The Pimple That Comes and Goes

Correct answer: D. Chronic apical abscess with pulp necrosis

• A. Incorrect. A nasopalatine duct cyst is a developmental cyst in the midline anterior maxilla, appearing as a heart-shaped radiolucency between the central incisors. It is unrelated to a molar apex.
• B. Incorrect. A periodontal abscess arises from a periodontal pocket in a tooth with a vital pulp and normal thermal response. This tooth is non-responsive to cold and the tract traces to the apex.
• C. Incorrect. A residual cyst forms from epithelial rests left behind after a tooth is extracted. Tooth #14 is present, so the term cannot apply.
• D. Correct. Pulp necrosis with an associated sinus tract that drains intermittently over a prolonged period, with minimal pain, defines a chronic apical abscess. The gutta-percha tracing confirms the source, which is the single most useful diagnostic step in a draining lesion.

Note: Caries is not the only route to necrosis. A tooth with no restoration and no caries can lose vitality through occlusal trauma, a crack, attrition, or a remote traumatic event. Always trace a sinus tract with gutta-percha before assuming which tooth is responsible.

Correct answer: B. Lymphocytes and plasma cells

• A. Incorrect. Basophils are rare in tissue and are associated with immediate hypersensitivity reactions.
• B. Correct. Chronic inflammation is characterized by mononuclear cells — lymphocytes, plasma cells, and macrophages. The plasma cells produce the antibody that reflects sustained antigenic stimulation from bacteria in the canal system, and this pattern defines a lesion of long duration.
• C. Incorrect. Neutrophils dominate acute inflammation and appear in the first hours to days. They are certainly present within the purulent exudate itself, but they do not characterize a two-year lesion.
• D. Incorrect. Eosinophils are prominent in parasitic infection and allergic disease, not in chronic bacterial periapical inflammation.

Note: Read the question stem carefully. If it asks about the purulent exudate itself, the answer is neutrophils. If it asks about the chronic lesion overall, the answer is lymphocytes and plasma cells.

Correct answer: D. Pulp vitality status

• A. Incorrect. The opposing tooth is relevant to occlusal assessment but is not the first evaluation on a fractured cusp.
• B. Incorrect. Shade selection is a restorative detail addressed after the tooth is confirmed treatable and the material chosen.
• C. Incorrect. Percussion is one component of a full examination but tells you only about the periapical tissues. On its own it does not establish the pulpal status that drives the treatment decision.
• D. Correct. Whether the pulp is vital, inflamed, or necrotic determines the entire treatment pathway — whether the tooth can simply be restored or requires endodontic treatment first. Cold testing with a comparison to a control tooth is the appropriate starting point, alongside assessment of how far subgingivally the fracture extends.

Note: Both are defensible and in practice they are assessed together: pulpal status determines whether endodontic treatment is needed, and the subgingival extent of the fracture determines whether the tooth is restorable at all. If a question offers both, read carefully for whether it emphasizes symptoms or structural loss.

Correct answer: B. External root resorption

• A. Incorrect. Replacement resorption is progressive substitution of root structure by bone following loss of periodontal ligament vitality, typically after avulsion or severe luxation. It causes ankylosis with loss of the ligament space and a high metallic percussion note.
• B. Correct. Sustained pressure from the impacted tooth stimulates clastic activity on the outer root surface. The defect originates externally at the point of contact, producing the concave saucer-shaped radiolucency described. The canal outline remains intact and traceable through the defect.
• C. Incorrect. Physiologic resorption is the normal process by which primary tooth roots are resorbed to permit exfoliation. It does not occur in permanent teeth.
• D. Incorrect. Internal resorption originates within the pulp space and expands outward, producing a balloon-like enlargement of the canal that is symmetrical and centered on the canal itself. The canal outline is lost at the site of the lesion.

Note: A useful radiographic discriminator: shift the horizontal angle and take a second view. An external defect moves relative to the canal; an internal lesion remains centered on the canal in both projections.