Comparative analysis of torque and apical force to assess the cutting behaviour of ProTaper Next and ProTaper Universal endodontic instruments

Effect of preset torque setting on torque/force generation, shaping ability and surface changes of nickel titanium rotary instrument in different root canal curvature locations: An ex vivo study

The aim of this study was to evaluate how preset torque settings influence the torque, vertical force, and root canal-centering ability of ProGlider and ProTaper NEXT nickel-titanium rotary instruments in canals with different curvature locations. Based on micro-computed tomography, mesial roots of human mandibular molars (25°-40° curvature) were allocated to the apical curvature (apical 1-5 mm) or the middle curvature (apical 5-9 mm) groups, and mandibular incisors (curvature <5°) to the straight canal group. Each group was subjected to automated instrumentation and torque/force measurement with the preset torque of 1, 2.5, or 5 N•cm. Canal-centering ratios were determined with micro-computed tomography. Instrument fracture occurred only in the 2.5 and 5 N•cm groups in curved canals. The preset torque setting and curvature location did not influence canal shaping ability.

Dynamic torque and screw-in force of four different glide path instruments assessed in simulated single- and double-curved canals: An in vitro study

Background/purpose

The glide path instruments are the introductory instruments into the canals; thus, they should be durable enough to withstand torsional stress/screw-in force. This study aimed to investigate the torque and screw-in force of TruNatomy Glider (TN), ProGLIDER (PG), Hyflex EDM (EDM) and Dent Craft RE (RE) glide path instruments in single- and double-curved canals.

Materials and methods

Each instrument brand was divided into two groups (n = 7 each) according to the canal configuration. Torque and screw-in force were recorded during automated instrumentation of simulated resin canals with XSmart IQ cordless motor after the canal patency was checked with a #10 K-file. The values were statistically analyzed using the Kolmogorov-Smirnov test followed by the Kruskal Wallis test and the Mann-Whitney U test with Bonferroni correction (α = 0.05).

Results

TN produced significantly higher torque than RE in single-curved canals and PG in double-curved canals (P < 0.05). EDM yielded significantly higher screw-in force than TN and RE in single-curved canals (P < 0.05), but there was no significant difference in double-curved canals (P > 0.05). A significant effect of different canal configurations was only detected for screw-in force in EDM (P < 0.05).

Conclusion

TN in single-curved canals and RE in double-curved canals yielded higher torque values, while EDM exhibited greater screw-in force in both canal configurations. No effect of different canal configurations was detected for torque, but a significant impact was detected for screw-in force in EDM.

Effect of Different Downward Loads on Canal Centering Ability, Vertical Force, and Torque Generation during Nickel-Titanium Rotary Instrumentation

This study aimed to examine how downward loads influence the torque/force and shaping outcome of ProTaper NEXT (PTN) rotary instrumentation. PTN X1, X2, and X3 were used to prepare J-shaped resin canals employing a load-controlled automated instrumentation and torque/force measuring device. Depending on the torque values, the handpiece was programmed to move as follows: up and down; downward at a preset downward load of 1 N, 2 N or 3 N (Group 1N, 2N, and 3N, respectively; each n = 10); or upward. The torque/force values and instrumentation time were recorded, and the canal centering ratio was calculated. The results were analyzed using a two-way or one-way analysis of variance and the Tukey test (α = 0.05). At the apex level, Group 3N exhibited the least canal deviation among the three groups (p < 0.05). The downward force was Group 3N > Group 2N > Group 1N (p < 0.05). The upward force, representing the screw-in force, was Group 3N > Group 1N (p < 0.05). The total instrumentation time was Group 1N > Group 3N (p < 0.05). In conclusion, increasing the downward load during PTN rotary instrumentation improved the canal centering ability, reduced the instrumentation time, and increased the upward force.

Cyclic fatigue resistance for six types of nickel titanium instruments at artificial canals with different angles and radii of curvature

This study evaluated the cyclic fatigue resistance for six types of 25# NiTi instruments. A traditional manufacturing instrument, an M wire instrument, a gold treatment instrument, a controlled memory (CM) wire instrument, a CM wire instrument with electrical discharge machining (EDM), and an R-phase heat treatment instrument, were operated in the different curved artificial canals. The fracture time (FT) and number of cycles to fracture (NCF) of the NiTi instruments were higher at 45° angles and double-curvature canals than at 60° angles. Except for the instruments with gold technology and EDM technology, others showed the longest FT and the highest NCF at an 8 mm radius of curvature. Morphological characteristics of cyclic fatigue were exhibited on the cross-section and lateral view of fracture fragments. The use of M-wire, R-phase wire, CM-wire, gold technology, EDM technology, and reciprocating movement were beneficial to enhance the cyclic fatigue resistance of NiTi files.

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

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.