Let Me Fill You In: Amalgam vs Composite Fillings

Jul 30, 2018

Filling It All In

Fillings are one of the primary treatments provided by all general dentists. Fillings are needed when caries (tooth decay) is detected, to repair cracked or broken teeth, and to build teeth up when they are worn down (through bruxism/teeth grinding or other causes). The most common need for fillings is the presence of caries. The dentist will drill out and remove all the caries and replace the hole with filling material to minimise exposure of the tooth’s internal structure to bacteria and potential future caries.

But the question remains: what is the best type of filling material? The ongoing debate for the past few decades has been between amalgam and composite resin fillings. Below, we’ll discuss the pros and cons, and what each filling material is made out of.

Amalgam Fillings

Amalgam fillings are made of a combination (amalgamation) of several different types of metals: mercury, silver, tin, and copper. Mercury makes up almost 50% of amalgam fillings but not to worry – because it’s mixed with other metals, they all form a strong, stable, and safe compound. Amalgam fillings have been used since 1895 and there has never been a case of mercury poisoning from amalgam fillings as the mercury exposure is practically negligible.

What are the pros of amalgam fillings?

  • They are generally long-lasting, between 10 and 15 years of use, so you don’t need to replace them very often;
  • Secondary caries (further tooth decay developed under the filling) occurs less frequently next to or under amalgam fillings than composite resin ones;
  • They are the most economical option as amalgam fillings generally cost less than composite resin fillings;
  • Because of the metal compound, they are strong and very durable, holding up against heavy biting forces; and
  • They can be completed in one dental visit.

What are the cons of amalgam fillings?

  • The filling doesn’t actually bond to the tooth – your dentist has to prepare the cavity by creating undercuts or ledges to keep the filling in place (which means your dentist may have to remove more tooth structure to create a secure cavity/pocket for the filling to go into);
  • Amalgam is silvery grey in colour and does not match the colour of teeth (this aesthetic reason is generally the main reason for why a lot of patients don’t want to use amalgam, especially for front teeth – it is far less noticeable with your back teeth such as molars);
  • They can corrode, tarnish, or stain over time (possibly leading to discolouration of your teeth);
  • Metal responds to heat and cold more readily then other materials so teeth with amalgam fillings may be more sensitive to hot and cold foods and drinks;
  • Amalgam fillings expand over a long period of time, which could lead to the tooth cracking; and
  • Some people may be concerned about allergic reactions or sensitivity to the metals used in amalgam fillings.


It is generally recommended to use amalgam fillings in teeth at the back of the mouth, where it can’t be seen and where there is a lot more biting force.

Composite Fillings

Composite resin fillings are composed of a mixture of plastic and fine glass (ceramic) particles. They are tooth-coloured so they are practically invisible to the naked eye. That is, of course, unless you ingest a lot of foods and drinks that discolour your teeth, in which case the filling will not stain but the natural tooth will.

What are the pros of composite fillings?

  • They maintain a nice aesthetic look to your teeth (which means they can be used for both the front and back teeth so long as the filling isn’t too large);
  • Composite fillings actually bond to the surface of your tooth so it’s less likely to fall out;
  • The composite material is flexible and therefore there is far less drilling required for the filling to be placed (which means you can preserve the maximum amount of your tooth);
  • Composite fillings can be used with other materials (like glass ionomer for example) to provide benefits of both materials;
  • They don’t stain like amalgam fillings do; and
  • There’s no risk of metal allergy/sensitivity.

What are the cons of composite fillings?

  • They don’t last as long as amalgam fillings so they will need more frequent replacement;
  • The filling process takes longer with composite fillings as there are more steps involved to bond the filling to the tooth (dentists generally only need one appointment but sometimes they may need two to complete the procedure);
  • They cost more than amalgam fillings; and
  • They are not as strong when it comes to holding up under heavy chewing force for years and years;
  • Composite resin may shrink when placed (which could lead to bacteria entering the gaps between the tooth structure and the filling and causing more secondary caries/further tooth decay).


It is generally recommended to use composite fillings in teeth at the front of the mouth, where it can be seen and where there is not much biting force. Also, it’s not recommended in teeth that need large fillings.