Comparative Evaluation of Dentinal Microcrack Formation before and after Root Canal Preparation Using Rotary, Reciprocating, and Adaptive Instruments at Different Working Lengths-A Micro-computed Tomographic Study

Shaping Efficiency of Rotary and Reciprocating Kinematics of Engine-driven Nickel-Titanium Instruments in Moderate and Severely curved Root Canals Using Microcomputed Tomography: A Systematic Review of Ex Vivo Studies

INTRODUCTION

This systematic review aimed to compare reciprocating with continuous rotary instrumentation kinematics, by means of microcomputed tomography evaluations, in extracted human permanent teeth with moderate and severe canal curvatures.

METHODS

The research protocol was registered in the International Prospective Register of Systematic Reviews and given the reference number CRD42023404035. An electronic search was undertaken in MEDLINE (PubMed), EBSCO, Scopus, Web of Science databases until December 2021. Manual screening of issues in endodontic journals and references of relevant articles were assessed individually. The risk of bias (RoB) of the included articles was evaluated with the QUIN tool (Quality Assessment Tool for In Vitro Studies).

RESULTS

Among 1640 retrieved articles, 49 were included in the qualitative synthesis. Fifteen articles had low RoB, 33 articles had medium RoB, and only 1 study was at high RoB. Continuous rotary systems had better centering ability in both moderate and severe canal curvatures and resulted in less apical transportation in severely curved root canals. None of the kinematic systems was capable of instrumenting the entire canal surface area. Reciprocating kinematics systems tended to provide higher increase in surface area of severely curved canals and produced fewer dentinal microcracks in moderately curved canals.

CONCLUSIONS

The evidence presented in this review suggests that continuous rotary system seems to be better than reciprocating system in solving the major issues encountered during root canal instrumentation of extracted teeth with moderate and severe curvatures.

A review of the latest developments in rotary NiTi technology and root canal preparation

The introduction of nickel-titanium (NiTi) mechanical instruments dramatically changed clinical endodontics over the last few decades. Before NiTi, it was necessary to use more instruments to create an ideal root canal shape, and many approaches, sequences and techniques were developed over the years. Recently, NiTi endodontic instruments have undergone a series of changes brought about by modifications in design, surface treatments, and thermal treatments to improve their root canal preparation outcomes and reduce associated canal preparation risks during root canal treatment. Heat treatment is one of the most fundamental approaches to improving the fatigue resistance and flexibility of NiTi endodontic instruments. In addition, new kinematics have been developed to offer greater safety and efficiency. This narrative review describes the general properties and manufacturing of NiTi instruments, and the mechanical system evolution of NiTi instruments.

Evaluation of the rotary kinematics between actual and set speeds of X-Smart Plus, VDW.Silver and iRoot motors

The present study evaluated the actual rotational speed of three different endodontic motors compared to the values provided by the manufacturers. A total of three endodontic motors (X-Smart Plus, VDW.Silver, and iRoot) were tested at 400 rpm and 800 rpm and 2 N/cm2 torque. The kinematics of the devices was recorded by using a custom angle-measuring disc with a 50-mm diameter attached to the handpiece provided by the manufacturer, whereas their movement was captured by a high-speed camera at 2,400 frames per second, 800 x 800 pixel-resolution and distance of 0.3 m from the target object. Statistical analysis was performed at a significance level of 5%. At 400 rpm, the iRoot motor had a value of 17.94 rpm above that indicated by the manufacturer, which was significantly different from those of X-Smart Plus (5.20 rpm below that indicated by the manufacturer) and VDW.Silver (0.62 rpm above that indicated by the manufacturer) motors (P < 0.05). At 800 rpm, the iRoot motor had a value of 51.34 rpm below that indicated by the manufacturer, whereas the X-Smart Plus motor had a value of 13.00 rpm below that indicated by the manufacturer (P > 0.05). The VDW.Silver motor statistically differed from the iRoot and X-Smart Plus ones, showing a value of 1.68 rpm above that indicated by the manufacturer. In conclusion, the X-Smart Plus, VDW.Silver, and iRoot motors showed lower variations in the rotational speed values compared to those reported by their manufacturers. The endodontic motors presented different behaviors between them, with the VDW.Silver motor presents the most accurate values and the iRoot presents the most divergent values.

A critical analysis of research methods and experimental models to study dentinal microcracks

The purpose of this narrative review was to discuss the scientific milestones that led to the current understanding of the root dentinal microcrack phenomenon based on the interplay between the usage of micro-computed tomography (micro-CT) as an analytical tool alongside a close-to-mouth experimental model. In 2009, reports on the development of dentinal microcracks in extracted teeth after root canal preparation triggered an awareness of the potential for vertical root fractures (VRFs) of endodontically treated teeth could be developed from defects created by the mechanical stress of nickel-titanium preparation systems on dentine. This assumption was taken for granted, even though no cause-effect relationship had been scientifically demonstrated. Since then, several studies using the sectioning method with extracted teeth have been published and the large discrepancy amongst their outcomes soon become evident. Moreover, the high frequency of reported dentinal microcracks largely contrasted with the clinical incidence of VRFs, raising doubts on their methodological reliability. Using micro-CT technology, it was demonstrated by several studies that, in extracted teeth, dentinal defects already existed before the endodontic procedures, indicating that the initial reports framed a non-existing cause-effect relationship between canal preparation and dentinal microcracks. Although these new findings contributed to a better comprehension of this phenomenon, the misconception that microcracks were the starting point for VRFs was only surpassed with a new in situ approach using fresh cadavers. Surprisingly, microcracks were not identified in sound teeth. As a conclusion, dentinal microcracks in extracted teeth can be considered a non-natural occurrence observed only in a laboratory set-up as a consequence of dehydration and storage conditions. Thus, dentinal microcracks shall not be considered as the starting point for VRFs as they do not manifest in non-extracted teeth. Identifying dentinal microcracks as a laboratory phenomenon highlights the impact of recent scientific developments to disclaim the clinical relevance of laboratory-obtained outcomes.