| ObjectiveTo study the effect of mold temperature on the accuracy and surface layer structure of the Ti castings invested with ZrP99 investment. Evaluate the properties of ZrP99 investment from the point of clinic. At the same time provide theoretical and practical basis for the use of ZrP99 investment in clinic.Methods30 artificial stone dies simulated the post - tooth and their corresponding complete crown wax patterns were made with a truncated cone - shape standard brass model with round sleeves. They were divided randomly into five groups and each group has six samples. Measure the distance between the gingival margin of wax pattern and the shoulder of its corresponding artificial stone die with a micro - picture analysis system under the traveling microscope. Four group wax patterns were invested with ZrP99 investment as test groups and one group was invested with Titavest - CB investment as the control. Heat the test group moulds with the same heating procedure to the target temperature, then cast at the mould temperature 600 , 450 ,300 , 150 respectively with a Cyclarc titanium casting machine. The heating procedure and mold temperature of the control group was recora-mened by the manufacturer. Ocular observed the casting surface char-acters such as structure integrity, casting deficiency, surface color, etc. Measured the distance separating the gingival margin of the crown and the shoulder of the die in the same way as for the wax patterns. The discrepancies derived from the space distance measurements made with wax patterms and cast crowns. The discrepancies represented the casting accuracy. The discrepancy was smaller, the casting accuracy was more accurate. The microstructures of the castings were observed by a MM - 5 type metallography microscope. The micro - hardness of each casting was measured through the cross - section from the surface to the inside 150 m at 25 m intervals with a M - II type hardness tester at a load of 100g. All results were subjected to student t test and one -factor ANOVA with SPSS10. 0 software.ResultsOcular observation of the casting surface characters showed the five group castings had smooth and integrity surfaces and no contracted cores and no casting deficiencies. The casting surfaces of castings invested with Titavest - CB investment and those investd with ZrP99 investment and casted at mold temperature 300 , 150 appeared siliv-er grey and little oxidizing color. The casting surfaces of investd with ZrP99 investment casted at mold temperature 600 , 450 appeared dark grey and deep oxiding color. Measurement of the casting accuracy indicated that the casting accuracy of the control group was higher than all the test groups. When the mold temperature was lower than 450 , the accuracy of the castings invested with ZrP99 investment was improved significiantly with the mold temperature increased and when the mold temperature was higher than 450 , the temperature had no significiant effect on the accuracy of the castings invested withinvestment. Metallography analysis of castings showed that the thickness of the reacted layer of the castings invested with Titavest - CB investment was only less than 30 m. Those invested with ZrP99 investment were more than 50 m. The mold temperature affected not only the surface structure but also the interior structure of the test group castings invested with ZrP99 investment. With the mold temperature changed, the shape, size, range and trend of the casting crystalline grain were changed. The results of the micro - hardness measurement of the castings showed that the mean micro - hardness value of five group castings was reducing from the surface to the inside and tending towards stabilization. The surface micro - hardness of the control group casting was the smallest of the five group castings. The mean micro - hardness value of the test group castings was reducing with the lower of the mold temperature. The measurement results of the reacted layer thickness measured by the hardness were nearly equal to t...
|
PDF Full Text Request