ADC - Australian Dental Council Radiographic Interpretation and Diagnosis Questions and Answers

Question 1

An orthopantomogram (OPG) of an asymptomatic 18-year-old reveals a well-defined, corticated, unilocular radiolucency surrounding the crown of an unerupted mandibular third molar. The lesion appears attached at the cementoenamel junction. What is the most likely radiographic diagnosis?

Accepted Answer

Dentigerous Cyst

Answer

A dentigerous (or follicular) cyst is the most common developmental odontogenic cyst and is characteristically associated with the crown of an unerupted or impacted tooth. Radiographically, it presents as a well-defined, unilocular radiolucency with a sclerotic border attached at the cementoenamel junction. A radicular cyst is associated with a non-vital tooth, while ameloblastomas and OKCs, although they can appear in this location, are less common, and OKCs may have a more aggressive growth pattern.

Question 2

Which of the following radiographic features is most suggestive of a benign lesion rather than a malignant one?

Accepted Answer

A well-defined, corticated margin

Answer

Benign, slow-growing lesions typically displace surrounding structures rather than invading them, allowing the body to form a reactive, dense bony border (cortex or sclerosis) around the lesion. This appears as a clear, well-defined white line on a radiograph. Malignant lesions grow rapidly and infiltrate tissue, resulting in ill-defined, invasive borders, a 'moth-eaten' appearance, and destruction of the cortex.

Question 3

A periapical radiograph of a maxillary first molar shows the palatal root superimposed over the distobuccal root. A second radiograph is taken with the X-ray tube head moved more mesially. In this new image, the palatal root now appears distinctly mesial to the distobuccal root. Based on the SLOB rule, what is the buccolingual position of the palatal root?

Accepted Answer

It is lingual (palatal) to the distobuccal root

Answer

The SLOB rule states 'Same Lingual, Opposite Buccal'. The X-ray tube head moved mesially, and the image of the palatal root also moved mesially relative to the distobuccal root. Since the object of interest (palatal root) moved in the 'Same' direction as the tube head, it must be the 'Lingual' (or palatal) object.

Question 4

A routine panoramic radiograph of a 50-year-old asymptomatic male reveals a well-defined, ovoid radiolucency with a sclerotic border, located entirely inferior to the mandibular canal, near the angle of the mandible. What is the most likely diagnosis?

Accepted Answer

Stafne Defect (Static Bone Cavity)

Answer

A Stafne defect has a classic radiographic presentation: a well-defined, corticated radiolucency located below the inferior alveolar canal in the posterior mandible. It is an anatomical depression on the lingual surface of the mandible containing ectopic salivary gland tissue and is considered a developmental anomaly, not a true cyst. Its position inferior to the canal is a key diagnostic feature that helps differentiate it from odontogenic lesions.

Question 5

Which of the following clinical situations presents the strongest justification for using Cone Beam Computed Tomography (CBCT) over conventional two-dimensional radiography for diagnosis and treatment planning?

Accepted Answer

Evaluating the precise three-dimensional position of a horizontally impacted maxillary canine and its relationship to the roots of adjacent incisors

Answer

CBCT provides a three-dimensional view, which is invaluable for assessing complex spatial relationships. For an impacted canine, CBCT can precisely locate the tooth, assess for root resorption of adjacent teeth (which is difficult on 2D films), and determine its proximity to vital structures. This is critical for safe and effective surgical and orthodontic planning. The other options are typically well-managed with conventional radiography like bitewings and periapicals.

ADC - Australian Dental Council Practice Test

ADC - Australian Dental Council Practice Test

ADC - Australian Dental Council Radiographic Interpretation and Diagnosis Questions and Answers