Biomechanical Effects of Angiotensin 1-7 in Diabetes Rats Femur / Efectos Biomecánicos de la Angiotensina 1-7 en el Fémur de Ratas Diabéticas

SUMMARY: It is known that diabetes mellitus has late complications, including microvascular and macrovascular diseases. Diabetes can affect bones through biochemical markers of bone structure, density, and turnover. This study aimed to biomechanically investigate the bone-protective effects of angiotensin 1-7 (Ang 1-7), one of the active peptides in the renin-angiotensin system, in rats with diabetes. Thirty male Wistar albino rats, three months old and weighing 250-300 g, were divided into four groups: diabetes, Ang 1- 7, diabetes plus Ang 1-7, and control. One month later, diabetes developed in rats; the rats were sacrificed, and their right femur was removed. Three-point bending biomechanical tests were performed on the femurs. The diabetic group had significantly higher bone fragility than the other groups (Pr >.05). Bone fragility was lower, and bone flexibility was higher in the Ang 1-7 groups (Pr>F value 0.05). As a result of our study, the effect of Ang 1-7 on the bones of rats with diabetes was investigated biomechanically. Ang 1-7 has a protective impact on the bones of rats with diabetes.

Se sabe que la diabetes mellitus tiene complicaciones tardías, incluyendo enfermedades microvasculares y macrovasculares. La diabetes puede afectar los huesos a través de los marcadores bioquímicos de la estructura, la densidad y el recambio óseo. Este estudio tuvo como objetivo investigar biomecánicamente los efectos protectores en los huesos de la angiotensina 1-7 (Ang 1-7), uno de los péptidos activos en el sistema renina-angiotensina, en ratas con diabetes. Treinta ratas albinas Wistar macho, de tres meses de edad y con un peso de 250-300 g, se dividieron en cuatro grupos: diabetes, Ang 1-7, diabetes más Ang 1-7 y control. Un mes después, se desarrolló diabetes en ratas; se sacrificaron los animales y se extrajo su fémur derecho. Se realizaron pruebas biomecánicas de flexión de tres puntos en los fémures. El grupo diabéticos tenía una fragilidad ósea significativamente mayor que los otros grupos (Pr > 0,05). La fragilidad ósea fue menor y la flexibilidad ósea fue mayor en los grupos Ang 1-7 (valor Pr>F 0,05). Como resultado de nuestro estudio, se determinó biomecánicamente el efecto de Ang 1-7 en los huesos de ratas con diabetes. Se concluye que Ang 1-7 tiene un impacto protector en los huesos de ratas diabéticas.

Establishment and evaluation of rabbit model of closed tibial fracture / 中国骨伤

OBJECTIVE@#To explore the effect of a modified three-point bending fracture device for establishing a rabbit model of closed tibial fracture.@*METHODS@#The model of closed tibial fracture was established in 40 6-month-old male New Zealand white rabbits with a body weight of 2.5 to 3.0 kg, and the model was verified at 6 weeks after operation. Five rabbits underwent pre modeling without temporary external fixation before modeling, and then were fractured with a modified three-point bending fracture device;35 rabbits underwent formal modeling. Before modeling, needles were inserted, and splints were fixed externally, and then the fracture was performed with a modified three-point bending fracture device. The fracture model and healing process were evaluated by imaging and histopathology at 2 hours, 4 weeks, and 6 weeks after operation.@*RESULTS@#Two hours after modeling, the prefabricated module showed oblique fracture in varying degrees and the broken end shifted significantly;Except for 1 comminuted fracture, 2 curved butterfly fractures and 2 without obvious fracture line, the rest were simple transverse and oblique fractures without obvious displacement in formal modeling group. According to the judgment criteria, the success rate of the model was 85.71%. Four weeks after modeling, the fixed needle and splint of the experimental rabbits were in good position, the fracture alignment was good, the fracture line was blurred, many continuous callus growths could be seen around the fracture end, and the callus density was high. Six weeks after modeling, many thick new bone trabeculae at the fracture, marginal osteoblasts attached, and a small number of macrophages were seen under the microscope. The intramembrane osteogenesis area was in the preparation bone stage, the medullary cavity at the fracture had been partially reopened, the callus was in the absorption plastic stage, and many osteoclasts were visible. The X-ray showed that the fracture line almost disappeared, part of the medullary cavity had been opened, the external callus was reduced around, the callus was in the plastic stage, and the bone cortex was continuous. It suggests that the fracture model showed secondary healing.@*CONCLUSION@#The improved three-point bending fracture device can establish a stable rabbit model of closed tibial fracture, and the operation is simple, which meets the requirements of closed fracture model in basic research related to fracture healing.

Mechanical properties of rat tibia under high-G environment / 中国组织工程研究

BACKGROUND: With the development of Chinese space industry, pilots are exposed to high-G mechanical environment, which will seriously affect their bones. However, as one of the bones that are most prone to fracture, the biomechanical behavior of the tibia under extreme mechanical environment is rarely reported. OBJECTIVE: To explore the effects of different high-G mechanical environments on the rat growth and development and the mechanical properties of the tibia. METHODS: Male Wistar rats were provided by Laboratory Animal Center of Academy of Military Sciences. The cantilever was set to run at different speeds and accelerations with a high-G centrifugal loading device, and the high-G rat model was made. The rats were weighed weekly. The left tibia of rats was used for undergoing a three-point bending experiment, and the deflection and elastic modulus of the tibia were calculated. The right tibia was subjected to a creep test, and constant stress was applied on the surface of tibial cortical bone and kept 3 600 seconds, so as to observe the changes of creep strain. The study was approved by the Laboratory Animal Ethical Committee of Tianjin University of Technology. RESULTS AND CONCLUSION: The high-G environment affected the normal growth and development of rats, inhibited weight gain and reduced the mechanical properties of the tibia, and reduced the limit deflection of the tibia by 8.1%, 12.2%, 37.8%, and 51.4%, respectively. Limit loads were decreased by 16%, 9%, 25.2%, and 29% respectively. To conclude, extremely high-G environment exerts serious negative effects on rats.

Simulation accuracy of cortical bone fracture based on different types of strain criterion / 中国组织工程研究

BACKGROUND: Cortical bone crack caused by accident or other external factors is one of the main causes of fracture, so the mechanism of crack formation and propagation for cortical bone under different loads should be understood primarily to avoid fracture. Bone specimens may be destructed in experiments, which can lead to a difficulty to observe the interior mechanical state of bone structure before and after fracture. Therefore, it is important to find a finite element method that can accurately simulate the processes of cortical bone crack formation, propagation, and fracture. Current simulations mainly use the principal strain or the equivalent strain to determine the mechanical state of the element in the finite element model and to perform fracture simulation, but there are few studies on the simulation accuracy when using these two types of strains. OBJECTIVE: To testify the simulation accuracy of cortical bone fracture with the principal strain and the equivalent strain. METHODS: The principal strain and the equivalent strain were applied to perform the three-point bending simulation, and the simulation results were compared with the experimental results to determine which strain was more accurate. RESULTS AND CONCLUSION: (1) The failure time of the cortical bone simulated by the principal strain was significantly later than that obtained by the equivalent strain. (2) Compared with the experimental results, it was found that the simulation results obtained by equivalent strain were closer to the experimental results. (3) Therefore, simulating cortical bone crack and fracture using the equivalent strain is accurate.

Metal-ceramic bond strength between a feldspathic porcelain and a Co-Cr alloy fabricated with Direct Metal Laser Sintering technique

PURPOSE: The aim of the present study was to record the metal-ceramic bond strength of a feldspathic dental porcelain and a Co-Cr alloy, using the Direct Metal Laser Sintering technique (DMLS) for the fabrication of metal substrates. MATERIALS AND METHODS: Ten metal substrates were fabricated with powder of a dental Co-Cr alloy using DMLS technique (test group) in dimensions according to ISO 9693. Another ten substrates were fabricated with a casing dental Co-Cr alloy using classic casting technique (control group) for comparison. Another three substrates were fabricated using each technique to record the Modulus of Elasticity (E) of the used alloys. All substrates were examined to record external and internal porosity. Feldspathic porcelain was applied on the substrates. Specimens were tested using the three-point bending test. The failure mode was determined using optical and scanning electron microscopy. The statistical analysis was performed using t-test. RESULTS: Substrates prepared using DMLS technique did not show internal porosity as compared to those produced using the casting technique. The E of control and test group was 222 ± 5.13 GPa and 227 ± 3 GPa, respectively. The bond strength was 51.87 ± 7.50 MPa for test group and 54.60 ± 6.20 MPa for control group. No statistically significant differences between the two groups were recorded. The mode of failure was mainly cohesive for all specimens. CONCLUSION: Specimens produced by the DMLS technique cover the lowest acceptable metal-ceramic bond strength of 25 MPa specified in ISO 9693 and present satisfactory bond strength for clinical use.

Comparative study on bond strength of porcelain fused to CAD/CAM and to cast pure titanium / 实用口腔医学杂志

Objective:To compare the titanium-porcelain bonding strength between CAD/CAM and cast pure titanium.Methods:Pure titanium samples were prepaired by CAD/CAMand casting respectively and fused with porcelain.The bond strength between tita-nium and porcelain of the samples was measured with three-point test.The titanium-porcelain interface was investigated under scanning electronic microscope(SEM).Results:The bond strength of CAD/CAMpure titanium to porcelain was (35.95 ±3.74)MPa and cast pure titanium to porcelain was (28.37 ±1 .98)MPa(P <0.05).SEMobservation showed that there was thin transition layer between titanium substrate and ceramic in CAD/CAM bond interface,titanium and porcelain combined closely,no obvious pores.However, there was thicker transition layer and small pore in cast pure titanium to porcelain bonding interface.Conclusion:The bonding strength of porcelain to CAD/CAMpure titanium is greater than that of porcelain to casting pure titanium.

Biomechanical study on helical long PHILOS plate fixation for proximal metaphyseal-diaphyseal humeral shaft fractures / 医用生物力学

Objective To compare biomechanical properties of the helical and straight long PHILOS (proximal humerus internal locking system) plates (Synthes Inc., Switzerland), so as to provide some biomechanical evidence for treating proximal metaphyseal-diaphyseal humeral shaft fractures in clinic. Methods Twelve Synbone artificial bones of right humerus (SYNBONE Inc., Switzerland) were divided into two groups. In control group (n=6), the humerus was fixed with the 10 hole long straight PHILOS plate, while in experimental group (n=6), the humerus was fixed with the same long PHILOS plate which was precontoured for moulding (i.e. helical PHILOS plate). After the proximal metaphyseal-diaphyseal humeral shaft fractures were made in all artificial bones, the biomechanical properties of the specimens in two groups under 6 loading modes (i.e., axial tension and compression, torsion in the same and reverse direction, medial-lateral and anterior-posterior three-point bending) were tested en bloc and compared. ResultsCompare with control group, under 100-500 N tensile and compressive loads, the axial displacement at the fractured end in experimental group increased by about 95% and 58%, respectively. Under 0.6-3 N•m torsional moment in reversed direction, the tensional angle in experimental group was obviously smaller than that in control group, with a decrease of 55%-64%. Under medial-lateral bending moment of 1.5 and 3 N•m, no significant difference was found in deflection of the experiment and control group, while under medial-lateral bending moment of 4.5, 6 and 7.5 N•m, the deflection in experimental group decreased by 20%-30% as compared to control group. Under 0.6-3 N•m torsional moment in the same direction and 1.5-7.5 N•m anterior-posterior bending moment, both the torsional angle and the deflection in experimental group were larger than those in control group, with a significant difference (P＜0.05). Compared with control group, the tensile stiffness and compressive stiffness decreased by 49% and 36%, the torsional stiffness in the same direction decreased by 19% and that in reversed direction increased by 150%, three-point bending stiffness in medial lateral direction increased by 18% and that in anterior posterior direction decreased by 70% in experimental group, all with a significant difference (P＜0.05). ConclusionsCompared with the long straight PHILO plate, the long helical PHILOS plate has better biomechanical properties, which can meet the clinical need of proximal metaphyseal-diaphyseal humeral shaft fracture fixation and postoperative rehabilitation. This surgical technique is expected to be widely applied in clinic, especially with the advantage of minimal invasive surgery.

Construction and identification of humerus three-dimensional finite element model in children / 中国组织工程研究

BACKGROUND:Mechanical experiment of finite element numerical simulation is the effective method to research the biomechanical structure of human body. OBJECTIVE:To establish the three-dimensional finite element model of a normal 6-year-old child’s humerus. METHODS:CT images of a 6-year-old child volunteer were imported to the Mimics 10.01 software. The threshold segmentation method was used to rebuild the humerus three-dimensional model. The surface optimization treatment and surface patches dicision were performed on the surface of the model with Geomagic Studio 12.0 software. Then the mesh generation was completed in the software TrueGrid. Final y, the material properties were set and the finite element model was completed. The boundary conditions and constrains were exerted to simulate the three-point-bending test of humeurs. After the simulation, the results were outputted. RESULTS AND CONCLUSION:The humerus finite element model included 3 024 nodes and 18 758 nodes-hexahedron elements. The 0.01 m/s and 3 m/s dynamic loads were loaded respectively, then the central humerus fracture occurred and the load-displacement curve was close to the cadaver test results. The simulation results show that the simulation results of children humerus finite element model are close to the cadaver’s test, and the finite element simulation method can simulate the physical properties of the human skeleton very wel .

Propriedades em flexão de fios de liga de Ni-Ti / Bending properties of Ni-Ti alloys wires

As ligas de niquel-titânio (Ni-Ti) são usadas na fabricação de fios ortodônticos devido principalmente a sua maior resiliência e menor módulo de elasticidade quando comparadas com outras ligas metálicas, especialmente o aço inoxidável. O objetivo do presente trabalho foi comparar as propriedades mecânicas em flexão de fios de liga com memória de forma de diferentes fabricantes e lotes. Dois lotes de três fabricantes foram ensaiados em flexão três pontos de acordo com a norma ISO 15841:2006(E). Os resultados mostraram que os fios designados como termoativados geram tensões menores que os fios designados como superelásticos, observou-se variações de até 28% entre fios designados como superelásticos e 31% entre fios designados como termoativados. Na comparação dos lotes do mesmo fabricante observou-se também a não homogeneidade entre os fios.

The nickel-titanium (Ni-Ti) alloys are used in the manufacture of orthodontic wires mainly due to its greater resilience and low modulus of elasticity when compared to other alloys, particularly stainless steel. The aim of this study was to compare the mechanical properties of shape memory alloys wires in three-point bending in different manufacturers. Two lots of three manufacturers were tested in three-point bending according to ISO 15841:2006 (E). The results showed that wires designated as termoactivated generated lower tensions than the designated as superelastic, variations of up to 28% between wires designated as superelastic and 31% between wires d esignated as termoactivated were found. In the manufacturer lots comparison was also not observed homogeneity between wires.

Transformation Behaviour, Bending Properties and Surface Quality of 22 Commercial Nickel- Titanium Wires: A Batch-to-Batch Evaluation.

Aims: The aims of this study were to investigate batch-to-batch differences in mechanical and thermal properties of 22 commercial nickel-titanium wires and evaluate the surface quality. Secondly the percentages of superelasticity at mouth temperature were measured. Study Design: In vitro laboratory study. Place and Duration of Study: Sample: Department of Oral Health Sciences – Orthodontics and Metallurgy and Materials Engineering KU Leuven, between January 2010 and May 2011. Methodology: The sample comprised 22 NiTi wires of the upper jaw from 7 different manufacturers. For each brand two different batches were investigated (LOT A, LOT B). Three different investigations were carried out. First transformation behaviour and transition temperatures were determined by differential scanning calorimetry, second a three point bending test was done to evaluate the mechanical properties and third scanning electron microscopy was performed on all samples to evaluate surface quality. Results: Absolute batch-to-batch differences in the investigated properties were all deviating from zero, although most differences were clinically acceptable. Significant interbatch differences in thermal properties were found in 4 wires. Mechanical interbatch differences were found remarkable for 5 wires. Percentage of elasticity showed a non- superelastic curve below a deflection of 1500 μm, which represents clinical small deflections. Surface topography showed also interbatch differences for 4 wires. Conclusion: This study shows that batch-to-batch differences are obvious in each sample. One has to be careful in the selection of archwires. Therefore more standardized consument information should be provided.

Influence of fluoride-containing acidic artificial saliva on the mechanical properties of Nickel-Titanium orthodontics wires.

Objective: This study aimed to investigate the influence of fluoride and an acidic environment on the mechanical properties of NiTi orthodontic wires (NiTiW) in artificial saliva. Design: A prospective laboratory investigation. Setting: Department of Stomatology, First Affiliated Hospital, Zhejiang University, Hangzhou, China. Materials and Methods: Commercial, round 0.016-inch NiTiW were immersed in 0% or 0.05% Natrium-Fluoride-containing artificial saliva at a pH of 4 or 6 for one or three days, respectively. NiTiW were examined with a three-point bending test, Vickers' microhardness tests and surface morphology observation (SEM). Results: A pH of 4 increased microhardness and decreased the three-point bending strength significantly (P≤0.05), whereas immersion time and fluoride concentration had no significant influence on the microhardness or on the three-point bending strength (P>0.05). When examining the test group NiTiWs after three days of immersion at a pH of 4 the SEM revealed a rough surface morphology, a damaged oxide layer and signs of corrosion. Conclusions: The most influential factor for decreasing the unloading force and increasing the hardness seems to be the pH value, whereas immersion time and NaF addition do not have a major influence.

Effect of Incremental Exercise on the of Maximum Force of Femur and Lumbar Vertebrae in SD Rats / 中国运动医学杂志

Objective The aim of the study is to investigate whether the progressive incremental exercise can induce the change in bone maximum force.Methods One hundred and seventy healthy SD rats,aged 3 months,were used as samples after adaptive exercise for one week,and then they were divided to a basic control group(C_0),8 control groups and 8 exercise groups according to the training duration(2W,4W,6W,8W,9W,11W,13W and 15W).Based on Bedford and our pre-study.the longest training duration of the rats was 15 weeks.The maximum force(F) of femoral bone and the 2nd lumbar vertebrae(L_2)were tested by three-point bending test and compressive test separately.Results It was shown that there was no pronounced difference in F of femoral bone between con trol groups and exercise groups.But significant differences in F of L_2 were found between the control groups and exercise groups(P<0.001).Conclusions Changes in different degree were found in the F of femoral bone and L_2 during the process of growth.The differential effects of incremental exercise on F were caused by the difference in training intensities and in the bone types.

Morphological and Mechanical Changes in Ovariectomized Rat Tibia with Treatments of Ibandronate and Parathyroid Hormone / 대한골다공증학회지

Osteoporosis is a debilitating disease affecting the elderly population, associated with compromised stability and reduced mobility of the bone. Osteoporosis is diagnosed as a condition when the measured bone mineral density (BMD) falls below 2.5 standard deviations of peak mass. However, BMD alone might not be enough to define the osteoporotic condition because it does not accounts on the micro-architectural changes in the bone trabeculae. Thus, this study aimed at studying the micro-architecural changes in trabeculae rich bone metaphysis of ovariectomized rat models in comparison with the conventional BMD measurements and the mechanical parameters. In this study, proximal tibiae of twenty-five female rats from four different groups (SHAM, OVX, IBAN and PTH) were evaluated using micro-CT, pQCT and three point bending tests. The micro-CT analysis showed that the deterioration of trabecular bone was significant during the first 6 weeks after OVX surgery. During the early stage of osteoporosis, the trabecular density decreased more rapidly than the cortical density. Morphological analysis showed that early administration of both ibandronate and parathyroid hormone has a beneficial effect on restoring the trabecular structures. Bone mechanical properties of treatment groups did not show significant difference, but followed the overall trend as morphological indices. The results suggest that early administration of either ibandronate or PTH is effective in restoring the trabecular bone loss caused by osteoporosis. However, larger-scale studies should be conducted to better understand the effect of both anti-resorptive and anabolic treatments in terms of morphological and mechanical properties.

The fracture resistance of heat pressed ceramics with wire reinforcement / 대한치과보철학회지

STATEMENT OF PROBLEM: Ceramics have been important materials for the restoration of teeth. The demands of patients for tooth-colored restorations and the availability of various dental ceramics has driven the increased use of new types of dental ceramic materials. Improved physical properties of theses materials have expanded its use even in posterior crowns and fixed partial dentures. However, ceramic still has limitation such as low loading capability. This is critical for long-span bridge, because bridge is more subject to tensile force. PURPOSE: The wire reinforced ceramic was designed to increase the fracture resistance of ceramic restoration. The purpose of this study was to evaluate the fracture resistance of wire reinforced ceramic. MATERIAL AND METHODS: Heat pressed ceramic (ingot No.200 : IPS Empress 2, Ivoclar Vivadent, Liechtenstein) and Ni-Cr wire (Alfa Aesar, Johnson Matthey Company, USA) of 0.41 mm diameter were used in this study. Five groups of twelve uniform sized ceramic specimens (width 4 mm, thickness 2 mm, length 15 mm) were fabricated. Each group had different wire arrangement. Wireless ceramic was used as control group. The experimental groups were divided according to wire number and position. One, two and three strands of wires were positioned on the longitudinal axis of specimen. In another experimental group, three strands of wires positioned on the longitudinal axis and five strands of wires positioned on the transverse axis. Three-point bending test was done with universal testing machine (Z020, Zwick, Germany) to compare the flexural modulus, flexural strength, strain at fracture and fracture toughness of each group. Fractured ceramic specimens were cross-sectioned with caborundum disc and grinded with sandpaper to observe interface between ceramic and Ni-Cr wire. The interface between ceramic and Ni-Cr wire was analyzed with scanning electron microscope (JSM-6360, JEOL, Japan) under platinum coating. RESULTS: The results obtained were as follows: 1. The average and standard deviation in flexural modulus, flexural strength and fracture toughness showed no statistical differences between control and experimental groups. However, strain was significantly increased in wire inserted ceramics (P < .001). 2. Control group showed wedge fracture aspects across specimen, while experimental groups showed cracks across specimen. 3. Scanning electron microscopic image of cross-sectioned and longitudinally-sectioned specimens showed no gap at the interface between ceramic and Ni-Cr wire. CONCLUSION: The results of this study showed that wire inserted ceramics have a high strain characteristic. However, wire inserted ceramics was not enough to use at posterior area of mouth in relation to flexural modulus and flexural strength. Therefore, we need further studies.

Influência da ciclagem térmica na resistência à flexão de resinas laboratoriais / The effect of thermo-cycling on flexural strength of laboratorial resins

Introdução: Uma nova geração de resinas laboratoriais contendo micro-partículas cerâmicas em sua composição tem sido introduzida no mercado com a finalidade de melhorar suas propriedades mecânicas. Objetivo: O objetivo deste estudo foi avaliar o efeito da termociclagem na resistência à flexão de três resinas laboratoriais. Materiais e método: Foram confeccionadas 48 barras com medidas de 2 mm × 2 mm × 25 mm, utilizando as resinas laboratoriais: G1 - RESILAB MASTER (Wilcos, Brasil), G2 - VITA VM LC (Vita Zanhfabrik, Germany), G3 - VITA ZETA LC (Vita Zanhfabrik, Germany). A metade das barras de cada grupo foi submetida a 3000 ciclos térmicos (5ºC/55ºC ± 1, com banhos de 30 s). Os ensaios mecânicos foram efetuados em máquina de ensaio universal EMIC com capacidade de carga de 100 kg e velocidade de 0,5 mm/min. Resultados: Os dados obtidos foram analisados estatisticamente pelo teste de ANOVA (two-way) e Tukey (p < 0,05). As médias (± DP) observadas para os grupos sem ciclagem foram: G1(112,6 ± 25,39), G2(116,5 ± 18,51) e G3(136,1 ± 24,34); e para os grupos com ciclagem: G1(91,8 ± 18,86), G2(101,9 ± 20,61) e G3(89,9 ± 23,05). Conclusão: Concluiu-se que a diminuição da resistência à flexão em MPa está diretamente dependente da ciclagem térmica nos grupos testados, sendo que os maiores valores foram obtidos pela resina VITA VM LC. Entretanto, na condição sem ciclagem térmica a VITA ZETA apresentou os maiores valores.

Introduction: A new laboratorial resin generation that content ceramic microparticles in its composition has been introduced in the market with the purpose to improve its mechanical properties. Objective: The objective of this study was to evaluate the effect of the thermocycling in the flexural strength of three laboratorial resins. Method: Forty-eight specimens with measures of 2 mm × 2 mm × 25 mm were made using laboratorial resins: G1 - RESILAB MASTER (Wilcos, Brazil), G2 - VITA VM LC (Vita Zanhfabrik, Germany) and G3 - VITA ZETA (Vita Zanhfabrik, Germany). After their confection, half of each group was submitted to 3000 thermal-cycles (5ºC/55ºC ± 1, with rinse bath of 30 s). The mechanical essays were done in Universal essay machine EMIC with the loading capacity of 100 kg and the equispeed of 0,5 mm/min. Results: The obtained data was analyzed statistically by the ANOVA test (two-way) and Turkey?s test (p < 0,05). The averages (± DP) observed for the groups without cycles were: G1(112,6 ± 25,39), G2(116,5 ± 18,51) and G3(136,1 ± 24,34); and for the groups with cycles: G1(91,8 ± 18,86), G2(101,9 ± 20,61) and G3 89,9 ± 23,05). Conclusion: It was concluded that the decrease in the flexural strength in MPa is directly dependent on the thermo-cycling in the tested groups, being that the highest values were obtained by VM LC resin. However, in the group without thermo-cycling the VITA ZETA showed the highest values.UNITERMS: three point bending; thermo-cycling; composite resin.

Effects of heat treatment on the load-deflection properties of nickel-titanium wire / 대한치과교정학회지

OBJECTIVE: Nickel-titanium alloy wire possesses excellent spring-back properties, shape memory and super-elasticity. In order to adapt this wire to clinical use, it is necessary to bend as well as to control its super-elastic force. The purpose of this study is to evaluate the effects of heat treatment on the load-deflection properties and transitional temperature range (TTR) of nickel-titanium wires. METHODS: Nickel-titanium wires of different diameters (0.016" x 0.022", 0.018" x 0.025" and 0.0215" x 0.028") were used. The samples were divided into 4 groups as follows: group 1 , posterior segment of archwire (24 mm) without heat treatment; group 2, posterior segment of archwire (24 mm) with heat treatment only; group 3, anterior segment with bending and heat treatment; group 4, anterior segment with bending and 1 sec over heat treatment. Three point bending test was used to evaluate the change in load-deflection curve and obtained DSC (different scanning calorimetry) to check changes in Af temperature. RESULTS: In the three point bending test, nickel-titanium wires with heat treatment only had higher load-deflection curve and loading and unloading plateau than nickel-titanium wires without heat treatment. Nickel-titanium wires with heat treatment had lower Af temperature than nickel-titanium wires without heat treatment. Nickel-titanium wires with heat treatment and bending had higher load-deflection curve than nickel-titanium wires with heat treatment and nickel-titanium wires without heat treatment. Nickel-titanium with heat treatment of over 1 sec and bending had the highest load-deflection curve. Nickel-titanium wires with heat treatment and bending had lower Af temperature, Nickel-titanium wires with heat treatment of over 1 sec and bending had the lowest Af temperature. CONCLUSION: From the results of this study, it can be stated that heat treatment for bending of Nickel-titanium wires does not deprive the superelastic property but can cause increased force magnitude due to a higher load-deflection curve.