Success of Ultrasonic Technique in Removing Fractured
Rotary Nickel-Titanium Endodontic Instruments from Root
Canals and Its Effect on the Required Force for Root Fracture
Hasan Shahabinejad, DDS, MS, Amirreza Ghassemi, DDS, Lida Pishbin, DDS, MS,
and Arash Shahravan, DDS, MS
Introduction:
Fracture of rotary nickel-titanium files is
a real concern among endodontists; it affects the long-
term prognosis of treatment. Ultrasound is a favorable
technique for removing broken files, although it may
result in some complications. The aim of this study
was to determine the success rate of ultrasonic tech-
nique in removing file fragments and to evaluate its
influence on the force required to fracture a tooth
root.
Methods:
An in vitro study was carried out on
70 extracted maxillary premolars. In the experimental
group a #30/.04 taper Hero file was guided into the
canal to break and lodge therein. The lodged file was
removed by ultrasonic vibration and use of a dental
operating microscope. The canals were instrumented
with Hero files by using crown-down technique and
then obturated. All the teeth were prepared for mechan-
ical testing in Testometric machine to measure the
required force for root fracture. The Fisher exact test
and independent two-sample t test were used to
analyze data.
Results:
Ultrasonic technique exhibited
a success rate of 80% in removing broken files.
Success rate in the roots with file fracture before the
curve was 11.5 times more than that of file fracture
cases beyond the curve. Other factors such as bypass
possibility did not affect success rate. The average
time required for removing file fragments was 36.3
` 7.15 minutes, which did not significantly differ in
different file locations within the canal. According to
mechanical test results, ultrasonic application did not
significantly affect the required force for root fracture.
The force required to fracture a root did not signifi-
cantly differ in various file locations. Vertical fracture
in the buccolingual direction (split tooth) was the
most incident fracture pattern. Procedural errors
observed in this study predominantly included trans-
portation, perforation, and craze line.
Conclusions:
Ultrasonic technique was successful in removing 80% of fractured rotary files and did not significantly affect the required force for root
fracture.
(J Endod 2013;39:824–828)
Key Words
Fractured rotary endodontic instruments, removal, required force for root fracture,
ultrasonic technique
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