Why Zirconium crowns are replacing Porcelain fused to metal crowns?

Why are monolithic Zirconium crowns becoming the most popular type of crown for posterior restorations? Probably because they exhibit of a number of obvious advantages . These include the fact that cadcam zirconium crowns have more affordable lab fees, are more resistant to fracture, require less tooth preparation and more biocompatible than porcelains or the metals used in most dental restorations. 

While earlier versions of full contoured zirconium crowns were often too opaque and less esthetic than a well made porcelain fused to metal crown, newer versions are more translucent and are esthetic enough to satisfy most patients who need posterior crowns. In addition, when their margins are supragingival, no grey collar is visible as often is the case with ceramometal restorations. Their margins can be placed either supra or sub gingival and unlike lithium disilicate restorations they can be cemented with resin modified glass ionomer or traditional dental cements without  sacrificing their resistance to fracture.

In addition, they are compatible with a number of different types of finishing lines ( shoulder, chamfer, or 45 degree chamfer) and because they can be milled to a thickness of .5mm , more conservative chamfer preparations will not compromise their esthetics or strength. In addition, after milling their margins can be thinned even further, using an appropriate polishing wheel. This can allow dentists to prepare preparations that conserve cervical tooth structure and keep preparations further away from a tooth's pulp. 

Dentists who are critical of using Zirconium for crowns often point out that Zirconium is harder than either porcelain or Emax restorations and may cause additional wear or breakage of opposing teeth or their restorations. This probably isn't the case when zirconium restorations have their occlusion properly adjusted and their surface texture is polished appropriately after these adjustments are performed. There is also some debate about whether their inner surface bonds well with composite cements, but many clinicians maintain this isn't a problem ,if the inner surface is properly sandblasted and manufacturers recommendations for composite cementation are adequately followed. 

They do have some drawbacks. Since they are digitally designed and milled, these crowns are most satisfactory when a tooth has a more or less ideal preparation with a definitive finsih line. I actually spend more time prepping teeth for these restorations . Unlike crowns made with the lost wax technique or using pressable lithium disilicate, digitally produced cadcam restorations have a more limited ability to compensate for  imperfections in tooth preparation.  I also have found that zirconium restorations can be less ideal for short teeth, and  either bonded lithium disilicate or more old fashioned analogue restorations ( Gold crowns or PFM's) maybe work better for these teeth.  

Another negative feature of Zirconium restorations  is that  adjusting the occlusion or contact areas of these crowns can take more time because zirconium is extremely hard and takes more time to adjust than crowns made of other materials. When adjustments are made using a high speed diamond, water must be used a coolant in order to avoid the formation of microscopic cracks.

Even though they have a few drawbacks, overall , full contoured zirconium crowns are a great option for crowning most posterior teeth, especially when employed by a dentist who understands their strengths and limitations. When teeth are properly prepared and impressioned, inserting them usually take less time than alternative types of crowns and their advantages far outweigh any disadvantages. I personally give them a big thumbs up!