Short answer: A porcelain inlay or onlay is a restoration made in a laboratory or with digital systems from an impression of a large decayed or fractured area of a tooth, and then fixed to the tooth with special adhesives. The type that sits between the cusps of the tooth is called an inlay, the type that covers one or more cusps is called an onlay, and the type that covers the entire chewing surface is called an overlay. It is preferred for losses that are too large for a composite filling but too early for a crown.
When a large cavity is cleaned out or an old, large filling is replaced, the dentist sometimes recommends a "porcelain filling" instead of a conventional filling. Known as inlays and onlays, these restorations differ from fillings shaped directly in the mouth: they are made outside the tooth and then bonded to it. In this article we take a detailed look at what porcelain inlays and onlays are, when they are preferred, how they differ from composite fillings and crowns, and what the treatment process involves.
What are inlays, onlays and overlays?
Inlays, onlays and overlays are types of fillings named according to the size and location of the lost tooth structure; they are made outside the tooth and bonded to it. All of them are called "indirect restorations," meaning they are prepared not in the mouth but from an impression or digital scan.
- Inlay: A restoration that fills the hollow area between the cusps on the chewing surface of the tooth. It is preferred when the cusps are intact.
- Onlay: A restoration that also covers one or more cusps. It is used to strengthen the tooth when one of the cusps has weakened or broken.
- Overlay: A restoration that covers the entire chewing surface of the tooth; it is close to a crown but more conservative.
These restorations are most often used on molars and premolars. The materials most commonly used are glass ceramics, reinforced ceramics such as lithium disilicate, or zirconia; in some cases lab-made composite materials may also be preferred. Which material is chosen depends on the tooth's position, chewing forces and esthetic expectations.
How does it differ from a composite filling?
The fundamental difference between a porcelain inlay or onlay and a composite filling is how it is made: a composite filling is shaped in the mouth layer by layer and hardened with light, whereas a porcelain restoration is made outside the tooth and bonded to it in one piece. This difference has important consequences, especially for large losses.
A composite filling is a quick, esthetic and tooth-preserving option for small and medium-sized cavities. However, as the filling gets larger, certain limitations become more evident:
- Shrinkage: Composite shrinks somewhat as it hardens. In large fillings this can lead to leakage at the margins and sensitivity. Because a porcelain restoration is made outside the mouth, this problem is largely reduced.
- Contact with the neighboring tooth: With large losses, creating an ideal contact point and tooth anatomy with composite can be difficult. With indirect restorations, contact points are shaped in a more controlled way in the laboratory or digitally.
- Wear and color: Ceramic materials are generally more resistant to wear and discoloration than composite.
On the other hand, a porcelain inlay or onlay usually requires two visits and costs more. For small cavities, a composite filling is often sufficient and the more suitable option.
How does it differ from a crown?
A porcelain inlay or onlay removes much less tooth structure than a crown; only the lost and weakened part is repaired, and healthy tooth tissue is preserved. With a crown, by contrast, all surfaces of the tooth are reduced by a certain amount and a cap is placed over the tooth.
The general principle in dentistry is to preserve healthy tooth tissue as much as possible. In this respect, porcelain inlays and onlays are a middle ground for situations that are "too large for a filling but too early for a crown." Their advantages can be summarized as follows:
- More healthy tooth tissue is preserved.
- Since the margins often stay above the gumline, cleaning and monitoring are easier.
- Tooth tissue remains in reserve in case a crown is needed in the future.
However, if most of the tooth has been lost, if its walls have become very thin or if it is a weakened molar that has had a root canal, a crown may be the more suitable option. To make this decision, the thickness of the remaining walls, the presence of cracks and the bite relationship are assessed.
When are porcelain inlays and onlays preferred?
Porcelain inlays and onlays usually come into consideration in the following situations:
- Large losses of tooth structure in back teeth due to extensive decay or fracture
- Replacing old, leaking or broken large fillings
- Strengthening a weakened cusp to reduce the risk of it breaking
- Replacing amalgam fillings for esthetic reasons and to preserve tooth tissue
- Restoring the upper part of the tooth after a root canal, in suitable cases
For patients with inadequate oral hygiene, a high risk of active decay or a marked clenching habit, planning is done more carefully; if necessary, these problems are addressed first. This is because how long the restoration lasts depends as much on the health of the oral environment as on the quality of the material.
How does the treatment process work?
A porcelain inlay or onlay is usually completed in two visits; in some cases where digital design and manufacturing systems are used, it can be done in a single visit.
- Examination and planning: The condition of the tooth is assessed, X-rays are taken if needed and the appropriate type of restoration is determined.
- Preparation: Under local anesthesia, the decay and old filling are removed; the tooth is prepared so the restoration can seat on it.
- Impression or digital scan: An impression of the prepared tooth is taken or a three-dimensional digital model is created with an intraoral scanner. The shade is selected.
- Temporary filling: In two-visit treatments, the tooth is protected with a temporary filling until the restoration is ready.
- Fabrication: The restoration is made in the laboratory or with a digital milling system.
- Bonding: The fit, contact points and color of the restoration are checked; it is then fixed to the tooth with special adhesive cements. Finally, the bite is adjusted and the surface is polished.
After bonding, there may be slight sensitivity to cold in the first days; this usually passes quickly. The fee varies by type of restoration and material and is communicated in writing after the examination.
How long do they last, and how should they be cared for?
Porcelain inlays and onlays placed for the right indication and well cared for are restorations that clinical studies have shown can function for many years. However, their lifespan varies from person to person depending on chewing habits, clenching, oral hygiene and regular check-ups.
To protect your porcelain inlay or onlay:
- Brush twice a day with fluoride toothpaste and floss every day; cleaning between the teeth is important to prevent decay from developing at the edges of the restoration.
- Avoid biting very hard objects such as ice, hard candy or nutshells.
- If you clench or grind your teeth, use the night guard your dentist recommends.
- Go for a check-up every 6 months; regular assessment of the marginal fit and the surrounding tooth tissue helps catch problems early.
For other questions about types of fillings, take a look at our frequently asked questions page.
When should you get your large fillings assessed in Ankara?
If you notice cracks, discoloration or darkening at the edges of old fillings in your back teeth, or if you feel a sharp pain when chewing, it is worth having an examination to assess the tooth and determine whether a filling, a porcelain inlay or onlay, or a crown is the suitable option. At our polyclinic in Park Oran Ofis in Oran, we examine your teeth and explain the options to you with all their pros and cons. To book an appointment, you can use our contact page.
Frequently asked questions
What is the difference between a porcelain inlay and a composite filling?
A composite filling is shaped in the mouth and hardened with light; a porcelain inlay is made outside the tooth and bonded to it. For large losses, a porcelain restoration can offer advantages in terms of shrinkage, wear and discoloration; for small cavities, composite is often sufficient.
What is the difference between an onlay and a crown?
An onlay repairs only the lost and weakened part; with a crown, all surfaces of the tooth are reduced. That is why an onlay is an option that preserves more healthy tooth tissue.
How many visits does a porcelain inlay or onlay take?
It is usually done in two visits: at the first, the tooth is prepared and an impression is taken; at the second, the restoration is bonded. In some cases where digital manufacturing systems are used, it can be completed in a single visit.
Can a porcelain inlay or onlay break?
Ceramic materials are durable; however, biting very hard objects or a clenching habit can increase the risk of fracture. If you clench your teeth, wearing a night guard and having regular check-ups help protect the restoration.
