Multilayer Zirconia Sintering for Reduced Stripe Visibility
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional short firing schedules for zirconia-containing ceramics result in visible stripes between layers with different yttria contents, compromising the shade and strength of dental prostheses.
Innovation Solution
A specific short firing schedule is applied to a zirconia molded or pre-sintered body with multiple layers of varying stabilizer content, involving three temperature-increasing steps with controlled rate changes to minimize transparency differences between layers, using an atmospheric furnace.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional short firing schedules are used to reduce sintering time, then productivity is improved, but manufacturing precision deteriorates due to visible stripes between layers with different yttria contents
Solution Approach 1:
The sintering process is segmented into multiple heating stages with different heating rates. The first heating stage uses a first heating rate, the second heating stage uses a second heating rate, and the third heating stage uses a third heating rate. This segmentation allows different parts of the sintering process to be optimized independently, reducing stripe formation while maintaining short overall sintering time.
Solution Approach 2:
The heating rate is made dynamic by changing it at different stages of the sintering process. The heating rate is adjusted based on the current temperature and sintering progress, transitioning from a first heating rate to a second heating rate, and then to a third heating rate. This dynamic adjustment prevents stripe formation by optimizing heat distribution at each stage.
2Loss of time
If short firing is applied to zirconia multilayer blanks, then loss of time is reduced, but manufacturing precision worsens due to stripe formation between layers
Solution Approach 1:
The firing process is divided into three distinct heating stages, each with specific heating rates and temperature ranges. This segmentation allows the stabilizer distribution to be controlled more precisely throughout the short firing process, preventing stripe formation between layers with different yttria contents while maintaining reduced firing time.
Solution Approach 2:
The heating rate parameter is changed at different stages of the firing process. By adjusting the heating rate from the first heating rate to the second heating rate and then to the third heating rate, the patent optimizes stabilizer distribution and prevents stripe formation during short firing, maintaining manufacturing precision while reducing time loss.
3Productivity
If high heating rates are used to shorten sintering time, then productivity is improved, but manufacturing precision deteriorates due to non-uniform sintering and stripe formation
Solution Approach 1:
The heating rate is dynamically adjusted through three stages rather than maintaining a constant high heating rate. This dynamic control ensures uniform sintering by optimizing heat distribution at each temperature range, preventing stripe formation while maintaining high overall sintering speed for improved productivity.
Solution Approach 2:
The high-speed sintering process is segmented into three heating stages with different heating rates. This segmentation allows the sintering process to maintain high speed overall while ensuring uniformity at each stage, preventing the stripe formation that would result from a single constant high heating rate.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method produces a zirconia sintered body with minimal visible stripes and maintains ideal shade and strength, replicating dental prosthesis quality in a significantly reduced firing time.
Implementation Method 1
a zirconia molded body or zirconia pre-sintered body is sintered in a short time period
Implementation Method 2
three temperature-increasing steps with controlled rate changes to minimize transparency differences between layers
Data Source
Figure 1
AI summary
The present invention provides a method of production of a zirconia sintered body by which a zirconia molded body or zirconia pre-sintered body having a plurality of layers containing different amounts of stabilizer is sintered in a short time period to produce a zirconia sintered body having hardly noticeable stripes between layers differing in yttria content. The present invention relates to a method for producing a zirconia sintered body, comprising a firing step of firing a zirconia molded body or a zirconia pre-sintered body, the zirconia molded body or the zirconia pre-sintered body comprising a plurality of layers containing a stabilizer, the plurality of layers including layers having different stabilizer contents, the firing step comprising at least three stages of temperature-increasing process including a first temperature-increasing step (H1), a second temperature-increasing step (H2), and a third temperature-increasing step (H3), the method satisfying HR2 = more than 0°C/min and less than 50°C/min, HR3 = 5 to 150°C/min, and HR3/HR2 > 1, where HR2 is a rate of temperature increase in H2, and HR3 is a rate of temperature increase in H3, the temperature-increasing process having start temperatures that are 1,000°C or less in H1, more than 1,250°C and 1,450°C or less in H2, and 1,450°C or more and 1,550°C or less in H3, the temperature-increasing process having end temperatures that are more than 1,250°C and 1,450°C or less in H1, 1,450°C or more and 1,550°C or less in H2, and 1,500°C or more and 1,750°C or less in H3.