目的利用锥形束CT(cone-beam computed tomography,CBCT)研究不同年龄段的下颌第一磨牙独立远中舌根的根管,探讨其增龄性变化,以期为临床根管治疗有所指导。方法选取200例具有独立远中舌根的门诊患者,其中年龄≤40岁者(≤40岁组)100例,...目的利用锥形束CT(cone-beam computed tomography,CBCT)研究不同年龄段的下颌第一磨牙独立远中舌根的根管,探讨其增龄性变化,以期为临床根管治疗有所指导。方法选取200例具有独立远中舌根的门诊患者,其中年龄≤40岁者(≤40岁组)100例,年龄>40岁者(>40岁组)100例。2组均进行CBCT扫描,图像分析包括:1)远中舌根根管口与远中颊根根管口间距(DL-DB)的测量;2)近中舌根根管口与远中舌根根管口间距(ML-DL)的测量;3)远舌根管的近远中向及颊舌向弯曲度及弯曲部位的判定。结果 1)DL-DB间距:≤40岁组为( 3.20±0.85)mm,>40岁组为(3.05±0.76)mm,2组比较差异有统计学意义( P <0.05)。2)ML-DL间距:≤40岁组为(3.74±0.44)mm,>40岁组为(3.69±0.52)mm,2组比较差异无统计学意义( P >0.05)。3)远舌根管颊舌向弯曲度:≤40岁组为(35.5±6.7)°,>40岁组为(37.6±7.2)°,2组比较差异有统计学意义( P <0.05);远舌根管近远中向弯曲度:≤40岁组为(9.1±8.2)°,>40岁组为(9.7±6.1)°,2组比较差异无统计学意义( P >0.05);≤40岁组和>40岁组弯曲部位均绝大多数位于根中1/3。结论下颌第一磨牙随着年龄的增长,DL和DB根管口间距离会缩小,远舌根管弯曲度会增大。展开更多
This paper discusses the seismic analysis of concrete dams with consideration of material nonlinearity. Based on a consistent rate-dependent model and two thermodynamics-based models, two thermodynamics-based rate-dep...This paper discusses the seismic analysis of concrete dams with consideration of material nonlinearity. Based on a consistent rate-dependent model and two thermodynamics-based models, two thermodynamics-based rate-dependent constitutive models were developed with consideration of the influence of the strain rate. They can describe the dynamic behavior of concrete and be applied to nonlinear seismic analysis of concrete dams taking into account the rate sensitivity of concrete. With the two models, a nonlinear analysis of the seismic response of the Koyna Gravity Dam and the Dagangshan Arch Dam was conducted. The results were compared with those of a linear elastic model and two rate-independent thermodynamics-based constitutive models, and the influences of constitutive models and strain rate on the seismic response of concrete dams were discussed. It can be concluded from the analysis that, during seismic response, the tensile stress is the control stress in the design and seismic safety evaluation of concrete dams. In different models, the plastic strain and plastic strain rate of concrete dams show a similar distribution. When the influence of the strain rate is considered, the maximum plastic strain and plastic strain rate decrease.展开更多
文摘目的利用锥形束CT(cone-beam computed tomography,CBCT)研究不同年龄段的下颌第一磨牙独立远中舌根的根管,探讨其增龄性变化,以期为临床根管治疗有所指导。方法选取200例具有独立远中舌根的门诊患者,其中年龄≤40岁者(≤40岁组)100例,年龄>40岁者(>40岁组)100例。2组均进行CBCT扫描,图像分析包括:1)远中舌根根管口与远中颊根根管口间距(DL-DB)的测量;2)近中舌根根管口与远中舌根根管口间距(ML-DL)的测量;3)远舌根管的近远中向及颊舌向弯曲度及弯曲部位的判定。结果 1)DL-DB间距:≤40岁组为( 3.20±0.85)mm,>40岁组为(3.05±0.76)mm,2组比较差异有统计学意义( P <0.05)。2)ML-DL间距:≤40岁组为(3.74±0.44)mm,>40岁组为(3.69±0.52)mm,2组比较差异无统计学意义( P >0.05)。3)远舌根管颊舌向弯曲度:≤40岁组为(35.5±6.7)°,>40岁组为(37.6±7.2)°,2组比较差异有统计学意义( P <0.05);远舌根管近远中向弯曲度:≤40岁组为(9.1±8.2)°,>40岁组为(9.7±6.1)°,2组比较差异无统计学意义( P >0.05);≤40岁组和>40岁组弯曲部位均绝大多数位于根中1/3。结论下颌第一磨牙随着年龄的增长,DL和DB根管口间距离会缩小,远舌根管弯曲度会增大。
基金supported by the National Natural Science Foundation of China (Grant No. 90510018)
文摘This paper discusses the seismic analysis of concrete dams with consideration of material nonlinearity. Based on a consistent rate-dependent model and two thermodynamics-based models, two thermodynamics-based rate-dependent constitutive models were developed with consideration of the influence of the strain rate. They can describe the dynamic behavior of concrete and be applied to nonlinear seismic analysis of concrete dams taking into account the rate sensitivity of concrete. With the two models, a nonlinear analysis of the seismic response of the Koyna Gravity Dam and the Dagangshan Arch Dam was conducted. The results were compared with those of a linear elastic model and two rate-independent thermodynamics-based constitutive models, and the influences of constitutive models and strain rate on the seismic response of concrete dams were discussed. It can be concluded from the analysis that, during seismic response, the tensile stress is the control stress in the design and seismic safety evaluation of concrete dams. In different models, the plastic strain and plastic strain rate of concrete dams show a similar distribution. When the influence of the strain rate is considered, the maximum plastic strain and plastic strain rate decrease.
