Abstract
The aim of this study was to investigate the shaping ability and cyclic fatigue resistance of Genius (GN) and WaveOne (WO) nickel-titanium (NiTi) instruments. Forty mesial root canals of mandibular molars were randomly divided into two groups, according to the instrument system used for root canal preparation (n = 20): GN and WO. Root canals were prepared to the full working length using the crown-down technique, with up to 40.04 instruments for GN group and 40.08 instruments for WO group. Specimens were scanned with a µCT before and after instrumentation. The changes in 3D parameters and degree of canal transportation were evaluated in the apical, middle and coronal thirds of root canals. Size 25, taper 0.04 (GN) and 0.08 (WO) instruments (n = 20) were used in simulated root canals until fracturing, and the number of cycles to failure (NCF) was recorded. The fractured files were investigated under a scanning electron microscope to characterize fractured surfaces. Data were analyzed using ANOVA post hoc Tuckey’s tests with the significance level set at 5%. The GN system was able to prepare the higher percentage of the canal surface with less canal transportation in all root canal thirds and displayed the higher resistance to cyclic fatigue in comparison to WO instruments (p < 0.05). However, the length of the fractured segments was not significantly different among the groups; meanwhile, SEM investigations revealed the typical topographic characteristics of fractured surfaces. Hybrid GN instruments demonstrated superior shaping ability and resistance to cyclic fatigue. However, both NiTi instrument systems prepared the root canals with no significant shaping errors, considerable changes in 3D parameters and no significant differences in the topographic appearances of the instrument surfaces after fractures.
Highlights
The quality of root canal cleaning and shaping directly impacts the outcome of endodontic treatment and is one of the most challenging tasks in endodontics [1,2]
Numerous studies have shown that procedural mishaps, such as canal transportations, perforations, blockages or ledges, can occur during endodontic treatment, leading to complicated canal obturation, an unsatisfactory apical seal or worse clinical outcomes [1,3,4,5]
The previous studies have shown that the alloy, design and kinematics of the instrument are essential features of the files affecting the efficiency and the shaping ability of the instruments, and resistance to torsional stresses and fractures [4,6]
Summary
The quality of root canal cleaning and shaping directly impacts the outcome of endodontic treatment and is one of the most challenging tasks in endodontics [1,2]. Numerous studies have shown that procedural mishaps, such as canal transportations, perforations, blockages or ledges, can occur during endodontic treatment, leading to complicated canal obturation, an unsatisfactory apical seal or worse clinical outcomes [1,3,4,5]. The introduction of the nickel-titanium (NiTi) instruments for root canal shaping in 1988 was a substantial innovation in endodontics and clinically appealing in terms of minimizing the number of Metals 2020, 10, 172; doi:10.3390/met10020172 www.mdpi.com/journal/metals. Metals 2020, 10, 172 procedural errors occurring during root canal instrumentation [3,4]. Fractures of NiTi instruments usually occur suddenly without any visible sign of deformation, and it is a significant clinical problem. It has been shown that instrument fractures are related to cyclic fatigue and torsional failure during canal preparation
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