Cyclic fatigue resistance of Mtwo NiTi rotary instruments used by experienced and novice operators – an in vivo and in vitro study

Abstract

SummaryBackgroundThe aim of the present study was to evaluate the cyclic fatigue resistance of Mtwo NiTi rotary instruments after clinical use by 1 experienced and 1 novice operator.Material/MethodsCyclic fatigue testing of instruments was performed on tapered artificial canals with a 5 mm radius of curvature and 60° angle of curvature. Twenty Mtwo instruments for each size were selected and divided into 2 groups: group A consisted of 10 instruments of each size used for shaping 10 root canals in molar teeth of patients by an experienced operator; group B consisted of 10 instruments of each size used for shaping 10 root canals in molar teeth of patients by a novice operator. Instruments were rotated until fracture occurred and the numbers of cycles to failure (NCF) were recorded. Data obtained were subjected to an independent sample t-test to determine statistical differences. The significance was determined at a 95% confidence level.ResultsNo statistically significant difference (P<0.05) was noted between the instruments of groups A and B for all sizes. More instruments with visible signs of plastic deformation were identified for the novice operator.ConclusionsThe clinical use of Mtwo NiTi rotary instruments by a novice operator did not significantly affect the cyclic fatigue resistance when compared with the control group of the same instrument sizes used by an experienced operator. It can be concluded that novice operators can use these instruments safely under the recommended technical guidelines.

Effect of two different temperatures on resistance to cyclic fatigue of one Curve, EdgeFile, HyFlex CM and ProTaper next files

“…When the endodontic literature is reviewed, it is shown that there are many factors that affect the CFR of NiTi rotary files. These factors include angle and radius of the canal curvature, instrument size and taper, movement kinematics, speed of rotation, effect of sterilisation, as well as many other variables such as operator's skill and experience, which may help to explain the variations in the prevalence of CFR among different studies . Recently, some studies focused on whether or not temperature affects the CFR of NiTi rotary files in addition to the factors mentioned above .…”