There are different types of porcelain that can be used and they vary in their structure, features and benefits. Most dentists have a particular type that they prefer and commonly use.
New types and improvements are being made all the time. Your dentist will select what they feel is the most appropriate based on their experience and the success of their patients.
More retention can be gained for the traditional porcelains (Emax, Empress are some of the trade names), because where large open cavities are concerned, the porcelain can be etched and bonded to the tooth.
Zirconia (which has received a lot of attention of late) is a much harder material which needs to be cemented in using a very strong glue. As there is no bonding, it tends to be better in situations where the natural cavity shape has a bit more retention- a classic inlay would be an ideal. That said, because of its incredible strength it can be useful in patients who clench and grind their teeth.
The type of porcelain used affects the colour and in areas where a really good match is needed, it is much better to have a restoration built up by hand and fired in the furnace.
Those milled out of a solid block of porcelain of a particular shade can have less of a natural appearance and are more difficult to match to neighbouring teeth- which may have a variety of shades. The laboratory can get very 'arty'- adding stains and tints to make the tooth as life-like as possible.
is a relatively new type of technology that can allow an inlay/ onlay or crown to be made and placed in a single visit, thus avoiding the need to come back and spend a week with a temporary.
The machine itself is based on a CAD- CAM computer, where an impression is taken of the tooth with a special 3D sensor- the tooth shape and contacts are designed on the computer, then it is milled from a block of porcelain in an attached machine, ready to be put into the mouth. Because of the cost ($70,000+) of the machine, not all private dentists have this facility.
The quality of these restorations is good and improving all the time with advances in technology. It is more durable than a large composite filling, but not quite yet the quality of hand made laboratory inlays and onlays.
The experience of the operator in using the CEREC machine is an important factor in the quality of restoration. Because a digital image is needed for the impression, the walls of the cavity must be more divergent (tapering) and so they tend to be a bit less retentive. Since we are bonding-in these restorations (not just cementing them) whether this affects the life of the restoration is debatable.