Onlays are often used to restore teeth that are missing more than half of the natural tooth structure. In some situations, there is not an adequate amount of tooth to hold a filling with any degree of predictability and another avenue must be explored. One option would be a Crown. This is a complete covering that can protect and strengthen your tooth. However sometimes the remaining tooth structure is the wrong shape for a Crown or too much natural tooth will have to be removed for the Crown to fit, so an Onlay would be a better treatment option.
So Onlays are utilized mostly at times when the restoration is too large for a filling, yet a crown is not suitable to protect the tooth.
Onlays can be made of Porcelain or Gold cast sections that are bonded to the damaged area of a tooth. Typically fillings can reduce the strength of the tooth by up to 50%. Onlays, however, because they are bonded directly into the tooth with special resins, can actually increase the strength of the tooth by up to 75%; as a result, they can last from 15-40 years, and in many cases can provide a good alternative to a crown.
Some of the indications for Onlays are:
1. The need for a long-term, durable restoration.
2. Desire to limit the amount of healthy tooth structure removed.
3. Need to strengthen and reinforce the tooth.
Onlays are incredibly strong due to the fact that they are created in a laboratory in the same manner as jewellery. This protects the tooth from fracturing and actually strengthens the tooth. Onlays require the removal of only decayed areas of the tooth, leaving more healthy tooth structure intact. This can help prevent the expense of root canal therapy in the future.
Onlays are placed in two dental visits as they have to be constructed in a laboratory before being bonded onto the tooth.
At the first visit, the old filling, or decay, is removed and the tooth is prepared for the onlay. The dentist will then make an mould of the tooth, and send this mould to a dental laboratory. This mould will be used by the laboratory to construct, a porcelain, or gold onlay that will fit exactly into your tooth. At the end of this appointment the dentist will place a temporary Onlay on your tooth which will keep your tooth happy for the two weeks it takes for the onlay to be made. A second appointment will then scheduled.
Second Appointment (14 Days later):
At the second visit, the temporary Onlay is removed. Your dentist will then ensure that the onlay fits properly in the tooth and does not interfere with your bite. Once the fit has been confirmed the Onlay is bonded onto the tooth with a strong bonding resin, and polished smooth. It is not unusual for the new onlay to be mildly sensitive to cold temperatures for a few weeks. However, if the sensitivity is severe, does not subside, or if the bite feels uncomfortable, contact your dentist. Further adjustments to the onlay may be necessary. There is a possibility of the nerve in the tooth dying during or after the onlay process, especially if the tooth has been previously heavily filled. The risk is usually less than 5% per tooth but this does depend on the teeth. It is always good to ask your dentist for a more specific estimation of risk.