Which factor most increases the long-term risk of vertical root fracture in an endodontically treated tooth?

Correct answer: B. Placement of a post in the canal

• A. The endodontic treatment itself removes relatively little structure. The dehydration and 'brittleness' of endodontically treated teeth has been substantially overstated — the loss of CORONAL tooth structure to caries and access is the real weakening factor.
• B. CORRECT. A post requires removal of radicular dentin to create space, and under function it acts as a wedge generating tensile stress within the root. Both effects raise fracture risk substantially, and post-related vertical root fracture is typically catastrophic and unrestorable.
• C. A rubber dam protects the tooth and airway and has no bearing on fracture risk.
• D. Pins are placed in coronal dentin and can cause crazing there, but they do not create the radicular wedging stress that drives vertical root fracture.

Note: Current thinking: place a post ONLY when there is insufficient coronal structure to retain a core. The post retains the core; it does not reinforce the root. What actually protects the tooth is a FERRULE — 1.5 to 2 mm of circumferential sound dentin above the margin encircled by the crown. Ferrule matters far more than post material or length.