They join Sweden and Norway in banning amalgam, which has been linked to neurological and kidney problems.
Dentists in all the 28 member states of the European Union are forbidden from using the material in pregnant and breastfeeding women, and in children under the age of 15.
Under the 2018 ruling, the member states have also been asked to submit plans for the phased withdrawal of amalgam from all dental surgeries. Ireland, Finland and Slovakia have been among the first to respond.
The ruling follows pressure from lobby groups such as the Campaign for Mercury-Free Dentistry, which is now turning its focus to North America. Although the American Dental Association still supports the use of amalgam, and claims it doesn't have any health risks, the campaign is confident the US's Food and Drug Administration (FDA) may soon shift its position.
Campaign president Charles Brown said: "We congratulate these countries on taking this important step to protect our planet and patients from this outdated mercury product. Now the heat is on the FDA and Health Canada to get off the dime."
Regulators are concerned about any backlash to an outright ban. A sudden announcement that amalgam is unsafe could trigger millions of demands for the removal of dental fillings, and there is also the worry that people may sue the authorities if they link neurological problems to their fillings.