Post Space Calculator

Recommended post length takes the larger of two thresholds — two-thirds of root length, or root length multiplied by the crown-to-root ratio — and then caps that figure so at least 4mm of apical seal remains, using whichever of the two length rules ends up smaller. Because both thresholds scale directly with root length, a longer root supports a proportionally longer, more retentive post, while a short root sharply limits achievable post length regardless of the other inputs.

It is the minimum thickness of gutta-percha that should remain undisturbed at the root apex after post space preparation, preserving the endodontic seal that keeps bacteria from re-entering the canal system. Removing more gutta-percha than that to fit a longer post risks compromising the apical seal and increasing the chance of reinfection or retreatment.

At least 2mm of sound, circumferential tooth structure above the margin is generally considered the minimum for an adequate ferrule effect. Less than that increases the risk of root fracture and restoration failure under function, independent of how well-designed the post and core are, since the ferrule is what resists lateral forces on the crown.

Only up to a point. The maximum recommended post diameter is capped at one-third of the root's diameter at any level to avoid weakening the canal walls, so while a wider root does permit a proportionally thicker post, the post is deliberately kept narrow relative to the root rather than sized to fill the available space.