![]() Their unique surface color comes from a proprietary thermal treatment process, which gave them more flexibility and resistance to cyclic bending fatigue than conventional NiTi instruments. WaveOne Gold (WOG, Dentsply Sirona, Switzerland), and Reciproc Blue (RB, VDW, Germany) are two popular nickel–titanium single-file systems using reciprocating motion. Therefore, it is necessary to evaluate the preparation outcome of these various types of single-file systems in curved canals to provide guidance for the dentists. Among them, the single-file system has been widely used because it greatly enhanced the efficiency of clinical work, thus relieving the patient’s pain and the work intensity of dentists. To improve flexibility and cyclic fatigue resistance, the manufacturers have sought innovation in metallurgy, instrument design, and movement strategies such as various thermo-mechanical treatments, different cross-sectional designs, and new manufacturing processes, leading to a great variety of these endodontic instruments. Over the last decades, to circumvent such limitations, the nickel–titanium instrument has made great progress. However, the files of the original NiTi instruments are stiff and remain vulnerable to fracture due to cyclical and torsional failure. Ĭompared with traditional stainless steel manual instruments, the nickel–titanium file system is superior in maintaining the original canal path to the greatest extent, which is eminently suitable for the preparation of curved root canals. Besides, it is pertinent to note that debris removal is much more difficult in the curved regions, thus leaving certain areas of root canal walls untouched, which may harbor bacteria and result in postoperative endodontic disease. Curved root canal preparation presents a greater incidence of procedural errors including root canal transportations, root perforations, and separation of instruments than straight canals. Studies have shown that most root canals of molars have some degree of curvature at the apical and cervical thirds, to a certain extent, irrespective of the plane of analysis. In particular, the curved root canal has so far been a challenge to dentists. Thorough cleaning of root canals is the key step in root canal therapy and is considered critical for successful endodontic treatment because of the anatomical complexity of root canal systems. Regarding cleaning ability, Reciproc Blue and XP-endo Shaper were associated with less smear layer than WaveOne Gold in the apical thirds. The five single-file systems evaluated performed equally in apically debris extrusion, dentin removal, and untouched root canal areas, while XP-endo Shaper and V-Taper 2H resulted in less canal transportation compared to M3-L and WaveOne Gold. ![]() Reciproc Blue and XP-endo Shaper showed fewer smear scores than WaveOne Gold in the apical thirds ( P < 0.01 and P < 0.05, respectively), and no statistical difference was found between other groups in the middle and coronal thirds. Debris and smear layers were present on the canal walls of all specimens, the apical thirds of the canal presented higher SEM scores than the coronal thirds in all groups ( P < 0.05). ![]() ![]() In terms of CT, no significant difference was noted at the straight section of canal and apical levels, while XP-endo Shaper showed less canal transportation than M3-L at the level of curved vertex ( P < 0.05), and the centering ability of V-Taper 2H was significantly better than WaveOne Gold at the initial point of bending ( P < 0.05). There were no significant differences between the five systems regarding the AD, VI, and UTA parameters ( P > 0.05). Data were statistically analyzed with ANOVA (UTA, AD, VI) or Kruskal–Wallis test (CT, SEM-score), the level of significance was set at α = 0.05. After that, all samples were separated into two parts and examined respectively by scanning electron microscope (SEM) to assess cleaning ability. Apically extruded debris (AD) was collected during preparation. Before and after root canal preparation, a Micro-CT scan was taken, and pre- and post-operative data were analyzed to evaluate the following parameters: volume increment of root canals (VI), untouched root canal areas (UTA), and canal transportation (CT). MethodsĪ total of 60 root canals were selected from extracted human molar teeth with curvatures ranging from 25° to 50° and divided into five groups based on the instrumentation system employed (n = 12). The ex vivo study is to compare the root canal preparation outcomes achieved by five nickel–titanium single-file instrumentation systems (M3-L, Reciproc Blue, V-Taper 2H, WaveOne Gold, XP-endo Shaper) in severely curved molar root canals. ![]()
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