A dental cyst is a fluid-filled sac, usually lined with epithelial tissue, that forms within the jawbone or the soft tissues of the mouth. These growths are typically benign but can slowly expand, causing pressure on surrounding structures like teeth and bone. Since they often begin without noticeable symptoms, cysts are frequently discovered during routine dental X-rays. Understanding their origin is important for effective treatment, as their causes fall into distinct categories.
Cysts Resulting from Infection and Inflammation
The most common type of dental cyst is the periapical cyst (or radicular cyst), which forms as a direct consequence of long-term infection. This process begins when bacteria from deep tooth decay, an untreated cavity, or a failed root canal reach the tooth’s inner pulp chamber. Once the pulp tissue dies, bacteria and toxins travel down the root canal to the tip of the root, called the apex.
The body’s immune system attempts to contain this infection at the root tip, leading to chronic inflammation and the formation of a periapical granuloma. Within the jawbone are dormant cells called the epithelial rests of Malassez, which are remnants from tooth development. These cells become stimulated by inflammatory signals and begin to multiply, forming an epithelial lining around the infected area.
As these cells proliferate and line the cavity, fluid is secreted into the space, often containing cellular debris. This fluid accumulation creates internal pressure, causing the cyst to slowly expand and resorb the surrounding bone tissue. The resulting fluid-filled, epithelial-lined sac is the mature periapical cyst, which can grow for months or years without causing pain until it presses on nerves or surrounding structures.
Cysts Originating from Tooth Development
A separate category of cysts arises not from infection but from remnants left over during the process of tooth formation, known as odontogenesis. These developmental cysts form when epithelial cells responsible for building the tooth structure become trapped in the jaw and are later stimulated to grow. This stimulation causes the cells to proliferate and form a fluid-filled lesion, independent of active dental decay.
The dentigerous cyst (or follicular cyst) is the second most prevalent type and is a prime example of a developmental cyst. It forms around the crown of an unerupted or impacted tooth, most commonly wisdom teeth or maxillary canines. The cyst originates when fluid accumulates between the crown and the reduced enamel epithelium, the layer of cells covering the tooth crown before it erupts.
Another type is the odontogenic keratocyst (OKC), which has a developmental origin from the epithelial remnants of the dental lamina, known as the rests of Serres. The OKC is known for its aggressive growth and high rate of recurrence, often growing by epithelial proliferation rather than simple fluid accumulation. Its formation is sometimes linked to specific genetic syndromes, indicating a defect in cellular control.
Cysts Linked to Gum Tissue and Trauma
A residual cyst is an inflammatory cyst that remains in the jawbone after the tooth that caused the initial periapical infection has been extracted. It occurs because the epithelial lining of the original radicular cyst was not completely removed during the tooth extraction, allowing the sac to persist and continue growing in the now toothless area.
The lateral periodontal cyst is an uncommon developmental lesion that forms along the side of the root of a tooth that is otherwise healthy and vital. Its origin is thought to be from the epithelial rests of Malassez or the rests of Serres. Unlike the infectious periapical cyst, it is not triggered by a dying tooth pulp. These cysts are most frequently found in the mandibular canine and premolar regions of adults.
Physical trauma to the mouth or face can be a direct or indirect cause of cyst formation. A severe injury can damage the blood supply to a tooth, causing the pulp to die and initiating the infectious pathway leading to a periapical cyst. Trauma can also stimulate dormant epithelial remnants in the jaw to begin proliferation, which may lead to cyst formation.