What Types of Inlay and Onlay are there?
There are three main types of inlay/onlay material:
- Porcelain (of which there are different subtypes)
Most inlays are now made of porcelain, as the desire for a more natural looking tooth increases and the ability to bond these restorations to your tooth improves.
Gold is a truly fantastic material and has been used successfully for many years. Composite inlays are a way to overcome the problem of the traditional composite filling material shrinking in very large cavities – they are quite effective but not widely used.
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.
Gold is a fantastic material, but due to rising prices and the desire for natural looking teeth, it is becoming much less widely used.
However, when done properly, it is regarded as the ultimate restoration, with extremely high strength, toughness, durability and resistance to wear, even in thin sections. This means a minimum amount of tooth preparation is necessary.
Quality gold restorations can last over 30 years and often look as good as the day they were put in.
Lots of the older dentists really love gold, and if they need work done, will choose this over the other materials because of it’s superior qualities.
An indirect composite, (one that is made ‘outside’ of the mouth) is also a useful alternative. Its advantage is that the dentist can often complete the procedure in a single visit.
It doesn’t require the lab to make it, so it is cheaper, plus the composite causes less wear on opposing teeth when compared to porcelain. It also can be added to more easily if there is a problem. Some dentists like them and do lots of them, but the majority of dentists probably prefer the other options.
Setting the composite outside the mouth and cementing it in, reduces the amount of shrinkage that is seen. This means the inlay/onlay doesn’t stress the tooth in the way that placing a composite fillingdirectly into the cavity would.
Like composite fillings, the material still has a tendency to pick up some stain at the margins. They will discolour and wear more over time than their porcelain and gold counterparts.