Periapical abscess on the lower right first molar

Correct answer: C. Root canal treatment

• A. Antibiotics are ADJUNCTIVE. They are indicated for systemic involvement (fever, malaise, lymphadenopathy), spreading cellulitis, or in an immunocompromised patient — but they never replace removing the source.
• B. Incision and drainage relieves an acute fluctuant swelling but leaves the necrotic pulp — the cause — untreated.
• C. Correct. Definitive treatment of a periapical abscess on a RESTORABLE tooth is removal of the source of infection — ROOT CANAL TREATMENT, beginning with access and drainage through the canal. This eliminates the necrotic pulp tissue and the bacteria driving the periapical inflammation.
• D. Extraction is reserved for a non-restorable tooth; the case gives no indication that the molar cannot be saved.

Correct answer: D. Necrotic pulp

• A. Hematogenous seeding of the periapex is exceedingly rare (anachoresis) and is not the standard mechanism.
• B. Salivary gland infection produces sialadenitis, an entirely separate condition.
• C. A periodontal abscess arises from an existing PERIODONTAL POCKET in a tooth with a VITAL pulp — a different entity, and pulp testing is what distinguishes the two.
• D. Correct. A periapical abscess arises from a NECROTIC PULP. Bacteria and their toxins exit through the apical foramen and provoke acute inflammation in the periapical tissues. The pathway is usually caries, then pulpitis, then necrosis, then periapical involvement.

Note: When facing an endodontic-versus-periodontal abscess question, PULP VITALITY is the deciding test: non-vital points to endodontic origin, vital points to periodontal origin. Combined endo-perio lesions exist and require both therapies.