Stereomicroscopic evaluation of defects caused by torsional fatigue in used hand and rotary nickel-titanium instruments.
OBJECTIVE
The aim of this study was to evaluate defects caused by torsional fatigue in used hand and rotary nickel-titanium (Ni-Ti) instruments by stereomicroscopic examination.


METHODS
One hundred five greater taper Ni-Ti instruments were used including Protaper universal hand (Dentsply Maillefer, Ballaigues, Switzerland), Protaper universal rotary (Dentsply Maillefer, Ballaigues, Switzerland), and Revo-S rotary (MicroMega, Besançon, France) files. Files were used on lower anterior teeth. After every use, the files were observed with both naked eyes and stereomicroscope at 20× magnification (Olympus, Shinjuku, Tokyo, Japan) to evaluate defects caused by torsional fatigue. Scoring was assigned to each file according to the degree of damage.


METHODS
The results were statistically analyzed using the Mann-Whitney U test and the Kruskal-Wallis test.


RESULTS
A greater number of defects were seen under the stereomicroscope than on examining with naked eyes. However, the difference in methods of evaluation was not statistically significant. Revo-S files showed minimum defects, while Protaper universal hand showed maximum defects. The intergroup comparison of defects showed that the bend in Protaper universal hand instruments was statistically significant.


CONCLUSIONS
Visible defects in Ni-Ti files due to torsional fatigue were seen by naked eyes as well as by stereomicroscope. This study emphasizes that all the files should be observed before and after every instrument cycle to minimize the risk of separation.
Department of Conservative Dentistry and Endodontics, Government Dental College and Hospital, Ahmedabad, Gujarat, India.
Geeta
G
Asthana
Department of Conservative Dentistry and Endodontics, Government Dental College and Hospital, Ahmedabad, Gujarat, India.
Marsrat I
MI
Kapadwala
Department of Conservative Dentistry and Endodontics, Government Dental College and Hospital, Ahmedabad, Gujarat, India.
Girish J
GJ
Parmar
Protaper universal for hand use; Protaper universal for rotary use; Revo-S; torsional fatigue