Evaluation by Scanning Electron Microscopy and Energy Dispersive X-Ray Spectroscopy of the Effects of Root Canal Instrumentation on the Radicular Dentine

One area of technological advancement has been the shift from stainless steel hand tools to nickel-titanium (Ni-Ti) rotary tools. This paper aims to perform an in vitro comparative study to evaluate the efficacy of five endodontic manual and rotary instruments such as Kerr files, Orodeka Plex V, ProTaper Flydent NiTi super files, and ProTaper Flydent NiTi super files in combination with an ultrasonic endodontic E3D Diamantata EMS scaler used for root canal shaping. The following aspects were highlighted: effective removal of smear layer (SL) from the dentinal tubules in the coronal 1/3, middle 1/3, and apical 1/3 of the root canal, appearance of cracks in the dentinal walls by SEM analysis, and highlighting of dentin mineral content and remnant debris by EDX analysis. In the study, 48 monoradicular, uninjured teeth were taken and divided into four groups, each with 12 teeth to be canal modeled, then longitudinally sectioned; the active surface was metallized for SEM–EDX analysis. From the SEM micrograph analysis, the morphology of the crystallites, the distribution of SL components, and the highlighting of instrumentation path traces/amplitudes were observed. By analyzing the SEM photomicrographs at 750 and 800× magnification, it was possible to highlight the cracks in the root dentinal walls. Thus, in comparison with Lots I and II which did not present cracks, in Lot III multiple cracks of the root dentinal walls were identified, especially in the coronal 1/3, and in Lot IV cracks were present with preponderance in the coronal and apical 1/3 of the root canals. The EDX images with atom mapping show very well the rather homogeneous elemental distribution for Ca, N, and P, respectively inhomogeneous for Na, Ca, Si, C, N, O, and P elements, as a result of the presence of remnant products from the processing of the root dentinal walls. Root canal instrumentation performed with both manual Kerr needle instrumentation by a convection technique and the rotary, Orodeka system, by crown-down technique, resulted in minimal SL formation in all three root canal areas, unlike the ProTaper FlyDent system. Most cracks were recorded in the case of the ProTaper Flydent rotary instruments and the one in which it was paired with a diamond ultrasonic scaler. The occurrence of dentinal cracks causes a decrease in dentinal microhardness, favoring the occurrence of root fractures.