Present status and future directions: Canal shaping

Abstract

This narrative review will focus on the evolution, present and future of engine-driven root canal preparation. Root canal preparation changed drastically when Walia in 1988 introduced the use of nickel-titanium (NiTi) alloys in Endodontics. In 2013, five generations of NiTi endodontic instruments had been established based on their metallurgical, mechanical properties and design features. Since then, manufacturers have been introducing further major changes in instrument design and characteristics that have not been translated in new recognized generations of instruments. In general, those changes have demonstrated enhanced instrument properties, but it is not clear yet if all those improvements are directly translated to an improvement in clinical success. This narrative review attempts to address the present status of engine-driven instruments in terms of both evidence from laboratory-based studies and clinical data, to identify potential further generations of instruments, and last to anticipate future directions for research and development.

Keywords: clinical outcomes; generation of instruments; nickel titanium; shaping goals; test design.

FIGURE 1

Examples of desired outcomes of root canal shaping even with the challenge of molar root canal anatomy. (a) Second and third mandibular molar. Case by Dr. Ana Arias, Madrid, Spain. (b) Second mandibular molar. Case by Dr. Ahmed Salman, Denver, CO, USA

FIGURE 2

Typical cross‐sections of nickel‐titanium instruments generations 1–3, shown as scanning electron micrographs. (a) Passive cutting with radial lands and u‐shape design. (b) Active cutting with various triangular designs

FIGURE 3

Principles for various clinical approaches to file sequencing in root canal preparation. (a) Step back, non‐tapered instruments. (b) Crown down, tapered instruments. (c) Single‐length instrumentation, continuous rotation. (d) Single‐length instrumentation, reciprocation. Note: Line spacing is 1 mm, hashed line 0.5 mm

FIGURE 4

Cross‐sections at various root canal levels shown in micro‐computed tomography images. Typical axial canal changes after canal preparation at the different levels with WaveOne Gold Primary in combination with the four different glide path groups. From Vorster M et al, J Endod 44, 1430–1435 (2018), reprinted with permission

FIGURE 5

Different approaches to fatigue testing to determine the numbers of cycles until failure. (a) Form block and rod assembly. (b) Steel peg assembly. Note higher magnification images that show the specific arrangements. From Peters et al, Dent Clin North Am 61, 37–58 (2017), reprinted with permission

FIGURE 6

Issues with quality assurance.in the production of nickel‐titanium instruments. (a) SEM images from the instruments’ surface in which some minor manufacturing defects were noted such as minor metal roll‐over (ProTaper Next), discontinuity of the blades (X‐File) and distinct metal rollover on the ProTaper Next counterfeit. The smoothest surface can be observed in the X‐File instrument. Modified from Martins et al, Int Endod J 54, 780–792, (2021), reprinted with permission. (b) Variable conditions during heat treatment as indicated by different colours in a single batch of files taken from a commercialised sample