Akhlaghi NM, Kahali R, Abtahi A, Tabatabaee S, Mehrvarzfar P, Parirokh M. Comparison of dentine removal using V-taper and K-Flexofile instruments.Aim To compare the dentine removal ability of VTaper and K-Flexofile instruments in mesiobuccal canals of extracted mandibular first molar teeth. Methodology Preoperative images of 40 mesiobuccal canals of mandibular first molars (with a curvature between 20°and 35°) were obtained at 2, 4.5, and 7 mm from the root apices by CT-scan and divided into two groups. Group F was prepared with K-Flexofiles and Gates Glidden drills and Group V with V-Taper Ni-Ti rotary and stainless steel hand instruments. Post-instrumentation images were then obtained and compared with the preoperative images. The ratio of dentine removal based on pre-and postoperative images was calculated, and data was analysed by anova and Tukey post hoc test. Results In group F in the coronal sections, the least ratio of the dentine removal to the initial root thickness was on the buccal aspect (15.14% ± 6.72), and the greatest ratio was found on the distolingual (29.38% ± 8.19). In group V in the coronal, the least ratio of the dentine removal to the initial root thickness was on the buccal aspect (9.81% ± 3.26); the greatest ratio was found on the distolingual surface in the coronal sections (34.38% ± 10.51). In the middle sections, the least ratio was on the buccal (10.51% ± 3.39) and the greatest on the distolingual aspects (27.46% ± 12.34) of the roots. In the apical sections, the amount of the dentine removed from the mesial and distal surfaces in group V was significantly more than group F (P < 0.01). Conclusion The distolingual aspect of the root canal is a danger zone for the mesiobuccal canal of the mesial root in mandibular molar teeth, and preparation of that area should be performed with caution. Except the apical part of the canal, no significant difference was found between the two preparation files or techniques used. Apart from the apical part of the canal, neither instrument maintained the original shape of the coronal and middle parts of the canal.
Laser surface hardening is a method used for surface modification without affecting the bulk properties of materials. Due to rapid cooling and little thermal penetration in the surface layer, a homogenous structure and little distortion are usually obtained. When a high power laser irradiates a material surface, a part of the laser energy is absorbed and conducted into the interior of the material. If the absorbed energy is high enough, the material surface will melt and even vaporizes. Consequently the temperature of the process is of promote importance to incorporate an appropriate structural layer. In this regard, a study has been carried out to implement a mathematical modeling method to control the temperature gradient, which affects on the depth of the hardened layer. The model is based on solving the heat transfer equation and such a condition by assuming that the thermo-physical properties of the material are independent of the temperature. To evaluate the application of the proposed model, laser surface hardening was carried out to AISI 1050 steel, using a 1 kW CO2 laser. It was shown that the experimental results obtained are in good agreement with the proposed model.
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