Analysis of Torque and Force Induced by Rotary Nickel-Titanium Instruments during Root Canal Preparation: A Systematic Review

Myint Thu,Sherif Adel,Takashi Okiji,Arata Ebihara

doi:10.3390/app11073079

Myint Thu, Sherif Adel + Show 2 more

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https://doi.org/10.3390/app11073079

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Abstract

The aim of this review was to provide a detailed literature analysis of torque and force generation during nickel-titanium rotary root canal instrumentation. We followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. An electronic search was performed using in PubMed and in journals for articles published in English from 1987 to June 2020 on studies that investigated dynamic torque and force in vivo or in vitro. We assessed article titles and abstracts to remove duplicates, and the titles and abstracts of the remaining articles were screened for eligibility. Full texts were read to verify eligibility by considering predetermined inclusion and exclusion criteria. Fifty-two out of 4096 studies met the inclusion criteria, from which we identified 26 factors that influence torque or force generation. Factors associated with higher torque or force generation and supported by multiple studies with mostly consistent results included convex triangle cross-sectional design, regressive taper, short pitch length, large instrument size, small canal size, single-length preparation technique, long preparation time, deep insertion depth, low rate of insertion, continuous rotation (torque), reciprocating motion (force), lower rotational speed and conventional alloy. However, several factors are interrelated, which obscured the independent effect of each factor, and there was insufficient scientific evidence supporting the influence of some factors.

Highlights

Nickel–titanium alloy (Ni-Ti) rotary instruments must exert torque to cut and eradicate septic dentin during canal preparation; torsional stress, associated with friction between the instrument and dentin wall, accumulates in the instruments [1,2]
The engagement of rotary instruments, especially those with spiral-shaped active cutting edges, with the dentin wall can generate apically-directed screw-in forces, causing the instrument to become locked in the canal [4]
We identified the following 26 factors that influence Ni-Ti rotary instrument torque and force: type of sample [17], canal curvature [17,18], cross-sectional design [11,15,19,20,21], taper [21], blade [15], pitch length [11,12,13,14,15], helix angle [13,15,20], rake angle [11,12,15], cutting efficiency [11,12], instrument size [9,11,12,22,23,24], glide-path preparation [25,26], canal size [27,28,29,30,31], contact area [32,33], preparation technique [8,23,32,33,34,35,36,37,38], preparation time [21,39], insertion depth [17,23,28,29,30,31,32,33,34,35,36,37,38,40,41,42,43,44,45], insertion rate [41,46], displacement [40], motor [39], kinematics [3,4,20,38,47,48,49,50,51,52], operative motion [53], rotational speed [36,41], pecking speed [42], lubricant [54,55], experience of the operators [23], and metallurgy [14,20,21,43,44,50,56,57,58,59]

Summary

Introduction

Nickel–titanium alloy (Ni-Ti) rotary instruments must exert torque to cut and eradicate septic dentin during canal preparation; torsional stress, associated with friction between the instrument and dentin wall, accumulates in the instruments [1,2]. The engagement of rotary instruments, especially those with spiral-shaped active cutting edges, with the dentin wall can generate apically-directed screw-in forces, causing the instrument to become locked in the canal [4]. When this occurs, additional torque is required for the instrument to continue rotating. Screw-in forces may cause the instrument to engage beyond the apical foramen [8] and result in the extrusion of microbes into periapical tissue [9], root weakening, and cracks in the apical area [10]

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