Which post type is LEAST likely to cause root fracture in an endodontically treated tooth?

Correct answer: C. Fiber post

• A. Prefabricated TAPERED metal posts are the highest risk in this group: they act as a WEDGE within the canal, generating high radial stress and the greatest incidence of vertical root fracture.
• B. A cast post and core is CUSTOM-FITTED to the canal, which spreads load better than an ill-fitting prefabricated post, and it remains the choice for a severely flared canal or a markedly angled abutment. But its high rigidity means that when it fails, it commonly fails as a root fracture.
• C. CORRECT. A FIBER POST has a modulus of elasticity close to that of DENTIN (roughly 20 GPa, versus 100-200 GPa for metal posts). Because post and root flex together under load, stress is distributed along the root rather than concentrated at the post tip. When a fiber-post restoration does fail, it tends to fail in a RESTORABLE mode — debonding or post fracture — rather than in the catastrophic, unrestorable vertical root fracture typical of rigid metal posts. Fiber posts are also aesthetic and easier to retrieve for retreatment.
• D. Prefabricated PARALLEL-sided metal posts are more retentive than tapered ones and distribute stress more evenly along their length, but they are still rigid and they require removal of more apical dentin.

Note: These reflect two different eras of thinking. Contemporary evidence favours the fiber post for teeth with adequate remaining structure. The far more important variable than post type is the FERRULE: 1.5-2 mm of sound circumferential dentin above the margin outperforms any post choice.