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Onlays and Inlays: When Is One Recommended Over the Other?

Dental Restorations Franklin, TN

Teeth that are broken or severely decayed may require onlays and inlays for complete restoration. These dental treatments are similar to one another in that each is fashioned specifically to the shape of the tooth. Another similarity is that only certain teeth, specifically the chewing teeth in the back of the mouth, can support inlays or onlays.

Despite being considered older restoration techniques, these options are still effective and in some cases represent the most appropriate dental treatment option. Like traditional fillings, inlays and onlays can both be made of either metal or a tooth-colored material, such as ceramic, to maintain a natural appearance.

Differences between onlays and inlays

Despite the similarity of the names, inlays and onlays have more in common with other restoration techniques than they have with each other. An onlay is similar to a crown, and different from an inlay, in that it covers at least a portion of the chewing surface of a tooth. By contrast, an inlay is similar to a filling, and different from an onlay, in that it is contained within the tooth. The molars and premolars have points or eminences called cusps extending from the surface. The difference between an inlay and an onlay is that the former remains within the cusps, while the latter covers at least one of the cusps, maybe more.

However, onlays and inlays are also different from other restoration techniques. An onlay covers only a portion of the chewing surface, while a crown encapsulates the entire tooth structure above the gum line. An inlay is different from a filling in that a filling is built up inside the tooth while an inlay is crafted outside the mouth and then cemented to the tooth.

Situations calling for inlays or onlays

An onlay is appropriate when it is necessary to remove too much of the tooth's structure to support an inlay or a filling. It can have an advantage over a crown in that it does not cover the entire tooth's surface. Placing an onlay involves removing less of the tooth's structure, making it a less aggressive restoration technique than a crown. It requires a skillful dentist because it is more difficult to place correctly.

When a cavity is too large for a traditional filling but it is not necessary to cover or remove one of the cusps of the tooth, an inlay may be appropriate. Because the inlay is created outside the mouth as a single, solid piece rather than built up inside the tooth, it is necessary to fit it exactly to the shape of the cavity. Otherwise, further decay can develop due to bacteria and food getting into the gap that is left behind.


Onlays and inlays are different restorations, and various situations may call for either one or the other. Whether you require an inlay or an onlay depends on the extent of the damage to the tooth.

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