| Summary: | 碩士 === 臺北醫學大學 === 牙醫學系碩博士班 === 96 === Ni-Ti alloy instruments are extensively used in the endodontic treatment due to their outstanding mechanical property. Unfortunately, the nickel titanium rotary file separates unexpectedly during the treatment procedure. There is no proper method to detect the instrument fracture in advance so far. The purpose of this study is to develop a device for checking the fatigue status of the instrument.
Resonance frequency analysis is a method wildly applied in the nondestructive tests. It is affected by alerting mass, elastic modulus and boundary conditions of a structure.
When Ni-Ti alloy rotary instruments have crack, there will be some micro-crack over the metal. And the elastic modulus will decrease, so when the mass and the boundary condition is fixed, the resonance frequency will change with the decreased elastic modulus of the instruments.
In this investigation, modal testing was performed by a commoditized device, IMPLOMATES®, to monitor the frequency responses of the profiles used clinically. Our preliminary results demonstrated that the cyclic loading on the profile results in decreasing the natural frequency. The frequency significantly decreased with a value of about 400 Hz ~ 950 Hz (558+146 Hz)when the test profiles preceded 77 % to 85 % of total life spam. In addition, our in vivo experiments also revealed that the resonance frequencies of the three-month used nickel titanium rotary files (8800 Hz~ 9300 Hz, average= 9271+220 Hz) are significantly lower than the new files (10000 Hz ~11000 Hz, average= 10054+252 Hz, p < 0.05)
These results showed that resonance frequency can be treated as an effective parameter in the fracture status evaluation of nickel titanium rotary instruments subjected to a series of cyclic loadings.
|
|---|
