Avoiding Microfractures
On one of the recent discussion threads, there was a question about sandblasting the internal of e.max restorations and whether or not that may cause the restoration to fail prematurely.
After coming out of the oven, there is sometimes residue left over from the firing process. What’s the best way to remove this residue? Can you sandblast the internal of an e.max to clean out the debris?
Any time you alter the internal of a piece of porcelain, you risk microfractures that can spread.
Microfractures start out small but over time can spread and cause eventual failure of the restoration. If I take a handpiece to the outer surface of an e.max, chances are that the glaze or polishing the surface will remove the defects that I have created, and keep them from spreading.
On the internal however, because we don’t polish or glaze, there is a chance that the defect will spread. Whether that defect is created by a handpiece or by a sandblaster is not important – what is important is that we avoid causing any unnecessary stress to the porcelain itself. With weaker porcelains the stress can spread more quickly. With e.max – because of its strength, it typically takes longer for the stress to appear.
The bottom line: To avoid these microfractures, avoid altering the internal of the restoration at any cost. If you do have debris, try removing it with a tooth brush. If you must use some form of a sandblasting device, limit it to a small microetcher with the 25 microns of powder. Do not under any circumstances use an air abrader that has large particle size or has high pressure.
By minimizing any contact with the internal of the restoration, we minimize the potential for microfractures and the eventual failure of the restoration.
There is a great discussion on this topic happening here:
I use a micro sandblaster to quickly remove the object fix putty from the internal. I use 25 micron aluminum oxide. I find it very difficult to believe that would cause more fracture propagation than the course diamond burr that the crown is milled from.
