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Introduction NiTi archwires are distinguished by their ability to deliver gentle, continuous forces over a wide activation range, over time, their crystalline structure has evolved: beginning with conventional NiTi, progressing to super-elastic variants, and then advancing to heat-activated. In this study, we examined three 0.016″ × 0.022″ NiTi rectangular wires: (1) super-elastic NT3 SE®, (2) heat-activated Thermal Ti-D® (active at ~ 25 °C), and (3) heat-activated Thermal Ti-Lite® (~ 35 °C)—by measuring their force release at molar, premolar, and incisor positions to determine whether unloading forces differ by location. Materials and methods A randomized, in-vitro trial was conducted at Aleppo University. Each group included six 30 mm wire sections for each wire type and position (total n = 18 per position). A three-point bending test at 37 °C (Deflection: 3.1 mm at 1 mm/min over a 10 mm span) measured unloading forces at 0.5, 1-, 2-, and 3-mm. Plateau length (3 to 0.5 mm), average force, and slope were recorded. Data were analyzed using one-way ANOVA with post-hoc Sidak’s test; reliability was confirmed via Pearson correlation ( r  = 0.877). Results NT3 SE® and Thermal Ti-D® wires showed similar unloading forces across positions (molar: 2.65 ± 0.11, 1.60 ± 0.18, 1.40 ± 0.18, 1.09 ± 0.19 N; incisor: 2.55 ± 0.12, 1.50 ± 0.18, 1.30 ± 0.18, 1.00 ± 0.15 N at 3, 2, 1, and 0.5 mm, respectively), with molar values approximately 10% higher than incisor values; differences were not statistically significant ( p  > 0.05), and 95% confidence intervals overlapped. Thermal Ti Lite® wires exhibited significantly lower forces overall and clear site-dependent differences (molar: 2.28 ± 0.21, 1.76 ± 0.10, 0.52 ± 0.09, 0.56 ± 0.14 N; premolar: 1.92 ± 0.12, 0.56 ± 0.10, 0.32 ± 0.09, 0.31 ± 0.09 N; incisor: 1.57 ± 0.20, 0.36 ± 0.10, 0.12 ± 0.09, 0.12 ± 0.09 N at 3, 2, 1, and 0.5 mm, respectively), with molar forces on average 50% higher than premolar and 70% higher than incisor values ( p  < 0.05); average and slope also varied significantly by position, though plateau lengths were consistent—only Ti Lite® showed positional force variability. Conclusion Thermal Ti-Lite® archwires, with higher austenite-finish temperature (~ 34 °C), demonstrated significant positional force differences, suggesting their potential for site-specific biomechanical control. In contrast, NT3-SE® and Thermal Ti-D® provided uniform force profiles across arch positions. Considering crystalline transformation temperatures and anatomical variation may improve clinical force application during alignment.

Background: Copper (Cu), nickel (Ni), chromium (Cr) ion release, and surface topography change from the orthodontic wire are the initial processes of corrosion that may affect the mechanical properties of the archwire. In this study, we aim to evaluate the effect of CHX, NaF, and chitosan on the corrosion of CuNiTi wire nickel and copper ions released, surface roughness change, and archwire deflection. Methods: Ninety samples of CuNiTi Tanzo™ archwires were divided into five groups according to their immersion solution: Artificial Saliva, CHX, NaF, CHX-NaF, and chitosan group. Each group was further divided into three subgroups (n=6) corresponding immersion time, i.e., two, four, and six weeks. The corrosion of the samples was analyzed with an atomic absorption spectrophotometer (AAS), scanning electron microscope (SEM), and universal testing machine (UTM). Results: The amount of nickel ion releases was increasing, but the copper ion releases were reduced by the time of observations. The highest nickel ion was released in the CHX-NaF group and the lowest in the chitosan group for six-week immersion. It also corresponded to the surface topography by SEM analysis which showed the most extended cracks and deep pits in the CHX-NaF group and a smoother surface in the chitosan group. Copper ion release showed the highest ion release in the NaF group and the lowest release in the chitosan group. The unloading force of CuNiTi archwire deflection remains the same at week two and week four for all mouthwashes. Conclusion: The use of mouthwashes that contained CHX, NaF, and chitosan could further alter the passive layer and cause higher nickel and copper ion release and increased CuNiTi archwire surface structure porosity. But there is no distinction between mouthwashes to release the unloading force within two until four weeks.

Background Copper (Cu), nickel (Ni), chromium (Cr) ion release, and surface topography change from the orthodontic wire are the initial processes of corrosion that may affect the mechanical properties of the archwire. In this study, we aim to evaluate the effect of CHX, NaF, and chitosan on the corrosion of CuNiTi wire nickel and copper ions released, surface roughness change, and archwire deflection. Methods Ninety samples of CuNiTi Tanzo™ archwires were divided into five groups according to their immersion solution: Artificial Saliva, CHX, NaF, CHX-NaF, and chitosan group. Each group was further divided into three subgroups (n=6) corresponding immersion time, i.e., two, four, and six weeks. The corrosion of the samples was analyzed with an atomic absorption spectrophotometer (AAS), scanning electron microscope (SEM), and universal testing machine (UTM). Results The amount of nickel ion releases was increasing, but the copper ion releases were reduced by the time of observations. The highest nickel ion was released in the CHX-NaF group and the lowest in the chitosan group for six-week immersion. It also corresponded to the surface topography by SEM analysis which showed the most extended cracks and deep pits in the CHX-NaF group and a smoother surface in the chitosan group. Copper ion release showed the highest ion release in the NaF group and the lowest release in the chitosan group. The unloading force of CuNiTi archwire deflection remains the same at week two and week four for all mouthwashes. Conclusion The use of mouthwashes that contained CHX, NaF, and chitosan could further alter the passive layer and cause higher nickel and copper ion release and increased CuNiTi archwire surface structure porosity. But there is no distinction between mouthwashes to release the unloading force within two until four weeks.

In orthodontics, nickel-titanium wires are used for teeth alignment and leveling. For leveling the curve of Spee, reversed curve archwires are often used to increase the vertical force needed to correct a deep bite.Objectives: The aims of this study were to investigate and compare the mechanical properties (unloading force, stiffness, springback, and surface hardness) of the pre-formed plain and reversed curved NiTi archwires.Materials and Methods: NiTi wires of dimensions 0.016x0.022 inch were divided into two groups, Group 1 - plain and Group 2- reversed curve NiTi archwires. For each type of the archwire, load-deflection curve obtained from a three-point bending test, performed by a Texture Analyser (TA.XT.plus, Stable Micro System, United Kingdom) with 5 kg load cell at room temperature, was used to analyze unloading force, springback, and stiffness. Surface hardness was measured by Vickers micro-hardness tester. Kruskal-Wallis test was used to analyze the variables of this study.Results: The results showed that the unloading force of each deflection point of the reversed curve NiTi archwire was more than the plain archwire. The means of unloading force, stiffness, and springback were 2.42 N, 2.76 N; 0.28 N/mm, 0.49 N/mm; and 2.94 mm, 2.98 mm for the plain archwire and reversed curve NiTi archwire, respectively. The properties of reversed curve NiTi archwire were significantly higher (p<0.05) than the plain NiTi archwire, except the springback. The surface hardness of the plain archwire was significantly higher (p<0.05) than reversed curve NiTi archwire in each segment.Conclusion: The reversed curve NiTi archwire had more unloading force and stiffness than plain NiTi archwire. For the correction of deep curve of Spee in orthodontic treatment, clinicians must be aware of the vertical force needed during intrusion of lower incisors or the wires should be used in the later leveling and aligning stage.

Infilled joints or faults are often subjected to long-term stable shear forces, and nature surface processes of normal unloading can change the frictional balance. Therefore, it is essential to study the sliding behavior of such granular materials under such unloading conditions, since they are usually the filling matter. We conducted two groups of normal unloading direct shear tests considering two variables: unloading rate and the magnitude of constant shear force. Dry sands may slide discontinuously during normal unloading, and the slip velocity does not increase uniformly with unloading time. Due to horizontal particle interlacing and normal relaxation, there will be sliding velocity fluctuations and even temporary intermissions. At the stage of sliding acceleration, the normal force decreases with a higher unloading rate and increases with a larger shear force at the same sliding velocity. The normal forces obtained from the tests are less than those calculated by Coulomb’s theory in the conventional constant-rate shear test. Under the same unloading rate, the range of apparent friction coefficient variation is narrower under larger shear forces. This study has revealed the movement patterns of natural granular layers and is of enlightening significance in the prevention of corresponding geohazards.

To compare mechanical properties of three commercial NiTi orthodontic round wires, three commercial brands of NiTi round wire (Nic-China, Ormco-USA, and Smart-Thailand) with sizes 0.014’’, 0.016’’, and 0.018’’were studied. Five specimens each size of each brand were used to test mechanical properties; unloading force (N), spring back (mm), and yield strength (N/mm) with three-point bend test using an Instron Universal Testing Machine. Kolmogorov-Smirnov test and one-way ANOVA were employed to test the differences among groups with statistical difference at p<0.05.The average unloading force from lowest to highest were Ormco, Smart and Nic with 0.014”, Smart, Ormco and Nic with 0.016”and Smart, Nic and Ormco with 0.018”, respectively. The Nic brand had the highest value of unloading force, spring back, and yield strength in all wire sizes, except unloading force 0.018” Ormco and spring back 0.018” Smart. There were no statistically significant differences in unloading forces among all wire sizes. The three brands of commercial orthodontic NiTi wires presented similar unloading force, spring back, and yield strength properties. These mechanical properties are related to lower rates of deformation and are appropriate to be used in the initial phase of orthodontic treatment.

Anterior cruciate ligament (ACL) injuries are one of the most common knee pathologies sustained during athletic participation and are characterised by long convalescence periods and associated financial burden. Muscles have the ability to increase or decrease the mechanical loads on the ACL, and thus are viable targets for preventative interventions. However, the relationship between muscle forces and ACL loading has been investigated by many different studies, often with differing methods and conclusions. Subsequently, this review aimed to summarise the evidence of the relationship between muscle force and ACL loading. A range of studies were found that investigated muscle and ACL loading during controlled knee flexion, as well as a range of weightbearing tasks such as walking, lunging, sidestep cutting, landing and jumping. The quadriceps and the gastrocnemius were found to increase load on the ACL by inducing anterior shear forces at the tibia, particularly when the knee is extended. The hamstrings and soleus appeared to unload the ACL by generating posterior tibial shear force; however, for the hamstrings, this effect was contingent on the knee being flexed greater than ~ 20° to 30°. The gluteus medius was consistently shown to oppose the knee valgus moment (thus unloading the ACL) to a magnitude greater than any other muscle. Very little evidence was found for other muscle groups with respect to their contribution to the loading or unloading of the ACL. It is recommended that interventions aiming to reduce the risk of ACL injury consider specifically targeting the function of the hamstrings, soleus and gluteus medius.

To address the issue of deformation in prefabricated segmental subway tunnels caused by partial excavation unloading which affects the safety of subway operational safety. In this article, the subway tunnel of Zhengzhou metro, which partial unloading due to pit excavation on the underground expressway reconstruction project, was taken as an example to study this issue. First, the mechanism of partial unloading of upper bar pit excavation on the mechanical response of lower existing tunnel structure was investigated. Then, a three-dimensional finite element model was developed to simulate the interaction between the excavation pit and the tunnel. The influence of partial unloading caused by strip foundation pit excavation on the mechanical response and deformation characteristics of underlying existing tunnel segment structures were analyzed. Finally, the reinforcement effects of tunnel deformation control measures were compared, and the optimal solution to control tunnel deformation affected by partial excavation and unloading was proposed. Results indicate that the tunnel structure mainly produces overall uneven uplift, which is affected by the partial unloading of the upper bar pit excavation. The vertical displacement at the top of the tunnel is the largest, the vertical displacement near the centerline of the pit is significant, and the maximum vertical displacement usually occurs at the joints. The force of bolts generated in the prefabricated segment structure under partial unloading conditions was tensile force, which was related to the variation trend of the segment joints and the magnitude of the bending moment at the joint locations. After comparing the different methods, portal reinforcement and counterpressure can significantly control deformation generated by partial unloading.

The coupling of in situ stress, seepage, and fracture makes the strata exhibit complex strain behavior and permeability evolution under the stress path of cyclic loading‐unloading. In this study, the cyclic loading‐unloading experiments of constant amplitude axial stress of sandstone under the combination of different initial confining pressures and loading‐unloading rates are conducted. The experimental results show that the heterogeneity of sandstone, Poisson's ratio produced by adjacent loading‐unloading, and confining pressure determine the deformation characteristics of sandstone in lateral and axial directions. Sandstone can produce significant shear dilatancy at a low rate; this is because stress perturbation can activate more particle slippage and fracture structure changes. However, the fracture preferentially propagates along the end or edge of the crack with strong stress sensitivity to form a shear failure plane at high rate. The normalized permeability of sandstone decreases with an increase in the loading‐unloading rate before failure. The evolution of normalized permeability is closely related to the shear slip of fracture structure and sandstone particles. For the prevention of rock engineering disasters, the high loading‐unloading rate results in lower normalized permeability, which favors the prevention of gas‐type disasters in rocks with higher gas potential energy; however, it is not conducive to the prevention of rockburst. Under the identical confining pressure, the stress perturbation induced by low loading rate can activate the motion of more sandstone particles and cause more structural changes of fracture, so that the sandstone can produce significant shear dilatancy. The normalized permeability of sandstone decreases with the increase of loading‐unloading rate at the moment of failure. The evolution of normalized permeability is closely related to the dilatancy capacity of sandstone.

Slabbing/spalling and rockburst are unconventional types of failure of hard rocks under conditions of unloading and various dynamic loads in environments with high and complex initial stresses. In this study, the failure behaviors of different rock types (granite, red sandstone, and cement mortar) were investigated using a novel testing system coupled to true-triaxial static loads and local dynamic disturbances. An acoustic emission system and a high-speed camera were used to record the real-time fracturing processes. The true-triaxial unloading test results indicate that slabbing occurred in the granite and sandstone, whereas the cement mortar underwent shear failure. Under local dynamically disturbed loading, none of the specimens displayed obvious fracturing at low-amplitude local dynamic loading; however, the degree of rock failure increased as the local dynamic loading amplitude increased. The cement mortar displayed no failure during testing, showing a considerable load-carrying capacity after testing. The sandstone underwent a relatively stable fracturing process, whereas violent rockbursts occurred in the granite specimen. The fracturing process does not appear to depend on the direction of local dynamic loading, and the acoustic emission count rate during rock fragmentation shows that similar crack evolution occurred under the two test scenarios (true-triaxial unloading and local dynamically disturbed loading).