Generally speaking Emax crowns perform better when done correctly as they are bonded to the tooth and usually do not require extensive tooth reduction. However in some cases zirconia crowns may be the better option. It all depends on the tooth condition and bite. I suggest you find a dentist who is trained in biomimetic dentistry and discuss which material is better for your case.
Emax is a more esthetic restoration than zirconia. Choosing between the two is determined by multiple factors. If you are a grinder, zirconia would be better if it is a molar tooth. If it is an anterior tooth, emax looks nicer and it is also a strong material.
I hope this helps.
Emax and Zirconia have different properties, which means they will have pros and cons. The first thing to consider is what type of restoration is being done (crown, veneer, implant crown, etc.). The second thing to consider is which tooth being restored (front or back). The third thing to consider the adjacent teeth. Emax generally has slightly better aesthetics; however, it is much weaker than zirconia. If it is a back tooth then the choice is clearly zirconia as it can be stained to look quite nice and you get the superior strength. If it is a front tooth, then you have a couple choices. Zirconia has an aesthetic version now which is not as strong, but looks even nicer. You can use Emax, but you run the risk of it breaking. Looking at the teeth next to the one being worked on will help as that is the aesthetics you have to match.
Hope this helps.
My best to you!
William F. Scott IV, DMD