To preface this section, let’s start with some background. There are three types, or families, of crowns that are available from dental offices: Porcelain (a type of glass) fused to metal or PFM, similar to the bathroom sink; full cast solid metal, usually a high gold alloy; and all-ceramic. The PFM crown has been the main crown used for decades. Chances are, if you have a crown in your mouth, it is a PFM. Because porcelain is so weak, it is fused to a thin metal layer to add strength. If you have a PFM, you may notice a grey line at the gum line. This is the metal layer shining through.
At About Dental Care, we primarily use monolithic, all-ceramic crowns. There are basically four materials that non-metal crowns can be made from currently. Three types are ceramics and one type is a resin composite. These materials all have different properties. From weakest to strongest flexural strength: Porcelain is between 90 to 160 MPa, Composite Resin can be up to 230 MPa, Lithium Disilicate is 360 to 400 MPa, and Zirconium Oxide is from 1200 up to 1465 MPa.
Watch this short video demonstrating the strength of Zirconium Oxide compared to the PFM.
The majority of ceramic crowns that we make are Zirconium Oxide. We use it primarily on the back teeth. While Zirconium Oxide is strong and durable, esthetically it is not quite as natural looking as the other types of ceramics, though it still looks pretty darn good. It is great for back teeth where most people won’t be staring at them. However, we have placed them on the front teeth for patients who have requested it. The untrained eye probably wouldn’t detect the difference. For front teeth, we like to use Lithium Disilicate. It is strong enough to put on the back teeth but looks as good and realistic as any other type of ceramic.
All of these ceramics except for Zirconium Oxide can be milled by CAD/CAM scanning/milling machines at dental offices that have the equipment to do so. That is where you hear the term “one-visit crowns”. We should say, all of these ceramics except for Zirconium Oxide can realistically be milled in-office. Zirconium could be milled on these machines, but because the material is so hard, it would take a long, long time to make a crown.
Since the majority of crowns made are for back teeth, and these CAD/CAM machines cannot realistically make same-day Zirconium Oxide crowns, we outsource these crowns to a well-known dental lab in California. This lab is known for their quality. In fact, the lab we use is the same lab that pioneered Zirconium Oxide for use in crowns in 2009. This lab has a turn-around time about half that of other dental labs. They require six business days. So if you need a crown, you will still have to wear a temporary crown, but probably only about half the time as you would at most other offices.