Most fillings today are tooth-coloured composite, which bonds to the tooth and preserves more of it than older materials required. Where a cavity is very large, a filling may no longer be the right answer at all — an onlay or a crown restores strength that a filling cannot.
Which material suits your tooth depends on where it is, how big the cavity is, how heavily you bite, and whether the area can be kept dry while it is placed.
The materials
Composite resin
Tooth-coloured, and the default for most fillings. It bonds chemically to the tooth, which means the cavity can be prepared conservatively — only the decayed tissue needs removing rather than a shape designed to hold a filling in mechanically. It is placed in layers and set with a light.
Limitations: it is technique-sensitive and requires the tooth to be kept genuinely dry while it is placed, which is not always easy at the back of a lower jaw. Very large composite fillings in heavy-load areas are less durable than the alternatives, and composite picks up staining at the margins over the years.
Amalgam
The traditional silver filling, a metal alloy. Extremely durable, tolerant of moisture, and long-established. It does not bond to the tooth, so the cavity has to be shaped to retain it mechanically, which means removing more sound tooth. It is visibly metallic, and over many years it can contribute to cracking in the remaining tooth walls.
Its use has declined in many countries for environmental reasons relating to mercury in dental waste, alongside the improvement in bonded alternatives. Existing amalgam fillings that are sound and sealed are generally not replaced simply because they are amalgam; replacing a functioning filling means removing more tooth. If you want to discuss replacing yours, that is a reasonable conversation to have — it should be a decision, not an assumption in either direction.
Glass ionomer
Bonds to tooth structure and releases fluoride slowly, which is useful in higher-risk situations. It is weaker than composite and not suited to heavy biting surfaces, so it is commonly used at the gum line, on root surfaces, in children’s teeth, and as a temporary or interim restoration.
Inlays and onlays
Made in a laboratory from ceramic or composite and bonded into or over the prepared tooth. Used where a cavity is too large for a direct filling but the tooth does not need a full crown. An onlay covers one or more cusps and restores strength, which is exactly what a large direct filling cannot do. Two appointments rather than one, and more expensive — but on a heavily broken-down back tooth it is often the better decision.
Crowns
Where too little sound tooth remains for anything else — see crowns and bridges.
When a filling is no longer the right answer
This is worth asking about directly. Each time a filling is replaced, a little more tooth goes with it, and the walls that remain get thinner. A tooth that has been filled, refilled and refilled again eventually reaches the point where another filling will simply crack the tooth.
Signs that the conversation should shift: a filling occupying most of the biting surface, cusps that are thin and unsupported, a tooth that has been root-treated, or a tooth that is already showing crack lines. In those cases an onlay or crown is not over-treatment — it is what prevents a fracture that ends the tooth altogether.
What the appointment involves
Local anaesthetic in most cases, though very small fillings sometimes do not need it. The decay is removed, the tooth is prepared, the material is placed and shaped, and the bite is checked and adjusted.
Tell the dentist if the filling feels high when you bite afterwards. It is adjusted in a minute or two and should never be lived with — a high filling causes pain on biting and can inflame the nerve.
Afterwards
Some sensitivity to cold for a few days to a couple of weeks is normal, particularly after a deep filling. It should be settling steadily.
Contact the clinic if it feels high, if sensitivity is worsening rather than improving, if pain lingers for minutes after cold, or if pain arrives spontaneously. Those can mean the nerve has been more affected than expected — see toothache: what the pain is telling you.
With composite you can eat as soon as the anaesthetic has worn off, since it is set hard immediately.
How long fillings last
There is no fixed lifespan. What ends them, usually, is new decay at the margin rather than the material wearing out — which means the answer depends more on your cleaning, your diet and your bite than on what the filling is made of. If you grind, a night guard protects fillings as well as teeth.
Frequently asked questions
Should I have my amalgam fillings replaced?
Not routinely if they are sound. Replacing them removes more tooth. If you want them changed for appearance or preference, that is a legitimate choice to discuss.
Are white fillings as strong?
Modern composites perform well in most situations. For very large restorations on heavy-load back teeth, an onlay or crown is more durable than any direct filling.
Why did my dentist say I need a crown when the last one only needed a filling?
Usually because less sound tooth remains. Ask to be shown the radiograph and the remaining tooth walls.
Can I choose the material?
Often, within clinical limits. Some situations genuinely rule an option out — ask why if you are told so.
Do fillings hurt?
The injection is the part most people notice. The rest should be painless; say so if it is not.
Ask what is left of the tooth
Before agreeing to a filling or a crown, ask how much sound tooth remains and what each option would preserve. See our general dentistry page and how tooth decay develops.
To arrange a consultation at our clinic on Abbas El-Akkad in Nasr City, call +20 101 969 7597 or message us on WhatsApp.
