Which procedural mishap carries the WORST prognosis?

Correct answer: C. Perforation through the furcation

• A. A separated file is well tolerated if the canal was clean, and even when it is not, the prognosis is far better than a furcal perforation.
• B. Transportation straightens the canal and may leave uninstrumented tissue, but it does not breach the periodontal attachment.
• C. CORRECT. A FURCATION perforation is the worst of these because it communicates directly with the periodontal attachment at the crest. Epithelium migrates down the defect, a periodontal pocket forms, and the resulting endodontic-periodontal lesion is extremely difficult to reverse. The more coronal the perforation, the worse the outlook — crestal perforations frequently end in extraction.
• D. A small amount of sealer beyond the apex is usually resorbed and is a minor concern by comparison.

Note: Perforation prognosis by site: apical third (best) > middle third > crestal/furcal (worst). Immediate MTA repair markedly improves any of them.