A periapical radiograph of a mandibular first molar shows a mesial root in which a single canal leaves the chamber, divides into two canals within the root, and rejoins to exit through ONE apical foramen. This is which Vertucci canal configuration?

Correct answer: B. Type III (1-2-1)

• A. Type IV is 2-2: two entirely separate canals from chamber to two separate apical foramina, the classic mesiobuccal root of a maxillary first molar.
• B. CORRECT. VERTUCCI TYPE III is the 1-2-1 pattern: one canal leaves the pulp chamber, divides into two within the body of the root, and the two rejoin before exiting through a single apical foramen. It is a common configuration in the mesial root of mandibular molars and in maxillary premolars, and it matters clinically because the divided middle portion — including the isthmus between the two canals — harbours tissue and bacteria that instrumentation cannot reach directly.
• C. Type I is a single canal running from chamber to apex without division, most typical of a palatal root or a mandibular incisor with a simple anatomy.
• D. Type V is 1-2: one canal leaves the chamber and divides short of the apex into two SEPARATE foramina — it does not rejoin.

Note: The eight Vertucci types in shorthand: I = 1; II = 2-1; III = 1-2-1; IV = 2-2; V = 1-2; VI = 2-1-2; VII = 1-2-1-2; VIII = 3. For the maxillary first molar remember MB = Type II or IV (the MB2 problem), DB = Type I, palatal = Type I.