These sit in the gap between a filling and a crown, and they exist for a specific reason: some teeth need more than a filling can give but do not need to lose the amount of structure a full crown requires. An inlay or onlay sits between a filling and a crown, replacing damaged tooth structure inside or over the cusps with a custom-made piece of porcelain or composite, so it preserves more natural tooth than a full crown and is stronger than a large filling in a molar that takes heavy chewing forces.
What usually brings up inlays and onlays
- A cavity too large for a straightforward filling
- A cracked cusp that needs covering
- Replacing a very large old filling
- Wanting to preserve more tooth than a crown would
- A tooth under heavy biting forces
Treatment paths a dentist may weigh
- Composite or ceramic inlay
- Onlay covering one or more cusps
- A conventional filling where the cavity allows
- A full dental crown where too little tooth remains
- Monitoring rather than treating, where the tooth is stable
Filling, inlay/onlay and crown compared
| Factor | Filling | Inlay or onlay | Crown |
|---|---|---|---|
| Tooth removed | Least | Moderate | Most |
| Made where | In the mouth | Laboratory or milled | Laboratory or milled |
| Visits | One | One or two | One or two |
| Best for | Small to moderate cavities | Large cavities with sound walls | Little sound tooth remaining |
| Covers cusps | No | Onlay does | Yes, entirely |
| Cost | Lowest | Middle | Highest |
Start with an assessment
Select the closest restorative option.
Common questions
Inlays and Onlays: questions people ask
Why not just have a big filling?
Very large direct fillings flex and can split the remaining tooth. An inlay or onlay is made outside the mouth and bonded in, which is more stable across a wide span.
Why not just have a crown?
A crown removes considerably more sound tooth. If the walls of your tooth are still strong, an onlay preserves them: that structure cannot be put back later.
Do they last as long as crowns?
Well-made bonded restorations perform well, and the more conservative preparation is the point. Longevity depends on the bite, the bond and cleaning, as with any restoration.
What options sit between a filling and a crown?
A composite or ceramic inlay. An onlay covering one or more cusps. A conventional filling where the cavity allows. A full dental crown where too little tooth remains. Monitoring rather than treating, where the tooth is stable. Doing less than you expect is often a reasonable option.
When is an inlay or onlay proposed?
For a cavity too large for a straightforward filling. For a cracked cusp that needs covering. When replacing a very large old filling. When you want to preserve more tooth than a crown would. For a tooth under heavy biting forces.