Abstract
Aims: To evaluate the effect of the burn-out heating on the compressive strength of investment materials. Materials and Methods: Three commercial investment materials were used in this study. Seventy two cylindrical shape specimens were prepared to evaluate the compressive strength of the investment materials at room temperature (cold strength) and at two different burn-out heating temperatures : 700 oC and 1000 oC (hot strength). Three groups were prepared according to tested investment materials, The specimens were then subdivided into three subgroups according to burn-out heating temperatures,eight specimens for each subgroup. The compressive strength (kg /cm2) was evaluated by using Instron testing machine. Mean values were compared statistically with one way analysis of variance (ANOVA),Duncan , s multiple range test and t-test to determine the significant difference among the tested groups at (p<0.05) level of significance .Results: The results showed that there is a significant difference of the means value of the compressive strength among the three tested investment materials. The compressive strength value significantly decreased with increasing burn-out heating temperature. Conclusion: The result of this study showed that the increase of burn-out heating had a significant decrease the compressive strength of the investment materials, and cold compressive strength gives an indication of the hot strength .
