2. Data, Model, Applications and Influences

As shown in Figure 1, 4096 articles were identified. After duplicates were removed and preliminary screening was conducted, 75 articles underwent full-text review. Fifty-two studies (Table 1) were eligible for inclusion.

Figure 1. Summary of the search processs.

From these studies, we identified the following 26 factors that influence Ni-Ti rotary instrument torque and force: type of sample ^[19][17], canal curvature ^[19][29][17,18], cross-sectional design ^{[11][15][33][49][53]}[11,15,19,20,21], taper ^[53][21], blade [15], pitch length ^{[11][12][13][14][15]}[11,12,13,14,15], helix angle ^[13][15][49][13,15,20], rake angle ^[11][12][15][11,12,15], cutting efficiency ^[11][12][11,12], instrument size ^{[9][11][12][43][16][30]}[9,11,12,22,23,24], glide-path preparation ^[44][40][25,26], canal size ^{[35][18][20][21][22]}[27,28,29,30,31], contact area ^[17][24][32,33], preparation technique ^{[8][16][17][24][23][37][31][32][57]}[8,23,32,33,34,35,36,37,38], preparation time ^[53][54][21,39], insertion depth ^{[19][16][18][20][21][22][17][24][23][37][31][32][57][28][34][52][36][58][42]}[17,23,28,29,30,31,32,33,34,35,36,37,38,40,41,42,43,44,45], insertion rate ^[34][48][41,46], displacement ^[28][40], motor ^[54][39], kinematics ^{[3][4][49][57][41][56][51][46][39][50]}[3,4,20,38,47,48,49,50,51,52], operative motion ^[47][53], rotational speed ^[31][34][36,41], pecking speed ^[52][42], lubricant ^[25][26][54,55], experience of the operators ^[16][23], and metallurgy ^{[14][49][53][36][58][46][27][55][45][38]}[14,20,21,43,44,50,56,57,58,59].

Pro-branded systems, such as ProFile, ProTaper Next, ProTaper and ProTaper Universal, were most frequently investigated (Figure 2). The highest numbers of articles were published in 2019 and in the first half of 2020 (Figure 3), and 48% of the articles included in this review were published in Journal of Endodontics (Figure 4).

Figure 2. Instrument systems used in the studies included in the review.

Figure 3. Publication year of the articles included in the review.

Figure 4. Journals in which articles included in the review were published (by percentage). “Proc. Inst. Mech. Eng. H” refers to “Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine”.

The main findings obtained from the present systematic review can be summarized as: Higher torque or force generation was related to 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.