Routine radiographic survey

Correct answer: C. External resorption

• A. Physiologic resorption is the programmed loss of primary tooth roots preceding exfoliation. It is not applicable to a permanent third molar.
• B. Idiopathic cervical (invasive) resorption starts just apical to the epithelial attachment at the CEJ, not along the mid-root against a follicle.
• C. CORRECT. The defect originates on the OUTER root surface, at the interface with the follicle and adjacent tooth, and eats inward. External resorption is clast-cell activity initiated in the periodontal ligament or follicle, most often driven by pressure — impaction against a neighbouring tooth, an expanding cyst, or an orthodontic force. Radiographically the outline of the root is ragged and the canal remains a normally-traceable line running THROUGH the defect.
• D. Internal resorption begins in the PULP and balloons outward. Its signature is a smooth, oval, well-circumscribed radiolucency that is CONTINUOUS with the canal, with the canal outline lost at the level of the lesion. It requires vital, chronically inflamed pulp tissue.

Note: The quick discriminator: trace the canal. If you can follow it through the lesion, the resorption is EXTERNAL. If the canal outline disappears into the lesion, it is INTERNAL.

Correct answer: A. A foreign body

• A. CORRECT. Metallic foreign bodies are recognised by density and by SHAPE: they are more radiopaque than any bone or tooth structure, have sharply defined geometric or manufactured outlines, and ignore anatomic boundaries. Broken instrument fragments, retained root-canal materials, bullet or shrapnel fragments, and surgical wire all present this way.
• B. Condensing osteitis is a diffuse sclerotic bone response to chronic low-grade pulpal inflammation, always centred on the apex of a tooth with a carious or restored crown, and it blends into the surrounding trabeculae.
• C. Idiopathic osteosclerosis (dense bone island) is a well-defined but bone-density opacity with no inflammatory source and no capsule, usually in the premolar-molar mandible.
• D. A complex odontoma is a disorganised mass of enamel, dentine and cementum. It has a soft-tissue capsule and a thin radiolucent rim, and its density matches tooth structure rather than metal.

Correct answer: A. Amalgam tattoo

• A. CORRECT. Amalgam tattoo is metal debris driven into the mucosa during restorative or surgical procedures. It is flat, blue-grey to black, asymptomatic, does not blanch, and does not change over time. Larger particles are visible on a radiograph as fine radiopaque flecks — which is exactly the correlation being tested here. When particles are radiographically demonstrable, biopsy is unnecessary.
• B. Oral melanoma is a genuine concern for any pigmented lesion, but it is typically raised or ulcerated, irregular and asymmetric in outline, and enlarges. A flat blue-grey macule with radiopaque flecks in a restored area does not fit.
• C. A varix is a dilated vein, most often on the ventral tongue or lip, which is compressible and BLANCHES on diascopy.
• D. An oral melanotic macule is brown rather than blue-grey, arises from melanin rather than metal, and has no radiographic correlate.

Note: Rule of thumb: a pigmented lesion with matching radiopacities is an amalgam tattoo. A pigmented lesion with NO radiographic correlate that is growing, raised or irregular gets a biopsy.

Correct answer: D. The mental foramen

• A. A traumatic (simple) bone cyst is a larger, irregular lucency that characteristically scallops upward between the roots of vital teeth. It is not a small round apical radiolucency.
• B. A lateral periodontal cyst sits along the LATERAL root surface, most often between mandibular canine and premolar, and is typically a well-corticated teardrop shape rather than a round apical lucency.
• C. A periapical granuloma requires a NON-VITAL pulp. This tooth is vital and caries-free, so an inflammatory periapical lesion cannot be the explanation.
• D. CORRECT. The mental foramen is a normal anatomic radiolucency projected in the mandibular premolar region, usually between or near the apices of #28 and #29. It can convincingly mimic periapical pathosis. The two things that settle it are PULP VITALITY — normal response to cold excludes a lesion of endodontic origin — and shifting the horizontal angulation, which moves the foramen relative to the apex while a true periapical lesion stays attached.

Correct answer: C. A processing or handling artifact from bending the receptor

• A. A dentinal or root fracture line stays confined to the tooth, follows the long axis or an oblique plane within it, and does not run out across the bone and beyond the image.
• B. Cervical burnout is a diffuse, ill-defined radiolucent zone at the CEJ between the enamel edge and the alveolar crest, caused by the abrupt change in absorbing thickness. It is a triangular shadow, not a linear band.
• C. CORRECT. A sharp, linear or crescentic radiolucent band that crosses anatomic structures without respecting them is an ARTIFACT. Bending or creasing the film or a flexible phosphor plate cracks the emulsion and produces exactly this thin dark line. It is recognised by the fact that it ignores anatomy — a real structure has to belong to something.
• D. A cone-cut is a clear-cut CURVED border with total absence of exposure beyond it, produced when the beam misses part of the receptor. It appears as a blank region, not a line.

Note: The habit worth building: any finding that crosses anatomic boundaries as though they weren't there is an artifact until proven otherwise. Retake rather than interpret.