Heat treatment of nickel-titanium rotary endodontic instruments: effects on bending properties and shaping abilities

• Published in: International endodontic journal Vol. 44; no. 9; pp. 843 - 849
• Main Authors: Ebihara, A., Yahata, Y., Miyara, K., Nakano, K., Hayashi, Y., Suda, H.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.09.2011
• Subjects: bending property; Dental Alloys - chemistry; Dentistry; Equipment Failure; heat treatment; Hot Temperature; Humans; Metallurgy; Nickel - chemistry; nickel-titanium; Pliability; Root Canal Preparation - instrumentation; shaping ability; Titanium - chemistry
• ISSN: 0143-2885; 1365-2591
• DOI: 10.1111/j.1365-2591.2011.01891.x

Ebihara A, Yahata Y, Miyara K, Nakano K, Hayashi Y, Suda H. Heat treatment of nickel–titanium rotary endodontic instruments: effects on bending properties and shaping abilities. International Endodontic Journal, 44, 843–849, 2011. Aim  To evaluate the bending properties and shaping abilities of nickel–titanium endodontic instruments processed by heat treatment. Methodology  K3 files were heated for 30 min at 400 °C (group 400), 450 °C (group 450) and 500 °C (group 500). Files that were not heat treated served as controls. A cantilever‐bending test was used to evaluate changes in specimen flexibility caused by heat treatment. Curved root canal models were prepared. The times required for preparation, deformation and fracture were recorded. Pre‐ and postoperative images were superimposed. The amounts of resin removed from both the inner and the outer sides of the curvature in the apical 6 mm were determined. Results  In the cantilever‐bending test, load values of the control group and group 500 were higher than those of groups 400 and 450 at the elastic range (P < 0.05). At the superelastic range, the bending load of the control group was the highest amongst all groups (P < 0.05). Regarding shaping ability, in the control group, root canals at the apex were transported more to the outer side of the curvature compared with those of all heat‐treated groups (P < 0.05). Root canals of group 400 at 3 mm from the apex were transported less compared with those of other groups (P < 0.05). No significant difference was found in working time amongst the groups. In group 450, there was no plastic deformation or fracture of the file. Conclusions  Heat treatment of files might improve their flexibility, making them more effective for preparation of curved canals.