There is a concern that long-term immersion of impressions in disinfectant solutions may cause changes in the dimensions of the resulting stone casts. This study investigated the dimensional changes in stone casts resulting from immersion of five brands of addition-type silicone rubber impressions in disinfectant solutions for 30 min and 24 h. Impressions of a master cast designed to simulate an abutment tooth were immersed in 2% glutaraldehyde and 0.55% ortho-phthalaldehyde. The diameter of the stone cast was measured using a laser scan micrometer. For four brands of impression materials, 30-min immersion in disinfectant solutions produced no dimensional changes in the stone casts. For four brands of impression materials, 24-h immersion caused a significant decrease in the stone cast dimensions.

The properties of several different investments were investigated including phosphate bonded, magnesia bonded, and alumina cement investments. Measurements included the setting expansion, thermal expansion, and compressive strength of investments, as well as the tensile strength, elongation, Vickers hardness (VHN) and surface roughness of titanium castings. For phosphate bonded investment, the setting expansion after being mixed with its own mixing solution was 2.10%, which was larger than the other investments; the thermal expansion was -0.25% at 200 degrees C, the compressive strength 14 and 5 MPa after heating. For titanium cast in phosphate bonded investment, the hardness on its top surface was 655 Hv, the tensile strength was 379 MPa, the elongation was 19.4%, and the surface roughness was 2.29 microm. Athough the thermal expansion of phosphate bonded investment is small, the setting expansion is large enough to compensate for the shrinkage of titanium castings. As its thermal expansion at T >/= 600 degrees C was constant and its heating-cooling cycle was almost reversible, these two properties can reduce the thermal shock and thus avoid cracking of the investment.

In this study, wedge-shaped CP titanium castings and Ti-6Al-7Nb alloy castings were produced by three types of investment.

This study evaluated the bond strengths between experimental Ti-20Cr-1X (X=Nb, Mo, Fe, Zr) alloys and porcelain (Duceratin). The results of this bond strength testing indicated that all the Ti-20Cr-1X alloys exceeded the lower limit value in the ISO 9693 standard for the 3-point bending test (25 MPa), and were all higher than that of commercially pure titanium (c.p. Ti). The coefficient of thermal expansion (CTE) values of all Ti-20Cr-1X alloys were higher than that of c.p. Ti, and this result of a closer match between CTEs shows the fact that the Ti-20Cr-1Mo alloy had a significantly higher bond strength than both the other Ti-20Cr-1X alloys and c.p. Ti.

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