Abstract
This study investigated the impact of a one-sided radial-landed cross-sectional design of a heat-treated nickel-titanium rotary instrument (JIZAI, MANI, Japan; JZ) on torque/force generation and canal-shaping ability, using an experimental non-landed instrument (non-landed JZ) for comparison. Both instruments had tip sizes of 25 and 0.04 or 0.06 taper and were similar in metallurgy and geometry, except for the presence/absence of a radial land. Twenty J-shaped simulated resin canals were instrumented in a two-instrument single-length sequence using an automated root canal instrumentation device with a torque/force analyzing unit. Pre- and post-instrumentation images of the resin canals were analyzed for canal-centering ability at 0–3 mm from the apex. The mean centering ratio was not significantly different between JZ and non-landed JZ (p > 0.05). In the 2nd instrumentation, JZ showed a significantly smaller torque compared with the non-landed JZ (p < 0.05). Regardless of instrumentation sequence, JZ showed a significantly smaller maximum upward force, representing screw-in force (p < 0.05), and a larger maximum downward force (p < 0.05) than the non-landed JZ. JZ generated smaller screw-in forces and had similar canal-centering ability compared with the non-landed JZ.
Highlights
Nickel-titanium (NiTi) rotary instruments are considered suitable for preparing curved root canals because of their higher flexibility [1] and superior canal-centering ability [2]
Materials and on Information the effect of design features of NiTi rotary instruments on their canalshaping ability and screw-in force generation [9,13,22] has been gained through numer2.1
The cross-section of JZ is a quasi-rectangle with radial land on one of the short sides, and that of the non-landed JZ is a rectangle without radial lands
Summary
Nickel-titanium (NiTi) rotary instruments are considered suitable for preparing curved root canals because of their higher flexibility [1] and superior canal-centering ability [2]. Intracanal fracture of NiTi rotary instruments is a problem that has not yet been fully resolved [3]. Tight binding of a rotating instrument with the canal wall may induce torsional overload and, is considered as a cause of the fracture [4]. The binding may produce a pulling force toward the root apex on the rotating instrument due to the helical design of the flutes. This phenomenon, termed the screw-in effect, may cause instantaneous engagement of the instrument giving rise to sudden torsional fracture [5]. The screw-in effect may cause over-instrumentation, which could induce postoperative pain [6] and increase the risk of apical crack formation [7]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call