Fillings are placed directly in the tooth in one appointment — the material is applied and shaped chairside. Inlays and onlays are fabricated in a dental lab from an impression and bonded to the tooth at a second visit. The lab process produces a more precise fit, stronger materials, and a restoration that typically lasts two to three times longer.
The most fundamental difference is how they’re made. A filling is applied directly to the tooth in one appointment. An inlay or onlay is made in a dental laboratory from an impression, then bonded precisely in place at a second visit. That difference in process creates restorations that are more accurate, fit better, and last significantly longer.
Key Takeaways
- Fillings are direct restorations — placed and shaped chairside in a single visit
- Inlays and onlays are indirect — custom-made in a lab, then bonded at a second appointment
- Inlays and onlays last 10 to 30 years, versus 5 to 10 years for composite fillings
- Fillings are the right choice for small cavities — inlays and onlays make more sense for larger damage
How They’re Made — Direct vs. Indirect
Direct filling. At a single appointment, the dentist removes decay, applies composite resin or amalgam directly to the tooth in layers, shapes it, and cures it. Done in one visit. The material is soft during placement and hardens quickly once cured.
Indirect inlay or onlay. At the first visit, decay is removed and the tooth is shaped. An impression is taken and sent to a lab, where technicians fabricate the restoration precisely to the tooth’s exact dimensions. A temporary covers the tooth in the meantime. The permanent restoration is bonded at the second visit, typically 1 to 2 weeks later.
The extra time is what allows the lab to produce a better result. The material is stronger. The fit is more precise. The seal against bacteria is tighter.
How They Compare — Side by Side
Here’s how the two approaches stack up across the key variables:
| Feature | Direct filling | Inlay or onlay |
|---|---|---|
| Visits needed | One | Two |
| Where it’s made | Chairside | Dental laboratory |
| Fit quality | Good | Excellent — custom-fitted to impression |
| Materials | Composite resin or amalgam | Porcelain, composite, or gold |
| Shrinks during set | Yes — can stress tooth | No — solid when bonded |
| Typical lifespan | 5 to 10 years | 10 to 30 years |
| Cost | Lower | Higher |
| Best for | Small to moderate cavities | Larger cavities, cusp damage, replacing large fillings |
Are Inlays and Onlays Better Than Fillings?
For larger cavities: yes — inlays and onlays are more precise, more durable, and significantly longer-lasting. For small cavities, fillings are completely appropriate and far more efficient. Neither option is universally better. The right choice depends on the size and location of the damage.
For small, straightforward cavities, a composite filling is fast, well-proven, and perfectly appropriate. Recommending an inlay for every small cavity would mean two visits and higher cost where one visit and lower cost gets the same job done.
For larger cavities, the material limitations of direct fillings matter more. Composite resin shrinks slightly as it cures. In a small filling, that’s inconsequential. In a large filling, the shrinkage can create micro-gaps at the margins and place stress on the surrounding tooth walls. Inlays are solid when they’re bonded — no shrinkage, no stress, tighter fit.
If you have a cavity your dentist has flagged as too large for a filling, or a large old filling that’s been in for years, schedule your appointment at our Edmonds office and we’ll take a look at what the best option is for your situation.
