Tooth decay, also known as caries (, from Latin),The word 'caries' is a mass noun, and is not a plural of 'carie'. is the breakdown of teeth due to acids produced by bacteria. The resulting dental cavities may be many different colors, from yellow to black. Symptoms may include pain and difficulty eating. Complications may include periodontal disease (i.e., inflammation of the tissue around the tooth), tooth loss, infection, or dental abscess formation. Tooth regeneration is a field of ongoing stem cell-based study that aims to find methods to reverse the effects of decay; current treatments are limited to symptom management.
The cause of cavities is acid from bacteria dissolving the hard tissues of the teeth (enamel, dentin, and cementum). The acid is produced by the bacteria when they break down food debris or sugar on the tooth surface. Simple sugars in food are these bacteria's primary energy source, and thus a diet high in simple sugar is a risk factor. If tooth demineralization is greater than tooth remineralization from sources such as saliva, caries results. Risk factors include conditions that result in less saliva, such as diabetes mellitus, Sjögren syndrome, and some medications, including psychostimulants, antihistamines, and antidepressants. Dental caries is also associated with poverty, poor oral hygiene, and receding gums, resulting in gingival recession (i.e., exposure of the roots of the teeth).
Prevention of dental caries includes regular teeth cleanings, a low-sugar diet, and small amounts of regular fluoride exposure. Brushing one's teeth twice daily and flossing between the teeth once daily is recommended. Fluoride may be acquired from water, salt, or toothpaste, among other sources. Treating a mother's dental cavities may decrease the risk in her children by decreasing the number of certain bacteria she may spread to them. Screening can result in earlier detection. Depending on the extent of destruction, various treatments can be used to restore the tooth to proper function, or the tooth may be removed. There is no known method to grow back large amounts of tooth. The availability of treatment is often poor in the developing world, according to the World Health Organization. Paracetamol (acetaminophen) or ibuprofen may be taken for pain.
, approximately 3.6 billion people (48% of the global population) had dental caries in their permanent teeth. The World Health Organization estimates that nearly all adults have dental caries at some point in time. In baby teeth, it affected about 620 million people, or 9.02% of the global population, in 2010. Bagramian and colleagues reported in 2009 that caries had become more common in both children and adults. The disease is most common in the developed world due to greater simple sugar consumption, but less common in the developing world.
Signs and symptoms
A person experiencing caries may not be aware of the disease.Health Promotion Board: Dental Caries , affiliated with the Singapore government. Page accessed August 14, 2006. The earliest sign of a new carious lesion is the appearance of a chalky white spot on the surface of the tooth, indicating an area of demineralization of enamel. This is referred to as a white spot lesion, an incipient carious lesion, or a "micro-cavity".
As the lesion continues to demineralize, it can turn brown but will eventually progress into a cavitation ("cavity"). A lesion that appears dark brown and shiny suggests dental caries were once present, but the demineralization process has stopped, leaving a stain. Active decay is lighter in color and appears dull.Johnson, Clarke. "Biology of the Human Dentition ." Page accessed July 18, 2007.
As the enamel and dentin are destroyed, the cavity becomes more noticeable. The affected areas of the tooth change color and become soft to the touch. Once the decay passes through the enamel, the dentinal tubules, which have passages to the nerve of the tooth, become exposed, resulting in pain that can be transient, temporarily worsening with exposure to heat, cold, or sweet foods and drinks. A tooth weakened by extensive internal decay can sometimes suddenly fracture under normal chewing forces. When the decay has progressed enough to allow the bacteria to overwhelm the pulp tissue in the center of the tooth, a toothache can result, and the pain will become more constant. Death of the pulp tissue and infection are common consequences. The tooth will no longer be sensitive to hot or cold, but can be quite tender to pressure.
Dental caries can also cause bad breath and foul tastes.Tooth Decay, hosted on the New York University Medical Center website. Page accessed August 14, 2006. In highly progressed cases, an infection can spread from the tooth to the surrounding soft tissues. Complications such as cavernous sinus thrombosis and Ludwig angina can be life-threatening.Cavernous Sinus Thrombosis , hosted on WebMD. Page accessed May 25, 2008.Hartmann, Richard W. Ludwig's Angina in Children , hosted on the American Academy of Family Physicians website. Page accessed May 25, 2008.
Cause
Four things are required for caries to form: a tooth surface (enamel or dentin), caries-causing bacteria, fermentable carbohydrates (such as sucrose), and time. This involves adherence of food to the teeth and acid creation by the bacteria that makes up the dental plaque. However, these four criteria are not always enough to cause the disease and a sheltered environment promoting development of a cariogenic biofilm is required. The caries disease process does not have an inevitable outcome, and different individuals will be susceptible to different degrees depending on the shape of their teeth, oral hygiene habits, and the buffering capacity of their saliva. Dental caries can occur on any surface of a tooth that is exposed to the oral cavity, but not the structures that are retained within the bone.
Tooth decay is caused by biofilm (dental plaque) lying on the teeth and maturing to become cariogenic (causing decay). Certain bacteria in the biofilm produce acids, primarily lactic acid, in the presence of fermentable carbohydrates such as sucrose, fructose, and glucose.
Caries occur more often in people from the lower end of the socioeconomic scale than in those from a higher socioeconomic background. This is due to a lack of education about dental care and poor access to professional dental care, which may be expensive.Watt RG, Listl S, Peres MA, Heilmann A, editors. Social inequalities in oral health: from evidence to action . London: International Centre for Oral Health Inequalities Research & Policy; www.icohirp.com
Bacteria
The most common bacteria associated with dental cavities are the mutans streptococci, most prominently Streptococcus mutans and Streptococcus sobrinus, and lactobacilli. However, cariogenic bacteria (the ones that can cause the disease) are present in dental plaque. They are usually in concentrations too low to cause problems unless there is a shift in the balance. Alt URL This is driven by local environmental change, such as frequent sugar intake or inadequate biofilm removal (toothbrushing). If left untreated, the disease can lead to pain, tooth loss and infection.Cavities/tooth decay , hosted on the Mayo Clinic website. Page accessed May 25, 2008.
The mouth contains a wide variety of oral bacteria. Only a few specific bacterial species are believed to cause dental caries: Streptococcus mutans and Lactobacillus species among them. Streptococcus mutans are gram-positive bacteria that constitute biofilms on the surface of teeth. These organisms can produce high levels of lactic acid following fermentation of dietary sugars and are resistant to the adverse effects of low pH, properties essential for cariogenic bacteria. As the cementum of root surfaces is more easily demineralized than enamel surfaces, a wider variety of bacteria can cause root caries, including Lactobacillus acidophilus, Actinomyces spp., Nocardia spp., and Streptococcus mutans. Bacteria collect around the teeth and gums in a sticky, creamy-coloured mass called plaque, which serves as a biofilm. Some sites collect plaque more commonly than others, for example, sites with a low rate of salivary flow (molar fissures). Grooves on the occlusal surfaces of molar and premolar teeth provide microscopic retention sites for plaque bacteria, as do the interproximal sites. Plaque may also collect above or below the gingiva, where it is referred to as supra- or sub-gingival plaque, respectively.
These bacterial strains, most notably S. mutans, can be transmitted to a child from a caretaker's kiss or through feeding pre-masticated food.
Dietary sugars Bacteria in a person's mouth convert glucose, fructose, and most commonly sucrose (table sugar) into acids, mainly lactic acid, through a glycolytic process called fermentation. If left in contact with the tooth, these acids may cause demineralization, which is the dissolution of its mineral content. The process is dynamic, however, as remineralization can also occur if the acid is neutralized by saliva or mouthwash. Fluoride toothpaste or dental varnish may aid remineralization. If demineralization continues over time, enough mineral content may be lost so that the soft organic material left behind disintegrates, forming a cavity or hole. The impact such sugars have on the progress of dental caries is called cariogenicity. Sucrose, although a bound glucose and fructose unit, is more cariogenic than a mixture of equal parts of glucose and fructose. This is due to the bacteria using the energy in the saccharide bond between the glucose and fructose subunits. S.mutans adheres to the biofilm on the tooth by converting sucrose into an extremely adhesive substance called dextran polysaccharide by the enzyme dextran sucranase.Madigan M.T. & Martinko J.M. Brock – Biology of Microorganisms. 11th Ed., 2006, Pearson, USA. pp. 705
Exposure
The frequency with which teeth are exposed to cariogenic (acidic) environments affects the likelihood of caries development. After meals or snacks, the bacteria in the mouth metabolize sugar, resulting in an acidic by-product that decreases pH. With time, the pH returns to normal due to the buffering capacity of saliva and the dissolved mineral content of tooth surfaces. During every exposure to the acidic environment, portions of the inorganic mineral content at the tooth surface dissolve and can remain dissolved for two hours.Dental Caries , hosted on the University of California, Los Angeles School of Dentistry website. Page accessed August 14, 2006. Since teeth are vulnerable during these acidic periods, the development of dental caries relies heavily on the frequency of acid exposure.
The carious process can begin within days of a tooth's erupting into the mouth if the diet is sufficiently rich in suitable carbohydrates. Evidence suggests that the introduction of fluoride treatments has slowed the process.Summit, James B., J. William Robbins, and Richard S. Schwartz. "Fundamentals of Operative Dentistry: A Contemporary Approach." 2nd edition. Carol Stream, Illinois, Quintessence Publishing Co, Inc, 2001, p. 75. . Proximal caries take an average of four years to pass through enamel in permanent teeth. Because the cementum enveloping the root surface is not nearly as durable as the enamel encasing the crown, root caries tend to progress much more rapidly than decay on other surfaces. The progression and loss of mineralization on the root surface is 2.5 times faster than caries in enamel. In very severe cases of very poor oral hygiene and when a person's diet is very rich in fermentable carbohydrates, caries may cause cavities within months of tooth eruption. This can occur, for example, when children continuously drink sugary drinks from baby bottles (see later discussion).
Teeth
Certain diseases and disorders that affect the teeth may increase an individual's risk for cavities.