Mohammad , can you please explain more about the polishing thing ? I have seen that the surface after zir liner is like it is sandblasted , and when I put the glaze liquid for sprinkling it , the liquid actually stays in place . Same goes for the porcelain . If I have a polished surface , the surface tension makes things a lot more difficult . And baking at that high of temperature , acts like a re-generation cycle for zirconia as well . In any case , I still stick to it . I feel safer than experimenting .
yes sure,
we get the zircon framework milled and sinterd, the milling bur make micro grooves all over the surface,
those groves is tiny and parallel and those grooves are idle to receive the porcelain.
when we were doing PFM, we were afraid of any micro grooves or sharp corners because they may propagate a crack.
those cracks actually caused by flexibility of the metal framework and by the assistance of those sharp corners and grooves.
now with zircon we don't have such flexibility, indeed the framework of the zircon would mostly brake before propagating a crack if its bent out.
so we should not be afraid of those micro grooves and elevations.
that's mean the best surface we can get is the sinterd milled surface just right out of the sinter furnace.
the main problem with the milling is the margins,
all dental cad consider that and offset the margins to avoid chip off during milling.
and this offset must be polished down to get the perfect fit.
if we cancel the offset or bring it near 0 we are risking the margins during milling.
also we always prefer a deeper interdental space, so we mostly adjust that area after milling.
since zirconia is extremely hard material, then any abrasive material in the lab will smooth the zirconia or polish it, it wont roughen it.
those polished and smooth areas are our nightmare when building up porcelain, because of the wetting issue.
to solve all of those problems, we should do the following:
first we need to avoid any smoothing or polishing, simply by good design and by using diamond infused stone(looks green or white we can find it easy , with any distributor.
that is the best to adjust zirconia with minimum smoothing.
now to make our build up of porcelain easier and problem free, we should make wash layer to zirconia framework, the wash layer must not give a shiny surface and its better to have a higher temp than the body and enamel porcelain.
so its good to use margin porcelain because the manufacturers of porcelain add little amount of bender and flux material to it so it will not deform during multi bake.
and this will give it a matt surface after firing which we are looking for, that surface will make building up porcelain with easy.
some technique use some sort of liquid and sprinkle on some powder, personally i don't like this way.
however, it is fast and working well.
i like to mix a margin porcelain with its liquid make it a little thick mixture and apply it unevenly on a thin layer, dry it slowly and bake it about 10* less than its final temp recommended by its manufacture.
hopefully this will help
best wishes
