Preclinics of Conservative Dental Medicine · MU Sofia
42. Preparation of the root canal system with hand instruments – types, movements, enlargement techniques; step back technique.
Explains hand instrument shaping of the root canal: the aims of a tapering funnel with an apical stop, the design of reamers, K-files, H-files and K-Flex or Flexofile instruments, and the movements used such as reaming, filing, watch-winding and balanced force. It then covers standardised and step-down enlargement and walks through the step-back sequence with its master apical file and recapitulation. A table compares instrument designs, and the note closes with procedural errors such as ledges, zips and perforation.
Topic 42 of 53 in the MU Sofia syllabus for Preclinics of Conservative Dental Medicine (Dental Medicine, Year 3). The free AceMed note covers it in 7 sections, about 879 words (7 min of reading), with 17 flashcards.
In this note
Introduction
Aims of shaping
Hand instruments
Movements
Enlargement techniques
Procedural errors
Key points
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.
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