Influence of Surface Roughness on the Fatigue Life of Nickel-Titanium Rotary Endodontic Instruments

• The depth of the surface grooves affected the NCF of the instruments tested.
• The smaller the groove depth, the greater the NCF.

IntroductionThe goal of the present study was to evaluate the influence of surface grooves (peaks and valleys) resulting from machining during the manufacturing process of polished and unpolished nickel-titanium BR4C endodontic files on the fatigue life of the instruments.MethodsTen electropolished and 10 unpolished endodontic files were provided by the manufacturer. Specimens were from the same batch, but the unpolished instruments were removed from the production line before surface treatment. The instruments were evaluated with a profilometer to quantify the surface roughness on the working part of the instruments. Then the files were subjected to rotating bending fatigue tests.ResultsAnalysis with the profilometer showed that surface grooves were deeper on the unpolished instruments compared with their electropolished counterparts. In the rotating bending fatigue test, the mean and standard deviation for the number of cycles until fracture (NCF) were greater for instruments with less pronounced grooves. Student t test revealed significant differences in all tests (P < .05).ConclusionsThe results from the present study showed that the depth of the surface grooves on the working part affected the NCF of the instruments tested; the smaller the groove depth, the greater the NCF.