Introduction
Shaping with stainless-steel hand instruments enlarges the root canal into a smooth, tapered form that irrigants can clean and a root filling can seal. This note covers instrument types, movements, enlargement techniques and the step-back technique (ISO sizes: topic 39; rotary NiTi: topic 43).
Aims of shaping
Shaping aims at a continuously tapering funnel with an apical stop at working length that follows the original canal and leaves the foramen where it was (Schilder's objectives):
- continuous taper: narrowing at every point towards the apex;
- apical stop (apical seat): a definite resistance at working length (WL) – the apical constriction, about 0.5–1 mm short of the radiographic apex – against which the root filling is compacted;
- original path and foramen: curvature kept, foramen in its original position and as small as practical;
- biological: debris and instruments stay inside the canal.
The apical size is set by the master apical file (MAF), the largest file taken to full WL: usually 3 ISO sizes above the initial apical file (IAF, the first file that binds at WL) and at least ISO 25.