Inlays and onlays: what they are, cost in NZ, and inlay vs onlay vs filling

There is no national survey figure for inlays and onlays cost in New Zealand, but the NZDA Fee Survey (late 2023, including GST) gives the two prices they sit between: a median of $369 for a large multi-surface composite filling and $1,600 for an all-ceramic crown. A ceramic onlay is often priced closer to a crown than a filling, because it involves lab work and two appointments.

What are inlays and onlays?

An inlay or onlay is an indirect filling: instead of being placed soft and set in the mouth, it is made outside the mouth from a scan or impression, then bonded or cemented into the tooth. Because it is made in one solid piece, it is stronger and seals better than a large direct filling.

Inlay vs onlay comes down to the cusps, the raised points of a back tooth. If they are strong, an inlay is enough. If one or more are weak, cracked or undermined, an onlay covers and protects them, a bit like a partial crown.

The main types of inlays and onlays are:

• Ceramic and porcelain inlays and onlays, usually in E.max or another glass-ceramic. They are tooth-coloured and bonded to the tooth.
• Composite inlays, made in the lab from a hard resin. Lower cost and easy to repair, but less wear-resistant than ceramic.
• Gold inlays and onlays. Very durable and gentle on opposing teeth, but not tooth-coloured. See gold crown cost in NZ for how gold restorations compare.

How to get an inlay or onlay: the steps

1. Assessment. Your dentist checks the tooth and decides whether a filling, an inlay, an onlay or a crown suits it best.
2. Preparation. Under local anaesthetic, the old filling and any decay are removed and the cavity is shaped with smooth walls so the inlay or onlay can slide into place.
3. Scan or impression. A digital scan or impression is taken and a temporary filling is placed.
4. Lab work. A technician designs the restoration in CAD software, then mills or presses it in ceramic, or casts it in gold, and finishes it by hand.
5. Bonding. At the second visit your dentist checks the fit, bonds ceramic or composite in place with resin cement, or cements gold, then adjusts and polishes the bite.

Some clinics mill ceramic inlays and onlays chairside in one visit. Dentists can see how we make inlays and onlays in ceramic and gold.

How to use and care for an inlay or onlay

• You can eat normally once the restoration is bonded and any numbness has worn off.
• Brush twice a day and floss daily; the edges are where new decay can start.
• Avoid biting very hard things such as ice, and wear a bite splint if you grind.
• Keep regular check-ups so your dentist can check the margins and the bite.

Ceramic inlays and onlays last well: a 2016 meta-analysis estimated about 92 to 95% survival at five years and about 91% at ten years, with fractures the most common reason for failure.

Tips & gotchas

• Inlays and onlays vs fillings. A direct filling is quicker and cheaper and is fine for small to medium cavities. Indications for inlays and onlays include large cavities, failing large fillings, cracked or weakened cusps, and teeth where a strong, well-sealed restoration matters.
• Onlay or crown? An onlay keeps more healthy tooth than a crown, so ask whether it is an option before a crown is prepared. A crown is still better when most of the tooth is missing.
• Root-treated teeth. A back tooth that has had a root canal usually needs its cusps covered, with an onlay or a crown, because it becomes brittle.
• Bonding needs a dry tooth. Ceramic is bonded with resin cement, which needs good moisture control, so very deep cavities near the gum may suit a crown or gold better.
• Porcelain inlays and onlays can wear opposing teeth if left rough, so the bite should be polished smooth after any adjustment.

For the price of a full crown and what affects it, see how much does a dental crown cost in NZ, and for material choices, zirconia vs porcelain vs E.max vs gold crowns.