You’ve probably heard of e.max crowns. In a prior post, I discussed the latest ceramic technology and how confusing it can be. There are a lot of products being pushed on the market by different companies and every sales representative will show you a “study” that proves their product is the greatest invention since sliced bread.
But the hype behind e.max (Ivoclar Vivadent) is very real and worth our attention. Let’s take a look again at the three porcelain categories, based on material:
Now let’s look at a chart of porcelain that takes brands into consideration:
There are more brands out there, but these are the ones that I’m using in my practice right now. A longer list of brands can be found in my dental ceramic post.
So you can see that “e.max” can mean a restoration made of lithium disilicate or zirconia. “e.max” is a brand, not a specific restoration.
I haven’t used e.max ZirCAD yet, but I’m sure it’s just fine. Personally, when I’m using zirconia, I use NobelProcera Zirconia (Nobel Biocare). Why? It’s been around for a while and I’ve had great success with it. As an aside, you can actually use Procera scanning technology for the CAD part of e.max ZirCAD. Totally compatible.
Anyway, the real excitement over e.max restorations has been due to their lithium disilicate product line. Here’s why:
(1) It can be pressed or made with CAD/CAM
There are now two ways to fabricate your lithium disilicate restorations: pressed to the model or CAD/CAM. Pressing the material is done in a similar way that metal frameworks are cast to a model. A wax-up of the planned contours is created on the model, sprued, invested, and heated material is spun into the void in the stone. The average compressive strength of e.max Press is 400 MPa.
Alternatively, a scan of the model allows the technician to design a digital wax pattern and mill it from a solid block of lithium disilicate. This is faster and less expensive than the press technique. The compromise is that the compressive strength of e.max CAD drops to 360 Mpa.
It is important to note that 360-400 MPa are in the middle range of compressive strengths for the new porcelains and that frequent fractures of lithium disilicate have not been reported. That being said, e.max CAD is not recommended for posterior full coverage crowns by the manufacturer.
(2) It can be monolithic or veneered
One of the major complaints about all-ceramic crowns is that the veneering ceramic chips or fractures from the underlying ceramic coping. If you’re using zirconia as your coping, you’ll definitely need a veneering ceramic to mask the bright white color of zirconia.
But lithium disilicate is actually quite esthetic. Thus it can be made monolithic, or full contour, in areas that are not esthetically demanding without a problem. If your restoration is in an area that requires maximum esthetics, you may want to have the lab leave room in the lithium disilicate coping for some cosmetic veneering porcelain. It’s nice that you have both options with the same material.
(3) It can be used for inlays, onlays, or crowns
Ever hear of a zirconia inlay? Me neither. Bonding concerns and an unesthetic, bright white appearance prevent zirconia from routinely being used as an inlay/onlay material.
The ideal inlay/onlay material is monolithic (doesn’t require veneering porcelain) and is able to be bonded to the tooth, rather than cemented. Which leads me too…
(4) It can be predictably bonded to the tooth
As I discussed in my last post, not all porcelains can be predictably bonded. Let’s look at the current cements on the market that permit bonding to porcelain:
Only total-etch and self-etch resin cements can truly, predictably, and esthetically bond to a porcelain with a glassy matrix, e.g. glass ceramics and glass ceramics with fillers. Glass-free ceramics, like zirconia, are better suited to cementation with a self-adhesive or resin-modified glass ionomer cement. There won’t really be much adhesion, so you will have to rely on traditional porcelain-fused-to-metal crown preparation techniques for mechanical retention.
Since lithium disilicate can be bonded to the tooth, we are allowed to use more conservative preparation techniques that don’t remove unnecessary tooth structure. More on that coming soon!