When a tooth has decay or damage beyond a simple filling, your dentist has several restoration options: a crown, an inlay, or an onlay. All three are custom-made restorations that strengthen and protect the tooth—but they cover different amounts of tooth structure. Understanding the difference can help you make sense of your treatment plan and feel confident in the choice. Here's a clear breakdown.
What Is an Inlay?
An inlay fits inside the cusps (the pointed bumps) of the tooth. It's used when the damage is confined to the center of the chewing surface—typically in the grooves of a molar or premolar. An inlay is more conservative than a crown because it preserves more of your natural tooth. It's often used when a filling would be too large or weak, but the damage doesn't extend to the cusps.
What Is an Onlay?
An onlay covers one or more cusps of the tooth. It's a middle ground between an inlay and a crown—more coverage than an inlay, but less than a full crown. Onlays are used when the damage extends beyond the center of the tooth but doesn't require full coverage. They're strong, durable, and allow your dentist to preserve more healthy tooth structure than a crown would.
What Is a Crown?
A crown (or "cap") covers the entire visible portion of the tooth. It's used when the tooth is significantly damaged, has had a root canal, or needs full coverage to restore strength and function. Crowns require more tooth preparation than inlays or onlays because they must fit over the entire tooth. They're the most comprehensive option—and the right choice when a tooth needs maximum protection.
Key Differences at a Glance
| | Inlay | Onlay | Crown | |--|-------|-------|-------| | Coverage | Inside cusps only | One or more cusps | Entire tooth | | Tooth prep | Minimal | Moderate | More extensive | | Best for | Contained decay in center | Damage to cusps | Significant damage, root canal | | Preservation | Most tooth preserved | More than crown | Full coverage |
How Your Dentist Decides
The choice depends on the size and location of the damage. Your dentist will assess how much of the tooth is affected and recommend the most conservative option that will reliably restore strength and function. When possible, inlays and onlays are preferred because they preserve more natural tooth structure. When the damage is too extensive, a crown is the appropriate choice.
The Bottom Line
Inlays, onlays, and crowns are all effective restorations—each designed for a different level of damage. Your dentist will recommend the one that best fits your situation. If you have questions about why a particular option was chosen, ask. Understanding your treatment helps you feel confident in the plan.