Amalgam or composite fillings: which to choose, and should old ones come out?

The short answer: two materials, two approaches

Today most cavities are restored with composite, a tooth-coloured resin bonded to the enamel and dentine. Amalgam, the silver-grey filling, was used for more than a century and is still a strong material, but its use is declining worldwide, mainly for environmental reasons linked to mercury. An old amalgam in good condition generally does not need to be removed: it is replaced when it is damaged, when the tooth underneath has a problem, or in a few rare medical situations.

Three questions matter when deciding: the actual condition of the filling, the size of the cavity, and what you expect cosmetically. This article goes through each of them, without scaremongering and without brushing aside legitimate concerns.

What each material is made of

Dental amalgam is an alloy made by mixing liquid mercury with a metal powder (silver, tin, copper). Once set, the mercury is bound to the other metals. Amalgam does not stick to the tooth: it is held in place by the shape of the cavity, which the dentist has to cut with undercuts, sometimes removing healthy tooth structure.

Composite combines a resin with very fine mineral fillers. It is bonded with an adhesive and then hardened layer by layer with a curing light. Because it bonds, the preparation can be limited to the decayed tissue, which preserves more of the tooth.

Other materials are used for specific purposes:

• glass ionomer cements, which release fluoride and are useful for baby teeth, root surfaces near the gum or as an interim filling;
• inlays and onlays in ceramic or composite, made outside the mouth when a lot of tooth has been lost (see our article on ceramic inlays and onlays).

The mercury question: what the authorities say

This is the question patients ask most often. Here are the official positions in plain words:

• The World Health Organization and the FDI (World Dental Federation) consider that an amalgam filling already in place poses no proven danger to the general population. A small amount of mercury vapour can be released, especially when a filling is placed or removed, or with heavy grinding, but measured levels remain low.
• The Minamata Convention on Mercury, adopted in 2013, calls for a gradual phase-down of amalgam. Its main motivation is environmental: mercury from dental waste pollutes water and soil.
• The European Union first restricted amalgam in children under 15 and in pregnant or breastfeeding women (2018), then banned its general use from 2025, except where there is a specific medical need.
• The US FDA has recommended since 2020 that new amalgam fillings be avoided, where appropriate, in certain higher-risk groups (pregnancy, breastfeeding, young children, neurological or kidney disease, mercury allergy), while stating clearly that amalgam fillings in good condition should not be removed without a reason.

In short: amalgam is now rarely placed, but the fillings already in your mouth are not a health emergency.

Composite and amalgam: strengths and limits

Each material has genuine advantages:

• Appearance: composite matches the tooth shade; amalgam is visible and, over the years, can give the tooth a grey tinge.
• Tooth preservation: bonded composite needs less drilling, whereas amalgam requires a mechanically retentive shape.
• Difficult conditions: amalgam copes better with a very deep cavity below the gum that is hard to keep dry. Composite is demanding: the area must stay completely free of saliva during bonding, ideally with a rubber dam.
• Repair: a slightly chipped composite can often be repaired without redoing the whole filling.
• Large cavities: when a tooth has lost a lot of structure, neither is ideal. A bonded restoration made in a laboratory or by CAD/CAM, or a crown, protects weak walls better.

Some patients also ask about resins: traces of bisphenol derivatives may be released just after placement, but European assessments consider this exposure very low. Rinsing after the appointment removes most of it.

When should an old amalgam be replaced?

Replacement is justified when a problem is found, not simply because a filling is old:

• fracture of the filling or of a cusp (one of the tooth walls);
• visible cracks in the enamel around the amalgam, which put the tooth at risk of breaking (our article on a broken or cracked tooth explains this risk);
• recurrent decay under the edge, seen on examination or on an X-ray;
• an open margin where food gets trapped;
• a lesion of the lining of the mouth in contact with the amalgam (a so-called lichenoid reaction) or a confirmed mercury allergy, both rare and discussed with your doctor;
• a cosmetic wish, for example on a visible premolar, after clear information.

On the other hand, removing all your amalgams to "detox" is not recommended: no reliable study shows improvement in general symptoms, drilling releases more vapour for a short time than a filling left in place, and every replacement makes the cavity slightly larger. A grey spot on the gum next to an old amalgam (an amalgam tattoo) is usually harmless, but any pigmented spot should be shown to your dentist.

How replacement is carried out

When replacement is decided, it is done under local anaesthesia with simple precautions to limit mercury exposure:

• isolating the tooth, ideally with a rubber dam;
• high-volume suction close to the tooth;
• drilling under a water spray, sectioning the amalgam into pieces rather than grinding it away;
• collecting the waste through appropriate disposal channels.

The dentist then checks the dentine under the old filling, which is often stained, and removes anything decayed. Depending on the remaining walls, a direct composite, an onlay or a crown is proposed. It is often more sensible to replace amalgams one at a time, as they need it, rather than all at once. Mild sensitivity to cold may follow for a few days; if it persists, or if the tooth hurts when you bite, it should be checked.

Reviewing your fillings in Agdal

The right decision cannot be made on appearance alone: a dull amalgam can be perfectly sealed, while a recent composite can hide leakage. During a check-up at German Dental Clinic in Agdal, the dentist examines each filling, looks for cracks and recurrent decay and uses digital radiography where needed. For larger restorations, digital impressions and on-site CAD/CAM fabrication are among the options discussed.

You leave with a clear list: what needs redoing, what can wait and what simply needs monitoring. To learn more about cavity treatment, see our dedicated page, or book an appointment if you are in Rabat.