What Causes Oral Cysts?
Oral cysts typically form when epithelium begins multiplying in the jaw around a tooth root or over the crown of a wisdom tooth that has not yet emerged. Epithelial cells normally make up part of the skin, mucous membranes and periodontal ligament (the ligament that helps hold a tooth in its socket). These cysts are filled with clear serum. However, they may fill up with pus if the cyst is infected. Oral cysts in the mucous membranes lining the inside of the mouth (mucoceles) are a little different. They usually have an outer shell made up of granulation tissue (collagen-rich scar tissue) rather than epithelium. The fluid inside these cysts is typically mucous from saliva.
What Causes Mucoceles to Form?
Mucous-filled oral cysts on the tongue, inside the cheeks, on the lips, and elsewhere in the lining of the mouth are usually the result of some type of trauma or irritation. For example, if you accidentally bit the inside of your cheek where a small salivary gland is located, a cyst may form in the damaged tissue as a result of mucous accumulation. Oral piercings and persistent chewing of the lips as a nervous habit have also been linked to the formation of mucoceles.
Why Do Oral Cysts Form Around Wisdom Teeth?
Wisdom teeth that have not emerged into the mouth are often the site of inflammation in the overlying gums. A partly-erupted wisdom tooth may be covered with a flap of gum tissue. This area is difficult to clean and may become contaminated with rotting food debris and bacteria. This chronic irritation and low-level infection overstimulates the epithelial cells in the area and leads to the formation of a cyst. This kind of cyst may form over the crown of the third molar or around the base of the tooth, deep in the jaw. These "dentigerous" dental cysts are fairly rare, so there’s no way to tell if a particular wisdom tooth will develop a cyst.
Why Do Oral Cysts Form Around Decayed Teeth?
If a tooth has become infected or died, the interior where the living pulp used to be is often filled with bacteria and pus. This infectious material can leak out into the "periapical" region through the tooth root and infect the tooth socket and nearby gums. A periapical cyst is created as a byproduct of the body’s immune response to infection in the tooth root and surrounding tissue. The lump starts out as a granuloma – a ball of fibrous collagen laden tissue with a healthy blood supply that brings immune system cells to the area to fight off infection. This granuloma provides the right environment for "epithelial rests of Malassez" cells that played a role in the initial formation of the tooth to begin multiplying again, forming a round cyst. As the cyst grows, the inner layers of epithelial cells no longer have access to the blood supply that would keep them alive. They die off and liquefy. This leaves a shell or sac of epithelium forming the lining of the cyst and a center filled with fluid.
Other Causes of Dental Cysts
There are rarer types of oral cysts that can form due to many other factors including:
- A genetic disorder called Gorlin Syndrome that also increases the risk of basal cell skin cancer
- Abnormal development of dental tissue in infants and children when things go wrong with normal tooth growth
- Trauma leading to a blood clot in the jaw bone
- Cyst remnants left behind after attempted removal (residual cysts)
The underlying cause is generally determined when the type of cyst is identified with radiography and a biopsy. A wide range of non-malignant oral growths may be referred to as either cysts, tumors or lesions depending on the characteristics of the particular growth. If your dentist or doctor diagnoses you with an oral cyst, be sure to get more details about what kind it is as well as what may have caused it. Sometimes, dental cysts form for no apparent reason. However, knowing what caused your cyst may help you better understand the purpose and results of treatment.