Tooth Caries: Causes, Symptoms, Treatment, Pathophysiology, Classification, Prevention

What are Tooth Caries?

Tooth caries, also known as tooth decay, dental caries, dental cavities, or just simply caries is a condition where there is breakdown of teeth due to bacterial activities resulting in formation of cavities. The cavities can be of different colors which can range from yellow to black. Symptoms of tooth caries consist of pain in the affected tooth and difficulty eating. If the tooth caries is not treated, then patient can have complications, such as inflammation of the tissue surrounding the tooth, loss of tooth, abscess formation and infection.

The cause of tooth caries is breakdown of enamel, dentin and cementum, which are the hard tissues of the teeth, by the bacteria. This breakdown occurs because of formation of acid made from the sugar or food debris present on the surface of the tooth or trapped in the teeth. The simple sugars present in our food become the primary source of energy for these bacteria. Therefore a diet which is high in simple sugar poses as a very big risk factor for tooth caries. If the breakdown of mineral is more than the build up from saliva, then it results in caries. So, risk factors of caries include conditions which cause decreased production of saliva such as: Sjogren’s syndrome, diabetes mellitus and certain medications, such as antidepressants and antihistamines. Caries is also seen in people who live in underdeveloped countries or poverty from improper cleaning of the mouth, and receding gums which exposes the roots of the teeth.

Prevention of tooth caries includes: proper and regular cleaning of the teeth by brushing them twice a day, daily flossing, low sugar diet and small amounts of fluoride. Sources of fluoride include salt, water or toothpaste. Regular dental checkups and screening can lead to earlier detection of tooth caries.

Treatment depends on the extent of destruction by the caries and includes restoration of the tooth by different types of fillings to removal of the tooth. As of now, there is no known method to restore or re-grow the natural enamel or tooth. Developing countries do not have proper availability of treatment for tooth caries. For pain or toothache form dental caries medicines such as paracetamol or ibuprofen can be taken.

What are Tooth Caries?

Pathophysiology of Tooth Caries

The saliva coats our teeth, which also have a layer of bacteria on them known as biofilm. There is continuous formation of this biofilm. The minerals that are present in the hard tissues of the teeth, such as dentin, enamel, and cementum are under the constant processes of demineralization and remineralisation. Tooth caries occur when the rate of demineralization is faster than the rate of remineralisation resulting in net mineral loss. The cause of this is an ecologic shift in the biofilm of the teeth, which changes from a balanced population of bacteria to a population which produces acids and has the ability to survive in an acid environment. After there is loss of minerals from the enamel, there is progression of dental caries. There is development of multiple distinct areas on the enamel that can be seen under a microscope. The identified zones on the enamel are:

The translucent zone is the first indication of caries.

Dark Zone: There is slight re-mineralization of enamel in the dark zone.

Body of the lesion: The zone of the body of the lesion is the greatest part of decay and demineralization.

Surface Zone: The surface zone is fairly mineralized and is present till there is cavitation from the loss of tooth structure.

Classification of Tooth Caries

Tooth caries or dental caries are classified according to etiology, location, rate of the hard tissues which are affected and progression of caries. Given below is the G.V. Black classification of tooth caries:

Class I: In this stage, the caries affect the occlusal surfaces of the posterior teeth, lingual or buccal pits on molars or lingual pit near cingulum of maxillary incisors

Class II: The proximal surfaces of the posterior teeth are involved.

Class III: The interproximal surfaces of anterior teeth are involved, but the incisal edge of the teeth is not affected.

Class IV: In this class, there is involvement of the incisal edge along with the interproximal surfaces of anterior teeth.

Class V: There is involvement of the cervical third of lingual or facial surface of tooth.

Class VI: There is wearing away of the occlusal or incisal edge from attrition.

Causes of Tooth Caries

For formation of tooth caries, four things are required which are: the surface of the tooth (enamel/ dentin), bacteria responsible for causing caries, fermentable carbohydrates and time. The time factor involves the sticking of the food to the teeth and production of acid by the bacteria which forms the dental plaque. However, these four factors need not always be present to cause tooth or dental caries because another thing, which is required for development of caries, is a sheltered environment, which promotes the development of cariogenic biofilm. Tooth caries do not always have the same outcome, as it depends and differs from one individual to another, as some people are more vulnerable to tooth caries than others and it also depends on the shape of the teeth, oral hygiene, the amount of saliva and its buffering capacity. Caries can develop on part surface of the tooth which is exposed to the oral cavity, however, not on those areas which are present within the bone.

Caries develop in teeth due to dental plaque (biofilm) present in the teeth, which goes on to mature and becomes cariogenic, i.e. causes decay. There are some types of bacteria present in the biofilm which produce acid when there are fermentable carbohydrates (glucose, fructose, sucrose) present.

Cause of Tooth Caries # 1: Bacteria: Streptococcus mutans, Streptococcus sobrinus and lactobacilli are the commonest bacteria which are present with dental cavities or tooth caries. However, dental plaque contains cariogenic bacteria which are responsible for causing tooth caries; however, they are often present in very less amounts to cause any type of disease unless there is a change in the balance of the environment which can be brought on by frequent or increased sugar consumption, lack of oral hygiene which causes delayed presence of biofilm on the tooth. If this is not treated, then patient experiences pain, infection and even tooth loss. Our mouth has different types of oral bacteria, however, only some of the bacterial species are responsible for causing dental caries such as Lactobacillus and Streptococcus mutans. These bacteria produce increased levels of lactic acid after there is fermentation of dietary sugars along with being resistant to the adverse effects of low pH. All these characteristics are required for cariogenic bacteria. The cementum of surface of the root is more easily demineralized when compared to the enamel surface, which is the reason why wider variety of bacteria results in root caries. The collection of bacteria, such as Lactobacillus acidophilus, Nocardia spp, Actinomyces spp, and Streptococcus mutans occurs around the gums and teeth in a plaque, which is a creamy-colored sticky mass. This plaque acts as a biofilm on the teeth. There are some sites which have a greater tendency for collection of plaque, such as those areas which have a decreased salivary flow as seen in molar fissures. Grooves present on the occlusal surfaces of premolar and molar teeth and interproximal sites act as microscopic retention sites for bacteria of the plaque. Collection of plaque above or below the gingiva is known as supra- gingival or sub-gingival plaque respectively.

Cause of Tooth Caries # 2: Dietary Sugars: The dietary sugars, such as sucrose, glucose and fructose are converted into acids by the bacteria present in a person’s mouth. This conversion takes place via a glycolytic process known as fermentation. When this remains in contact with the tooth, there is demineralization of the teeth from these acids. However, this is a dynamic process, and re-mineralization can also occur if a mouthwash or saliva neutralizes the acid. Dental varnish or fluoride toothpaste helps with the re-mineralization process. If the demineralization process is persistent, then there may be loss of sufficient mineral content so that there is disintegration of soft organic material resulting in formation of a cavity. The effect of these sugars on the progression of tooth caries is termed as cariogenicity. Sucrose is more cariogenic than other sugars.

Cause of Tooth Caries # 3: Exposure: The likelihood or risk of development of tooth caries depends on the frequency of exposure of the teeth to acidic (cariogenic) environments. After consuming any snack or a meal, the oral bacteria metabolize the sugar, which results in an acidic by-product that is responsible for decreasing the pH. As time goes on, the dissolved mineral content of the tooth surface and the buffering capacity of saliva help in getting the pH back to normal. After exposure to the acidic contents, there is dissolution of some parts of the inorganic mineral content present on the surface of the teeth and this can remain dissolved for a couple of hours. As our teeth are vulnerable during these periods of acidic environments, the development of tooth caries heavily depend on the frequency of exposure to acids. If a person’s diet is sufficiently rich in the required carbohydrates, then the carious process of the tooth can start within a few days after the tooth has erupted into the mouth. According to research, if there is introduction or usage of fluoride treatment, then it helps in slowing the carious process. The average time needed for proximal caries to pass through enamel in permanent teeth is around 4 years. As the cementum which encases the surface of the root surface is not as durable as enamel, which envelops the crown, there is rapid progression of root caries when compared to other surfaces. The loss of mineralization and progression of caries on the root surface is twice as faster or more than the caries present in the enamel. Severe cases where a person has a very poor oral hygiene and consumes a diet that is rich in fermentable carbohydrates; there is development of cavities from caries within months of tooth eruption. A good example of this is children who continuously drink milk or sugary drinks from bottles.

Cause of Tooth Caries # 4: Teeth Diseases: Certain teeth disorders/diseases increase the risk for caries and cavities and these are: Molar incisor hypomineralization; a condition caused by systemic factors, such as increased levels of polychlorinated biphenyl (PCB) or dioxins in breast milk, oxygen deprivation at birth, premature birth, certain diseases occurring during the first 3 years of the child, such as diphtheria, mumps, scarlet fever, hypoparathyroidism, measles, malnutrition, malabsorption, chronic respiratory conditions, hypovitaminosis D and untreated or undiagnosed celiac disease.

Amelogenesis imperfecta is a medical condition where there is incomplete or insufficient formation of enamel where the enamel can also fall off a tooth. In these scenarios, the teeth become more vulnerable for development of caries and decay as the enamel is not fully formed to protect the tooth. Most of the times, teeth disorders or diseases is not the main cause for tooth caries.

About 96% of the tooth enamel is made up of minerals.

Cause of Tooth Caries # 5: The Tooth: Demineralization of enamel starts when the pH level is at 5.5. Cementum and dentin are more susceptible for development of caries than enamel as they have lesser mineral content. So, when the root surfaces get exposed due to periodontal disease or gingival recession, then caries tend to develop more rapidly; even if the patient is following good oral hygiene, the tooth becomes susceptible to caries. Development of tooth caries also depends on the anatomy of the tooth. Places where there are more number of deep developmental grooves has more increased likelihood for development of fissure and pit caries. A person also has increased risk for development of tooth caries if he/she has food trapped between their teeth.

Cause of Tooth Caries # 6: Salivary Flow: Decrease in the rate of salivary flow also increases the risk of caries, as the protection mechanism of the saliva is decreased and is not able to counterbalance the acidic environment produced from certain foods. Some medical conditions can decrease the production of the saliva and lead to dry mouth, which in turn makes the teeth more susceptible to caries. Some of these medical conditions include diabetes mellitus, Sjogren’s syndrome, sarcoidosis and diabetes insipidus. Certain medications, such as antidepressants and antihistamines also affected the salivary flow. Stimulants, such as methylamphetamine, also impair the salivary flow which leads to “meth mouth.” Treatment for cancer such as radiation therapy to the neck and head also damages the cells of salivary glands and thus impairs the saliva flow and increases the likelihood of formation of tooth caries.

Cause of Tooth Caries # 7: Other Causes: Tobacco use also increases the risk for tooth caries and also increases the risk for periodontal disease, which causes receding of gingiva, which loses the attachment of gingiva to the teeth leading to more exposure of the root surface of the tooth. This results in root caries as the cementum which envelops the roots of teeth gets de-mineralized more easily by acids. Children who get exposed to secondhand tobacco smoke are also at increased risk for tooth decay/caries. Intrauterine and neonatal exposure to lead also increases the risk of tooth caries/decay. Tooth caries can also be considered as the disease of lower socio-economic status and poverty.

Signs & Symptoms of Tooth Caries

Patient is often not aware that he/she is developing tooth caries. Appearance of a chalky white spot on the tooth’s surface is the earliest sign of development of carious lesion. This indicates an area of enamel which has demineralized which appears as white spot lesion or a “microcavity”. As the demineralization continues, the lesion turns color into brown, which gradually becomes a cavity. This process is reversible before the formation of cavity; however, once the cavity forms, it is not possible to regenerate the lost tooth structure. If the lesion on the tooth appears shiny and dark brown in color, then it means that dental caries were once present, but the process of demineralization has stopped with only a stain left behind. If the decay is active, then the lesion appears dull in appearance and lighter in color.

As there is destruction of enamel and dentin, the cavity becomes more noticeable. Other areas of the tooth that are affected also undergo a color change and become soft to touch. After the decay has passed through enamel, the dentinal tubules, containing the passages to the nerve get exposed which produces pain. This pain can be transient and can temporarily worsen with exposure to cold, heat or sweet drinks and foods. If a tooth gets weakened from extensive internal decay, then it can fracture suddenly under the pressure of normal chewing process. If the decay has progressed so much that the bacteria destroy the pulp tissue present in the tooth center, then this produces pain or toothache, which is more constant and severe and also results in infection and death of the pulp tissue. The affected tooth becomes tender to pressure, but will no longer be sensitive to cold or hot substances.

Patient also experiences foul taste and bad breath from tooth caries. In severe cases, there is spreading of the infection to the adjacent soft tissues. Life-threatening complications such as Ludwig angina and cavernous sinus thrombosis can also occur.

Diagnosis of Tooth Caries

Majority of the tooth cavities can be discovered in its initial stages during routine dental exam. A dental exam also can reveal that the tooth’s surface is soft. Dental x-rays can also detect some cavities, which are not yet visible to the eye

Treatment of Tooth Caries

Treatment of tooth caries, if done on time, helps in preventing cavities and damage to the tooth. Treatment for tooth caries consists of fillings, root canals and crowns.

Patient is first given local anesthetic. The dentists then remove the decayed tooth region using a drill, then fill the cavity with material, such as composite resin, porcelain, silver alloy or gold. Composite resin and porcelain are the fillings that match the closest to the tooth’s natural appearance and color; and for this reason are preferred for front teeth. It is thought that gold and red silver amalgams is stronger and hence are used for posterior teeth. High strength composite resin can be used for posterior teeth also.

If tooth decay/caries is extensive and the remaining tooth structure is very less and causes weakening of the tooth/teeth, then crowns or “caps” are used. If large fillings are used to fill up a big cavity or if the tooth is weak from the loss of its remaining structure, then there is a risk of breaking or fracturing of the tooth. First the weakened or decayed part of the tooth is removed and filled/repaired. Then a crown is fitted over the remaining part of the tooth. Crowns are commonly made of porcelain, gold or porcelain that is attached to metal. Pain killers are prescribed for relief from pain.

It is recommended that a root canal be done if the nerve in a tooth dies from the decay or any injury, before a crown is placed. During root canal, the center of the tooth, which consists of the pulp (blood vessel tissue) and nerve, is removed. The decayed portions of the tooth are also removed. A sealing material is used to fill the roots. The tooth is also filled and a crown is then fitted over the affected tooth.


Treatment for caries tooth usually saves the tooth. It must be noted that early treatment is less painful and is less expensive that treatment of extensive decay in the tooth. You may need numbing medicine like Lidocaine and prescription medicines so as to relive pain during and after the dental treatment. Nitrous oxide with novocaine or other medicines may be preferred in case you are afraid of the dental treatments.

Complications of Tooth Caries

  • Pain and discomfort.
  • Inability to bite down on tooth.
  • Fracture of the tooth.
  • Tooth sensitivity.
  • Tooth abscess.

Prevention of Tooth Caries

Oral Hygiene: It is important to follow a good and proper oral hygiene to prevent tooth caries/decay/cavities. Patient should get regular professional cleaning along with brushing twice a day, and flossing once daily before going to bed. Yearly dental x-rays can be taken to help detect cavity at its early stages, especially in the high risk areas of the mouth.

Diet: Chewy and sticky foods, such as candy, should be avoided and should be eaten as a part of a meal instead of a snack. Snacking should be cut down, as it produces a constant acid supply in the mouth. Frequent sucking on mints and candy and constant sipping of sugary drinks should be avoided.

Fluoride: It is recommended that Fluoride be used to prevent tooth caries. According to research, people who use fluoride supplements or have fluoride in their drinking water have a lesser risk for having tooth caries. If fluoride is ingested during the development of teeth, then the fluoride gets incorporated into the enamel and provides protection against the acid. Topical fluoride in the form of mouthwash or toothpaste can also be used to protect the surface of the teeth.

Dental Sealants: Dental sealants, which are thin plastic-like coatings, can be applied to the molars on their chewing surfaces to prevent cavities. This coating of sealant helps in preventing the buildup of plaque in the deep grooves of the molars. In children, sealants are often used after the eruption of molars. Older individuals can also benefit from dental sealants.

Team PainAssist
Team PainAssist
Written, Edited or Reviewed By: Team PainAssist, Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:May 5, 2022

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