Cutting efficiency and corrosion resistance of heat-treated endodontic files after various disinfection protocols.

The aim of this study is to evaluate the effect of various disinfection protocols on the cutting efficiency and chemical composition of ProTaper, Twisted File, Twisted File Adaptive, and Hedström files. Four experimental groups (n = 10) were presoaked in either enzymatic solution or 1% sodium hypochlorite for 30 min, followed by either 5 or 15 min of ultrasonic cleaning and then autoclaved. Resin-simulated canals with a single curvature of 38-40° were prepared by each instrument system. Cutting efficiency of each instrument was analyzed by subtracting the final weight from the initial weight of the resin blocks. Chemical compositions were studied by field emission scanning electron microscopy and X-ray energy-dispersive spectrometry. The cutting efficiency of Hedström, ProTaper, and Twisted File instruments decreased compared to their control groups (p < 0.05) whereas it did not change for Twisted File Adaptive. More corrosion was detected with longer ultrasonication time. No difference was observed regarding the pre-soaking media. Disinfection protocols exerted a significant overall effect on the performance of Hedström, ProTaper, and Twisted File instruments. Corrosion, microcracks, and crevices were evident on all tested instruments after disinfection protocols applied. All disinfection protocols, regardless of the pre-soaking media used or the ultrasonic cleaning time applied, have some effect on the cutting efficiency and the surface characteristics of the files.

Bur Choice When Removing Zirconia Restorations.

PURPOSE: Removal of zirconia restorations can be challenging and time consuming, requiring dental burs with optimal cutting efficiency to minimize iatrogenic complications. Yet, there are very few burs marketed for this purpose and little evidence of their comparative benefit. This study evaluated one specialized bur and compared its cutting efficiency with three general-purpose burs (one single use and two multiple uses). MATERIALS AND METHODS: This study was designed to assess the cutting efficiency of 4 burs on a high-strength zirconia substrate. One of these burs is a multiple-use bur marketed for high-strength ceramics (Komet 4ZR), another is a single-use general-purpose bur (Piranha 837.012 coarse), and two are multiple-use general-purpose burs (Brassler 6837.31.012C coarse and Komet 6837.314.012 coarse). The cutting efficiency of each bur was determined by measuring the time taken to perform serial 2 mm cuts into a block of zirconia. Ten burs in each group were tested with repeated cuts until the time taken for a 2 mm cut was twice that of the first 2 mm cut (50% loss of efficiency). This study was performed under reproducible conditions using a custom-designed and fabricated rig assembly. RESULTS: The results demonstrated a statistically significant difference in the cutting efficiency between bur types. The single-use general-purpose bur (Piranha 837.012) was the most efficient for all cut numbers p <2.2 × 10-16 . The performance of all burs decreased with each cut, with cutting efficiency dependent on time point/cut number (p = 0.02). The rate of deterioration varied between burs, but this difference was not sufficient to be statistically significant. CONCLUSIONS: This study demonstrated that a single-use bur is more efficient than 3 multiple-use burs. The cutting efficiency of a single-use general-purpose bur (Piranha 837.012 coarse) on Cerec Zirconia Mono L was statistically superior to that of multiple patient use burs in this study, including one marketed for use on high-strength ceramics. Because single-use burs are comparatively inexpensive and require no sterilization, they should be strongly considered for the removal of zirconia restorations.

A critical analysis of research methods and experimental models to study the physical properties of NiTi instruments and their fracture characteristics.

The aim of this review is to provide a critical overview of the physical properties (surface hardness, cutting efficiency, bending properties, flexibility and cyclic fatigue resistance) of NiTi instruments. Frequently used experimental models regarding these aspects will be presented and discussed with regard to their strengths and weaknesses. For all these aspects, a plethora of experimental models have been described. Based on a critical appraisal and especially taking the appropriate translation of experimental findings to clinical endodontics into account, suggestions for future research based on clearly defined and valid experimental methodologies will be provided. Up to now, very few attempts have been made to assess which particular physical properties of NiTi instruments exert an impact on the clinical outcome of root canal treatment. Departure from merely focusing on physical properties and fracture characteristics towards more biological aspects in terms of treatment outcome is essential.

On the WEDM of WNbMoTaZrx (x = 0.5, 1) Refractory High Entropy Alloys.

As a potential candidate for the next generation of high-temperature alloys, refractory high entropy alloys (RHEAs) have excellent mechanical properties and thermal stability, especially for high-temperature applications, where the processing of RHEAs plays a critical role in engineering applications. In this work, the wire electrical discharge machining (WEDM) performance of WNbMoTaZrx (x = 0.5, 1) RHEAs was investigated, as compared with tungsten, cemented carbide and industrial pure Zr. The cutting efficiency (CE) of the five materials was significantly dependent on the melting points, while the surface roughness (Ra) was not. For the RHEAs, the CE was significantly affected by the pulse-on time (ON), pulse-off time (OFF) and peak current (IP), while the surface roughness was mainly dependent on the ON and IP. The statistical analyses have shown that the CE data of RHEAs have relatively-smaller Weibull moduli than those for the Ra data, which suggests that the CE of RHEAs can be tuned by optimizing the processing parameters. However, it is challenging to tune the surface roughness of RHEAs by tailoring the processing parameters. Differing from the comparative materials, the WEDMed surfaces of the RHEAs showed dense spherical re-solidified particles at upper recast layers, resulting in larger Ra values. The proportion of the upper recast layers can be estimated by the specific discharge energy (SDE). Following the WEDM, the RHEAs maintained the main BCC1 phase, enriched with the W and Ta elements, while the second BCC2 phase in the Zr1.0 RHEA disappeared. Strategies for achieving a better WEDMed surface quality of RHEAs were also proposed and discussed.

Operative Torque Analysis to Evaluate Cutting Efficiency of Two Nickel-Titanium Rotary Instruments for Glide Path: An In Vitro Comparison.

AIM AND OBJECTIVE: The aim and objective of this study was to evaluate and compare the cutting efficacy of two different nickel titanium rotary instruments by a novel methodology: the operative torque (torque and time needed to progress toward the apex). MATERIALS AND METHODS: Ten fresh extracted upper first premolars with two canals were instrumented with a KaVo (Biberach, Germany) and a KaVo 1:1 handpiece at 300 rpm with maximum torque set at 2 N. One canal was instrumented with ProGlider NiTi rotary instruments (Dentsply Sirona Endodontics, Ballaigues, Switzerland), with tip size of 16.02, and the other one with EgdeGlidePath rotary instrument (EdgeEndo, Albuquerque, New Mexico). Mean instrumentation time, mean torque values, and maximum torque values were evaluated for each instrument. The significance level was set at p <0.05. RESULTS: EdgeGlidePath instruments reached the working length in significantly less time with a significantly smaller amount of torque when compared to ProGlider (p >0.05). No instruments exhibited flute deformation or underwent intracanal failure. CONCLUSIONS: Operative torque is related to the capability to cut dentin and progress toward the apex: the smaller the torque values, the higher the cutting ability (and safety). Operative torque is also dependent on debris removal and irrigation techniques. Nevertheless, both operative torque and instrumentation time are clinically relevant parameters for evaluating instruments' performance (i.e., cutting ability). CLINICAL SIGNIFICANCE: Operative torque during endodontic instrumentation helps understanding the overall performance in terms of both cutting efficiency and safety.

Muscle recruitment and stone tool use ergonomics across three million years of Palaeolithic technological transitions.

Ergonomic relationships that minimize muscle activity relative to the creation of cutting stress underpin the design of modern knives, saws, and axes. The Palaeolithic archaeological record, and the > 3 million years of technological behavior that it represents, is predominantly characterized by sharp stone implements used for cutting. To date, we do not know whether Palaeolithic hominins adhered to ergonomic principles when designing stone tools, if lithic technological transitions were linked to ease-of-use advances, or even how muscularly demanding different Palaeolithic tools are on an empirically defined relative basis. Here, we report the results of an experimental program that examines how four key stone tool types, produced between ∼ 3.3 million and ∼ 40 thousand years ago, influence muscle activation in the hominin upper limb. Using standardized laboratory-based tests designed to imitate Pleistocene cutting behaviors, surface electromyography recorded electrical activity (amplitude) in nine muscles across the hand, forearm and shoulder of modern humans during the use of replica Lomekwian, Oldowan, Acheulean and Mousterian stone tools. Results confirm digit flexors and abductors, particularly the first dorsal interosseous and flexor pollicis longus, to be the most heavily recruited muscles during the use of all tool types. Significant differences in muscle activation are, however, identified dependent on the type of stone tool used. Notably, the abductor digiti minimi, flexor pollicis longus, and biceps brachii were highly activated during handaxe use, particularly when compared to the use of Oldowan and Levallois flakes. Results are discussed in light of current understanding on the origin of Lower and Middle Palaeolithic technologies, why specific tool types were produced over others during these periods, and the extent to which early hominins produced ergonomically designed tools.

Cutting efficiency of conventional and heat-treated nickel-titanium rotary or reciprocating glide path instruments.

AIM: To compare the cutting efficiency of several glide path files: HyFlex EDM Glidepath File (HEGF), One G (OG), R-Pilot (RP) and WaveOne Gold Glider (WOGG) at different cutting inclinations. METHODOLOGY: Cutting efficiency of 120 new HEGF, OG, RP and WOGG was tested at 90°, 70° and 45° inclination in relation to the sample. Depending on manufacturer instructions, instruments were tested in continuous rotation or reciprocating motion against standardized gypsum samples for 120 s using a customized apparatus. Cutting efficiency was determined by measuring the weight loss and the length of the sample cut. Data were analysed using two-way analysis of variance and Tukey t-test (P < 0.05). RESULTS: RP and WOGG had greater cutting ability than HEGF and OG in all tested angles. RP tested at 45° had significantly greater cutting efficiency than when tested at 90° and 70° (P < 0.05). OG was not significantly different in terms of cutting ability at 90°, 70° and 45° (P > 0.05). HEGF and WOGG had significantly greater cutting efficiency at 45° and 70° compared to 90° (P < 0.05), with no significant difference between 45° and 70° (P > 0.05). RP had the greatest cutting ability at all tested angles. CONCLUSIONS: Reciprocating glide path instruments had greater cutting efficiency compared to those in continuous rotation. An inclined insertion (45° or 70°) increased the cutting ability of glide path files except for One G conventional NiTi files.

Lateral and axial cutting efficiency of instruments manufactured with conventional nickel-titanium and novel gold metallurgy.

AIM: To isolate the effect of metallurgy in lateral and axial cutting efficacy against plastic and bovine dentine substrates by comparing two rotary systems with identical design but manufactured with either conventional nickel-titanium or heat-treated gold alloy. METHODOLOGY: A total of 258 ProTaper Universal (PTU) and ProTaper Gold (PTG) Shaping instruments were used. Bending behaviour was assessed to determine the appropriate displacement associated with a 2 N force in lateral cutting. Ten instruments of each type were used in lateral action for 60 s against bovine dentine or plastic substrates four consecutive times producing four notches in each specimen. Ten further instruments of each type were used in on axial action in four standardized simulated root canals fabricated from 4-mm thick plastic or dentine discs. Both tests were performed at 300 rpm in a computer-controlled testing platform. Notch area and torsional load were compared with Student's t-tests. Repeated measures ANOVA was used to compare cutting efficiency across the four different time-points. Pearson correlation coefficients between substrates were also determined. RESULTS: For lateral action, all three PTG instruments cut significantly more effectively (P < 0.05) than PTU on the plastic substrate. S1 and S2 PTG cut significantly more after 120 and 180 s (P < 0.05) on bovine dentine substrate. For axial action, S1 and S2 PTG were significantly more efficient in cutting at 180 s on plastic and 120 s on bovine dentine (P < 0.05). CONCLUSION: Instruments made from heat-treated nickel-titanium gold alloy had equal or greater cutting efficiency when compared to those made from conventional nickel-titanium.

Efficiency of powered systems for interproximal enamel reduction (IER) and enamel roughness before and after polishing-an in vitro study.

OBJECTIVE: This aims to evaluate the efficiency of three different powered interproximal enamel reduction (IER) systems and to assess enamel roughness before and after polishing using different polishing times. MATERIAL AND METHODS: Four metal strips of the G5 ProLign Set (swissdentacare, SDC, Grancia, Switzerland), four segmental discs of the ASR-Set 4594 and two sonic tips of the SonicLine Set (both Gebr. Basseler GmbH & Co. KG, Komet, Lemgo, Germany) were evaluated. Human extracted incisors served as the medium. Enamel reduction was determined in five intervals of 15 s each. Polishing was performed for 15 and 30 s using the manufacturers' recommended polishing systems. Enamel roughness (Ra) was quantitatively assessed by confocal laser scanning microscopy (CLSM). RESULTS: Significant differences in terms of enamel reduction were found among the working ends of all tested systems. The time needed to remove 0.1, 0.2 and 0.3 mm of enamel was determined. Surface analysis showed significantly higher mean Ra values for nine out of ten working ends before polishing. This was still the case for five working ends after 15 s and for two after 30 s of polishing. CONCLUSION: The graining and the system used have a significant influence on enamel reduction. The time needed for polishing depends on the last working end used; a polishing time of 30 s is not always appropriate. CLINICAL RELEVANCE: Knowledge about the cutting efficiency of powered IER working ends might help the clinician to estimate better the amount of enamel reduction during the stripping process.

Cutting efficiency of nickel-titanium rotary and reciprocating instruments after prolonged use.

The aim of the present study was to compare the cutting efficiency of Twisted File instruments used in continuous rotation or TF Adaptive motion and evaluate if prolonged use significantly affected their cutting ability. 20 new NiTi instruments were used in the present study (TF tip size 35, 0.06 taper; Sybron-Endo, Orange, CA, USA), divided into 2 subgroups of 10 instruments each, depending on which movement was selected on the endodontic motor. Group 1: TF instruments were activated using the program TF continuous rotation at 500 rpm and torque set at 2 N; Group 2: TF instruments were activated using the reciprocating TF Adaptive motion. Cutting efficiency was tested in a device developed to test the cutting ability of endodontic instruments. Each instrument cut 10 plastic blocks (10 uses) and the length of the surface cut in a plastic block after 1 min was measured in a computerized program with a precision of 0.1 mm. Maximum penetration depth was calculated after 1 use and after 10 uses, and mean and standard deviation (SD) of each group was calculated. Data were statistically analyzed with a one-way ANOVA test (P < 0.05). TF instruments used in continuous rotation (Group 1) cut a mean depth of 10.4 mm (SD = 0.6 mm) after the first use and 10.1 mm (SD 1.1 mm) after 10 uses, while TF instruments used with the Adaptive motion cut a mean depth of 9.9 mm (SD = 0.7 mm) after the first use and 9.6 mm (SD = 0.9 mm) after 10 uses. There was no statistically significant difference between the two groups investigated (P > 0.05) nor between instruments after 1 or 10 uses. In conclusion, the TFA motion showed a lateral cutting ability similar to continuous rotation and all tested instruments exhibited the same cutting ability after prolonged use.

Cutting efficiency of diamond burs operated with electric high-speed dental handpiece on zirconia.

Zirconia-based dental restorations are becoming used more commonly. However, limited attention has been given to the difficulties experienced, concerning cutting, in removing the restorations when needed. The aim of the present study was to compare the cutting efficiency of diamond burs, operated using an electric high-speed dental handpiece, on zirconia (Zir) with those on lithium disilicate glass-ceramic (LD) and leucite glass-ceramic (L). In addition, evaluation of the cutting efficiency of diamond burs on Zir of different thicknesses was performed. Specimens of Zir were prepared with thicknesses of 0.5, 1.0, 2.0, and 4.0 mm, and specimens of LD and L were prepared with a thickness of 1.0 mm. Cutting tests were performed using diamond burs with super coarse (SC) and coarse (C) grains. The handpiece was operated at 150,000 rpm with a cutting force of 0.9 N. The results demonstrated that cutting of Zir took about 1.5- and 7-fold longer than cutting of LD and L, respectively. The SC grains showed significantly higher cutting efficiency on Zir than the C grains. However, when the thickness of Zir increased, the cutting depth was significantly decreased. As it is suggested that cutting of zirconia is time consuming, this should be taken into consideration in advance when working with zirconia restorations.

Determining cutting efficiency of nickel-titanium coronal flaring instruments used in lateral action.

AIM: To develop a method to evaluate the cutting behaviour of nickel-titanium (NiTi) coronal flaring instruments. METHODOLOGY: BioRaCe BR0 (BR), HyFlex CM 1 (HY), ProFile OS No. 2 (PF) and ProTaper Sx (PT) instruments were used in simulated coronal flaring using a lateral action against bovine dentine blocks, at 250 and 500 rpm. Cutting efficiency was assessed by three methods: first, areas of notches produced by instruments were directly measured under a stereomicroscope. Second, dentine specimens were then analysed by surface profilometry to determine the maximum cutting depth and finally by microcomputed tomography to assess the volume of removed dentine. Data were compared using parametric tests with the significance level set at 0.05. RESULTS: For all three methods, HY and PF were the most and the least cutting-efficient instruments, respectively (P < 0.05). Significant differences were detected between 250 and 500 rpm for HY and PT (area); for BR, HY and PT (depth); and for BR and HY (volume). There were strong positive correlations between the results obtained with those three different methods with r-values ranging from 0.81 to 0.92. CONCLUSION: Measuring the amount of material removed in a specific time under stereomicroscopy is a simple and rational way to assess the cutting behaviour of NiTi rotary instruments in lateral action. HyFlex, manufactured with thermomechanically treated NiTi wire, was the most efficient instrument, and increased rotational speed was associated with increased cutting efficiency.

Cutting Efficiency of Diamond Grinders on Composite and Zirconia.

This in vitro study was carried out to compare the cutting efficiency of diamond grinders on zirconia and resin-based composite materials. Grinders were employed with a special holder for the handpiece to apply a constant load (160 g) for resin-based composite (8 cuts, 40 s each) and zirconia materials (4 cuts, 5 min each; n = 10 for each material and grinder). To assess the efficiency of the grinders, weight measurements of the material were taken before and after the grinding process. Scanning electron micrographs were captured for instrument surfaces before and after testing and for the resulting surface of the materials. In the resin-based composite group, there were significant differences in weight removal between the burs for both the baseline (first cut; p = 0.009) and removal after the eighth cut (p = 0.049). Statistically significant decreases in weight removal compared to the baseline values were noted for the third, fourth, sixth, and seventh steps (p ≤ 0.046). For the zirconia group, significant differences existed in weight removal between the burs for the baseline (first cut; p < 0.001) and removal after the fourth cut (p < 0.001). A significant positive correlation was observed between removal and the number of cuts (Pearson: 0.673; p < 0.001). A statistically significant decrease in removal compared to the respective baseline value was found for the fourth step (p = 0.006). The initial wear removal and durability significantly differed between the grinders used on resin-based composite and zirconia. Achieving comparable weight removal took five times longer when grinding zirconia compared to the resin-based composite.

Comparative Evaluation of Cutting Efficiency of Three File Systems-Kedo-SH Manual, Pedoflex Rotary, and Manual K File: An In Vitro Study.

Aims: The purpose of this study was to comparatively evaluate the cutting efficiency of Pedoflex rotary, Kedo SH manual file, and manual K file systems used in root canal instrumentation while performing pulp therapy of deciduous teeth with a stereomicroscope. Materials and Methods: Forty-five extracted primary human root canals were chosen, and following the removal of pulp tissue, the canals were dyed with Indian ink and left to dry for 2 h. The samples were randomly divided into three groups, Group A: Kedo SH manual file system (n = 15), Group B: Pedoflex rotary file system (n = 15), and Group C: Manual K files (n = 15). After root canal instrumentation, all the root canals were cleared to make them transparent. The teeth after clearing were observed under stereomicroscope and scored according to the amount of dye present in the root canals. The data were tabulated and statistically analyzed with SPSS version 16 using Chi-square, Kruskal-Wallis, and Dunn's test (post-hoc). Results: With regards to cutting efficiency, there was a statistically noteworthy difference among groups A and C [P = 0.000] and groups B and C [P = 0.000]. Furthermore, groups A and B did not differ statistically significantly [P = 0.950]. Conclusions: Cutting efficacy of the Pedoflex rotary files was seen to be superior to that of Kedo SH and manual K files. Clinical Significance: Rotary files in deciduous teeth have various benefits over manual files, resulting in a noticeable reduction in working time, which has aided in maintaining patient participation by reducing the risk for fatigue. We conclude that NiTi rotary devices result in a superior cutting efficiency and, as a result, greater clinical success.

Comparative study of the cutting efficiency and working life of carbide burs.

PURPOSE: The aim of this study was to establish the wear and cutting efficiency of tungsten carbide burs from different manufacturers by performing cutting tests with machinable glass ceramic. MATERIALS AND METHODS: Cutting tests were performed with 70 tungsten carbide burs from seven manufacturers: (A) Coltene/Whaledent, (B) CEI, (C) Meisinger, (D) Axis, (E) Komet, (F) Kerr, (G) Edenta. All groups were examined under scanning electron microscope (SEM) before and after the cutting efficiency test for similarities and differences. A specially designed cutting device was used. An electric handpiece was operated at 200,000 rpm with a 120 ml/min coolant water supply rate. The burs were tested under a 165 g constant load using 3 mm wide Macor ceramic as substrate. For each bur the cutting procedure involved a total of five cuts of 3 minutes on every cut, with a total cutting time for each bur of 15 minutes. Data were analyzed using one-way ANOVA at 95.0% confidence level. RESULTS: Significant differences (p < 0.05) were found in the mean cutting rates of the different groups. Groups A and B showed the highest cutting rates. Higher cutting rates were associated with a longer bur lifespan. SEM photomicrographs of the burs and substrates revealed significant changes on the surfaces after the cutting process. CONCLUSIONS: The morphology characteristics of tungsten carbide burs are related to their effectiveness. The group that presented the worst working life also showed substantial wear on its surface according to the results of SEM.

Bone cutting efficiency and heat generation using a traditional fluted Burr and a novel fluteless resurfacing tool.

BACKGROUND: Powered instrumentation is often used for bone preparation and/or removal in many orthopaedic procedures but does risk thermogenesis. This study compares biomechanical properties of a fluted burr and a novel fluteless resurfacing tool. METHODS: Twenty cadaveric metatarsals were tested with four predetermined cutting forces to evaluate heat generation and cutting rate for the fluted burr and fluteless resurfacing tool over 40 s or until a depth of 4 mm was reached. Cutting rate was calculated from displacement transducer data. Heat generation was measured by thermocouples placed in the bone adjacent to the burring site. Assuming a body temperature of 37 °C, a 10 °C increase in heat was used as the threshold of inducing osteonecrosis. FINDINGS: At 1.0 N and 1.7 N, the thermal osteonecrosis threshold was reached at comparable times between burrs, while the bone removed by the resurfacing tool was on average five times greater than fluted burr at 1.0 N and over twice as great at 1.7 N. Statistical analysis of these common cutting forces showed the resurfacing tool had significantly higher cutting rates (P < 0.01). As a result, the fluted burr produced higher temperatures for the same amount of bone removal (P < 0.01). INTERPRETATION: In a cadaveric study, the fluteless resurfacing tool demonstrated higher bone cutting rates and lower heat generation for the same amount of bone removed than a traditional fluted burr.

Influence of kinematics and incidence angles on the cutting efficiency of two single-file nickel-titanium rotary instruments.

To compare the cutting efficiency of F6 Sky Taper (F6ST) and One Curve (OC) with different kinematics and cutting inclinations. Cutting efficiency of 80 new F6ST and OC was tested at 90° and 70° inclination in relation to the sample, in continuous rotation and reciprocation, against standardised gypsum samples for 120 seconds using a customised device. Data expressed as weight loss and length of the sample cut were analysed using two-way analysis of variance and Tukey t-test (P<.05). F6ST showed significantly higher cutting efficiency in reciprocation, while OC in continuous rotation. Regardless of inclination, F6ST showed statistically higher values than OC in reciprocation, while OC exhibited higher cutting ability in continuous rotation. The 70° inclination significantly improved the cutting efficiency of both files. Reciprocation improved the cutting efficiency of F6ST while continuous rotation enhanced cutting ability of OC. An inclined insertion improved the cutting ability, independently from the movement.

Energy Efficiency in CO2 Laser Processing of Hardox 400 Material.

The use of laser technology for materials processing has a wide applicability in various industrial fields, due to its proven advantages, such as processing time, economic efficiency and reduced impact on the natural environment. The expansion of laser technology has been possible due to the dynamics of research in the field. One of the directions of research is to establish the appropriate cutting parameters. The evolution of research in this direction can be deepened by determining the efficiency of laser cutting. Starting from such a hypothesis, the study contains an analysis of laser cutting parameters (speed, power and pressure) to determine the linear energy and cutting efficiency. For this purpose, the linear energy and the cutting efficiency were determined analytically, and the results obtained were tested with the Lagrange interpolation method, the statistical mathematical method and the graphical method. The material chosen was Hardox 400 steel with a thickness of 8 mm, due to its numerous industrial applications and the fact that it is an insufficiently studied material. Statistical data processing shows that the maximum cutting efficiency is mainly influenced by speed, followed by laser power. The results obtained reduce energy costs in manufacturing processes that use the CO2 laser. The combinations identified between laser speed and power lead to a reduction in energy consumption and thus to an increase in processing efficiency. Through the calculation relationships established for linear energy and cutting efficiency, the study contributes to the extension of the theoretical and practical basis.

The Effects of Sterilization Procedures on the Cutting Efficiency of Endodontic Instruments: A Systematic Review and Network Meta-Analysis.

Sterilization processes guarantee the sterility of dental instruments but can negatively affect instrument features by altering their physical and mechanical properties. The endodontic instrumentation can undergo a series of alterations, ranging from corrosion to variation in the cutting angle and then changes in the torsional properties and torsional fatigue resistance. This systematic literature review and meta-analysis aims to investigate alterations to the cutting efficiency of endodontic instruments that are induced by procedures for their disinfection and sterilization. Methodologies adopted for this investigation follow the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) guidelines. The following were used as search terms on PubMed and Scopus: "endodontic sterilization", "endodontic autoclave", "cyclic fatigue", "torsional", "cutting efficiency", "sterilization", "surface characteristics", and "corrosion". At the end of the selection process, 36 articles were identified, and seven of them are included in this systematic review. The results of a meta-analysis conducted for the use of 10 autoclaving cycles shows a standardized mean difference (SMD) of 0.80 with a p-value equal to 0.04 with respect to effect on cutting efficiency. The network meta-analysis, through direct and indirect comparison between the different autoclave cycles (0, 1, 5, 10, and 15 cycles), revealed that treatment involving 15 autoclave cycles produced the most robust results in terms of having the greatest effects in terms of altered cutting efficiency with a probability of 57.7% and a SUCRA (surface under the cumulative ranking) of 80%. The alterations in the effects on cutting efficiency appear to be triggered after five cycles of sterilization by heat (autoclave). In conclusion, the meta-analysis of the data indicates that the autoclave sterilization protocol must not be repeated more than five times to preserve cutting efficiency. Within the limitations of this review, we can therefore establish that sterilization by autoclaving alone results in steel and NiTi instruments becoming less efficient in cutting after five cycles, as measured by a reduction in cutting efficiency.

Cutting efficiency of heat-treated nickel-titanium single-file systems at different incidence angles.

Cutting efficiency of Reciproc R25 (REC) and Reciproc blue R25 (REB) at different inclinations was evaluated. Sixty new files were tested at 90°, 70° and 45° of inclination in relation to the sample (n = 10), using a customised machine. All files were activated in reciprocation against standardised gypsum blocks for 120 s. Cutting efficiency was determined by measuring the block weight loss with an analytical balance and measuring the length of the block surface cut using a digital calliper. Data were statistically analysed (two-way ANOVA, Bonferroni t-test) with the significance level set at P < 0.05. There was no difference for REC among the tested angles. REB had no statistical difference between 90° and 70°; however, its cutting efficiency significantly increased at 45°. There was a significant difference between REC and REB at 45° only. Under these conditions, increased file inclination to 45° and blue heat treatment improved cutting efficiency of reciprocating files.