The first sign of caries is the appearance of a chalky white spot called “white spot lesion” [13], which eventually turns into a cavity exposing the deeper layers. In the interval of time between the appearance of the white spot lesion and the formation of the cavity, decay is still reversible and the lost tooth structure can be regenerated with appropriate measures. If decay is still in progress, the cavity appears light in color and dull in appearance, otherwise dark and shiny suggesting the presence f a lesion that has left a stain.

When decay reaches the dentin, dentinal tubules eventually become exposed. Since dentinal tubules have connections with tooth nerve, their exposure brings about pain which is worsened by heat, cold, foods and drinks. At this point the tooth is extremely fragile and might fracture under the pressure being exerted by normal chewing forces. When bacteria arrive at the pulp, pain reaches its maximum peak and death of the pulp and infection result.

Dental caries can be classified based on their relative localization according to the “G.V. Black Classification” [14], a system developed in the 19th century by Greene Vardiman Black, one of the fathers of modern dentistry, and still in use today. Dental caries might also appear in specific patterns, like for example the “rampant caries”, characterized by the appearance of points of decay on multiple teeth adjacent to each other.

Caries complications include bad breath, foul tastes and the spreading of the infection to the surrounding tissues, which can ultimately result in serious conditions such as cavernous sinus thrombosis and Ludwig angina.

Before performing the diagnosis of dental caries, it is useful to carry out a thorough assessment based on patient history, clinical examination, nutritional/salivary analysis and radiographic evaluation, to make a reasonable appraisal of the risks to which the patient is exposed. The primary diagnosis is undoubtedly represented by the visual-tactile examination using a good light source, a dental mirror and the explorer, particularly useful for detecting white spots, pits/fissures of caries [15] and other signs of carious structures. The use of explorer is very much advised against, because the explorer sharps tips and the probing process can easily cause fractures and cavitations on incipient lesions and might help the spread of pathogens in the mouth.

If there is a high degree of demineralization, it is possible to localize dental caries with radiography. This procedure is particularly useful when it comes to detect proximal or occlusal caries [16], frequently gone undetected with visual examination. Lasers too are largely used in dental diagnosis, especially for detecting decay between teeth (interproximal decay). Dental caries detection can also be performed by using dies, which help carry out both a quantitative and a qualitative analysis, although the stains left by the dies might help bacterial penetration.

The treatment of dental caries largely depends on the state of progress of tooth decay. If decay is at its early stages and has touched just the surface of the tooth, its further progress might be prevented by applying fluoride-based pastes or varnishes to the area concerned. Fluoride protects teeth by strengthening enamel, making them more resistant to acid and helping re-mineralization.

If decay has already worn away enamel and caused the formation of a cavity, the damage can be repaired by removing the decayed tooth part and replacing it with a filling or a crown. Silver alloys, gold, porcelain and composite resins are among the most used materials by dentists. If decay hasn’t stopped at the enamel, but has actually reached the pulp at the root, the pulp might be removed and replaced by an artificial one in a procedure known as “root canal treatment.”

In the most serious cases, where the damage has reached such an extent that it is no longer possible to repair the tooth, this can be completely removed to avoid the occurrence of additional complications such as the spread of infections to nearby teeth. Tooth removal can also be preferred in other circumstances, like the cases of limited budget from the side of the patient who cannot afford the expenditures for restoring the damaged tooth.

The prognosis of dental caries largely depends of the health of the patient, his/her oral hygiene practices and the extent of the caries itself. If the caries is limited to minor damages like superficial holes, reversing the decaying process is possible through small dental interventions and a better hygiene procedures. If the damage is much more significant, with the addition of the first signs of infections, tooth removal and infections treatment have to be considered.

Dental caries is caused by specific types of bacteria, which characterize themselves for their ability to use fermentable carbohydrates as energy source turning them in acids. Among the bacterial most responsible for dental caries there are the species of the genera Streptococcus and Lactobacillus, which produce lactic acid through fermentation and are resistant to low pH levels.

Teeth are in a constant back-and-forth state of mineralization/demineralization. When the mouth pH goes below 5.5, like for example after a meal, demineralization proceeds much faster than mineralization, and the outer tooth layer begins to erode and dissolve, causing the formation of a cavity with an inward pattern. If left untreated, the cavity will eventually reach the soft and deeper organic tooth layer and tooth decay begins.

The outcome of the dental caries development does not depend just on the presence of bacteria and fermentable carbohydrates, but also on other factors such as the shape of teeth, oral hygiene habits and saliva buffering capacity. Acid demineralization occurs when bacterial plaque is left untouched on the tooth surface, in plaque-retentive areas such as the spots between teeth or inside the pits and grooves of teeth surface, where brushing is very difficult. This is the reason why most of the caries develops on molars and premolars, notoriously difficult to reach with toothbrush. Sometime acid demineralization occurs in the absence of bacteria, such as in the presence of particular foods or during systemic complications like bulimia, stomach difficulties or vomiting. In this case tooth demineralization is called erosion.

Tooth decay might also be caused by reduced salivary flow rate, when saliva buffering capability is impaired and unable to counterbalance the acid conditions created by certain foods. This might be due to particular conditions, such as in complications with salivary glands like Sjogren's syndrome, the intake of particular drugs, like antihistamine and antidepressants, or particular medical procedures like radiation therapy. The use of tobacco can also increase the risk of caries formation, particularly certain brands of smokeless tobacco containing high sugar content [2] and cause gingival recession, which leads to an increased exposure of root surface to the external mouth chemical environment. This can easily result in tooth decay, since cemetum covering the teeth roots is much more easily to de-mineralize than enamel covering the teeth upper part.

It has been estimated that 36% of the population worldwide suffers of dental caries [3] and a percentage varying between 29% to 59% of adult over fifty years of age have experienced tooth decay at least once in their life. The disease is particular frequent in poorer countries, like in Latin America, Middle East and China, due to the low standards of oral hygiene. In the developed contraries, instead, better oral hygiene practices and treatments are responsible for the steady decrease of dental caries cases.

Despite the better hygiene conditions, developed countries experience a marked disparity in dental caries distribution, with the disease being especially frequent in the younger population. In the United States and Europe twenty percent of the children suffers from the sixty to eighty percent of all dental caries cases [4]. Worldwide, tooth decay affects 620 million children, or nearly 9% of the entire world population. The only exception is represented by Australia, Nepal and Sweden, where children dental care is provided free of charge by the state.

Dental caries pathophysiology is different according to the external tooth layer considered: enamel, dentin or cementum. Enemal caries is the first to occur, after the production of a substantial quantity of acid by bacteria laying all over the tooth surface. Bacterial acid begins to dematerialize enamel in a cone-shaped patter following the direction of the enamel rods, the structural units of this tooth layer [5]. As demineralization and the decay process move inwards, several distinctive zones begin to appear, easily visible with the light microscope [6], which underline different demineralization states in a gradual pattern of mineral loss: the translucent zone, dark zone, body of lesion, and surface zone.

The translucent zone is the first to emerge, soon after the appearance of a white spot with a fissure underneath as first demineralization point. Microdissection and chemical analysis reveal a 1.2% mineral loss in compounds rich in magnesium and carbonate [7]. Afterwards, the dark zone appears over the translucent one, characterized by a further demineralization with a 6% of mineral loss. The dark zone is followed by the body of the lesion, the real core of caries, with a mineral loss over 24%. The surface zone, instead, appears as a 30µ thick layer with the highest degree of mineralization that seems to contradicts the gradual decrease of mineral concentration seen so far. The reason of this greater resistance is the active re-precipitation of minerals coming from the bacterial plaque above and the rotten layers below soon after mineral dissolution, something which undoubtedly underlines the dynamic nature of dental decay. The surface zone ultimately breaks, exposing the rotting material below.

The caries of dentin too appears as a cone-shaped and brownish pattern moving inwards, which follows the direction of dentinal tubules radiating outward from the pulp chamber [8]. The relative orientation of the dentin decaying formation depends of the position of the caries itself. If the caries emerges on the upper part of the tooth, the decaying formation in the dentin will have the point towards the base of the tooth. On the opposite, if the caries emerges on the side of the tooth, the decay cone-shaped formation in the dentin will have the point towards the surface of the tooth.

On the contrary to enamel, the dentil does have active cells, the odontoblasts, residing at the border with the pulp. Odontoblasts offer a biological response against caries, whose defense mechanism include the formation of a sclerotic and tertiary dentin [9]. The formation of sclerotic dentin is due to the mineralization of the surrounding tubules [10], whose purpose is to slow down bacterial progression. The process is fed by the very minerals released after acid demineralization of the upper layers due to bacteria. It is believed that the fluids forming in dentin caries are responsible for triggering the pain receptors in the pulp [11]. Since sclerotic dentin prevents these fluids from entering the pulp, dental caries formation in dentin might often go undetected. If the response does not limit itself to mineralization, but actually brings about the formation of new dentinal tissue, this new dentin is called tertiary dentin. The tissue is produced towards and at the expense of the pulp, whose size decreases accordingly. Tertiary dentin is subdivided by the presence or absence of odontoblasts [12], if there are odontoblasts which survive after the new tissue formation, the dentin is called “reactionary”, otherwise it is called “reparative.”

Cementum caries is much easier to occur than enamel or dentin caries, because of the higher fragility of this layer. The frequency of this type of caries increases with age, as direct result of gingival recession due to aging. Since cementum caries is strictly linked to gums state, this is frequently a chronic condition.

Oral hygiene is paramount in preventing tooth decay, as it helps remove and prevent bacterial plaque formation. Among the oral hygiene measures suggested there is the use of toothbrushes, interdental brushes, water picks and mouthwashes.

Decay can also be prevented by making some dietary changes, especially those carried out to reduce sugar supply which might help bacterial acid production. A measure particularly advised in this regard is the reduction of snack consumption, as snack creates a continuous sugar supply which is not neutralized by a subsequent and opportune tooth wash.

Other measures for preventing tooth decay include the use of dental sealants, which avoid bacterial plaque formation in the difficult-to-reach pits and fissures, as well as calcium intake, which is particularly recommended to prevent future cases of demineralization [17]. Vaccine might also be employed in dental caries prevention, although their use is still under development [18].

Bacteria are normally found in the mouth, especially on the teeth surface. They use the food debris left after a meal to get the needed energy source, producing acids as final product of their energetic metabolism. Together with acids, food debris and saliva, bacteria form a sticky and creamy-colored substance on teeth surface called plaque, which if not removed through washing permanently adheres to teeth surface, especially on the hidden grooves of molars and premolars which provide the ideal retention sites for plaque formation. In time, plaques begin to harden and turn into a hard substance called tartar, usually found on the back molars at the edges between teeth and gum.

The acids produced by bacteria tend to breakdown the outer layers of teeth (enamel, dentin and cementum), but this tendency is counterbalanced by the mineral buildup from other sources like saliva. In normal circumstances there is an steady equilibrium between these two opposite processes, which can be broken in favor of the first in certain circumstances. One of this circumstances is the pH drop after a meal. When enamel is damaged, a cavity is created, which ends up becoming a useful way for bacteria in the inner tooth parts. When this happens, a dental caries (or tooth decay) begins.

The cavities can have different colors varying from yellow to black [1], and symptoms include pain and difficulty to eat, which can finally lead to complications such as inflammation, absence or tooth loss. There is no known way to grow back the decayed tooth parts, thus prevention is paramount. Dental caries is particularly frequent in poor countries, where poverty, poor oral hygiene and the absence of treatment and prevention lead to the exposure of tooth decay.

Dental caries (or tooth decay) is the decay of teeth due to the activity of bacteria lying all over the teeth surface. The acids produced by bacteria tend to breakdown the outer layers known as enamel, dentin and cementum, and when the enamel is damaged, cavities are created, which end up becoming a useful way for bacteria in the inner tooth parts. As decay moves inwards, it appears with a cone-shaped patter which follows the lines of the tooth structural units.

The treatment of dental caries largely depends on the state of progress of tooth decay itself. If the decay involves just the surface of the tooth, it can be repaired by applying fluoride-based pastes or varnishes. If the decay has reached the deeper tooth parts, other procedures might be needed, which mainly involve the replacement of the decayed parts with fillings or crowns mostly made of silver alloys, gold, porcelain and composite resins. If the damage is so extended to be no longer repairable, tooth removal should be performed. Although, treating dental caries might be a painful experience for the patient, it can be prevented with the right oral hygiene routine.

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