Undersizing of cast Ti crowns has been reported to be a problem. The diameter of standardized, cylindrical crowns was studied in this investigation using a photographic technique and cold moulds. The results show that the dimensional problem can be avoided by selecting a standard phosphate-bonded investment with a sufficiently high thermal expansion coefficient. Appropriate casting conditions with a good vacuum (13.3 Pa) gives only a thin (<10 μm) oxide film and reproducible dimensions of the castings. A ZrO2 coating eliminates or reduces the oxide film and follows the movements of the investment. The diameter of the crown can largely be accounted for by the measured expansion of the investment and thermal contraction of the Ti casting.
Dimensional fit of cast Ti-restorations.
Herø H, Syverud M, Waarli M, Kleven E
Journal of Materials Science: Materials in medicine March 1993; 4(2): 210-212