A comparative analysis of mechanical properties of different reciprocating Niti endodontic instruments

Abstract

Despite it is not questionable that static tests give readers only a partial view of the performance of an endodontic instrument they are currently accepted as valid ones to evaluate and compare mechanical properties of endodontic instruments. Therefore, aim of the present study was to evaluate a new single-file reciprocating instrument (Direct RGold 25, Direct Endo, Paris, France) and compare by using the three above-mentioned tests them with the same features of other reciprocating instruments which have been commercialized since many years and consequently have been widely investigated: Wave One Gold Primary (Dentsply- Maillefer, Baillagues, Switzerland), Reciproc and the Reciproc Blue (VDW, Munchen, Germany). For each of the four tested instruments (in size 25) 60 instruments were selected and randomly divided into three groups (n=20). Each group was subjected to a different in vitro mechanical test. Prior to test, each instrument was carefully examinated under magnification. Instruments with visible defects and flute deformation were discarded. Stiffness, cyclic fatigue, torsional resistance tests were performed using methodologies validated in previous studies. For each test data were recorded, then the mean values and the standard deviations were statistically analyzed using a 1-way ANOVA test followed by the post hoc Tukey test with significance set to a 95% confidence level. Results showed that Direct R Gold was significantly more resistant in terms of torsional resistance when compared with all the other instruments. In terms of cyclic fatigue resistance no statistically relevant differences were found amongst the three thermally treated instruments (Direct R Gold, Reciproc Blue and WaveOne Gold) which were all significantly more resistant than Reciproc. Flexibility of Direct R Gold and Reciproc was significantly lower than the other tested instruments. Since the tip and taper dimensions are almost the same for every instrument tested, and since the Direct R gold has the same cross-sectional design as Reciproc and Reciproc Blue, the explanation of these results must be due to the proprietary thermal treatments of the instruments. Direct R-Gold heat treatment allowed a significant increase in both torsional and fatigue resistance, which is a clinically relevant advantage in a single-file technique where only one instrument is used and, as a consequence, it is subjected to all instrumentation stresses.