Zirconia blocks for all ceramic dentures are divided into two groups. one is pre-heated block and the other is binder added block. In this study, the possibility of recycling the waste parts of binder added block, which was CAD/CAM machined, with slip casting process was investigated.
Owing to the waste parts of binder added block containing large amount of organic matter, binder burn-out process was must be carried out before ball milling for preparing the casting slips. Binder burn-out was accomplished at 600℃ for 10 hours. Casting slips was prepared with 300g 5mm zirconia ball, 100g zirconia powder, and 180g distilled water in 60mm diameter polyethylene bottle.
SEM photomicrograph showed 200~300nm of zirconia particles dispersed in casting slips. Slip casting was performed with plaster mold. Casted body was dried and sintered at 1500℃ for I hour. Casted waste block body showed 26% of linear shrinkage, 6.07g/㎤ of apparent density, and 470MPa of three point bend strength.
On the other hand, as received zirconia block which was sintered at the same conditions, showed 23% of linear shrinkage, 6.10g/㎤ of apparent density, and 680MPa of three point bend strength.
It is necessary to improve the physical and mechanical properties of casted body for recycling the waste parts of binder added block, therefore alumina was added to waste zirconia slip. When 3wt% of alumina was added to zirconia, sintered waste body showed 23% of linear shrinkage, 5.90g/㎤ of apparent density, and 780MPa of three point bend strength.
SEM photomicrograph and EDS analysis showed alumina particles uniformly dispersed in zirconia matrix, and XRD analysis showed no phase transformation of tetragonal zirconia particles was occurred when alumina was added.
The conclusion according to the all of this experimental results, the cast zirconia copping produced from the waste parts of binder added zirconia blocks was possible to use all ceramic denture.