effect of bridge orientation in casting machine on the castability and quality of base metal castings

The aim of this study was to evaluate the effect of bridge orientation in casting machine on castability and quality of base metal castings. Three groups of patterns with different direction and lengths in casting machine were casted and then studied qualitatively and quantitatively using mean and standard deviation in table of frequency. Larger nodules and porosities were on the joints of sprue in horizontal specimens [P=0.01 and 0.048, respectively]. There was no significant difference in castability between 3-, 5-and 6-unit bridges in relation to their direction in casting machine [P=0.5]. An increase in bridge length led to more variation in length and width. The position of bridges also played an important role in the length variation in bridges. The direction of bridges had no effect on base metal castability but a vertical position resulted in a better casting quality and an increase in length of the bridges caused more defects in castings

[Comparison of internal marginal gap in two methods of inceram coping fabrication]

Dental porcelains have an important role in fabrication of the most beautiful restorations. Biocompatibility and translucency in ceramics make them one of the most agreeable restorative materials. Introduction of inceram system has been considered as a great change in the field of restoration. Inceram is made by two ways including Sprint technique and Conventional Method. The purpose of this study was comparing internal marginal gap in Sprint and conventional Alumina methods for making Inceram copings. In this in vitro study, 60-die resin-base with 6-millimeter length and 5-millimeter diameter in the cervical area were fabricated. They were prepared with a 10-degree, convergence angle and 1-millimeter shoulder width with 90-degree shoulder angle. The specimens were then divided into two groups. Next, in one 30-item group, the cores were prepared via Sprint method and in the other group, via conventional method [Alumina]. After the cores were set, they were cemented by Panavia and for measuring the rate of internal gap, the specimens were examined via optical microscope Olympus BH60 with 1-micron precision. The data were compared statistically by students t-tests [alpha=0.05]. Examining the mean internal gap between two groups, it was revealed that the mean internal gap in the Sprint group [181.6 microns] was greater than Alumina group [114.2 microns] and the difference was significant [P=0.015]. Considering the limitations of this study, marginal adaptation in Sprint method was less than conventional method of core fabricating [Alumina]