| Budget Amount *help |
¥3,900,000 (Direct Cost: ¥3,000,000、Indirect Cost: ¥900,000)
Fiscal Year 2011: ¥1,820,000 (Direct Cost: ¥1,400,000、Indirect Cost: ¥420,000)
Fiscal Year 2010: ¥2,080,000 (Direct Cost: ¥1,600,000、Indirect Cost: ¥480,000)
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| Research Abstract |
It is known that the mechanical behavior of Ni-Ti rotary instruments is strongly affected by heat treatment. The aim of this study was to investigate the effect of heat treatment on bending properties, shaping abilities and fatigue properties of Ni-Ti rotary instruments.
Raw Ni. Ti files were heat-treated for 30 minutes at 400(group 400), 450(group 450) and 500(group 500) degrees centigrade. Non heat-treated specimens were used as control. A cantilever-bending test was used to evaluate changes in specimen flexibility both elastic and superelastic deformation range caused by heat treatment. Curved canal models were prepared. Deformed and fractured instruments during preparation were recorded. Pre-and post operative images were superimposed. The amounts of resin removed from both the inner and outer sides of the curvature in the apical 6 mm were determined. The rotational bending test was performed at a rate of 250 rpm until fracture. At 2 mm from the tip, each specimen was deflected horizontally to 1. 0 or 1. 5 mm. All specimens were tested under each deflection. The number of cycles until fracture(NCF) was counted.
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). In the rotational bending test, as compared to the control group, Groups 450 and 500 showed a higher NCF under 1. 0 and 1. 5 mm deflection, whereas Group 400 showed a higher NCF only under 1. 5 mm deflection(p<0. 05).
In conclusion, heat treatment of files might improve their flexibility and fatigue life, making them more effective for preparation of cured canals.
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