Is the construct stability of the acetabular cup affected by the acetabular screw configuration in bone defect models?

BACKGROUND: In revision surgery with significant segmental acetabular defects, adequate implant selection and fixation methods are critical in determining successful bony ingrowth. Commercially available total hip prosthesis manufacturers generally offer additional multi-hole options of acetabular shells with identical designs for use in revision THAs where screw holes configurations vary from product to product. This study aims to compare the mechanical stability of the two types of acetabular screw constructs for the fixation of acetabular components: spread-out and pelvic brim-focused configurations. METHODS: We prepared 40 synthetic bone models of the male pelvis. In half of the samples with acetabular defects, identical curvilinear bone defects were manually created using an oscillating electrical saw. On the right side, multi-hole-cups in which the direction of the screw holes are centered on the pelvic brim (brim-focused) and, on the left side, multi-hole-cups with the direction of the screw hole spread throughout the acetabulum (spread-out) were implanted into the pelvic synthetic bones. Coronal lever-out and axial torsion tests were performed with a testing machine, measuring load versus displacement. RESULTS: The average torsional strengths were significantly higher in the spread-out group over the brim-focused group regardless of the presence of the segmental defect of the acetabulum (p < 0.001). But for the lever-out strength, the spread-out group exhibited significantly higher average strength over the brim-focused group for the intact acetabulum (p = 0.004), whereas the results were reversed in the brim-focused group when the defects were generated (p < 0.001). The presence of acetabular defects reduced the average torsional strengths of the two groups by 68.66% versus 70.86%. In comparison, the decrease in the average lever-out strength was less significant for the brim-focused group than the spread-out group (19.87% vs. 34.25%) (p < 0.001). CONCLUSION: Constructs of multi-hole acetabular cups with the spread-out screw holes configuration exhibited statistically better axial torsional strength and coronal lever-out strength. With the presence of posterior segmental bone defects, the spread-out constructs demonstrated significantly better tolerance to axial torsional strength. Still, they exhibited inverted results of higher lever-out strength in the pelvic brim-focused constructs.

Comparative analysis of reciprocating and flat-side heat-treated rotary single-file systems: Design, metallurgical characteristics, and mechanical performance.

AIM: To compare two flat-side single-file rotary instruments with three single-file reciprocating systems through a multimethod assessment. METHODOLOGY: A total of 290 new NiTi single-file rotary (AF F One Blue 25/0.06 and Platinum V.EU 25/0.06) and reciprocating (One Files Blue R25, Reciproc Blue R25, Reciproc R25) instruments were selected, carefully examined for any major deformations, and evaluated regarding their macroscopic and microscopic design, nickel and titanium elements ratio, phase transformation temperatures, and mechanical performance (time/rotation to fracture, maximum torque, angle of rotation, microhardness, maximum bending, and buckling strengths). One-way anova post hoc Tukey, T-test, and nonparametric Mood's median tests were used for statistical comparisons (α = 5%). RESULTS: Tested instruments had identical blade counts and near-identical helical angles of approximately 24° (rotary instruments) and 151° (reciprocating instruments). The flat-side analysis revealed a few inconsistencies, such as discontinuity segments, different orientations, and gaps in the homogeneity of the bluish colour. Microscopically, flat-side instruments exhibited blade discontinuity and an incomplete S-shaped cross-section. The surface finish was smoother for One Files Blue and more irregular for both rotary instruments. There were distinct phase transformation temperatures amongst all instruments. All heat-treated instruments were in R-phase arrangement, and Reciproc was in R-phase plus austenite at test temperature (20°C). Compared with the reciprocating instruments, both flat-side instruments exhibited lower results in the cyclic fatigue tests using two different clockwise kinematics, maximum torque, angle of rotation, and maximum buckling strength (p < .05). The rotary systems also exhibited low flexibility (p < .05). AF F One Blue had the lowest microhardness, whilst Reciproc had the highest value. CONCLUSION: This multimethod investigation revealed that the flat-side rotary instruments underperformed the reciprocating instruments regarding cyclic fatigue (with two different clockwise kinematics), maximum torque, angle of rotation, maximum buckling strength, and flexibility. Manufacturing inconsistencies were also observed in some of the flat-side instruments, including discontinuity segments, different orientations, and in the homogeneity of their bluish colour given by the heat treatment.

Effect from Autoclave Sterilization and Usage on the Fracture Resistance of Heat-Treated Nickel-Titanium Rotary Files.

This study aimed to assess the effect of mechanical loading and heating on the cyclic fatigue and torsional fracture resistances of heat-treated nickel-titanium files after usage and autoclaving. Sixty files (One Curve) were tested for cyclic fatigue and torsional fracture resistances using customized devices. The files were divided into three groups according to the test conditions (n = 10); new (group-N), used for simulated canal shaping (group-U), and sterilized after use (group-S). For cyclic fatigue resistances, the files were freely rotated in a curved metal canal under body temperature; the time elapsed to fracture was recorded and the numbers of cycles to fracture (NCF) were calculated. For the torsional resistances, the file tip was fixed and rotated until the file fractured. The maximum torsional load and distortion angle were recorded. The toughness was calculated. Fracture fragments were examined with a scanning electron microscope. Data were analyzed using a one-way analysis of variance and Tukey's post hoc test at the significance level of 95%. Group-U showed significantly higher NCF than group-S (p < 0.05). However, there was no significant differences between groups-N and -S in the NCF (p > 0.05). Group-N showed a significantly bigger distortional angle and higher torsional toughness than groups-U and -S, but the ultimate torsional strength did not have significant difference between the groups. Under the limitation of this study, autoclave sterilization after single-usage did not improve the fracture resistance of heat-treated One Curve nickel-titanium files.

Process Parameter Investigation and Torsional Strength Analysis of the Additively Manufactured 3D Structures Made of 20MnCr5 Steel.

An ongoing growth of the available materials dedicated to additive manufacturing (AM) significantly extends the possibilities of their usage in many applications. A very good example is 20MnCr5 steel which is very popular in conventional manufacturing technologies and shows good processability in AM processes. This research takes into account the process parameter selection and torsional strength analysis of AM cellular structures. The conducted research revealed a significant tendency for between-layer cracking which is strictly dependent on the layered structure of the material. Additionally, the highest torsional strength was registered for specimens with a honeycomb structure. To determine the best-obtained properties, in the case of the samples with cellular structures, a torque-to-mass coefficient was introduced. It indicated the best properties of honeycomb structures, which have about 10% smaller torque-to-mass coefficient values than monolithic structures (PM samples).

Impact of kinematics on the efficiency and safety of an engine-driven file for glide path preparation in MB2 canals of maxillary molars.

AIM: To evaluate the influence of different kinematics on the efficiency and safety of an engine-driven file for glide path preparation in second mesiobuccal canals (MB2) of maxillary molars. In addition, the torsional resistance of the file was assessed after use. METHODOLOGY: Thirty-six maxillary first and second molars with two canals in the mesiobuccal root were selected and the anatomy of the canals was verified by micro-CT. The teeth were divided into 4 groups (n = 9) according to the kinematics used for glide path preparation: continuous rotation (CR), 30°/150° reciprocation (REC 30°/150°), 30°/90° reciprocation (REC 30°/90°), and 90° optimum glide path motion (OGP 90°). The duration of the procedure, number of canals in which the file reached the full working length (RFWL), canal volume before and after the procedure, rate of file fracture, and file torsional strength after use were evaluated. The ANOVA and Tukey tests or Kruskal-Wallis and Dunn tests were used for statistical analysis. RESULTS: No significant differences among the groups were found for procedure duration, success at reaching the FWL, distance from the file to apex, and number of fractured files (P > 0.05). The CR group showed a significant decrease in rotation angle compared with REC 90° and OGP 90° groups (P < 0.05). There was no significant difference in canal volume among the groups (P > 0.05). CONCLUSION: The type of kinematics used did not affect the efficiency, success rate, and shaping ability of the file during glide path preparation. CR seems to induce more torsional stress than the other kinematics. CLINICAL RELEVANCE: The glide path preparation of narrow canals such as the MB2 is difficult and accidents such as file fracture may occur. This study showed that reciprocation with different file angulations can be safer during this challenging stage.

Characterization of the file-specific heat-treated ProTaper Ultimate rotary system.

AIM: To compare design, metallurgy and mechanical performance of the ProTaper (PT) Ultimate system with instruments of similar dimensions from the ProGlider, PT Gold and PT Universal systems. METHODOLOGY: New PT Ultimate instruments (n = 248) were compared with instruments of similar dimensions from ProGlider (n = 31), PT Gold (n = 155) and PT Universal (n = 155) systems regarding their number of spirals, helical angle, blade symmetry, tip geometry, surface finishing, nickel/titanium ratio, phase transformation temperatures and mechanical performance. One-way anova and nonparametric Mood's median tests were used for statistical comparison (α = 5%). RESULTS: All instruments had symmetrical blades without radial lands or flat sides, similar surface finishing and an almost equiatomic nickel/titanium ratio, whilst the number of spirals, helical angles and the tip geometry were different. PT Ultimate instruments showed 3 distinct heat treatments that matched with the colour of their metal wire. Slider and ProGlider instruments had similar R-phase start (Rs) and R-phase finish (Rf) temperatures. SX, F1, F2, F3 and Shaper instruments showed equivalent heat treatments (Rs ~45.6°C and Rf ~28.3°C) that were similar to their PT Gold counterparts (Rs ~47.9°C and Rf ~28.2°C), but completely distinct to the PT Universal ones (Rs ~16.2°C and Rf ~-18.2°C). Amongst the PT Ultimate instruments, the lowest maximum torques were observed in the SX (0.44 N cm), Slider (0.45 N cm) and Shaper (0.60 N cm) instruments, whilst the highest was noted in the FXL (4.90 N cm). PT Ultimate Slider and ProGlider had similar torsional (~0.40 N cm) and bending loads (~145.0 gf) (p = 1.000), whilst the other PT Ultimate instruments showed statistically significantly lower maximum torque, higher angle of rotation and lower bending load (higher flexibility) than their counterparts of the PT Universal and PT Gold systems. CONCLUSIONS: The PT Ultimate system comprises instruments with 3 distinct heat treatments that showed similar phase transformation temperatures to their heat-treated analogues. PT Ultimate instruments presented lower torsional strength and superior flexibility than their counterparts, whilst maximum torque, angle of rotation and bending loads progressively increased with their sizes.

Mechanical Characterisation and Numerical Modelling of TPMS-Based Gyroid and Diamond Ti6Al4V Scaffolds for Bone Implants: An Integrated Approach for Translational Consideration.

Additive manufacturing has been used to develop a variety of scaffold designs for clinical and industrial applications. Mechanical properties (i.e., compression, tension, bending, and torsion response) of these scaffolds are significantly important for load-bearing orthopaedic implants. In this study, we designed and additively manufactured porous metallic biomaterials based on two different types of triply periodic minimal surface structures (i.e., gyroid and diamond) that mimic the mechanical properties of bone, such as porosity, stiffness, and strength. Physical and mechanical properties, including compressive, tensile, bending, and torsional stiffness and strength of the developed scaffolds, were then characterised experimentally and numerically using finite element method. Sheet thickness was constant at 300 µm, and the unit cell size was varied to generate different pore sizes and porosities. Gyroid scaffolds had a pore size in the range of 600-1200 µm and a porosity in the range of 54-72%, respectively. Corresponding values for the diamond were 900-1500 µm and 56-70%. Both structure types were validated experimentally, and a wide range of mechanical properties (including stiffness and yield strength) were predicted using the finite element method. The stiffness and strength of both structures are comparable to that of cortical bone, hence reducing the risks of scaffold failure. The results demonstrate that the developed scaffolds mimic the physical and mechanical properties of cortical bone and can be suitable for bone replacement and orthopaedic implants. However, an optimal design should be chosen based on specific performance requirements.

Improved Equations for the Torsional Strength of Reinforced Concrete Beams for Codes of Practice Based on the Space Truss Analogy.

Design codes provide the necessary tools to check the torsional strength of reinforced concrete (RC) members. However, some researchers have pointed out that code equations still need improvement. This study presents a review and a comparative analysis of the calculation procedures to predict the torsional strength of RC beams from some reference design codes, namely the Russian, American, European, and Canadian codes for RC structures. The reliability and accuracy of the normative torsional strengths are checked against experimental results from a broad database incorporating 202 RC rectangular beams tested under pure torsion and collected from the literature. The results show that both the readability and accuracy of the codes' equations should be improved. Based on a correlation study between the experimental torsional strengths, and geometrical and mechanical properties of the beams, refined yet simple equations are proposed to predict torsional strength. It is demonstrated that the proposed formulation is characterized by a significant improvement over the reference design codes. The efficiency of the proposed formulae is also assessed against another equation earlier proposed in the literature, and an improvement is noted as well. From the results, it can be concluded that the proposed equations in this study can contribute to a more accurate and economical design for practice.

Multimethod Assessment of Design, Metallurgical, and Mechanical Characteristics of Original and Counterfeit ProGlider Instruments.

A multimethod study was conducted to assess the differences between original (PG-OR) and counterfeit (PG-CF) ProGlider instruments regarding design, metallurgical features, and mechanical performance. Seventy PG-OR and PG-CF instruments (n = 35 per group) were evaluated regarding the number of spirals, helical angles, and measuring line position by stereomicroscopy, while blade symmetry, cross-section geometry, tip design, and surface were assessed by scanning electron microscopy. Energy-dispersive X-ray spectroscopy and differential scanning calorimetry were used to identify element ratio and phase transformation temperatures, while cyclic fatigue, torsional, and bending testing were employed to assess their mechanical performance. An unpaired t-test and nonparametric Mann−Whitney U test were used to compare instruments at a significance level of 5%. Similarities were observed in the number of spirals, helical angles, blade symmetry, cross-sectional geometries, and nickel−titanium ratios. Measuring lines were more reliable in the original instrument, while differences were noted in the geometry of the tips (sharper tip for the original and rounded for the counterfeit) and surface finishing with PG-CF presenting more surface irregularities. PG-OR showed significantly more time to fracture (118 s), a higher angle of rotation (440°), and a lower maximum bending load (146.3 gf) (p < 0.05) than PG-CF (p < 0.05); however, maximum torque was similar for both instruments (0.4 N.cm) (p > 0.05). Although the tested instruments had a similar design, the original ProGlider showed superior mechanical behavior. The results of counterfeit ProGlider instruments were unreliable and can be considered unsafe for glide path procedures.

Relationship to drill bit diameter and residual fracture resistance of the distal tibia.

BACKGROUND: The etiology of bone refractures after screw removal can be attributed to residual drill hole defects. This biomechanical study compared the torsional strength of bones containing various sized cortical drill defects in a tibia model. METHODS: Bicortical drill hole defects of 3 mm, 4 mm, and 5 mm diameters were tested in 26 composite tibias versus intact controls without a drill defect. Each tibia was secured in alignment with the rotational axis of a materials testing system and the proximal end rotated internally at a rate of 1 deg./s until mechanical failure. FINDINGS: All defect test groups were significantly lower (P < 0.01) in torque-to-failure than the intact group (82.80 ± 3.70 Nm). The 4 mm drill hole group was characterized by a significantly lower (P = 0.021) torque-to-failure (51.00 ± 3.27 Nm) when compared to the 3 mm drill hole (59.00 ± 5.48 Nm) group, but not different than the 5 mm hole group (55.71 ± 5.71 Nm). All bones failed through spiral fractures, bones with defects also exhibited posterior butterfly fragments. INTERPRETATION: All the tested drill hole sizes in this study significantly reduced the torque-to-failure from intact by a range of 28.4% to 38.4%, in agreement with previous similar studies. The 5 mm drill hole represented a 22.7% diameter defect, the 4 mm drill hole a 18.2% diameter defect, and the 3 mm drill hole a 13.6% diameter defect. Clinicians should be cognizant of this diminution of long bone strength after a residual bone defect in their creation and management of patient rehabilitation programs.

Mechanical and Metallurgical Evaluation of 3 Different Nickel-Titanium Rotary Instruments: An In Vitro and In Laboratory Study.

An in-depth evaluation of the mechanical and metallurgical properties of NiTi instruments is fundamental to assess their performance and to compare recently introduced instrument with widespread ones. According to this, since there are no data on this topic, the aim of the study was to mechanically and metallurgically evaluate an instrument recently introduced into the market (ZenFlex (ZF)), by comparing it with two well-known instruments with similar characteristics: Vortex Blue (VB) and EdgeSequel Sapphire (EES). According to this, 195 instruments were selected: 65 ZF, 65 VB and 65 EES. Each group was divided in subgroups according to the mechanical tests (i.e., cyclic fatigue resistance, torsional resistance and bending ability; (n = 20)) and the metallurgical test (differential scanning calorimetry (n = 5)). A scanning electron microscopy was performed to verify the causes of fracture after mechanical tests (cyclic fatigue and torsional tests). According to results, VB showed the highest flexibility and cyclic fatigue resistance in comparison to the other instruments, with a statistically significant difference (p < 0.05). Regarding torsional resistance, EES showed the lowest value of torque at fracture, with a statistically significant difference, whilst the comparison between ZF and VB showed no statistically significant difference (p > 0.05). DSC analysis pointed out that VB had the highest austenite start and finish temperatures, followed by ESS and then ZF. ESS sample showed the highest martensite start and finish temperatures followed by VB and ZF. Considering the results, it can be concluded that VB showed the best mechanical performance during static tests in comparison to ESS and ZF. This is fundamentally due to the interaction of parameters such as instrument design and heat-treatments that are able to enhance its mechanical performance.

Comparison of five rotary systems regarding design, metallurgy, mechanical performance, and canal preparation-a multimethod research.

OBJECTIVES: To compare the design, metallurgy, mechanical performance, and canal preparation of 5 rotary systems. MATERIAL AND METHODS: A total of 735 25-mm NiTi instruments (sizes 0.17[0.18]/.02v, 0.20/.04v, 0.20/.07v, 0.25/.08v, 0.30/.09v) from ProTaper Gold, ProTaper Universal, Premium Taper Gold, Go-Taper Flex, and U-File systems were compared regarding overall geometry and surface finishing (stereomicroscopy and scanning electron microscopy), nickel and titanium ratio (energy-dispersive spectroscopy), phase transformation temperatures (differential scanning calorimetry), mechanical performance (torsional and bending tests), and unprepared canal surface (micro-CT). One-way ANOVA and Mood's median tests were used for statistical comparisons with a significance level set at 5%. RESULTS: Stereomicroscopic analysis showed more spirals and high helical angles in the Premium Taper Gold system. All sets of instruments had symmetrical spirals, no radial lands, no major defects, and an almost equiatomic ratio between nickel and titanium elements, while differences were observed in their tips' geometry and surface finishing. At room temperature (20 °C), DSC test revealed martensitic characteristics for ProTaper Gold and Go-Taper Flex, and mixed austenite plus R-phase for the Premium Taper Gold, while ProTaper Universal and U-Files had full austenitic characteristics. Overall, larger instruments had higher torque resistance and bending load values than smaller ones, while a lack of consistency and mixed values were observed in the angle of rotation. The 0.25/.08v and 0.30/.09v instruments of ProTaper Universal and U-File had the highest maximum torques, the lowest angles of rotation, and the highest bending loads than other tested systems (P < .05). No significant difference was noted regarding the untouched root canal walls after preparation with the tested systems (P > .05). CONCLUSIONS: Although differences observed in the overall geometry and phase transformation temperatures have influenced the results of mechanical tests, unprepared canal surface areas were equivalent among systems. CLINICAL RELEVANCE: Root canal preparation systems with similar geometries might present different mechanical behaviors but equivalent shaping ability.

Evaluation of Design, Metallurgy, Microhardness, and Mechanical Properties of Glide Path Instruments: A Multimethod Approach.

INTRODUCTION: This study aims to compare the design, metallurgy, microhardness, and mechanical properties of 3 glide path nickel-titanium (NiTi) instruments. METHODS: A total of 132 ProGlider (Dentsply Sirona, Ballaigues, Switzerland), Edge Glide Path (EdgeEndo, Johnson City, TN), and R-Pilot instruments (VDW, Munich, Germany) (44 per group) were selected. Design was assessed through stereomicroscopy (blades, helical angle, measuring lines, and deformation) and scanning electron microscopy (symmetry, cross section, tip, and surface finishing). NiTi ratios were measured by energy-dispersive X-ray spectroscopy and phase transformation temperatures by differential scanning calorimetry. Microhardness and mechanical performance (torsion, bending, and buckling resistance tests) were also evaluated. Statistical analyses were performed with the Mood median test with a significance set at 5%. RESULTS: The Edge Glide Path had the lowest number of blades and the R-Pilot the greatest helical angle. All instruments had an almost equiatomic NiTi ratio, while showing different cross sections and tip geometries. The Edge Glide Path had a smoother surface finishing. The R-Pilot showed martensitic characteristics at room temperature, whereas mixed austenite plus R-phase was observed in the other instruments. The R-Pilot had higher results on the microhardness (436.8 hardness Vickers number), maximum torsion (0.9 Ncm), and buckling load (0.7 N) tests (P < .05), whereas the Edge Glide Path had a superior angle of rotation (683.5°) and the ProGlider was more flexible (144.1 gf) (P < .05). CONCLUSIONS: Differences in the design of the instruments and the phase transformation temperatures accounted for their mechanical behavior. The R-Pilot showed the highest torque, buckling, and microhardness, whereas the ProGlider instrument was the most flexible.

Optimum glide path motion is safer than continuous rotation of files in glide path preparation.

This study evaluated the resistance to flexural fatigue and torsional strength of files for glide path preparation in continuous rotation or Optimum Glide Path motion (OGP). ScoutRace 15.02 and ProGlider 16.02 files were used in a dynamic testing device during preparation of simulating curved root canals (40-degree curvature and 5 mm radius). For the torsional test, a machine was used to test torsion measured maximum torsional strength (N.cm). Two-way anova and Tukey's multiple comparisons test were used for statistical analysis. Files in OGP motion had a statistically better resistance to flexural fatigue (P < 0.05). ProGlider files took longer time to failure than ScoutRace files only when OGP was used (P < 0.05). The torsional test revealed that OGP produced significantly less torsional stress than rotary motions for both types of glide path files (P < 0.05) In conclusion, OGP motion increased substantially the mechanical safety of endodontic glide path files.

Design, metallurgical features, mechanical performance and canal preparation of six reciprocating instruments.

AIM: To compare six reciprocating instruments regarding their geometric design, metallurgical characteristics, mechanical behaviour and ability to prepare root canals. METHODOLOGY: A total of 246 new 25-mm NiTi instruments (41 per group) from six reciprocating systems (Reciproc, Reciproc Blue, One Files, One Files Blue, Reverso Silver, and WaveOne Gold) were evaluated throughout a multimethod approach regarding their design using stereomicroscopy (number of blades and helix angle) and scanning electron microscopy (blades symmetry, cross section and surface finishing), nickel-titanium composition, phase transformation temperatures, mechanical performance (cyclic fatigue, torsional and bending resistance) and unprepared canal surface area on anatomically matched mandibular molars assessed by micro-CT. One-way ANOVA and post hoc Tukey's or Mood's median tests were selected depending on sample distribution with significance level set at 5%. RESULTS: The instruments had similarities regarding their metal composition and unprepared canal area, whilst differences in phase transformation temperatures and geometric design (number of blades, surface finishing and tip geometry) were observed. Overall, no difference was observed regarding the maximum torque values (P > 0.05), whilst One Files (72 s) and One Files Blue (414 s) had the shortest and longest times to fracture, respectively (P < 0.05). Similar angles of rotation were observed in Reciproc (310°), One Files (285°) and Reverso Silver (318°) instruments (P > 0.05), which were significantly lower than Reciproc Blue (492°), One Files Blue (456°) and WaveOne Gold (492°; P < 0.05). Maximum bending load demonstrated that Reciproc Blue (201.3 gf) was significantly more flexible that the other instruments (P < 0.05). CONCLUSION: Although there were similarities in metal composition and percentage of unprepared canal surface, the instruments had differences in the overall geometric design, phase transformation temperatures and in the four mechanical resistance parameters (time to fracture, maximum torque, angle of rotation and maximum bending load).

Mechanical strength of stainless steel and titanium alloy mini-implants with different diameters: an experimental laboratory study.

BACKGROUND: The mechanical strength of mini-implants is a critical factor due to their small diameters. Currently, it is not possible to state whether there is a relevant difference between the mechanical properties of stainless steel (SS-MIs) and titanium alloy mini-implants (TA-MIs). The objective of this study was to test the null hypothesis that there is no difference in the mechanical strength of SS-MIs and TA-MIs, and to analyze, by scanning electron microscopy (SEM), the SS-MI, and TA-MI threads resistance to morphological damage after insertion. METHODS: A standardized sample of 504 SS-MIs and TA-MIs with diameters ranging from 1.2 mm to 1.8 mm was used. Torsional fracture was performed in 154 MIs. Flexural strength of 280 MIs was evaluated at 1 mm and 2 mm-deflection. The threads of 70 MIs were morphologically analyzed by scanning electron microscopy (SEM), before and after their insertion in high-density artificial bone blocks. Comparisons between SS-MIs and TA-MIs were performed with t tests or Mann-Whitney U tests. A multiple linear regression analysis was used to evaluate the influence of variables on the ranging of MI mechanical strength. RESULTS: SS-MIs had higher fracture torque. The mean difference between the SS-MIs and TA-MIs fracture torque was of 4.09 Ncm. The MI diameter explained 90.3% of the total variation in fracture torque, while only 2.2% was explained by the metallic alloy. The SS-MI group presented a higher deformation force during the 1mm and 2mm-deflection. The mean difference between the flexural strength of SS and TA-MIs at 1 mm and 2 mm-deflection was of 18.21 N and 17.55 N, respectively. There was no noticeable morphological damage to the threads of SS-MIs and TA-MIs. CONCLUSIONS: The null hypothesis was rejected. SS-MIs were 13.2% and 20.2% more resistant to torsional fracture and deflection, respectively. The threads of the SS-MIs and TA-MIs were not damaged during the insertion and removal process. Thus, the use of SS-MI can reduce the fracture risk without increasing the MI diameter.

Comparison of the Torsional Resistance of 4 Different Glide Path Instruments.

INTRODUCTION: The present study aimed to compare the torsional strength of the initial files of the Mtwo (VDW, Munich, Germany) and novel Rotate systems (VDW, Munich, Germany) with the ProGlider (Dentsply Sirona, Ballaigues, Switzerland) and R-Pilot (VDW) glide path instruments. METHODS: The Mtwo (10/.04), ProGlider (16/.02), R-Pilot (12.5/.04), and Rotate (15/.04) glide path files were compared regarding their torsional strength, which was tested using a specially designed test device (N = 20). The data obtained were statistically analyzed at 5% significance level using 1-way analysis of variance and the post hoc Tukey test. The fragment surfaces and separated instruments were examined with ×50, ×100, and ×1000 magnification under a scanning electron microscope. RESULTS: The R-Pilot group showed the highest torsional strength value among all groups (P < .05), whereas there was no significant difference between the torsional strength values of the Mtwo and ProGlider groups (P > .05). The Rotate group had the lowest torsional strength among all groups (P < .05). The Mtwo group showed the lowest angle of rotation among all groups (P < .05). CONCLUSIONS: Although the R-Pilot glide path file exhibited the highest torsional strength in all groups, Rotate showed the highest angle of rotation. Differences in torsional resistance of the instruments may be associated with their manufacturing methods and design features.

Comparison of design, metallurgy, mechanical performance and shaping ability of replica-like and counterfeit instruments of the ProTaper Next system.

AIM: To compare the ProTaper Next (PTN) system with a replica-like and a counterfeit system regarding design, metallurgy, mechanical performance and shaping ability. METHODOLOGY: Replica-like (X-File) and counterfeit (PTN-CF) instruments were compared to the PTN system regarding design (microscopy), phase transformation temperatures (differential scanning calorimetry), nickel-titanium ratio (energy-dispersive X-ray spectroscopy), cyclic fatigue, torsional resistance, bending strength, and untouched canal areas in extracted mandibular molars (micro-CT). anova, post hoc Tukey's and Kruskal-Wallis tests were used according to normality assessment (Shapiro-Wilk test) with the significance level set at 5%. RESULTS: Overall similarities in design and nickel-titanium (Ni/Ti) ratio were observed amongst instruments with the X-File having a smoother surface finish. PTN and PTN-CF had mixed austenite plus R-phase (R-phase start approximately at 45 ºC and near 30 ºC, respectively), whilst X-File instruments were austenitic (R-phase started at approximately at 17 ºC) at room temperature (20 ºC). PTN-CF had the greatest inconsistency in the phase transformation temperatures. Time to fracture of PTN-CF X2 and X3 was significantly shorter than PTN and X-File instruments (P < 0.05), whilst no difference was noted in maximum torque to fracture amongst the tested systems (P > 0.05). X-Files and PTN-CF had a stress-induced phase change during bending load. Mean unprepared surface areas of root canals were 25.8% (PTN), 31.1% (X-File) and 32.5% (PTN-CF) with no significant difference amongst groups (P > 0.05). CONCLUSION: Similarities amongst the systems were noted in the Ni/Ti ratio and maximum torque to fracture, whilst differences were observed in the design, phase transformation temperatures and mechanical behaviour. The ProTaper Next counterfeit instruments could be considered as the less secure system considering its low-cyclic fatigue resistance. Apart from these differences, the unprepared canal surface areas, obtained with the tested systems, were similar.

Efeito da sequência de processamento durante a fabricação de instrumentos endodônticos Niti em suas propriedades mecânicas / Effect of the processing sequence during the manufacture of niti endodontic instruments on their mechanical properties

As características geométricas e técnicas de fabricação das limas endodônticas afetam o desempenho clínico e sua resistência à fratura, flexibilidade e outras propriedades. Um parâmetro muito explorado na Endodontia é a utilização de tratamentos térmicos, que promovem um aumento na resistência à fadiga e flexibilidade destes materiais. Neste estudo pretendeu-se avaliar o efeito de diferentes processos de tratamento térmico/usinagem nas propriedades físicas, flexibilidade, resistência torcional e à fadiga flexural dos instrumentos Prodesign Logic (PDL), verificando se a sequência de processamento dos instrumentos levaria a comportamentos mecânicos diferentes. Este sistema é fabricado a partir de um método inovador que envolve a realização do tratamento térmico para obtenção de memória de forma no fio NiTi anteriormente à usinagem. A hipótese nula a ser testada é que o momento de aplicação dos procedimentos de tratamento térmico e usinagem não afetariam as propriedades físicas e mecânicas de instrumentos endodônticos de NiTi. Para grupos de comparação, foram utilizados protótipos de instrumentos com as mesmas características geométricas e dimensionais, sendo um grupo de instrumentos sem tratamento térmico aplicado (SEP) e outro com o tratamento térmico realizado de forma convencional, após a usinagem do instrumento (HTP). Foram realizadas caracterização física e microestrutural com ensaios de calorimetria exploratória diferencial (DSC) e testes de difratometria de Raios-X (DRX), além de ensaios mecânicos divididos em testes de torção, dobramento em 45 e resistência à fadiga flexural. Os resultados mostraram que macroscopicamente não houve nenhuma alteração importante nas características dos três grupos de instrumentos, exceto mudanças de cor devido a diferentes sequências de processamento. Os resultados de DSC mostraram que à temperatura ambiente a liga é principalmente austenítica no grupo SEP e que após o tratamento térmico realizado nos grupos PDL e HTP, houve uma mudança nas temperaturas de transformação, com um aumento da temperatura de Af e predominância da liga NiTi em fase R. Os resultados de XDR confirmaram os achados do DSC. As diferenças nos parâmetros medidos entre diferentes tipos de instrumentos nos ensaios de resistência torcional, dobramento a 45º e fadiga flexural foi sempre considerada com um nível de significância de 95%. Os resultados para os ensaios de flexão mostraram que o grupo HTP mostrou-se o mais flexível, com os mais baixos valores de momento de dobramento, seguido por PDL e SEP. Nos resultados dos ensaios de torção foi possível observar que SEP apresentou valores mais altos de torque seguido por PDL e HTP (p<.05). Os ensaios de resistência à fadiga mostraram valores médios de NCF maiores para HTP, seguido por PDL e SEP. Entretanto, um pior comportamento do PDL só seria evidenciado clinicamente se os instrumentos fossem usados um número de vezes maior do que o recomendado pelo fabricante. Pode-se concluir que alterar o processo de fabricação dos instrumentos endodônticos, invertendo-se as etapas de usinagem e tratamento térmico, levou, de fato, a uma mudança no comportamento mecânico de instrumentos Prodesign Logic em relação aos prótótipos.

The geometric characteristics and manufacturing techniques of endodontic instruments affect clinical performance, fracture resistance, flexibility and other properties. A parameter widely explored in Endodontics is the use of heat treatments, which promote an increase in the resistance to fatigue and flexibility of these materials. This study aimed to evaluate the effect of different heat treatment / machining processes on the physical properties, flexibility, torsional strength and flexural fatigue of Prodesign Logic (PDL) instruments, verifying whether the processing sequence of the instruments would lead to different mechanical behaviors. This system is manufactured using an innovative method that involves performing thermal treatment to obtain shape memory in the NiTi wire prior to machining. The null hypothesis to be tested is that the moment of application of the heat treatment and machining procedures would not affect the physical and mechanical properties of NiTi endodontic instruments. For comparison groups, instrument prototypes with the same geometric and dimensional characteristics were used, being one group of instruments without thermal treatment applied (SEP) and another with thermal treatment carried out in a conventional manner, after machining the instrument (HTP). Physical and microstructural characterization were performed with differential scanning calorimetry (DSC) tests and X-ray diffractometry (XRD) tests, in addition to mechanical tests divided into torsion tests, 45° bending and resistance to flexural fatigue. The results showed that macroscopically there were no major change in the characteristics of the three groups of instruments, except for color changes due to different processing sequences. The DSC results showed that at room temperature the alloy is mainly austenitic in the SEP group and that after the heat treatment carried out in the PDL and HTP groups, there was a change in the transformation temperatures, with an increase in the Af temperature and predominance of the NiTi alloy in phase R. The XRD results confirmed the DSC findings. Differences in the parameters measured between different types of instruments in the tests of torsional resistance, bending at 45º and flexural fatigue were always considered with a significance level of 95%. The results for the flexibility tests showed that the HTP group proved to be the most flexible, with the lowest values, followed by PDL and SEP. In the results of the torsion tests it was possible to observe that SEP presented higher values of torque followed by PDL and HTP (p <.05). Fatigue resistance tests showed higher mean NCF values for HTP, followed by PDL and SEP. However, a worse behavior of the PDL would only be evidenced clinically if the instruments were used several times greater than that recommended by the manufacturer. It can be concluded that changing the manufacturing process of endodontic instruments, inverting the machining and heat treatment steps, led, in fact, to a change in the mechanical behavior of Prodesign Logic instruments in relation to the prototypes.

Preparation of high-performance polyethylene tubes under the coexistence of silicone cross-linked polyethylene and rotation extrusion.

In this study, the silicone cross-linked polyethylene (Si-XLPE) powder with better thermoplastic performance and abundant cross-linked network points was attained by using solid-state shear mechanochemical (S3M) technology and it was added into high-density polyethylene (HDPE) matrix to prepare Si-XLPE/HDPE tubes by a rotation extrusion rheometer. SEM and 2D-SAXS experiments showed that the presence of Si-XLPE and rotation extrusion facilitated the formation of stable shish-kebabs which deviated from the axial direction in polyethylene (PE) tubes. This result was interpreted that introduction of Si-XLPE in PE tubes provided abundant molecular cross-linked network structures, which suppressed the thermal movement and relaxation of oriented molecular chains owing to intermolecular interaction. Moreover, the axial and hoop flow field further promoted orientation of the permanent cross-linked network entanglement points and formation of more stable cluster-like shish structures in the off-axial direction during the rotation extrusion process. Besides, our experimental results had also ascertained that molecular orientation and shish-kebabs in off-axial direction should be the primary responsibility for the remarkable enhancement of hoop torsional strength in PE tubes. Hoop torsional strength of PE tubes adding Si-XLPE reached 19.58 MPa when the mandrel rotation rate was 30 r.p.m., while that of conventional extruded PE tubes was only 9.83 MPa. As a consequence, PE tubes with excellent performance were prepared under the combined effect of Si-XLPE and rotation extrusion.