1. Resistance form in endodontics

2. When a GP root filling is being condensed, there is a tendency to be pushed through the apex.
Resistance form is a natural consequence of a tapered canal preparation.

3. Resistance form in endodontics
A canal with parallel walls has no resistance form
A tapered canal shape will help to spread the downward forces to the walls of the canals and lateral canals.

4. Tapered canal shape Vertical condensation Lateral forces No extrusion
Cone fit
Vertical condensation
Lateral forces
No extrusion
Because more force is transmitted laterally, less filling is squeezed through the apex.

5. Parallel walls Vertical condensation Vertical forces Extrusion
Cone fit
Vertical condensation
Vertical forces
Extrusion
There is little resistance to pushing the filling and sealer through the apical constriction.