When is it appropriate to transition from hand files to nickel-titanium rotary instrumentation during primary endodontic therapy?

• A. Immediately at the start.
• B. After establishing an adequate glide path and assessing canal morphology for safe rotary use.
• C. After obturation.
• D. Only in straight canals.

Answer: (B)

Transition to nickel-titanium rotary instrumentation should come after you have established a smooth, negotiable glide path and have assessed the canal morphology for safe rotary use. A glide path is a continuous tunnel from the canal orifice to the apex that guides rotary files and allows them to follow the natural curvature without scraping against irregular walls. When there’s no glide path, rotary instruments are more prone to creating ledges, transportation, or even separation, especially in curved or constricted canals. Therefore, you first use small hand files to negotiate and patently prepare the canal, confirming working length and cleanliness, and only proceed with rotary instrumentation once the glide path is reliable and the canal anatomy appears suitable for safe rotary shaping. If a canal is too calcified or severely curved, you’d reassess rather than force rotary; this is not limited to straight canals.

Choosing to transition immediately at the start, after obturation, or only in straight canals would bypass the essential safety checks that protect against mishaps and ensure predictable shaping.