Firing cycles for all on 4 zirconia cases

[LDent]

Greetings all,

Can someone point the way to general guidelines on baking protocols when layering on a full arch zirconia case. For all on 4 cases, what changes in firing times/ settings are necessary when creating a program on the porcelain furnace for these cases?

To what extent does one have to change the rate of temperature rise, and what is the minimum time necessary for cooling to avoid cracks or defects from each firing?

Any suggestions would be helpful

 

[CWilliams]

Start with the basic recommendations from whatever porcelain brand you use and as you grow, you customize and tweak them

General rule of thumb, the larger the structure the slower the rise/ cooling process

 

[CoolHandLuke]

every material has a unique way and rate at which it conducts heat; firebricks used in casting or in ovens are classified as fireproof on the basis that you can apply a vast quantity of heat before any part of their surface begins to absorb that heat and reflect it back.

this is why copper makes for good heatsinks

its why any gold or metal crown feels cold for a few days in the oral cavity before the sensitivity dies down,

with raw or green state zirconia it conducts heat in such a way that thick areas take longer to absorb the heat than the thinner coping areas, so bridges by and large require a slower heat rise so that during the rise the hot areas don't get so hot that they separate their grains from the thicker colder areas.

the same is true on the cooling, they must be controlled in cooling for much the same reason; the bridge is now densified so heat must be removed from the unit in a controlled manner so that the areas that are thinner which cool faster, don't cool too much faster than the thicker areas otherwise the grains separate and cracks or breaks form.

hope that helps.

 

[LDent]

Thank you all so far for your replies.

Does anyone have rate change differences or cooling times to suggest regarding layered porcelain to full arch zirconia

Let us say for example that the regular heat rate change is 45 degrees per minute for a single unit or 3 unit bridge with layered porcelain. How would this translate to a full arch restoration? Should the the heat rate be decreased by 5 or 10 degrees per minute?

Once high temp is reached, should hold times be reconsidered?

Should the cooling be lengthened to 30 mins? 1 hour, 2 hours?