PubMed · 133663
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C Frank. 1976. Sharing.. https://pubmed.ncbi.nlm.nih.gov/133663/
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Modern orthodontics requires defined treatment goals. To achieve them, known force systems must be used to control the active units (teeth being moved) and the reactive units (anchorage teeth). This article discusses the methods of controlling the force systems through the variables of spring design and anchorage selection. Continuous and segmented arch treatment are contrasted in their ability to achieve optimal and defined force systems with minimal side effects.
A comparison was made on the mechanical properties of three glass-ionomer cements, one of which was of experimental fiber-reinforcing and auto-curing type. Two others were proprietary auto-curing and light-activating cements. Biaxial flexure test was conducted on disc samples. Three-point bending test was also carried out on bar samples to determine modulus of elasticity and strength. All samples were kept at 37 degrees C and 100% RH for 24 h before testing under ambient conditions. A prolonged fracture process was observed in the experimental cement, demonstrating the effect of fiber incorporation in stabilizing the fracture process. The proprietary cements failed in a brittle manner. Comparison of the mechanical properties identified three characteristics. These were a high Weibull modulus resulting from the stabilization in fracture process, a modulus of elasticity value comparable to that of dentin, and a high biaxial flexure strength close to that of a dental resin composite.
A two-dimensional photoelastic stress analysis method was applied to study the relative magnitude of stress and concentration induced by four commercially available posts for endodontically treated teeth. Three types of threaded posts; VLock, Radix Anchor, and Flexi-Post, and one nonthreaded prefabricated post, the Para-Post Plus post were tested. Stress was recorded at installation, at vertical and inclined load, and the threaded posts were compared with the nonthreaded post. At installation and on loading, stress was induced where posts were in contact with the model. Higher apical stresses were demonstrated for the Para-Post Plus post whereas the threaded posts concentrated stress where they engaged the model through threads or flanges.