PubMed · 4440485
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1974. [Round table discussion: Impedance].. https://pubmed.ncbi.nlm.nih.gov/4440485/
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External fixators are standard devices to stabilize bone fractures and their compliance aims at producing an interfragmentary motion that promotes rapid and successful healing. While evaluation of their axial compliance is a routine test, the quantification and interpretation of their full 6 x 6 compliance matrix is an extensive and delicate task. In this context, the objective of this study was to develop, validate and demonstrate the potential of a rigorous method to quantify their 6 x 6 compliance matrix. An experimental system was developed to apply six independent static forces and moments to an external fixator in the field of view of two infrared cameras quantifying the induced motion. The system was then tested with a calibration structure which compliance could be calculated analytically and numerically. Finally, the system was applied to compare three configurations of a commercial external wrist fixator. The results of the method proved to be reproducible and highly consistent with the linear elasticity theory in the physiological range of small deformations. A rigorous method for evaluation of the 6D compliance becomes therefore available for research in mechanobiology of fracture healing by external fixation.
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OBJECTIVE: The purpose of the study was to measure the fatigue properties of four dental resin composites using a dynamic mechanical analysis and to relate the results with viscoelastic properties. METHODS: Dynamic torsional loading was conducted at resonance at 30-50Hz. Specimens were thoroughly cured and tested dry at 21 degrees C. RESULTS: All of the specimens showed a loss of strength following repeated stress, due to material fatigue. The material with the highest shear modulus had the lowest damping and the highest fatigue strength. SIGNIFICANCE: Dental composites exhibit a modest loss of strength due to fatigue. Since mastication involves many cycles of stress during the life of a restoration, fatigue properties should be taken into account in restoration design.