title: Endodontic instruments after torsional failure: nanoindentation test.
abstract: This study aimed to evaluate effects of torsional loading on the mechanical properties of endodontic instruments using the nanoindentation technique. ProFile (PF; size 30, taper 04; Dentsply Maillefer, Switzerland) and stainless steel (SS; size 30, taper 02; Mani, Japan) instruments were subjected to torsional test. Nanoindentation was then performed adjacent to the edge of fracture (edge) and at the cutting part beside the shank (shank). Hardness and elastic modulus were measured under 100-mN force on 100 locations at each region, and compared to those obtained from the same regions on new instruments. It showed that PF and SS instruments failed at 559 ± 67 and 596 ± 73 rotation degrees and mean maximum torque of 0.90 ± 0.07 and 0.99 ± 0.05 N-cm, respectively. Hardness and elastic modulus ranged 4.8-6.7 and 118-339 GPa in SS, and 2.7-3.2 and 52-81 GPa in PF. Significant differences between torsion-fractured and new instruments in hardness and elastic modulus were detected in the SS system used. While in PF system, the edge region after torsional fracture had significantly lower hardness and elastic modulus compared to new instruments. The local hardness and modulus of elasticity of endodontic instruments adjacent to the fracture edge are significantly reduced by torsional loading.
authors.affiliation: Department of Endodontics, College of Dentistry, King Saud bin Abdulaziz University for Health Sciences, National Guard Health Affairs, Riyadh, Saudi Arabia.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Jamleh
authors.forename: Alireza
authors.initials: A
authors.lastname: Sadr
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Nomura
authors.forename: Arata
authors.initials: A
authors.lastname: Ebihara
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Yahata
authors.forename: Takao
authors.initials: T
authors.lastname: Hanawa
authors.forename: Junji
authors.initials: J
authors.lastname: Tagami
authors.forename: Hideaki
authors.initials: H
authors.lastname: Suda
mesh_terms: D003188:Composite Resins; D006801:Humans; D055595:Mechanical Phenomena; D013193:Stainless Steel; D013314:Stress, Mechanical; D054159:Torsion, Mechanical
chemical_list: D003188:Composite Resins; D013193:Stainless Steel; C033469:profile resin
keywords: elastic modulus; hardness; nanoindentation; nickel-titanium; stainless steel