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This study assessed stress distribution, maximum stress values and fatigue life of experimentally designed NiTi rotary files with different cross-sectional geometry and pitch length using finite element analysis (FEA). Four cross-sectional shapes (Convex triangle, S-shaped, Triple helix and Concave triangle) and two pitch lengths (2 mm and 3 mm) were tested in simulated root canals with curvatures of 30°, 45° and 60°. The FEA results indicated that convex triangle and triple helix geometries exhibited lower stress values compared to the S-shaped and concave triangle designs. Increasing the canal curvature angle resulted in higher stress values, with the S-shaped instrument showing the most significant increase (up to 12%). Instruments with shorter pitch lengths showed more even stress distribution enhancing fatigue life. The maximum stress was concentrated 5-8 mm from the tip, varying across cutting edges, with S-shaped sections experiencing the lowest forces but higher stress due to lower moments of inertia., (© 2024 Australian Society of Endodontology Inc.)

This comprehensive study investigates the micro-milling of a Mg13Sn alloy, a material of considerable interest in various high-precision applications, such as biomedical implants. The main objective of the study was to explore the optimizations of variable feed per tooth (fz), cutting speed (Vc), and depth of cut (ap) parameters on the key outcomes of the micro-milling process. A unique experimental setup was employed, employing a spindle capable of achieving up to 60,000 revolutions per minute. Additionally, the study leveraged linear slides backed by micro-step motors to facilitate precise axis movements, thereby maintaining a resolution accuracy of 0.1 μm. Cutting forces were accurately captured by a mini dynamometer and subsequently evaluated based on the peak to valley values for Fx (tangential force) and Fy (feed force). The study results revealed a clear and complex interplay between the varied cutting parameters and their subsequent impacts on the cutting forces and surface roughness. An increase in feed rate and depth of cut significantly increased the cutting forces. However, the cutting forces were found to decrease noticeably with the elevation of cutting speed. Intriguingly, the tangential force (Fx) was consistently higher than the feed force (Fy). Simultaneously, the study determined that the surface roughness, denoted by Sa values, increased in direct proportion to the feed rate. It was also found that the Sa surface roughness values decreased with the increase in cutting speed. This study recommends a parameter combination of fz = 5 µm/tooth feed rate, Vc = 62.8 m/min cutting speed, and ap = 400 µm depth of cut to maintain a Sa surface roughness value of less than 1 µm while ensuring an optimal material removal rate and machining time. The results derived from this study offer vital insights into the micro-milling of Mg13Sn alloys and contribute to the current body of knowledge on the topic.

Aluminum Matrix Composite (AMC) represents an innovative class of materials that is extensively utilized in industries such as automotive, defense, aerospace, structural engineering, sports, and electronics. This study investigates the thrust force, exit burr formation, changes in the micro-tool, and drilled hole diameters during the micro-drilling of an aluminum-polyethylene composite panel (Al-PE). The panel consists of 3501 series aluminum skin materials bonded to a polyethylene (PE) core. Micro-drilling test parameters were designed using Taguchi's L16 (4 2 2 3 ) orthogonal array. Tests were conducted with five control parameters: cutting speed with four levels (10 m/min, 20 m/min, 30 m/min, 40 m/min), feed rate with four levels (0.5 µm/rev, 1 µm/rev, 2 µm/rev, 4 µm/rev), the tool diameter with two levels (0.7 mm, 1 mm), and tool point angle with two levels (100°, 140°) using both AlTiN-coated and uncoated drills. The maximum thrust force (F z ), maximum burr height, and changes in both the drill tool and hole diameters were measured for analysis of variance (ANOVA). The results showed that, in terms of impact on F z , tool point angle had the highest positive influence (64.54%) on the micro-drill at the entrance of composite (upper aluminum plate). The cutting speed had the highest positive influence (45.32%) on the tool in the core layer (PE core layer). The tool point angle also had the highest positive influence (68.95%) on the micro-drill at the lower layer of the composite (the lower aluminum plate). There was noticeable chip adhesion on the major cutting edge and nose area under micro-drilling conditions with higher thrust forces and burr height. The AlTiN coating had a positive effect on tool wear and hole diameter deviations, but it adversely affected the burr height.

Selective laser melting (SLM) is a three-dimensional (3D) printing process that can manufacture functional parts with complex geometries as an alternative to using traditional processes, such as machining wrought metal. If precision and a high surface finish are required, particularly for creating miniature channels or geometries smaller than 1 mm, the fabricated parts can be further machined. Therefore, micro milling plays a significant role in the production of such miniscule geometries. This experimental study compares the micro machinability of Ti-6Al-4V (Ti64) parts produced via SLM compared with wrought Ti64. The aim is to investigate the effect of micro milling parameters on the resulting cutting forces (F x , F y , and F z ), surface roughness (R a and R z ), and burr width. In the study, a wide range of feed rates was considered to determine the minimum chip thickness. Additionally, the effects of the depth of cut and spindle speed were observed by taking into account four different parameters. The manufacturing method for the Ti64 alloy does not affect the minimum chip thickness (MCT) and the MCT for both the SLM and wrought is 1 μm/tooth. SLM parts exhibit acicular α martensitic grains, which result in higher hardness and tensile strength. This phenomenon prolongs the transition zone of micro-milling for the formation of minimum chip thickness. Additionally, the average cutting force values for SLM and wrought Ti64 fluctuated between 0.072 N and 1.96 N, depending on the micro milling parameters used. Finally, it is worth noting that micro-milled SLM workpieces exhibit lower areal surface roughness than wrought ones.

Introduction: This study aimed to compare ProGlider (Dentsply Sirona, Ballaigues, Switzerland) and R-Pilot (VDW, Munich, Germany) instruments in terms of their cyclic fatigue resistance using an artificial stainless steel canal showing an abrupt apical curvature, torsional resistance according to the ISO specification, and topographic changes on the instrument surface after glide path management in mesial canals of mandibular first molars with the abrupt curvature selected based on their micro-computed tomographic examination., Methods: Eighty instruments were used: 40 ProGlider (size 0.16, .02v taper) and 40 R-Pilot (size 0.125, .04 taper) instruments. The cyclic fatigue resistance was tested in a static test model using an artificial canal with an abrupt apical curvature (angle of curvature of 90° and radius of curvature of 2 mm). The torsional resistance test was performed according to ISO 3630-1 specifications. To determine surface topography of the unused and used instruments, mesial root canals of mandibular molars with an abrupt apical curvature were selected to prepare a glide path with either the ProGlider or R-Pilot instrument. An optical profilometer and scanning electron microscopy were used to determine the surface properties. Normally distributed torsional and cyclic resistance data were analyzed using the Student t test, whereas quantitative data obtained by the optical profilometer were analyzed with the Kruskal-Wallis H test with a 5% significance threshold., Results: The R-Pilot showed significantly higher cyclic fatigue and torsional resistance than the ProGlider (P < .05). Angular deflection values were similar between instruments (P < .05). Measurements made from the blade area showed that the surface roughness values of the ProGlider were larger. Cutting blade measurements showed that unused instruments had significantly greater roughness values than used ones (P < .05). Although there was a 14% increase between the blade edge radii of the used and unused R-Pilot instruments, this difference was determined as 61% in ProGlider instruments., Conclusions: The R-Pilot exhibited greater cyclic fatigue strength than the ProGlider when tested in an artificial canal with an inner diameter of 1.0 mm and an abrupt apical curvature. Torsional resistance of the R-Pilot was higher than the ProGlider, but the angular deflection values were similar. Glide path preparation in a mesial root canal with an abrupt apical curvature did not increase the surface roughness of both instruments but resulted in a greater blade edge radius., (Copyright © 2021 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.)

The aim of this study was to evaluate the roughness of the apical surface after apical resection performed by six different methods with an optical profilometer. Sixty human single root premolar teeth were used in this in vitro study. After root canal preparation, root canals were filled with gutta-percha and AH Plus root canal sealers by lateral condensation technique. The teeth were randomly divided into six groups according to the apical resection method: steel fissure bur, tungsten carbide fissure bur, Lindeman bur, diamond fissure bur, laser, and ultrasonic surgical piezo with a diamond tip. The root ends were resected 3 mm away from the root apex and at a 90° angle. The time required for apicectomy was recorded for each group. After apical resection, the root surfaces were analyzed by an optical profilometer. The Kruskal-Wallis method was used to analyze the differences between groups. The significance level was set at 5%. The roughest surfaces were obtained by laser (25.54 ± 9.01 μm) and Lindeman bur (17.35 ± 6.03 μm), respectively. The longest mean resection times were recorded in piezosurgery and laser surgery (57 ± 14.39 s and 50.9 ± 16.86 s), respectively. Although the diamond-tipped piezo surgical cutting time is long, it has the best results in terms of surface roughness (5.50 ± 1.73 μm). The optical profilometer is a more convenient tool for evaluating the surface after apical surgery, as it provides an opportunity to evaluate objectively with both visual and numerical data., (© 2021 Wiley Periodicals LLC.)

Objective: The aim of this study was to investigate temperature and time variations during root-end resection., Material and Methods: Sixty human premolars were selected. The root canals were enlarged up to ProTaper X3 rotary instrument. A thermocouple was placed into the root canal 1 mm behind the resection line. The teeth were randomly divided into six groups according to the apical resection method: steel bur, tungsten carbide bur, Lindeman bur, diamond bur, laser and ultrasonic surgical piezo with a diamond tip. The root ends were resected 3 mm away from the root apex. The temperature of the root dentine during resection was recorded as maximum temperature, mean temperature and temperature change. The time required for apicectomy was recorded for each group. The Kruskal-Wallis method was used to analyse the differences between temperature changes during apical resections. The significance level was set at 5%., Results: There was no significant difference between bur groups in terms of temperature increase. The maximum temperature in piezo surgery was significantly higher than the Lindeman, tungsten and steel burs ( p  < .001). In addition, the maximum temperature in laser surgery was higher than the Lindeman bur ( p  < .05). An increase in the temperature was mostly seen in piezo surgery and the least temperature change occurred in the Lindeman bur. Mean time stayed under 1 min in each group., Conclusions: Although piezo caused the highest temperature increase, the measured temperature increase was within physiological limits in all tested techniques.