Abstract
ObjectivesThe aim of this study was to investigate whether file design and taper significantly influence microcrack initiation during machine preparation.Materials and methodsSixty extracted teeth with straight single canals were selected. The teeth were randomly assigned to four groups based on their root canal anatomy and the corresponding NiTi rotary file system (I, Mtwo; II, ProTaper Universal; III, F6 SkyTaper; control, no preparation and filling). The root canals of the experimental groups were filled using the single-cone technique. The tested teeth were all subjected to a mechanical chewing simulation with flat lead loading over a period of 3 years (corresponding to 150,000 cycles). The teeth were checked for dentinal defects (accumulative crack growth in length) under the digital microscope (Keyence VHX-5000) at time 0 (baseline prior to chewing simulation) and after 3, 6, 12, 24, and 36 months of loading. The cumulative crack increase was statistically analyzed using the Kruskal–Wallis test, Jonckheere–Terpstra test, and the Wilcoxon rank-sum test. The significance was set at p < 0.05.ResultsIn contrast to preparation with greater-tapered instruments, ProTaper Universal (group II) and F6 SkyTaper (group III) instrumentation with the smaller tapered Mtwo files (group I) showed less accumulative propagation of craze lines (p < 0.05) at all time points.ConclusionInstruments with greater taper for root canal instrumentation should be used with care to avoid negative long-term effects in the form of propagation of dentinal defects over time. A positive cutting-edge angle and a smaller taper have a positive effect on a lower craze line development.Clinical relevanceInstruments with a positive cutting-edge angle and a smaller taper are beneficial for the long-term preservation of dentinal tooth structure.
Highlights
Microcracks are defined as fine, incomplete craze lines that occur in areas of force concentration if the elastic limit of the tooth structure is exceeded, so they appear in most adults [1]
The propagation of microcracks may result in vertical root fractures (VRFs) which can potentially be a reason for extraction of the affected tooth [2,3,4,5]
The current study investigated the occurrence of superficial dentinal craze lines, a type of microcracks that can be detected on the root surface after endodontic therapy
Summary
Microcracks are defined as fine, incomplete craze lines that occur in areas of force concentration if the elastic limit of the tooth structure is exceeded, so they appear in most adults [1]. The propagation of microcracks may result in vertical root fractures (VRFs) which can potentially be a reason for extraction of the affected tooth [2,3,4,5]. The microcrack formation is said to be independent of the extraction technique but a consequence of the dehydration process outside the oral cavity [19, 20]. In this way, the methodology of the earlier mentioned studies is questioned [19]
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