Post and core: the ferrule effect matters more than the post material

The post and core is still placed from habit in every endodontically treated tooth. It is a superseded indication: the post does not reinforce the root, and in some configurations weakens it.

The post has one function: to retain the core material when the remaining coronal structure cannot hold it. It has no reinforcing role, and presenting it as such leads to placing it where it is not needed.

The criterion is the quantity of remaining coronal dentine. With four walls preserved a post is unnecessary; with one or none it becomes necessary. Intermediate situations require case-by-case judgement, considering the anticipated load.

What truly determines prognosis, however, is not the post but the ferrule effect: the band of sound circumferential dentine the crown encircles above the preparation margin.

Evidence converges on a minimum of 1.5 to 2 millimetres in height and about 1 millimetre in thickness, around the entire circumference. Below that, tooth survival falls markedly, whatever post is used.

This inverts the hierarchy of decisions. Before choosing the post material, one must verify whether sufficient ferrule exists; if not, crown lengthening or orthodontic extrusion is considered, or retention of the tooth is reconsidered.

Among materials, fibre posts have an elastic modulus close to dentine and therefore deform with the root under load. Metal posts are far more rigid and concentrate stress at defined points.

The clinical consequence lies in the type of failure, not its frequency. Fibre posts tend to fail by debonding or post fracture, both recoverable; metal posts more often fail with root fracture, which is not.

This is the main reason for their spread: not superior survival, but a failure that leaves the tooth restorable rather than condemning it to extraction.

Preparing the post space deserves attention because it removes dentine in a critical zone. The established rule is to preserve at least 4 to 5 millimetres of apical gutta-percha and not to exceed two thirds of the root length.

Diameter should be kept minimal: a wider post does not retain more but thins the walls. The post must fit the canal, not the canal the post — which is why oval canals are better managed with accessory post techniques or direct build-up.

Adhesive cementation of a fibre post is technically demanding: the canal is deep and narrow, access for curing light is limited, and moisture control is difficult. A dual-cure cement with self-curing capacity is preferable to a purely light-cured one.

In summary: a post is needed only where retention is lacking, the ferrule effect determines prognosis more than the post, and the material is chosen for the type of failure it produces. A tooth without adequate ferrule is not saved by a better post.