BACKGROUND:Irreducible femoral neck fracture was difficult to obtain anatomic reduction.As a new type of internal fixation,the femoral neck system is still blank for the treatment of non-anatomical reduced femoral neck fractures. OBJECTIVE:To explore the biomechanical stability of femoral neck system internal fixation under nonanatomical reduction in the treatment of femoral neck fractures based on finite element analysis. METHODS:CT data of the hip joint of a healthy female adult were obtained.Anatomical reduction of femoral neck fracture models with Pauwels angles of 30°,50°,and 70° were established using Mimics 21.0,Geomagic Wrap 2021,and SolidWorks 2020.The fracture proximal ends of the three anatomical reduction models were shifted upward by 2 mm along the fracture line,and three positive buttress models with different Pauwels angles were obtained.In the same way,three negative buttress models were acquired by shifting downward by 2 mm.SolidWorks 2020 was used to make the femoral neck system internal fixation,and the nine femoral neck fracture models were assembled with the femoral neck system.Then Ansys 19.0 was used for finite element analysis.The displacement distribution and maximum displacement,stress distribution and maximum stress of the femur and femoral neck system were recorded under 2100 N stress. RESULTS AND CONCLUSION:(1)When Pauwels angles were 30°,50°,and 70°,the maximum stresses of the femoral neck system appeared to be concentrated at the junction of the sliding hip screw and anti-rotation screw.The maximum femur stresses appeared to be concentrated in the medial cortex of the femur.The maximum displacement was concentrated at the upper of the femoral head and femoral neck system.(2)When Pauwels angles were 30° and 50°,the maximum displacement and maximum stress of the femoral neck system and femur were:negative buttress>anatomical reduction>positive buttress.(3)When Pauwels angle was 70°,the maximum displacement and maximum stress of the femoral neck system were:negative buttress>anatomical reduction>positive buttress;the maximum displacement and maximum stress of the femur were:negative buttress>positive buttress>anatomical reduction.(4)With the increase of Pauwels angle,the biomechanical advantage of the positive buttress was weakening.However,it was better than a negative buttress.When Pauwels angle was 30°,positive buttress was more stable than anatomical reduction.When Pauwels angle was 50°,the biomechanical difference between positive buttress and anatomical reduction became smaller.When Pauwels angle was 70°,the stability of anatomical reduction was slightly better than positive buttress.(5)If it was difficult to achieve anatomical reduction of femoral neck fracture during operation,but the positive buttress had been displaced within 2 mm,the femoral neck system could be used to offer stable mechanical fixation.It is necessary to avoid negative buttress reduction.

OBJECTIVE: This study aimed to compare the effects of water storage treatment and thermal cycling on the shear bond strength (SBS) of three self-adhesive dual-cure resin cements. METHODS: Six cubic zirconia specimens with side length of 2 cm were obtained by cutting and sintering. Three self-adhering dual-cure resin cements (i.e., Clearfil SAC, RelyX U200, and Multilink Speed) were selected. According to their bonding modes, they were divided into three groups: direct bonding group (direct coating with resin cement), adhesive group (applying universal adhesives and then coating with resin cement), and primer group (applying Z-Prime Plus and then coating with resin cement). According to experimental conditions, each group was divided into two subgroups: subgroup a (water storage at 37 ℃ for 24 h) and subgroup b (thermalcycling for 5 000 times). SBS data were analyzed by one-way ANOVA by using SPSS 19.0 software (P<0.05). The fractured zirconia surface was observed under a stereomicroscope. RESULTS: After water storage for 24 h, the SBS of the adhesive group and the primer group of the three resin cements was higher than that of the direct adhesive group (P<0.05), but the difference in SBS between the adhesive group and the primer group was not significant (P>0.05). After thermalcycling, the SBS of the three types of resin cements decreased (P<0.05); the SBS of the adhesive group was higher than that of the direct adhesive group and the primer group (P<0.05). Fracture mode analysis revealed that the type Ⅲ fracture mode evidently increased after the thermalcycling treatment compared with the water storage treatment. CONCLUSIONS The universal adhesives and the primer can improve the SBS of self-adhesive dual-cure resin cement in water storage at 37 ℃ for 24 h. The universal adhesives had a better bonding durability than the zirconia primer.
Ceramics ; Dental Bonding ; Dental Cements ; Dental Stress Analysis ; Materials Testing ; Resin Cements ; Shear Strength ; Surface Properties ; Zirconium

Objective:To investigate the status of satisfaction of postgraduates majoring in public health with the teaching material of The prevention and control of chronic non- communicable disease, so as to provide the basis for promoting the teaching and optimizing the reprint of the teaching material. Methods:An online survey was conducted among 180 public health postgraduates of Batch 2018 to Batch 2020 from China CDC who took the selective course of "prevention and control of chronic non-communicable diseases". The survey content included the overall satisfaction of the respondents with the teaching material and such four levels of satisfaction as primary indicators at the content level, thinking level, motivation level and arrangement level and 20 secondary indicators. The statistical analysis was made by SPSS 25.0.Results:The effective response rate was 90.56% (163/180), and the overall satisfaction of postgraduates with the teaching material was 88.96%. The satisfaction of "scientificity", "comprehensiveness", "internal coordination" and "hierarchy" at the content level, "systematic thinking" and "quality education" at the thinking level, "deepening the understanding and application of relevant knowledge in the field of chronic disease prevention and control" and "the content is convenient for self-study and helps guide the construction of new knowledge" at the motivation level, and "accurate words, fluent language and easy to read and understand" and "firm binding, good paper quality and clear printing" at the arrangement level of the teaching material was more than 90.00%. Only the satisfaction of "the critical thinking" at the thinking level and "stimulating learning enthusiasm" at the motivation level was less than 85.00%.Conclusion:The teaching material of The prevention and control of chronic non- communicable disease meets the learning needs of postgraduates majoring in public health, and students have high overall satisfaction evaluation on the teaching material. It is necessary to further optimize the two aspects of "the critical thinking" and "stimulating learning enthusiasm" in the revision of the teaching material.

OBJECTIVEThis study aimed to determine the effects of copper content on the corrosion resistance of CoCrMoCu alloy and its in vitro antibacterial performance.

METHODSCoCrMoCu specimens with different Cu contents (2%, 3%, 5%, and 7%) were prepared by vacuum melting method. CoCrMo without Cu served as control. The corrosion resistance of the specimens was measured by electrochemistry. The antibacterial effects of the specimens on Staphylococcus aureus and Escherichia coli were analyzed by coating-film method.

RESULTSCompared with CoCrMo without Cu, the addition of 2%-5% Cu to CoCrMo improved the pitting and uniform corrosion of CoCrMo alloy and decreased the corrosion current density. The antibacterial performance of CoCrMoCu alloy increased with increased Cu content. The antibacterial rate of alloy was 99% when Cu content exceeded 5%.

CONCLUSIONSCu addition had a statistically significant influence on the corrosion resistance and antibacterial performance of CoCrMoCu. CoCrMoCu has better corrosion resistance and antibacterial performance when Cu content is 5%.

OBJECTIVES: To explore the optimal maintenance dose of caffeine citrate for preterm infants requiring assisted ventilation and caffeine citrate treatment. METHODS: A retrospective analysis was performed on the medical data of 566 preterm infants (gestational age ≤34 weeks) who were treated and required assisted ventilation and caffeine citrate treatment in the neonatal intensive care unit of 30 tertiary hospitals in Jiangsu Province of China between January 1 and December 31, 2019. The 405 preterm infants receiving high-dose (10 mg/kg per day) caffeine citrate after a loading dose of 20 mg/kg within 24 hours after birth were enrolled as the high-dose group. The 161 preterm infants receiving low-dose (5 mg/kg per day) caffeine citrate were enrolled as the low-dose group. RESULTS: Compared with the low-dose group, the high-dose group had significant reductions in the need for high-concentration oxygen during assisted ventilation (P=0.044), the duration of oxygen inhalation after weaning from noninvasive ventilation (P<0.01), total oxygen inhalation time during hospitalization (P<0.01), the proportion of preterm infants requiring noninvasive ventilation again (P<0.01), the rate of use of pulmonary surfactant and budesonide (P<0.05), and the incidence rates of apnea and bronchopulmonary dysplasia (P<0.01), but the high-dose group had a significantly increased incidence rate of feeding intolerance (P=0.032). There were no significant differences between the two groups in the body weight change, the incidence rates of retinopathy of prematurity, intraventricular hemorrhage or necrotizing enterocolitis, the mortality rate, and the duration of caffeine use (P>0.05). CONCLUSIONS This pilot multicenter study shows that the high maintenance dose (10 mg/kg per day) is generally beneficial to preterm infants in China and does not increase the incidence rate of common adverse reactions. For the risk of feeding intolerance, further research is needed to eliminate the interference of confounding factors as far as possible.
Caffeine/therapeutic use* ; Citrates ; Humans ; Infant ; Infant, Newborn ; Infant, Premature ; Respiration, Artificial ; Retrospective Studies