Dental OSCE (Objective Structured Clinical Examination) Practice Exam

What is the likely diagnosis for a radiolucency seen behind a permanent second molar when no third molar exists?

1. Radicular cyst

2. Primordial cyst

3. Odontogenic keratocyst

4. Dental abscess

The correct answer is: Primordial cyst

The presence of a radiolucency behind a permanent second molar in the absence of a third molar is suggestive of a primordial cyst. Primordial cysts are odontogenic cysts that arise in place of a tooth that has not developed. They often occur in the location of missed tooth development, which in this case corresponds to the area where a third molar would typically form. This diagnosis is supported by the fact that the radiolucency is positioned in an area normally associated with tooth development. Radicular cysts typically develop at the apex of a non-vital tooth, which wouldn’t align as closely with this situation. An odontogenic keratocyst tends to occur more often in the posterior mandible but is usually associated with overlying teeth, and its presentation would differ in terms of associated symptoms or clinical appearance compared to a primordial cyst. A dental abscess is more commonly associated with clinical findings such as pain or swelling and would typically present as a more defined area of acute infection. In summary, the nature and positioning of the radiolucency imply that it represents a developmental anomaly in the tooth formation process, supporting the diagnosis of a primordial cyst.