Comparison of mechanical properties with density of pre-sintered zirconia block

Introduction:

The purpose of this study is to build a basis for creation of a new zirconia block by comparing mechanical properties with current commercialized zirconia block and examining the possibility of clinical usage of the test results which were pre-sintered zirconia block with variable density.

Materials and Methods:

Four zirconia blocks were designed for the present study. The control group was used the Kavo Everest ZS blank (KaVo, Germany) and the experimental groups were fabricated from the commercial ytrria-stabilized tetragonal zirconia powder (KZ-3YE Type A, KCM. corporation, Japan) with density of 2.7, 2.9, 3.2g/cm³ pre-sintered block. 12.48g powder was molded into dies (diameter 6cm, height 20cm) by single action press forming at a pressure of 3Pa (N/m²). The green bodies (2.01cm diameter X 1.44cm height) were presintered at heating rate of 1 ^oC/min from 64^oC to 950^oC, 1040^oC, 1070^oC and were kept with different time; 60min, 90min, 120min. According to this pre-sintering process, the experimental groups were classified into three groups. After the pre-sintered block was sintered, a number of mechanical tests were done such as shrinkage rate, biaxial flexural strength, and microhardness. The micro-structural analysis were measured and compared with the control group.

Results:

1. The average shrinkage rates of blocks in experimental groups were different from each other depending on density of the pre-sintered block.

2. The shrinkage rate of blocks which were divided into three equal parts of pre-sintered block was different at top, middle, bottom, respectively.

3. The mean biaxial flexural strength and micro hardness values showed no significant difference in all groups.

4. In SEM images, the fractured surface of disc specimens after biaxial flexural strength test shows that all groups have brittle fracture pattern. Post-sintered zirconia blocks show an increase of the particle size and aggregate grains.

Conclusion:

In this study, there was significant difference of the shrinkage rate with density of pre-sintered block. And the shrinkage rates were different with each other depending on area of pre-sintered block.