Inlays and onlays are a type of filling or partial coverage restoration of the tooth (as opposed to crowns which are a full coverage restoration) made of either resin composite, porcelain, ceramic or metal. The main difference with a regular or standard filling is that the inlay/onlay is fabricated outside the mouth, thus giving it improved properties such as resistance to wear, durability, and fit.
An onlay is basically the same concept as an inlay, but the onlay is made to extend and cover more of the tooth, particularly the cusps or the tips on the chewing surface of the tooth. This is done when the cavities or destruction of the tooth is more than a filling or an inlay can restore, but less of what is warranted for a full coverage restoration such as a crown. Think of an onlay as somewhere in between an inlay and a crown.
Even though the differences are more of a technical nature, the easy way to explain those differences is to think of the size of the cavity or fracture, or the amount of structure lost and remaining on the tooth to be restored. The smaller the cavity or fracture, the more tooth structure is available to support a restoration, in which case a small filling or inlay will do. The larger the cavity or fracture, the less tooth structure is available to support a restoration, in which partial coverage (onlay) or a full coverage (crown) restoration should be done.
There are two basic differences: aesthetics and strength. The strongest material but less aesthetic is the metal. A more aesthetic and somewhat strong material is the resin composite, as well as offering ease of repairs in case it needs it. And the most aesthetic and strong material is ceramic/porcelain.
The selection of the appropriate material is something that you can do with your dentist, and he/she will guide you as to which one fits your particular needs. You should consider your aesthetic requirements and financial budget, and your dentist should consider the amount of tooth structure to be preserved during restoration, in choosing the best material for you.
The cost is greatly dependent on the material is chosen and can be expected to be anywhere in between the cost of a standard resin composite filling and the cost of a full coverage crown, in the range of $450-950. Additional procedures may be needed depending on the conditions found during clinical treatment (i.e., buildup). The doctor will advise you whether these other procedures should be expected and the cost they carry with them.
The short answer is no. You will be numb during the whole procedure, so pain is a non-issue. Only a mild initial discomfort can be expected during the numbing procedure as the tip of the needle pinches the gum, and that’s about it! After the numbness goes away (usually after an hour or so), some discomfort can be expected as the tooth adjusts to changes in temperature, as well as some tenderness around the gum, but this shouldn’t last more than 24-48 hours.
After anesthetizing (numbing) the area, the cavity or fractured tooth is cleaned out, and the tooth is reduced on the weakened surfaces so that the inlay or onlay can fit into it or over it. A putty impression or mold is made of the prepared tooth and sent to the lab for the crown fabrication. This can take up to 2-3 weeks, and that is why a temporary acrylic inlay/onlay is fabricated and temporarily fitted on the tooth to wear during this time. On your second visit, the temporary inlay/onlay is removed, and the permanent one is bonded on the tooth with tooth-colored resin adhesives, strong enough that it is very unlikely for the final restoration (inlay/onlay) to come off the tooth.
Two visits are necessary to complete the procedure. Your first visit would be the lengthiest one, as this is when most of the work takes place. This visit should last about an hour. Your second visit for the permanent placement of the inlay/onlay once its returned from the lab, usually takes place about two weeks later and lasts between 10-20 minutes.
The choice of material may affect the longevity of your inlay/onlay, but when given proper care and maintenance, they can be expected to serve functionally for many years.