Case #7

July 1, 1996
A 26-year-old male visited a general dentist for his annual check-up. Radiographic examination revealed a small radiolucent lesion in the anterior mandible.

A 26-year-old male visited a general dentist for his annual check-up. Radiographic examination revealed a small radiolucent lesion in the anterior mandible.

Joen Iannucci Haring, DDS, MS


The patient was unaware of the lesion in the anterior mandible and denied any history of pain or sensitivity in the involved area. When questioned about trauma to the region, the patient stated that he had sustained an injury to the lower jaw five years earlier.

At the time of the dental visit, the patient appeared to be in a general good state of health. His past medical history included routine childhood diseases, a tonsillectomy, and broken bones as a result of an automobile accident. The patient was not taking any medications at the time of the examination.


The patient`s vital signs were all within normal limits. A physical examination of the head and neck region revealed no enlarged or palpable lymph nodes. No abnormal extraoral findings were identified.

After a thorough intraoral examination, a panoramic radiograph as well as selected periapical and bitewing radiographs were ordered. When the radiographs were reviewed, a solitary radiolucency was discovered on the mandibular anterior periapical film (see radiograph). The radiolucency appeared unilocular with well-defined borders, and it measured approximately 7mm in diameter.

After the radiolucency was identified, the soft tissues of the anterior mandible were re-examined, and the bone was evaluated for expansion. No bony or soft tissue abnormalities were identified. The teeth adjacent to the lesion were carefully examined and pulp tested for vitality. All adjacent teeth pulp tested vital.

When questioned concerning the missing lateral incisor (#26), the patient stated that, following trauma to this area, the lateral incisor was determined to be non-vital and extracted several years earlier.

Clinical diagnosis

Based on the clinical and radiographic information presented, which of the following is the most likely clinical diagnosis?

- radicular cyst

- residual cyst

- ameloblastoma

- odontogenic keratocyst

- lateral periodontal cyst


__ residual cyst


The residual cyst is a common odontogenic cyst. The lesion, as the name residual suggests, is a cyst that remains after a non-vital tooth is extracted. Essentially, this lesion is identical to a radicular cyst [also known as periapical cyst (RDH August 1990) that is left behind following extraction of a non-vital tooth. Similar to the radicular cyst, the lesion`s development is stimulated by the inflammation that occurs secondary to bacterial invasion and death of the dental pulp resulting from caries or trauma.

Clinical features

The residual cyst may occur at any age, and there is no sex predilection. This lesion may be found in any tooth-bearing area involving the extraction of a non-vital tooth. The residual cyst is typically asymptomatic and discovered during radiographic examination. The lesion appears as a persistent radiolucency at the site of a previous tooth extraction.

Radiographic features

The residual cyst appears as a solitary, unilocular radiolucency with a corticated or non-corticated border. The lesion size is usually small, measuring less than one centimeter in diameter. The lamina dura and periodontal ligament space of the teeth adjacent to this lesion appear intact. The residual cyst rarely displaces teeth, destroys roots or perforates cortical bone.

Differential diagnosis

It is difficult, if not impossible, to diagnose a residual cyst from a radiograph alone. The lesion must be surgically removed in order to make a definitive diagnosis. Other lesions that may resemble a residual cyst on a radiograph include the odontogenic keratocyst, lateral periodontal cyst and the ameloblastoma.

Diagnosis and treatment

A history of extraction of a non-vital tooth and histologic examination of the lesion are necessary in order to establish the diagnosis of a residual cyst. The treatment for the residual cyst is surgical removal. The residual cyst, as with all cysts of inflammatory origin, does not recur following removal.

Joen Iannucci Haring, DDS, MS, is an associate professor of clinical dentistry, Section of Diagnostic Services, The Ohio State University College of Dentistry.