Porcelain Inlays and Onlays

Inlays and onlays are fillings that are made outside the mouth from an impression and then bonded to the tooth, instead of being shaped directly in the mouth; this is why they are also called indirect restorations. An inlay fills the space between the cusps on the chewing surface of the tooth. An onlay also covers one or more of the cusps, protecting a larger part of the tooth. Wide onlays that cover the entire chewing surface are sometimes called “overlays”.

When made of ceramic, they bond to the tooth and become one with it, do not stain, and avoid the shrinkage problem that large composite fillings have as they harden in the mouth. Their real place is in teeth that are too damaged for an ordinary filling but too sound for a crown. This page is about ceramic restorations; we touch briefly on the composite option below.

Filling, inlay, onlay or crown: the differences

	Composite filling	Inlay	Onlay	Crown
What it covers	A small to medium cavity	The area between the cusps	One or more cusps	The whole tooth
Loss of healthy tissue	Least	Small	Small to moderate	All the way round
Where it is made	In the mouth	Outside the mouth	Outside the mouth	Outside the mouth
Visits	1	2	2	2

When is it better than a large filling?

The bigger the cavity, the clearer the limits of a composite filling made in the mouth become. The material shrinks slightly as it hardens; in a large filling, this shrinkage can later show up as gaps at the margins, sensitivity when chewing and, over time, new decay. Shaping the surface that touches the neighbouring tooth properly inside the mouth also gets harder, and food getting trapped there is the typical result.

We generally discuss an inlay or onlay in these situations:

• An old, large amalgam or composite filling has broken, or decay has started underneath it
• A cusp has cracked or a wall of the tooth has become very thin; an onlay covers the cusp and stops it from breaking
• A molar that has had root canal treatment still has enough tissue left, before moving on to a crown
• The contact with the neighbouring tooth simply cannot be rebuilt properly with a filling

None of these on its own makes an inlay compulsory. At the examination we look at the remaining walls of the tooth, your bite and whether you clench your teeth, and discuss filling, onlay and crown options side by side.

When is it unnecessary, and when is it not enough?

For small and medium-sized cavities an inlay is unnecessary. For a piece made from an impression to seat properly, the cavity has to be given a particular geometry; in a small cavity, that means losing healthy tissue for no good reason. There, the right treatment is a composite filling placed in the mouth.

At the other extreme, if most of the tooth's walls have been lost, or a fracture extends far below the gum, the bonding technique cannot be used reliably. How long a ceramic restoration lasts depends on keeping the area completely free of saliva during bonding. In these cases a zirconia crown is the more reliable option.

Porcelain or composite inlay?

Inlays and onlays can also be made from composite hardened in the laboratory. The two have different strengths:

• Ceramic keeps its shine and colour for years, resists wear and is well tolerated by the gum. On the other hand, it can fracture where it has to be left very thin, and when it fractures it is usually remade.
• Composite is more flexible, wears the opposing tooth less, and small chips can be repaired in the mouth. It picks up stains over time and wears faster than ceramic.

Clenching, the thickness of the remaining tooth walls and the type of tooth in the opposing jaw are the main factors in the choice. Although this page is about porcelain, for some teeth composite is the right thing to recommend.

How does the treatment go over two visits?

1. Preparation: Under local anaesthetic, the old filling and any decay are removed and the cavity is shaped to receive the ceramic.
2. Impression: The shape of the tooth is recorded with a digital scan or a conventional impression, and the shade is chosen.
3. Temporary filling: While the ceramic piece is being made, the tooth is sealed with a temporary filling. During this time, do not chew hard or sticky food on that side.
4. Try-in and bonding: The piece is tried in, and the margins, contact points and bite are checked. The tooth is then isolated from saliva, usually with a thin rubber sheet placed around it (a rubber dam), and the piece is fixed with adhesive cement and polished.

The piece is made in a dental laboratory, so treatment takes two visits, usually a few days apart. Thanks to the anaesthetic you usually feel no pain during the procedure; afterwards there may be mild sensitivity to cold or to chewing for a few days.

How long does it last, and how do you protect it?

Studies show that, in well-chosen cases, the great majority of ceramic inlays and onlays last more than ten years. Looking after them is the same as for a natural tooth: brushing, flossing and regular check-ups. The weak point is the margin where the ceramic meets the tooth; do not skip check-ups, so that any decay starting there is caught early. If the ceramic surface was ground during bite adjustment, it is important that it is polished again; rough ceramic can wear away the enamel of the opposing tooth. If you clench your teeth at night, a night guard protects both the ceramic and the opposing teeth.

What does the cost depend on?

The cost depends on whether it is an inlay or an onlay, the type of ceramic, how many teeth are being treated and whether a procedure such as root canal treatment is needed first. You receive a written, itemised quote after the examination and X-rays at our clinic in İzmir.