Dental Inlays: Where They Fit Between Fillings and Crowns

What inlay involves

An inlay is a restoration made outside the mouth and then cemented into a prepared cavity. Unlike a filling, which is shaped in place, an inlay is a solid custom piece — cast metal, pressed or milled ceramic, or lab-processed composite — that fits the preparation precisely. It sits within the contours of the tooth and does not cover the cusps. The advantage over a direct filling is in the material and the contour. A lab-made or milled restoration has no shrinkage stress, better wear resistance and a more accurate contact with the neighbouring tooth than composite placed freehand in a deep box. The disadvantages are the cost, the extra visit, and the need to remove enough tooth to create a shape the inlay can be seated into.

When this treatment is used

Chosen for moderate cavities in posterior teeth where a direct filling would be at the limit of what it does well, but the cusps are still sound enough not to need covering. In practice inlays have largely been displaced by large bonded composites at one end and onlays and crowns at the other, so they are now a relatively uncommon choice.

Inlay versus onlay — the distinction that matters

An inlay sits inside the tooth. An onlay extends over one or more cusps to protect them. That is the whole difference, and it is a clinical judgement about whether the remaining walls can survive being loaded. Once a cusp is cracked, undermined by decay, or thinned to the point where chewing force will eventually split it, an inlay is the wrong restoration — it fills the hole but leaves the weak cusp doing structural work. Many restorations that start as a planned inlay become onlays once the old filling comes out and the true state of the tooth is visible.

How the appointments run

Conventionally two visits: preparation, impression or scan, and a temporary at the first; cementation at the second, usually two weeks later. Practices with a milling unit can do it in one visit, designing and milling a ceramic inlay while the patient waits. Cementation technique varies by material. Ceramic and composite inlays are adhesively bonded, which takes time and a dry field; cast metal inlays are conventionally cemented. The bonded ones are more technique-sensitive but do not rely on the preparation shape for retention.

Costs and insurance in summary

Typical fee range across the group: $0–$0 where a single band applies. Several codes here are priced individually and carry their own range on their own page. Priced well above a direct filling and a little below a crown, scaling with the number of surfaces and the material.

Benefit category: Major, typically 50% on a typical plan. Treated as major restorative work with a deductible and the annual maximum applying. Many plans apply an alternate benefit and pay only the composite filling allowance.

Common restrictions: Waiting periods of 6–12 months are common on major benefits; Frequently downgraded to a direct restoration allowance; Replacement limited to once every 5–7 years per tooth.