Procedures
Onlays
Procedure overview
Learn about the dental procedure, when it is generally prescribed, and other information which can increase your knowledge of the topic.
Alternate terms: Partial crowns.
An onlay is a type of cusp-covering dental restoration that is made in a laboratory or by a computer controlled milling machine from either ceramic, composite resin, gold, titanium or other metals. It is cemented onto the tooth, usually at a separate appointment from the tooth preparation appointment. This will often mean having to numb the tooth at both appointments, and having a temporary restoration placed between appointments.
Onlays differ from inlays in that onlays cover one or more of the tooth's cusps, and achieve their retention to the tooth primarily from features cut in the exterior walls of the tooth (Figures 1a and 1b). Inlays achieve their rentention primarily from features cut into the interior walls of the tooth (Figure 2).
Onlays differ from crowns mainly in the amount of the tooth covered by the restoration. With an onlay the restoration overlaps the cusp tips minimally, extending only about a third of the way down the side of the tooth, whereas a crown typically extends beyond the tooth's greatest contour, frequently to the gum line or just above it, for at least part of the circumference of the tooth. Said another way, onlays are generally more conservative in the amount of tooth structure that has to be removed compared to crowns.
Some restorations have characteristics of inlays, onlays, and crowns, like the one shown in Figure 3, leading to some confusion about the type of restoration that it really being placed.
Figure 1a: A preparation reported as a ceramic onlay procedure by one dentist might be reported as a ceramic partial crown by another. The difference is semantic—both are ways of preventing the entire tooth from having to be reduced. Both restorations adhere to the convergent outer walls of the tooth.
Figure 1b: The ceramic restoration shown in place on the tooth. In this case the buccal wall (the side you can see when the patient smiles) was kept largely intact, with just the tip of that cusp being covered. The red marks on the teeth were made by marking ribbon.
Figure 2a: Inlays are held in place by interior walls cut into the tooth, while cutting out decay.
Learn more: Procedures › Inlays
Figure 2b: Onlays are often stabilized by preparing internal walls to help resist dislodgement of the restoration. This is known as "inlay retention."
Figure 3: This restoration has characteristics of inlays, onlays, and crowns. Like an inlay, part of its retention is from interior walls. Like an onlay, the restoration covers a cusp, without reducing the entire tooth, and like a crown, the gold extends all the way to the gum line. (Restoration and image courtesy Byron J. Greany, DDS).
Onlays and partial crowns are prescribed when a tooth is too badly decayed or broken down to be restored with a filling or inlay.
Post-operative discomfort
A common misconception about teeth is that working on them, like trimming fingernails, should not lead to any complications. In reality, though, working on teeth is a surgical procedure. Teeth are very well-supplied with two different types of nerve tissue. And unlike other tissues of the body that are living, teeth can't swell, and are poorly equipped to deal with inflammation. Working on teeth very commonly produces inflammation—just as making an incision in an arm or leg would. Inflammation is a process by which your body sends immune cells and healing cells to the affected area so that they can repair the "wound". It does so by increasing blood flow to the affected region.
When the surgery is performed on soft tissue (i.e. skin, muscle), increased blood flow to the area produces swelling—enlargement of the soft tissues—which are somewhat elastic (i.e. "stretchy"). Since teeth cannot swell, inflammation causes the blood pressure inside the tooth to increase. The increased pressure on the nerves inside may produce significant discomfort. Well-maintained dental instrumentation, skilled technique, and use of desensitizing medications can minimize post-operative discomfort, but may not eliminate it.
Learn more: Diagnoses › Irreversible pulpitis
Learn more: Diagnoses › Reversible pulpitis
Anything that causes a pressure change inside an inflamed tooth can provoke more discomfort. The most common culprits are cold temperatures and chewing. Cold causes the fluid inside the tooth to contract (shrink), changing the pressure. Chewing sends small hydraulic compression waves through the extra fluid in the tooth, and these pulses are perceived as pain. Sensitivity to heat is a symptom in some cases, but generally heat sensitivity is less common. Severe sensitivity to heat is a sign that there may be gas in the tooth. This is an unfavorable situation, because the gas is usually produced by bacteria (i.e. the tooth is infected). Sometimes the only way to reduce the pressure in the tooth is to make a hole into the pulp space (i.e. perform a root canal).
Learn more: Diagnoses › Acute apical abscess
Some people are inclined to think something must have been done wrong if they experience discomfort after a dental procedure. Although this can be the case, if proper procedure is followed, it is more likely the tooth's reaction to what was done that causes the problem. Does this mean you should wait until your tooth hurts to fix a problem that has been diagnosed? Definitely not! Very often problems with teeth (i.e. cavities, etc.) don't hurt unless they are advanced. Waiting until the problem is advanced to fix it is a big mistake. The bigger the problem is, the harder it is to fix and the more likely it is to produce complications; and it will frequently have a poorer prognosis (likelihood of long-term success) if you wait too long to have a problem fixed.
If your dentist can show you the problem (e.g. on the X-ray, with a photo, etc.) in such a way that you have a clear understanding of what it is, how it can be fixed, with how much urgency it should be addressed, any options you may have for fixing it, the risks, and intended benefits of each, the likelihood of success ("prognosis") of each, and the cost of each, you will experience better treatment outcomes.
