IPS e.max v zirconia based posterior single units, So many users prescribe a zirconia Substructure based single unit thinking that it is stronger than an IPS e.max crown. The zirconia coping maybe 900-1200 Mpa depending on the brand of zirconia, however the porcelain layered onto the coping will have a maximum strength of around 60-120Mpa plus support will have to be built into the coping on the mesial and distal sides of the preparation to support this porcelain. fracture of Zirconia based crowns usually involves the layered porcelain on top of the coping not the substructure. Due to the bright nature of zirconia (high Value) and its density (chroma) it is difficult to control these elements when layering to create a shade match even if the correct shade is selected!!. Cementation of zirconia is also a tricky one as you can not etch and bond the crown to the tooth, essentially its like trying to stick a piece of chewing gum to a plate, even after sandblasting the fittting surface.
IPS e.max lithium disilicate in the press form is 400 MPA in strength less than half that of a Zirconia coping! The big difference is that the crown is pressed to full contour. when used in the posterior region of the mouth and satined to create any translucency and other effect used in shade matching. No layering so effectively one homogeneous material providing maximum strength no weak spots no risk of porcelain fracturing off!! Plus the fitting surface of the crown is etched and bonded to the prepared tooth which has the effect of making the tooth and crown combine into one structure leaving a very low risk of fracture.
also the choice of LT,HT and MO make it suitable for every shade requirment.
So dentist stop thinking that a LAVA based crown is the strongest and will resist fracture more than every other type of crown.
dont be fooled by large MPa numbers
T0 quote the man himself “The future starts today with lithium dicilicate” Oliver Brix (master technician)
I take my hat of to the guys at 3M who have fooled everyone into thinking its the strongest and most aesthetic crown on the market!!
Try to restrict your choice of zirconia to posterior bridge work this is where it comes into its own.