Thermal expansion of dental casting alloys and phosphate-bonded investments.
For a dental investment to render accurate castings, it is essential 1) that the setting expansion is low enough not to cause any distortion of the wax pattern, and 2) that the thermal expansion is high enough to compensate fully for the solid thermal contraction of the casting alloy used1-8). However, all phosphate-bonded investments known today when used according to the manufacturers' instructions, are characterized by a relatively high setting expansion, and by a thermal expansion insufficient to compensate adequately for the solid thermal contraction of conventional casting alloys. Recent studies9) have shown that the setting expansion of representative European brands of phosphate-bonded investments may be reduced to an acceptable low value by modifying the mixing liquid. It was the purpose of the present work to study the thermal expansion of thus modified products, and for comparison also the thermal expansion of several dental casting alloys.
Deformation of Crowns Cast in Thermal Expansion Inhibited Investment.
Experimentally thermal expansion inhibited investment was produced to discuss a problem, the compensation of metal casting shrinkage is to be dependent upon setting expansion. Using the various concentration of colloidal silica solution as mixing liquid, idealized full cast crowns were made, the each size were measured and the following results were obtained. On this investment: 1. As the more concentration of silica, the more expansion appeared. 2. The shrinkage in cooling is slight. 3. The expansion in ringless method is greater than that of ring method. On the deformation of crowns: 1. In the external width, both ring and ringless method in 10% and 20% showed shrinkage, the more concentration, expansive tendency appeared. The inhibition of expansion appeared in 40% by ring method. The expansion of cervical showed larger than occlusal. 2. Internal width in 10% appeared shrinkage by both methods, they showed more expansion, increasing of concentration. The internal tendency appeared that occlusal was greater than cervical. The expansion of internal showed greater than external. 3. Despite of methods the more expansion appeared, increasing concentration. The more expansion appeared in the internal height than in external. The mention above following conclusion were obtained. It was cleared that the various deformation of crowns appeared due to the setting expansion of investment alone. Accordingly it was considered that the deformation occur in the stage of setting expansion before thermal stage in the present dental casting procedure. It can be said that the setting expansion is the great factor of the deformation in cast crowns.
An Optimization Approach to Occupant Safety and Fuel Economy in Vehicle Design
1. Abstract A major challenge in automotive design is the creation of safe vehicles with minimal environmental impact. This study presents a modeling framework for evaluating and optimizing body designs for improved occupant safety and fuel efficiency. Vehicle body mass is considered as the main link between safety and sustainability. The modeling framework includes frontal crash energy absorption, restraint system design and fuel economy. Preliminary results indicate a Pareto-optimal curve between safety and sustainability may exist when other factors are not taken into account. A more complete modeling framework that includes more sophisticated sustainability and safety metrics, cost and other market considerations, is suggested in order to support better design and regulatory decisions. 2. Keywords: Automotive body structures, fuel economy, occupant safety, optimal vehicle design, restraint systems