Zirconia Opaqueness & Shade issues after Sintering


Opaque and dead-looking after sintering?

As we all know,the translucency of zirconia is related to the amount and type of additives,the sintering temperature,the atmospheric conditions during the sintering process,and the heating methods. In particular, the final temperature of the sintering process and the heating method used are direct determinants of the density, porosity, and grain size of zirconia.A change in the sintering conditions would change the translucency of the zirconia core.

  • The actual sintering temperature does not reach the required temperature, the zirconia are undercooked - One problem we have found, most sintering furnace temperatures drift higher over time. Thus, 1450 last year could actually be 1550 now. Calibrate every 3-6 months regardless of furnace brand. If you find the temp is off by more than 25 degrees, calabrate more often.so test the sintering furnace temperature every 3 months to half a year,that will be necessary.

  • Missing drying processing in the dyeing solution after soaking, and the furnace will be polluted after soaking and sintering without drying - clean the furnace,break the waste zirconia(white zirconia disc-HT ST UT) into small pieces of size 5-10mm . Take 4-6 pieces and place them in the sintering tray (in the crucible), cover the filling, take another 8-10 pieces and place them on the shell, place the sintering plate in the middle of the furnace.

    Sintering procedure: room temperature --- 10℃/min heating rate --- heating to 1600℃ --- keeping warm for two hours --- natural cooling.repeatedly burning until the white zirconium has normal color permeability, and the furnace is clean.

You will get the perfectly sintering zirconia by observeing the following tips:

Green stage cleaning and handling is the same (air, brush, gloves)

Use same color liquied for one job (ZZ Acid based)

Brushes are metal free

Correct drying processing

Make sure the Heating elements and thermocouples of the furnace get changed before hitting recommended hours

Beads get changed every other week

No new sintering trays, no ancient ones

Sintering programs are manufacturer recommended

Furnaces think things are fine (no errors, no current fluctuations, logs look fine)

Other questiones that you might be concern for sinting:

Does the Yttria content alter the zirconia's time to sinter or high sintering temperature?

Yttria is a stabalizer as zirconia by itself is an unstable element. Adding different quantities of Yttria changes the properties of zirconia ie. translucency can be affected by addition of slight amounts of Yttria. That being said the Yttria content does not alter the time to sinter for Tetrahedral types of zirconia.

What is the fastest you can cool zirconia?

A typical recommended is that you cool 8-10 degrees Celcius per minute to at least 450 degrees Celcius and then a natural cool to room Temperature.

Does raising/lowering the sintering temperature change the way zi looks?

If so what happens when fired too low? Too high?

Answer: Yes it changes the Aesthetics of the zirconia in a big way. it all depends on weather it is high fusing zirconia, low fusing zirconia, cubic zirconia, tetrahedral zirconia or even shaded zirconia. Sintering Hold Temperatures plays a big part of how the final outcome of that product will turn out.

Typically if you fire the zirconia at to low of a temperature the color will not be correct and it will be a chalky dead look. If fired to high Depending on how high it will ether turn out milky or raise the translucency of the zirconia. For example: if you fired a crown at 1540DegC and wanted more translucency and bumped it up to 1550DegC you might get more translucency but if you go well over the recommendation of that zirconia it will come out the best result.

Do sintering times depend on the furnace or brand of Zr?

If times are dependent on brand of material, who offers the fastest sintering Zr?

Neither, it depends on the desired outcome.

Each zirconia does have it's manufacturer recommended programs for sintering (usually a standard program and a speed program). And if they have different sintering furnaces, they may even have different programs based on the zirconia and the furnace technology. I ALWAYS recommend talking with your zirconia manufacturer to get their approved sintering parameters, as they know this works. As you go outside of these, things are not as predictable.

Fast sintering (75 minutes for single copings, 90 minutes for bridge frameworks) is achievable because you don't need/want these to really be translucent, you want strength and are going to FULLY layer for esthetics. But you shouldn't think about doing a fast sintering program (75 minutes/90minutes) for full contour crowns and bridges unless the manufacturer gives you the proper parameters (there are some that work, depending on the material, but they are approximately 3 hours and 4.5 hours respectively. And NEVER if using coloring liquids when fast sintering).

ALWAYS do a standard program (7.5 hours or longer, depending on the zirconia and furnace) when doing Long span bridges, All-on-4 cases, or using coloring liquids.