids that attack tooth enamel. The stickiness of plaque keeps the harmful acids against the teeth, which can contribute to tooth decay.
Your tooth begins to break down when the pH (acidity) gets too low. This is caused by the acidity of the food or beverage you eat combined with the acid that the bacteria in all our mouths produce. Remember that the bacteria that live in our mouths do so because they eat the same food we do! It is not how much food you eat, but, it is how long it is allowed to stay in contact with your teeth. Each time you eat something bacteria produce acid for about 20 minutes. If you do absolutely nothing, in about 2 hours your saliva will replace the calcium that was lost.

The biggest source of decay I see is sweetened beverages. This is everything from sugar in your coffee to Mountain Dew. Just as important as how long the beverage is consumed, is which kind of acid it contains. Citric acid is very destructive for our teeth because your saliva cannot counteract it's strength very quickly. It is in just about everything. Lemonade is worse for your teeth than Coke, because lemonade is packed with citric acid and coke uses phosphoric acid which your saliva can deal with more effectively. Of course, chewy fruit and candy are a challenge for your body to fight off the acid attack. Many chewy candies also contain citric acid. Basically limit how much sipping and snacking you do and you will get less cavities.
Tooth decay is the result of the acids from dental plaque eating a hole into a tooth. Plaque accumulates on all teeth. It can be removed with brushing and flossing. Sugary foods and liquids feed the plaque and lead to acids which eat into the tooth. A hole develops into the tooth which is called a cavity. The cavity can be fixed with a filling. Limiting sugary foods and liquids, good brushing and flossing, and regular visits to the dentist can help cut down on cavities. 

Tooth decay is caused by acid attack on tooth enamel. This acid is a byproduct of bacteria breaking down the food, in particular sugars and carbohydrates, on your teeth. Hence, good brushing and flossing will decreasing the incidence of tooth decay.

Tooth decay occurs when acid attacks your teeth and damages the crystal structure that gives your teeth form and strength. The acid that does this damage is created by germs that live in a colony called a biofilm. This plaque biofilm occurs on all teeth, but only causes trouble for some people. Why? Because some lucky people have saliva that neutralizes the acid and discourages the plaque. The rest of us (who get cavities) have saliva that allows the plaque to generate and accumulate a higher concentration of acid, and the acid attacks the teeth and rots them away. This can be thought of as a kind of "biocorrosion". To avoid cavities you must reduce the amount of plaque and neutralize the acids that it generates, and for extra credit you can make your teeth more resistant to acid attack by getting Fluouide into them somehow (adults can use topical F, while kids can also use F in the diet to strengthen the teeth).

The cause of tooth decay is acidic bacterial by-products coming into contact with your tooth. The acidity in the mouth increases in the presence of sugary substances and carbohydrates. In fact, for each time you take in something with sugar in it the bacteria produce acid for about 20 minutes. Therefore it is best not to keep popping things in your mouth throughout the day. Chew Xylitol gum to help neutralize the acidity in your mouth.    

Bacteria in the mouth turn foods into acids that eat away at the tooth structure. Acidic foods (fruit juices) sugary foods, sodas, sports drinks, chewing gum ,sticky foods - all are part of the problem. Even diet sodas, though lacking in sugar themselves, have phosphoric acid as the preservative agent, so they too, can cause teeth to decay.

Flossing, Brushing with a fluoride toothpaste, after meals and adding a fluoride mouthwash before bedtime are things that can be done to reduce the effects of the bacteria.

The acidic waste products released by bacteria from digesting the food left in your mouth concentrate in the areas that are difficult for you to clean. The longer the acid persists the more damage it does to the surface of the tooth. The tooth starts out perfectly hard and very smooth but after prolonged exposure to the acid the smooth surface pits, roughens and "cavitates" and becomes a cavity. Then, depending on the size and location it may need a filling or a crown to repair the damage. 

Decay requires three components -- a tooth, bacteria, and nutrition for the bacteria to live. Eliminate any one of the three components and you will not have decay. We all like teeth, so let's keep those. Everybody's mouth is a sewer of bacteria but the kind and the numbers of bacteria you have determines whether or not you get decay. If you have high numbers of decay causing bacteria and you eat a lot of sugar, decay will result. You can reduce the number of decay causing bacteria in your mouth by good brushing and flossing habits, but that is only one half of the equation. You must also avoid sugar that the bacteria thrive on in order to reduce the opportunity for decay to develop.
Ruchi K. Sahota
To put it simply, you can think of the "cavity equation":
Bacteria + sugars = Acid. Acid + tooth = Decay!

Tooth decay is the weakening and destruction of tooth enamel. When foods containing carbohydrates (sugars and starches) such as milk, soda, raisins, fruit or candy are frequently left on the teeth, bacteria that live in the mouth thrive on these foods, producing acids as a result. These acids then destroy tooth enamel, resulting in tooth decay.
There are several answers to the question, each dependent on the last. For example, tooth decay is caused by bacteria on your teeth. But bacteria is caused by food particles left there. And certain foods (like sweets) cause more bacteria than others. And these food particles are caused by not brushing and flossing.

So in a roundabout way, we can say that tooth decay is caused by not brushing and flossing. I like that answer best, because it includes the prevention. :)
Acid and bacteria.

There are many types of bacteria in the mouth. Certain acid-producing species are the best at causing tooth decay or cavities. These acid-producing bacteria love to eat sucrose and fructose. As they ferment these sugars they produce acids which demineralize the enamel and make a hole in the tooth (they decay or eat the tooth away).

Because sucrose and fructose are in many of the foods and drinks we consume, our diets are also a significant factor in whether or not we will get a cavity. What is critical is the amount of time the sugars are in contact with the teeth. If I am sipping a soda for a couple of hours while I work or watch a movie my teeth are repeatedly or constantly bathed in acid and sugar and I could have a real problem. The stickier the candy the higher risk for a cavity. Having said that, if I mix my sugar with other foods or remove the sugar by rinsing, brushing, flossing soon after I eat or drink it I am at less risk and can many times be safe.

As we have long been taught, mechanical removal of the sticky plaque from the teeth and gums by brushing and flossing is imperative.

Some people genetically are at a higher risk for cavities. Their saliva does not neutralize acids well. Some people even have acidic saliva so their teeth are constantly bathed in acid. They may crave sugar because they do not like the taste of their mouth. Others have a higher level of the bad acid-producing bacteria. We know that cavities are contagious. The bad bacteria can be passed from family member to family member.

Our overall health also plays a role. For instance if I am sick it could be harder for me to take care of my teeth and my immune system may not be good at removing bacterial pathogens from my mouth.

The level of acid in the mouth is critical. If we stay above 5.6 on the pH scale we will not get cavities. There are many products now that can 1. neutralize acid 2. rid the mouth of the bad bacteria 3. strengthen the teeth. Thank you.
Kerri S. Gustafson, DDS
Pediatric Dentistry

I always remind parents of the following equation: tooth + carbohydrate (CHO) source + bacteria = dental decay. In this equation, it is easiest for the parent to limit a child's carbohydrate source and I work with the parent to help identify sources of CHOs in their child's diet. Sometimes, parents are surprised when we discuss some of the foods and drinks that contribute to dental decay including such "sticky" foods as fun fruits and raisins and non "sticky" foods like chips and crackers that break down into sugars when digestion begins in the mouth.

Tooth decay is caused by bacteria, which require certain foods to live. 

If you want to prevent tooth decay, the primary focus should be on reducing the bacterial load in the mouth. Brushing and flossing remove the sticky bacteria buildup on the teeth (plaque). An antimicrobial mouthrinse (such as Listerine or Scope) is effective in reducing the bacteria in the mouth when used with brushing and flossing. 
Abraham Speiser
Tooth decay is a bacterial disease of teeth called dental caries (pronounced the same as carries). There are three main types of this disease: pit and fissure caries (in the grooves on the biting surfaces and several other surfaces of the teeth), smooth surface caries (on the surfaces of the teeth next to the tongue, next to the cheek and between the teeth) and root caries (also called geriatric caries, since frequently the roots are exposed in older age when the gums recede). Each of these three types of caries is caused by different strains of bacteria.

Caries removes calcium from teeth, then structural proteins leaving a hole (a cavity). More advanced disease results in tooth infection (abscess).
The short answer is -- your diet! 

Cavities form when bacteria in the mouth have access to sugars and carbohydrates that break down into sugars. The cavity forming bacteria use the sugars to grow and through the process of acid demineralization, destroy the healthy tooth structure.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.