When a tooth is too damaged for a standard filling but does not need a full crown, you are in a grey zone. This is where inlays and onlays fit. They are a middle-ground restoration that many patients have never heard of, but they solve a specific clinical problem well.
This guide explains what inlays and onlays are, when your dentist might recommend one, and how they compare to the more familiar options of fillings and crowns.
What is an inlay?
An inlay is a custom-made restoration that fits inside the cusps (the raised points) of a back tooth. It replaces the damaged or decayed portion of the tooth without covering the cusps themselves.
Think of it as a precision-fitted insert. Rather than packing filling material into a cavity and shaping it by hand, your dentist takes an impression (or digital scan) of the prepared tooth and sends it to a dental lab. The lab fabricates the inlay from porcelain, composite resin, or gold to the exact shape and size of the space. It is then cemented into place.
The result is a restoration that fits more precisely than a hand-packed filling and preserves more tooth structure than a crown.
What is an onlay?
An onlay is similar to an inlay but covers one or more of the cusps of the tooth. It extends over the top of the tooth to replace a cusp that has been weakened, fractured, or lost to decay.
Onlays are sometimes called partial crowns because they cover part of the tooth's biting surface without encasing the entire tooth. The preparation is more conservative than a full crown, which requires reducing the tooth on all surfaces.
When are inlays and onlays used?
Your dentist may recommend an inlay or onlay when:
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A filling would be too large. Large direct fillings (particularly composite or amalgam) can weaken the remaining tooth structure. When more than about 50% of the biting surface needs to be replaced, a direct filling may not provide adequate strength. An inlay or onlay is fabricated from a stronger material and distributes forces more evenly.
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A crown would be too aggressive. A full crown requires removing tooth structure from all surfaces of the tooth. If the damage is limited to the top of the tooth, an onlay preserves the intact walls and reduces the amount of healthy tooth that needs to be removed.
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A cusp has fractured. If one or two cusps have broken but the rest of the tooth is sound, an onlay replaces the broken cusps without covering the entire tooth. See our guide on crown vs filling for more on this decision.
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Replacing a failing large filling. Old amalgam or composite fillings that have cracked or developed decay around their margins are common candidates for onlay replacement, particularly when the remaining tooth structure would be too thin to support another direct filling.
Materials
Inlays and onlays can be made from several materials. The choice depends on the location of the tooth, the forces it bears, and cosmetic preferences.
Porcelain (ceramic)
Porcelain inlays and onlays are tooth-coloured and can be closely matched to the surrounding enamel. They are strong, resistant to staining, and provide excellent aesthetics. Porcelain is the most commonly requested material for visible teeth.
Composite resin
Lab-fabricated composite inlays and onlays are also tooth-coloured but are softer than porcelain. They may be suitable for areas with lower bite forces. They are generally less expensive than porcelain but may wear faster over time.
Gold
Gold inlays and onlays are extremely durable and gentle on opposing teeth. They last for decades in many cases. The obvious drawback is appearance. Gold restorations are visible and are not suitable for patients who want a tooth-coloured result. They are used less frequently today than in previous decades but remain a valid clinical option for back teeth.
The procedure
The process for an inlay or onlay typically involves two appointments.
Appointment 1: Preparation
Your dentist removes the damaged or decayed portion of the tooth and shapes the remaining tooth to receive the inlay or onlay. A digital scan or impression is taken and sent to the dental lab. A temporary restoration is placed to protect the tooth between appointments.
Appointment 2: Fitting
Once the lab has fabricated the restoration (usually 1 to 2 weeks), you return for fitting. The temporary is removed, the inlay or onlay is tried in for fit and bite, and then it is permanently cemented or bonded to the tooth.
Some practices with in-house milling technology (CAD/CAM) can fabricate certain inlays and onlays in a single appointment. Ask your dentist whether this is an option for your case.
Inlays and onlays vs fillings
Factor | Direct filling | Inlay or onlay |
|---|---|---|
Fabrication | Placed and shaped directly in the mouth | Custom-made in a lab or milled from a block |
Strength | Adequate for small to moderate cavities | Stronger for larger restorations |
Fit | Shaped by hand | Precision-fitted to a scan or impression |
Appointments | One | Usually two |
Tooth preservation | Minimal preparation | Moderate preparation |
Cost | Lower | Higher |
For small cavities, a direct filling is usually the appropriate choice. The advantages of an inlay or onlay become relevant when the restoration needs to be larger.
Inlays and onlays vs crowns
Factor | Onlay | Full crown |
|---|---|---|
Coverage | Partial (one or more cusps) | Full (entire visible tooth) |
Tooth removal | Less | More |
Strength | High for the restored area | Maximum structural support |
When recommended | Moderate damage, intact tooth walls | Extensive damage, weakened walls, root canal treated teeth |
Cost | Similar range to crowns | From $1,600 |
Indicative pricing. Your quote may differ based on clinical assessment.
A crown is the stronger option when the tooth is severely compromised. An onlay is the more conservative option when the damage is significant but contained.
How long do inlays and onlays last?
Longevity depends on the material, your oral hygiene, and the forces the restoration is subjected to (including grinding or clenching habits).
Published research indicates that porcelain and gold inlays and onlays can last 10 to 20 years or longer. Composite restorations typically have a shorter lifespan, in the range of 5 to 10 years.
Factors that shorten the lifespan of any restoration include:
- Teeth grinding (bruxism). If you grind your teeth, your dentist may recommend a night guard to protect the restoration.
- Poor oral hygiene. Decay around the margins of the restoration can undermine it over time.
- Excessive force. Chewing ice, opening packaging with your teeth, or biting hard objects.
Are inlays and onlays covered by health funds?
Inlays and onlays have their own ADA item numbers and are typically covered under the major dental or restorative category of most health fund policies. The rebate amount varies by fund and level of cover.
We accept all major health funds with HICAPS on site for immediate claims. Visit our payment page for details on gap estimates and payment options.
Is an inlay or onlay right for your tooth?
The answer depends on how much tooth structure remains, where the damage is located, and what forces the tooth is subjected to. Your dentist will assess these factors and recommend the most appropriate restoration.
If you have been told you need a crown but want to explore whether a more conservative option is possible, raise this with your dentist. In some cases, an onlay may achieve the same functional outcome with less tooth removal.
Book a consultation at Ivy Dental
We see patients at our Everton Park and Nundah locations in Brisbane, open 7 days. Contact us to schedule a consultation. If you have a damaged tooth and want to understand your options, a consultation is the right starting point.
Call us on (07) 3266 7120 to book.
