2010 Fiscal Year Final Research Report
Influence of curvature and radius on fatigue fracture of nickel-titanium rotary instruments
| Project/Area Number |
21791840
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| Research Category |
Grant-in-Aid for Young Scientists (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Conservative dentistry
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| Research Institution | Tokyo Medical and Dental University |
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Principal Investigator |
HAYASHI Yousuke Tokyo Medical and Dental University, 大学院・医歯学総合研究科, 非常勤講師 (50451919)
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| Project Period (FY) |
2009 – 2010
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| Keywords | ニッケルチタンファイル / 低サイクル疲労破壊 / 脆性破壊 |
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| Research Abstract |
Fatigue fracture of Ni-Ti rotary instruments is a major problem in the practice of endodontics. Radius of curvature might be one of the most important factors that affect fatigue fracture. However, the relation between radius of curvature and load is not clarified. The aim of this study was to evaluate the influence of radius of curvature and load on fatigue fracture of rotary Ni-Ti instruments using a newly designed cyclic fatigue testing machine.
ProFile (size 30, 0.06 taper, Dentsply Maillefer, Switzerland) was subjected to cyclic fatigue testing. A newly designed cyclic fatigue testing machine which can define radius of curvature by three cylindrical stainless steel pins and measure applied load was used. Radius of curvature was set at 4, 5, 6, 7 and 8 mm. Instruments were rotated at 250 rpm until fracture occurred. Load-time curves were obtained from the fatigue test. The number of cycles before fracture (NCF) and mean load were obtained. Lower NCF and higher mean load of 4, 5 and 6 mm in radius were obtained when compared with those of 7 and 8 mm in radius. Super-elastic deformation occurred in 4, 5 and 6 mm in radius.
In conclusion, linear relationship was not found between NCF and the radius of curvature. It was suggested that fatigue fracture of Ni-Ti instruments may be accelerated when their deflection exceeds a certain threshold level.
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