Effect Of Different ZrO₂ Based Investments On The Quality Of Titanium Crown

This study assessed the characteristics of Ti crown invested with different ZrO2 based investment to determine whether these investments can be used in commercial pure titanium casting.Methods30 complete crown wax patterns were made with a truncated cone shape standard brass die with round sleeves . They were divided randomly into five groups and each group has six samples . Measure the distance between the gingi-val margin of wax pattern and the shoulder of the die with a micro - picture analysis system under the traveling microscope . Four group wax patterns were coated with 1 - mm layer of different ZrO2 based investments . Then the wax models with coatings were invested using a phosphate bonded investment as the test groups and one group was invested with Titavest CB investment as the control. The molds were fired according to the manufacter's instructions. Casting process were made with a cyclara titanium casting machine and using commercially pure titanium ingots . The castings were then carefully cleaned. Ocular observed the casting surface characters . Such as structure integrity , casting deficiency, surface colour, etc. Castings were examined with radiographic equipment to detect the presence of voids in the castings. Three specimens of each group were embe-ded in resin and studied metallographically after grinding, polishing and chemical etching . Measure the distance separating the gingival margin of the crown and the shoulder of the die in the same way as the wax patterns . Dimensionalaccuracy of the casting crowns were expressed by the discrepancy between the wax pattern and a casting prepared from the same die . All results were subjected to one way factor ANOVA with spss 11.5 software.ResultOcular observation of the casting surface characters showed a, b, c, e groups had smooth and integrity surfaces and no contracted cores . and no casting deficiencies. But d group had obvious inadequate filling of mold for titanium crown . So d groups specimen cant be used in other measures. The casting surfaces of the control group and c , e group appeared silver grey. The a , b group castings surface appeared dark grey . The d group appeared yellow and blue. The radio-graphic examination show one gas porosity in the specimen of the control group and one shrinkage porosity in one specimen of a group. In other specimens no obvious porosity and casting deficiency was detected. Metallographic examination showed that the thickness of the reacted layer of the casting invested with Titav-est CB investment was only 42um . But for the test groups the thickness of the reacted layer of the casting were more than 77 um. The thinkness value of the test group casting was reducing with the increase of the ZrO2 in the investment . Measurement of the casting accuracy indicated that the casting accuracy of the test group was higher than the control group. As the increase of the ZrO2 in the investment . The accuracy of the castings decline. Results of accuracy of different groups evaluated by using one way ANOVA followed by student Newman - keuls test realed a statistically significant difference among different groups.ConclusionAs the increase of the ZrO2 in the composition of the investment , the thickness of the reactive layer reduce and the casting accuracy reduce.Test group's investment can't get the same result as the control group, but c group' s investment' s character is similar with the control group.