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Dental caries are a bacterial infection in the hard tissue of a tooth. It is more commonly known as a cavity or tooth decay.


The bacteria that cause decay survive on the food debris left in our mouths after eating.  When they consume it, they produce an acidic byproduct that eats away at the hard tissue of the tooth allowing the bacteria to penetrate deeper into the tooth.


Cavities typically develop on one of three areas of a tooth: in the pits and fissures of the biting surface, on the smooth surfaces in between teeth where they contact, or along the gum line, usually after root exposure secondary to gum recession. 


In the first instance, without protective sealants, plaque, a combination of food debris and bacteria, can accumulate in the depths of the pits and fissures on the biting surface of the teeth.  As toothbrush bristles are often too wide to reach these areas, the bacteria can degrade the tooth structure rather easily in these regions without being disturbed.  These cavities are diagnosed

during the clinical exam by probing the pits and fissures of the teeth.  When they feel soft and sticky, they are decayed.

The smooth surfaces in between teeth where they contact frequently develop caries when someone doesn't floss, as toothbrush bristles cannot reach in between teeth to clean these areas.  When decay forms here it is called interproximal decay and typically ends up involving the contacting surface of both meeting teeth.  Because these cavities are hidden in between teeth they cannot be diagnosed clinically until they become so large the tooth breaks down around it.  Instead, these cavities are diagnosed with x-rays.


Finally, when the gum tissue recedes, the root surface of the tooth becomes exposed.  The root surface of a tooth is covered in cementum, as opposed to the enamel that covers the tooth structure above the gum line.  The cementum is a much more porous material that is significantly less resilient to decay.   In some cases where patients are developing large amounts of root caries, a prescription toothpaste may be provided to help prevent cavity formation.



To understand when decay is treated you first need to understand the anatomy of a tooth.  There are two hard layers: the enamel and the dentin.  The outer layer, enamel, is similar to a rock; there is no living material in it.  Once the cells that deposit enamel complete their job they die leaving a hard, calcified outer layer.  If bacteria infiltrates this layer and decay it, they cannot actually cause you harm.  In fact, if your hygiene improves, the calcium normally present in your saliva may actually remineralize the softened tooth structure.  Fluoride can also remineralize these areas preventing progression of the caries.


In contrast, finger-like projections of the nerve that supplies the tooth travel within the dentin.  As such, once a cavity reaches the dentin a patient will start to experience symptoms typically of hot, cold and sweet sensitivity.  Similarly, because of the living tissue present in the dentin, a cavity reaching this point can no longer be ignored as remineralization is not sufficient to treat it.  Once decay crosses into the dentin it must be treated with a filling.


In all instances however, the decision to treat or not treat is made on a case-by-case basis.  For example, in a patient with very high rates of decay or a history of fast progression one may be more 

prone to treat the decay in the earlier stages due to the high risk.  In contrast, a patient with a history of nearly no decay and great hygiene may be more likely to be monitored even after the cavities have progressed into the dentin, as long as it remains shallow.



Just as each person varies in appearance, so does each tooth.  Some have deeper grooves than others or more pits.  These "groovier" teeth are much more susceptible to cavity development.


Oral hygiene plays a major role in prevention of caries.  The more plaque accumulates the more bacteria that will be present to demineralize teeth.  As such, the better someone's brushing and flossing habits the less likely decay will develop.


Diet can also play a role.  A diet high in sweets and sugars will provide a better medium for the bacteria that causes decay to flourish.  High acid foods, such as sodas, also erode teeth making them less resilient to decay.


Saliva has high concentrations of calcium that serve to remineralize areas of teeth that have started to decay.  Similarly, there are antimicrobial properties to saliva that serve to help kill the bacteria in someone's mouth.  There are many medications that have the side-effect of reducing someone's salivary flow.  In fact, irrespective of an individual's exact medication list, studies show that a person's salivary flow decreases when they are on a minimum of three medications.  These patients are at a much greater risk of decay. 


Nothing in dentistry lasts forever.  All fillings and treatment can develop new decay, particularly as the margins of the old filling break down.  In fact, the margin of a where tooth and filling meets is significantly less resilient to decay than that of an original solid tooth structure.  As such, it is important to brush and floss to keep your dental treatment as clean as possible to ensure it will last as long as possible.


Unfortunately, often times the biggest contributor to cavity development is someone's oral flora.  We all have bacteria in our mouths.  For some people this bacterial population is benign, whereas others have a much greater percentage of virulent bacteria prone to cavity formation.  As with all things in life, some people are just luckier than others and our oral flora is something we inherit. 



Treating decay is as simple as removing the softened decayed tooth structure with a drill and replacing it with an alternative material that mimics tooth structure.


Now-a-days, composite or white fillings are the usual treatment.  These restorations are functional and esthetic.  However, there are still indications for silver or amalgam restorations.  Most commonly, the preference for amalgam is dictated by the location of the dental caries.  Since composite fillings cannot bond to a tooth in a wet environment, any location where maintaining a dry field during placement of a restoration is not possible prevents placement of a white filling. 


Despite public concern over amalgam restorations, the American Dental Association still endorses them.  In fact, there has not been a single study produced confirming negative medical consequences from the placement or existence of an amalgam restoration in someone's mouth.

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Sometimes fillings are recommended when there isn't any decay.  This is typically in instances when a portion of the natural tooth structure has chipped or broken away either creating an unaesthetic result or undermining the support of the tooth.  These fillings are often referred to as "bondings".  In these circumstances, white or composite fillings are the standard treatment.   Drilling is usually still required, but only minimally to expose a new tooth structure in order to improve the bonding strength of the restoration.



Unfortunately, once decay has crossed into the dentin it will not get any smaller on its own.  At best it may stay small for a few months or even a year, but in most cases it will continue to grow and spread within the tooth at a relatively standard pace. Over time, your decay will get larger requiring at minimum a larger, deeper filling when treatment is finally rendered.  If the decay is left unchecked for extended periods of time, it will eventually involve the nerve in the center of the tooth resulting in the need for a root canal.  Often times, the tooth may break when eating due to how soft it has become.  In the long run, extraction of a tooth may be indicated if the decay is left to become so extensive that the tooth can no longer be restored.

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