ADC - Australian Dental Council Radiographic Interpretation and Diagnosis Questions and Answers — 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?
- Ameloblastoma
- Odontogenic Keratocyst (OKC)
- Dentigerous Cyst (Correct answer)
- Radicular Cyst
Correct answer: Dentigerous Cyst
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?
- A well-defined, corticated margin (Correct answer)
- Ill-defined or ragged borders
- A 'moth-eaten' or permeative appearance of bone
- Evidence of cortical bone destruction and invasion into soft tissue
Correct answer: A well-defined, corticated margin
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?
- It is buccal to the distobuccal root
- Its position cannot be determined with this information
- It is directly in line with the distobuccal root
- It is lingual (palatal) to the distobuccal root (Correct answer)
Correct answer: It is lingual (palatal) to the distobuccal root
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?
- Traumatic Bone Cyst
- Stafne Defect (Static Bone Cavity) (Correct answer)
- Residual Cyst
- Odontogenic Keratocyst (OKC)
Correct answer: Stafne Defect (Static Bone Cavity)
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?
- Evaluating the precise three-dimensional position of a horizontally impacted maxillary canine and its relationship to the roots of adjacent incisors (Correct answer)
- Routine detection of interproximal caries in a patient with a low caries risk
- Generalised assessment of periodontal bone levels for a new patient examination
- Monitoring the healing of a small, uncomplicated periapical lesion following routine endodontic treatment
Correct answer: Evaluating the precise three-dimensional position of a horizontally impacted maxillary canine and its relationship to the roots of adjacent incisors
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.
Question 6: A periapical radiograph of a mandibular incisor shows a diffuse, ill-defined radiolucency at the apex with a loss of the lamina dura. The patient is systemically unwell with a fever and reports severe, spontaneous pain. The tooth is non-vital and extremely tender to percussion. What is the most likely radiographic diagnosis?
- Chronic Periapical Periodontitis (Granuloma)
- Radicular Cyst
- Condensing Osteitis
- Acute Periapical Abscess (Correct answer)
Correct answer: Acute Periapical Abscess
An acute periapical abscess is a rapid-onset infection often accompanied by systemic symptoms. Radiographically, early or acute lesions are characterized by a widening of the PDL space and a diffuse, poorly defined radiolucency as the infection spreads through the cancellous bone without a well-established border. This contrasts with chronic granulomas and cysts, which are slow-growing and typically appear as well-circumscribed radiolucencies. Condensing osteitis is a radiopaque lesion.
ADC - Australian Dental Council Radiographic Interpretation and Diagnosis Questions and Answers
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?