Date of Award

Spring 2014

Document Type


Degree Name

Master of Science (MS)



First Advisor

Stover, Sheila

Second Advisor

Hashimoto, Lance

Third Advisor

Berzins, David W.


Introduction: Modern nickel-titanium instruments have various tapers and have been marketed to have superior flexibility from previous generations. Current ISO standards require force measurements at a static point along the file. Unfortunately, root canal anatomy varies and produces multiple forces along the length of the file. The purpose of this study was to determine the influence of taper on the flexibility of various nickel-titanium files.

Materials and Methods: The flexibility of stainless steel hand files and nickel-titanium rotary files of various tapers was measured. The sample size was 10 for each type, taper and size. The files were measured at 3, 5 and 7 mm from the tip using a digital caliper and marked with a rubber stopper and a distance of 20mm from the tip was used as the deflection point. Each file was securely fastened on a load-sensing cell and bending was accomplished using a universal testing machine to a maximum deflection of 4.5 mm at a rate of 2 mm/minute under room temperature conditions (22OC ±1OC). Data was collected electronically via Merlin Software and transferred to Microsoft Excel. Statistical analysis was completed with IBM SPSS Statistics software and a two-way analysis of variance (ANOVA) was used as well as a Post-hoc Tukey test.

Results: The force and bending moments of EndoSequence .06 taper files was significantly greater (p<0.05) than EndoSequence .04 and stainless steel hand files at all lengths. No significant difference was noted between EndoSequence .04 and stainless steel hand files from 0.25 mm to 3.0 mm. From 3.5 mm to 4.5 mm, the force and bending moments for stainless steel hand files was significantly greater (p< 0.05) than EndoSequence .04 files. Within each file group, the force and bending moments were significantly greater (p<0.05) as the grasp length increased (7 mm>5 mm>3 mm).

Conclusions: With a vast array of root canal instruments currently available clinicians should consider the properties of instruments before cleaning and shaping. Nickel-titanium files with tapers greater than 0.04 should not be used for apical enlargement of curved canals because these files are significantly stiffer resulting in an increased chance of canal transportation.