A cavity is also called tooth decay, or dental caries. Cariology is the study of dental caries.  So what is a cavity?  What does decay in the tooth mean?  To understand let’s go over the basis components of a tooth.


A typical tooth consists of three layers: enamel, dentin, and pulp.  Enamel is the hard dense layer on the outermost surface of the tooth.  Dentin is a thinner layer underneath the enamel.   And directly underneath the dentin is the pulp, where it consists of live tissues, blood, and nerve.


A cavity is a bacterial infection that causes initial demineralization and subsequent enamel destruction.  Initially bacteria on the tooth ferments food debris, thereby producing acid.  If demineralization is greater than that of the mineralization process from calcium and fluoride in toothpastes and/or topical application in the dental office, the hard tissues (enamel) break down and the result is dental caries (cavities, decay, carious lesions).  Unfortunately dental caries is one of the most common diseases in the world.


Sometimes a patient with a cavity may not be aware the disease is present. Initial signs of carious lesion is a bright chalky white spot on the hard surface of the tooth. If the lesion continues to demineralize, the white spot can turn brown or black, and eventually turn into a cavitation, or cavity, or “hole” that extends beyond the enamel and into the dentin.  This process may be reversible via reminerlization processes before the cavity forms.  Once a full fledged cavity forms (cavitiaton or lost tooth structure) is gone and cannot be formed again.

If more enamel and dentin are further destroyed, the tooth may change to a darker brownish color. It may be softer to touch, and if the caries extends into the dentin via the dentinal tubules, one may feel: sensitivity to heat, cold, and/or sweet foods and drinks.  If there is extensive decay sometimes part of the tooth can fracture.  If the decay is sufficient enough to allow bacteria to infiltrate the nerve (pulp) there may be constant pain.  Given enough time, the pain may go away but lead to pulpal tissue death and necrosis with infection.  The tooth however may be sore and tender to touch and pressure.

Halitosis (bad breath) and foul tastes may be present.  In severe cases the infection from the cavity may spread to surrounding soft tissues and cause hard tissue destruction.  In rare causes the infection may be life threatening (cavernous sinus thrombosis, Ludwig’s angina).


In order for caries to form, four factors must be present: tooth surface via enamel or dentin, bacteria that is shown to cause dental caries, carbohydrate that bacteria can ferment, and time for the prior three substrates to interact.  It should be noted though that an individual possessing all known four criteria do not always develop dental decay.  Other variable factors also influence the outcome of dental caries: oral hygiene habits, saliva’s buffering capacity, and the shape of the tooth as small grooves and within the tooth can promote carbohydrate build up.

Bacteria that has been shown to cause dental cavities are Streptococcus mutans, Streptococcus sobrinus, and lactobacilli.

Dental caries disease requires said bacteria to produce acid via fermentable carbohydrates (ie. glucose, fructose, and sucrose).

Saliva also plays a role in that it enhances the tooth’s remineralization process as it undergoes a continuous demineralization and remineralization reaction.  A person with decreased salivary flow (ie. cancer patients who have underwent radiation therapy, people with autoimmune disorders like Sjogren’s syndrome) is prone to dental caries as the pH of the tooth surface decrease to 5.5 or lower.

The resulting dental caries disease results when demineralization of the enamel and/or dentin by the bacteria is greater than that of the remineralization abilities by fluoride and saliva. A tooth’s surface location also plays a role in that areas easier to clean by toothbrush and floss are less prone to cavities (i.e. facial and lingual surfaces) and areas more difficult to clean are more prone (ie. interproximal surfaces, pits, and fissures).


How caries presents itself can vary greatly. In its beginning stages it may look like a small bright white chalk like discoloration, and over time it can change into a cavitation.  Caries are sometimes visible in the mouth, and at which may look look dark brown and black.  If a cavity is large enough part of the tooth may be broken off.  X-rays are also used to detect caries for areas not as visible (interproximal surfaces of the teeth, area between the teeth).  When the dentist is removing caries, a disclosing solution may be used to visibly mark the cavity.  During the dental examination the dentist will do a visual inspection of all visible surfaces of the tooth with a bright source of light.  Via dental mirror and dental explorer, tactile inspection will also help assist caries detection.  X-rays are consulted when necessary to help detect cavities otherwise not visible.  Blowing air on the tooth’s surfaces will remove moisture, which allows the dentist to view demineralized enamel; the dental explorer sharp end is used to tactile feel for cavitation.

It should be noted that cavities in the tooth’s pit and fissures (deep grooves) may not be visible to the naked eye.  Such caries may only be visible on x-rays.


Dr. G.V. Black is one of the founders of modern dentistry.  He developed in the late 1800s a classification of dental caries still widely used today:

  • Class I caries – Occlusal decay, including affecting the tooth’s pits and fissures
  • Class II caries – Interproximal surfaces of posterior dentition (mesial and distal surfaces)
  • Class III caries – Interproximal surfaces of anterior teeth not involving the incisal edge
  • Class IV caries – Interproximal surfaces of anterior teeth involving the incisal edge
  • Class V caries – Caries involving the base 1/3 gingival and cervical surfaces of posterior and anterior teeth on the facial or lingual parts.
  • Class VI caries – Caries involving only the cusp tips of bicuspids (canines), premolars, and molars

Other types of caries include “baby bottle decay” or “baby bottle caries.”  Also know as “Bottle Rot” this a type of extensive generalized decay on infants and young children and toddlers on”Bottle their primary teeth (baby, or deciduous dentition).  Such rampant caries are due to children falling asleep with sweet liquids in the bottles, such as milk or juice.

“Rampant caries” is generalized severe decay on multiple teeth.  Rampant caries may be present on patients who have undergone chemotherapy and radiation treatment (radiation induced decay), xerostomia (dry mouth), poor home care and poor oral hygiene, lack of access to dental care, and drug use (either induced from recreational drugs or prescribed medications).


How your dentist treats caries depends on whether the carious lesion is noncavitated or cavitated.

If the carious lesion is noncavitated, the clinical exam needs to assess if the decay is arrested (cavity is not getting bigger) or if the decay is active (cavity is getting bigger).   With a noncavitated arrested lesion, attempts may be made to remineralize the tooth via improved oral hygiene habits and topical fluoride application.  If the noncavitated lesion is active, then operative treatment may be required depending on how extensive the decay is and if dentin is involved.  In some cases tooth extraction is also done if one does not want to restore the tooth due to financial expenses, difficult access, or if the tooth may be problematic later.

If the carious lesion is cavitated and has dentinal involvement, remineralizing the tooth may not be possible and operative treatment is usually indicated, such as fillings or crowns depending on how extensive the decay is. If the decay is extensive to the point where a restoration cannot predictably restore the tooth, extraction of the tooth may be required, with eventual replacement of the tooth by dental implants or bridge.

Local anesthetic is usually used for patient comfort, and prior to placement of the restoration, all decay needs to be removed to prevent the caries from further growth.  However, there are instances when a tiny amount of decay may be intentionally left if the area can be sufficiently enclosed to prevent the bacteria from accessing carbohydrates.  If the carious lesions extends beyond the dentin and has pulpal involvement, treatment via root canal and crowns may be required.

Unfortunately once a part of the tooth is destroyed via cavitation or fracture, enamel and dentin can not regenerate, and treatment may then be needed.

Topical fluoride, often applied during the 6 month checkup and cleaning appointment, can be used to enhance remineralization.

If you have any questions about cavities and tooth decay, contact us at (425) 614-1600 today.

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