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The aim of this study was to evaluate the fatigue property
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Heart Valve Prosthesis , Heart Valves , Materials Testing , Prosthesis Design , StentsABSTRACT
OBJECTIVES: The purpose of this study was to evaluate the cyclic fatigue, bending resistance, and surface roughness of EdgeEvolve (EdgeEndo) and ProTaper Gold (Dentsply Tulsa Dental Specialties) nickel-titanium (NiTi) rotary files. MATERIALS AND METHODS: The instruments (n = 15/each) were tested for cyclic fatigue in single- (60° curvature, 5-mm radius) and double-curved (coronal curvature 60°, 5-mm radius, and apical curvature of 30° and 2-mm radius) artificial canals. The number of cycles to fracture was calculated. The bending resistance of both files were tested using a universal testing machine where the files were bent until reach 45°. Scanning electron microscopy and x-ray energy-dispersive spectrometric analysis were used for imaging the fractured segments, while the atomic force microscope was used to quantify the surface roughness average (Ra). RESULTS: EdgeEvolve files exhibited higher cyclic fatigue resistance than ProTaper Gold files in single- and double-curved canals (p 0.05). EdgeEvolve files showed significantly lower Ra values than ProTaper Gold files (p < 0.05). CONCLUSIONS: Within the limitation of this study, EdgeEvolve files exhibited significantly higher cyclic fatigue resistance than ProTaper Gold files in both single- and double-curved canals.
Subject(s)
Fatigue , Microscopy, Electron, Scanning , Pliability , RadiusABSTRACT
Objective To investigate the prevalence of voice disorder and voice fatigue mental state in the pri-mary school teachers in a district of Chengdu.Methods A random sampling survey included 389 teachers from a dis-trict of Chengdu after they filled out the throat symptoms questionnaire,carried out voice fatigue tests,and strobo-scopic laryngoscopy.Results The most common voice of discomfort symptoms was hoarseness,followed by sore throat,dry throat and vocal fatigue.There were 189 teachers,48.5%,with voice disorders as the voice disorder group)and 200 teachers without throat and voice disorders as the control group.The failure rate was significantly higher at 80 dB than 75 dB,and for the study group,the failure rate was higher than that of the control group.The difference was statistically significant in 1,2 and 10 minutes between the two groups(P <0.05).Conclusion Voice fatigue is very common in the primary school teachers and when high volumes are required,the voice fatigue is more serious.To reduce voice fatigue and the incidence of primary school teachers'voice disease,we should strengthen the teacher's voice health care.
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Objective To evaluate the hemolysis and fatigue resistance self suspension ventricular assist device (NIVAD) in vitro.Methods Resettled NIVAD which is filled with 2 500 ml fresh anticoagulant blood from pig in vitro loop system.The speed of blood pump was adjusted to 8 000 rpm.The afterload and the flow of pump were set as 100 mmHg and 3.5 L/min respectively.Keep the temperature at around 37 degree centigrade which is equal to average internal temperature in pig.Then harvest and measure the free hemoglobin(FHB) of blood samples at different time points before and after working.Then calculated the normalized index of hemoylsis(NIH) by comparing to control group, the unused pig blood at the same period.In fatigue test, conditions remained unchanged, except the blood was replaced by pure water.The blood pump had operated for 90 d continuously and recorded its performance.Results The FHB of experimental blood is higher than that of the control.The normal index of hemolysis NIVAD is(0.0052 ±0.0019)mg/L.Fatigue test , the blood pump operated smoothly, and every parameters was stable.Conclusion The blood pump of NIVAD does a certain degree of destruction to blood, but the NIH is in criterion range of hemolysis, it has certain advantages compared to similar products in china and aboard.At the same time it has good resistance and stable property to fatigue.
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[Objective] To investigate the stability and function of atlantoaxial segment after atlas odontoid process artificial joint replacement.[Method]Ten fresh adult human head and neck specimens were chosen for biomechanical models.The range of motion(ROM),neutral zone(NZ)and stiffness under intact state,post-decompression,post-replacement surgery and post-fatigue were measured respectively.[Result]After decompression,ROM,NZ and stiffness in flexion,extension,right and left lateral bending,and right and left axial rotation increased significantly(P0.05)than that in intact state group.[Conclusion]Artificial atlantoaxial joint in this study has been proved to have biomechanical significance in morphology and dynamic.It has advantages of stable replacement,simple operation,less injury and low wear characteristics.It provides a new choice for the atlantoaxial fusion of anterior or posterior approach.
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STATEMENT OF PROBLEM: Chronic implant screw loosening remains a problem in restorative practices. Some implant manufactureres have introduced abutment screws with treated material, surfaces and macrostructures in an effort to reduce potential loosening. PURPOSE: This study evaluated the materials and loading cycles on detorque value after dynamic continous fatigue test in the sinulated conditions of posterior single restoration. MATERIAL AND METHOD: Fourteen of each of the following abutment screws - titanium alloy, gold alloy, gold-tite, and titanium alloy modified - were used in test. SEM is used to verify macrostructures of each screws. ZrO2/Al2O3 composite abutment was tightened on 4x10.0mm titanium external implant at 30 Ncm. Cyclic loading machine delivered dynamic loading forces between 20 and 320N for 100,000, 200,000, 300,000, 500,000, and 1,000,000 cycles at frequencies 14Hz. Torque and detorque value after loading was measured. RESULTS: All measued screws had different screw length and thread form. Titanium modified screw had greater detorque value than others before and after cyclic loadings(p<0.05). All abutment screws had no significant change in mean percentage of detorque value after loading to initial value after less than 500,000 cyclic loadings, but significant lower value after 1,000,000 cycles(p<0.05). CONCLUSION: Within limintations of this study, all abutment screws may be loosend after about1 year use. Annual check-up is nessasary to prevent screw loosening.
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Objective:To study retention force durability of root-type attachments.Methods:Five magnetic attachments(Magfit EX-600),semi-precise stud-type attachments(Bedent) and precise stud-type attachments(Dalbo-classic) were fixed on a thermal-cycling and mechanical-loading machine respectively.The retention force of each attachment was measured at the baseline and after every 1,000 cycles of seating-removing.Results:The average retention force of magnetic attachments was(3.85?0.107) N at the baseline which attenuated for 3.38% after 10,000 cycles;The retention force of semi-precise group was(14.10?0.144) N originally and decreased 90.06% of the original force after 10,000 cycles.The primary force of the precise group was 33.14 N and was adjusted to(11.95?0.082) N as baseline attenuating for 74.56%.Conclusion: The retention force of magnetic attachments is lower than the stud attachments but is stable for 10 years.The retention force of stud-type attachments is larger at the baseline but reduced rapidly.