Cyclic fatigue behavior of nickel-titanium dental rotary files in clinical simulated root canals

Determination of a Representative and 3D-Printable Root Canal Geometry for Endodontic Investigations and Pre-Clinical Endodontic Training-An Ex Vivo Study

Models of artificial root canals are used in several fields of endodontic investigations and pre-clinical endodontic training. They allow the physical testing of dental treatments, the operating of instruments used and the interaction between these instruments and the tissues. Currently, a large number of different artificial root canal models exist whose geometry is created either on the basis of selected natural root canal systems or to represent individual geometrical properties. Currently, only a few geometric properties such as the root canal curvature or the endodontic working width are taken into consideration when generating these models. To improve the representational capability of the artificial root canal models, the aim of the current study is therefore to generate an artificial root canal based on the statistical evaluation of selected natural root canals. Here, the approach introduced by Kucher for determining the geometry of a root canal model is used, which is based on the measurement and statistical evaluation of the root canal center line's curvatures and their cross-sectional dimensions. Using the example of unbranched distal root canals of mandibular molars (n = 29), an artificial root canal model representing the mean length, curvature, torsion and cross-sectional dimensions of these teeth could be derived.

Fatigue Analysis of NiTi Rotary Endodontic Files through Finite Element Simulation: Effect of Root Canal Geometry on Fatigue Life

This article describes a numerical procedure for estimating the fatigue life of NiTi endodontic rotary files. An enhanced finite element model reproducing the interaction of the endodontic file rotating inside the root canal was developed, which includes important phenomena that allowed increasing the degree of realism of the simulation. A method based on the critical plane approach was proposed for extracting significant strain results from finite element analysis, which were used in combination with the Coffin-Manson relation to predict the fatigue life of the NiTi rotary files. The proposed procedure is illustrated with several numerical examples in which different combinations of endodontic rotary files and root canal geometries were investigated. By using these analyses, the effect of the radius of curvature and the angle of curvature of the root canal on the fatigue life of the rotary files was analysed. The results confirm the significant influence of the root canal geometry on the fatigue life of the NiTi rotary files and reveal the higher importance of the radius of curvature with respect to the angle of curvature of the root canal.

Evaluation of Cyclic Fatigue of Hyflex EDM, Twisted Files, and ProTaper Gold Manufactured with Different Processes: An In Vitro Study

Introduction

The main aims of root canal instrumentation are to provide an environment that will lead to healing and to provide a root canal shape that is comfortable to clean and seal. When working with rotary endodontic instruments, the most significant concerns are that the instrument might fracture in the root canal, thus affecting the treatment outcome. Hence, it is of immense importance to know which file systems have more cyclic fatigue resistance. Methodology. This study evaluated the effect of the curved segment length of the artificial canal (the arch), and the number of cycles necessary in fracture of Hyflex EDM, Twisted files, and ProTaper Gold were recorded. Sixty NiTi rotary instruments of 25 mm length (Hyflex EDM (20), Twisted files (20), and ProTaper Gold (20)) were tested in a metal block with simulated canal having 90° angle of curvature. The study was performed with a specific radius and degree of curvature, i.e., 8 mm radius and 90⁰ angle of curvature, and data obtained were subsequently subjected to statistical evaluation using one-way analysis of variance and Tukey's post hoc test.

Result

The Hyflex EDM (774.29) exhibited the maximum cyclic fatigue resistance compared to Twisted files (654.875) and ProTaper Gold (375.575). A statistically significant difference was observed between the tested groups.

Conclusion

The Hyflex EDM files showed the highest cyclic fatigue resistance, followed by Twisted files and ProTaper Gold files.

Preventing nickel-titanium rotary instrument from breakage by continuous irrigation with different fluids during root canal preparation

To study the effect of continuous irrigation of rotating nickel-titanium instrument with several common clinical fluids on the diameter, breaking length and breaking position of nickel-titanium instrument, so as to provide some reference and theoretical basis for clinical operation and instrument improvement.A standardized curved root canal model was established, and ProTaper Universal (PTU) F1 instrument was selected for root canal preparation. The nickel-titanium F1 instrument was flushed with distilled water, 0.9% NaCl, 0.2% chlorhexidine, 1% sodium hypochlorite and 5% sodium hypochlorite, and the diameter, length and position of the instrument before and after breakage were recorded.Only 5% sodium hypochlorite influenced the diameter of 6 mm marker points under different irrigation conditions (P < .05). There was no statistical difference in the length of broken instruments among all the groups, and torsional deformation mainly occurred at the end of broken instruments. The broken positions of instruments in all the groups were located at the bending segment of the root canal. The breaking frequency of the 5% sodium hypochlorite group was the highest in the area 3-5.5 mm away from apical foramen, while the other 4 groups had the highest breaking frequency in the area 0 to 1.5 mm away from apical foramen.External irrigation with different fluids did not influence the breaking length of instruments. The closer to the apical foramen was, the higher the breaking frequency of instruments was. However, only 5% sodium hypochlorite can affect the diameter of rotary nickel-titanium instruments, and may lead to early breakage of the instrument, indicating that the use of disinfectants, except 5% sodium hypochlorite, cannot reduce breakage resistance of nickel-titanium instrument compared with distilled water flushing. Furthermore, 5% hypochlorite could not be recommended for irrigation in clinical practice.

A Mathematical Model for Root Canal Preparation Using Endodontic File: Part B

The aim of this article is to develop the mathematical model to describe response of endodontic file in curved root canal during the preparation of root canal using fracture mechanics approach. Any obturation process involves the filling of prepared root canal using bio-compatible materials like gutta-percha. During preparation of infected root canal, substrate, dead tissue and pulp is removed and tapered shape is formed so that any practitioner can fill it effectively. During preparation process of root canal, the canal wall applies locking action and causes resistance to motion of endodontic file, finally resulting into fatigue failure. This article described plastic behavior of endodontic file in curved root canal, mathematical model describing the necessary condition for crack growth in endodontic file, a mathematical model describing plastic zone size for crack on surface of endodontic file, a mathematical model describing crack tip opening displacement for crack on surface of endodontic file and mathematical model for pure-combined torsion and bending consideration for design of endodontic file. The mathematical model described is helpful for the Endodontic experts, researchers, design engineers. However the applicability of the described mathematical model limited to assumption of study. The gap between root canal to be prepared and endodontic file is zero while preparation. The endodontic file weight, speed of rotation and substrate removal rate is assumed to be constant. The mathematical model for endodontic file discussed above proved to be efficient tool for studying the root canal preparation.