Dental Fillings

Dental fillings are dental materials that have been used to repair a decayed tooth. The tooth is first prepared using dental drills to remove decay and create space for the dental material of choice – then the material is inserted.

Filling materials

The restored tooth’s final appearance, longevity, cost, and drilling method, are all  predetermined by what dental material is chosen. 

Dental materials are grouped into three main categories: silver amalgam, composite resin, and glass ionomer.

Each has its advantages and disadvantages, and where and when it can be used. Ask your dentist if your situation provides you with any choices - the location and size of the decay often limits your options.

Silver amalgam fillings (above) and composite resin fillings (below) pictured. 

Silver amalgam

Amalgam is the dental material commonly seen in “silver fillings”. A mixture of 45% mercury to 55% other metals (silver, copper and tin), amalgam is possibly the oldest and most thoroughly researched dental material.

Its advantages are abundant. It is strong, durable, and withstands biting forces amazingly well. It is easy to place, self-setting (does not require ultraviolet light), barely shrinks on setting, and has little leakage (bacteria cannot get through the filling-tooth interface to cause decay). It can be placed while the region is still wet (important in small children), and is the cheapest of all the dental materials.

While amalgam is clearly great, it does have significant limitations. Amalgam does contain traces of mercury, a toxic substance.  While agencies like the FDA, CDC and WHO have not found evidence of harm from dental amalgam, there are still online groups and some dentists that warn patients that amalgam may be toxic. This topic will be discussed more thoroughly later on in this page.

Some individuals may have metal allergies so amalgam is not indicated for them. Ultimately though, the greatest drawback to amalgam is its appearance. Being silver, your dentist is most likely to use it for back teeth, such as molars, only. With the advent of tooth-colored dental materials, more and more patients are requesting “white fillings” even with the great advantages that amalgam provides.

Composite resin

Composite is a mixture of acrylic resin and powdered glass-like particles that together produce a tooth-colored filling. It is applied in a semi-liquid state, but either self-hardens in minutes or as it is exposed to ultraviolet light.  Composite has been around for decades, and while previous composite materials shrank as they hardened (leaving space for bacteria to invade), today’s composite is considerably more advanced.

The main advantage of composite is evident: it is tooth-colored and produced in an assortment of shades to match natural teeth. There are three significant downsides though. Firstly, it is more technique sensitive so your dentist may not place it correctly. Secondly, most composite resins tend to shrink marginally while setting and this opens up gaps that allow bacteria to penetrate. Finally, while composites are relatively strong and can be placed in both front and back teeth, there are some limitations. For example, molars receive the majority of chewing forces, so if the decay is large and found in a molar tooth, composite resin should not be placed. Research has proven that under such conditions, composite material simply cannot withstand breaking (unlike amalgam) – no matter what the dental material companies claim. Nonetheless, far too many dentists place composite resin where it is not suited because they give into patient demands for a tooth-colored filling.

Glass ionomer

Glass ionomer materials are also tooth-colored since they are made from acrylic resins and powdered glass. Although they are tooth colored, they do not come in as many shades as composite resins. Structurally, glass ionomer is relatively weak compared to amalgam and composite resin, so it is reserved for smaller decays and almost never used on the chewing surface of adult teeth.

One large advantage of glass ionomer is its ability to release fluoride long after it has been placed inside the tooth. For this reason, glass ionomer is the material of choice for those suffering from root caries or who have rampantly decayed teeth. The fluoride release has an antibacterial effect in the region while also helping to strengthen the enamel. 

Dental amalgam - mercury controversy

Over the past several years, concerns have been raised about the mercury content of silver amalgam fillings. Some people think that amalgams are responsible for causing a number of diseases, including autism, Alzheimer's disease, and multiple sclerosis.

The American Dental Association (ADA), FDA, and World Health Organization, all say that there is no evidence to suggest this is the case. The causes of autism, Alzheimer's disease, and multiple sclerosis remain unknown. Additionally, there is no solid, scientific evidence to back up the claim that if a person has amalgam fillings removed, he or she will be cured of these or any other diseases.

Although amalgams do contain mercury, when they are mixed with other metals, such as silver, copper, tin, and zinc, they form a stable alloy that dentists have used for more than 100 years to fill and preserve hundreds of millions of decayed teeth. Research has proven, time-and-time again, that little to no mercury leaks out of dental amalgam fillings. In fact, a greater concentration of mercury comes from contaminated food than from dental fillings.

Based on current research, the dentists behind this publication wholly endorse the use of amalgam. In fact, the risk of mercury toxicity is greatest for the dentist who mixes the amalgam, not the patient receiving the mixed alloy.

Other sites, and even some dentists, are quick to suggest you remove amalgam fillings and replace them with tooth-colored composite. This is erroneous and harmful to both the patient and profession. Profiting from patients’ misplaced fears is unethical and against our code of conduct. Furthermore, every time silver amalgam fillings are drilled out to replace with composite resin, more natural tooth structure is lost, resulting in a weaker tooth.

Temporary fillings

Amalgam, composite resin and glass ionomer are all permanent filling materials. Temporary fillings use another class of material, such as zinc-oxide-eugenol, under the following circumstances:

  • For fillings that require more than one appointment – for example, if you have multiple decayed teeth, the dentist will use temporary filling to arrest the problem temporary before placing permanent fillings on another day

  • Following root canal therapy, a temporary filling is usually placed on the tooth to seal the medication that was placed inside the root canal. At the next appointment, the medication is removed, the canal is filled, and a permanent filling or crown is placed on the tooth.

  • For certain toothaches. If your dentist suspects the pain is coming from an irritated tooth nerve, he may place a temporary filling on the tooth. Temporary filling materials have the added benefit of “soothing the pulp”. Once the pain has settled, your dentist will place a permanent filling.

Temporary fillings are just that; they are not meant to last. They usually fall out, fracture, or wear out within 1 month. Be sure to contact your dentist to have your temporary filling replaced with a permanent one. If you don't, your tooth could become infected or you could have other complications.

Treatment procedure

Once your dentist is confident of there being tooth decay, he will numb the area surrounding the tooth using a local anesthetic. Using a drill, or laser instrument, your dentist will remove the decay and open up the tooth’s surface to receive the filling material. Your dentist will probe or test the area to ensure all decay has been removed –remnant bacteria can easily multiply and begin the decay process again.

Rubber dam application to a patient's mouth. While it looks odd, rubber dams are painless but excellent in isolating the decayed tooth and blocking moisture from reaching the dental material as it sets. 

Once the decay has been removed, your dentist will prepare the space for the filling by cleaning the cavity of bacteria and debris. Before placing the filling material, your dentist will work hard to isolate the tooth from moisture using a rubber dam device. A moist surface disrupts the setting reaction of many dental materials and needs to be avoided.  If the decay is near the root, your dentist may first put in a liner made of glass ionomer, composite resin, or other material to protect the nerve. Generally, after the filling is in, your dentist will finish and polish it.

Several additional steps are required for tooth-colored fillings. After your dentist has removed the decay and cleaned the area, composite resin is applied in layers. Next, a special light that "cures" or hardens each layer is applied. When the multilayering process is completed, your dentist will shape the composite material to the desired result, trim off any excess material and polish the final restoration.

Once the filling has set, your dentist will run tests to check that the filling is not interfering with your bite. Several modifications are made as your dentist polishes the surface to reduce the filling height and ensure it feels normal once you have left the dental office.

Post-treatment care

Once your filling has been placed, always remember that your tooth is not “as good as new”. No dental material on the market can truly replicate natural teeth – your tooth is at a greater risk for decay following treatment. To ensure another filling is not needed, follow good hygiene practices – visit your dentist regularly for cleanings, brush with a fluoride-containing toothpaste, and floss regularly.


Composite resin fillings usually cost more than their amalgam filling counterparts, but are only slightly costlier than glass ionomer fillings. This is because the material is more costly to purchase for the dentist, and its application is harder and more time consuming.

An amalgam filling will cost anywhere from $75 to $150 per filling (depending on size), and composite resin will cost $150 to $200 for the same treatment. Most dental insurance plans cover dental fillings, but often only 60-80% of the charge.


On average, amalgam fillings are expected to last approximately 12 years, while composite fillings are expected to last 5 to 7 seven years. These values are dependent on a host of variables such as your oral hygiene, frequency of dental visits, size and location of the filling, as well as, your dentist’s technique in placing the filling.

Possible future problems

Patching up a decayed tooth with dental material is often successful, but a small portion of patients experience post-treatment problems. The most frequent include:

  • Tooth sensitivity. This is a fairly common outcome where the sensitivity can be to anything from touch to temperature. Usually, the issue resolves within a couple weeks. If it does not, or is extremely sensitive to begin with, consult your dentist. You may be given special desensitizing toothpaste such as Sensodyne, or your dentist may replace the filling with a temporary filling to soothe the pulp irritation. At the extreme end, you may need a root canal.

  • Pain on biting. If you find that you are experiencing pain on chewing, or that the filling is “high”, then that is actually the likely cause. Your dentist has placed a filling that is higher than the natural tooth was, and it is interfering with your bite. See your dentist to have it reduced.

  • Toothache. If your pain is beyond that of typical sensitivity, and is present even when you are not biting on something, the problem is likely more severe. This “toothache” response may indicate that the tooth is no longer healthy and a root canal treatment will most likely be required.

  • Allergies. Allergic reactions are most common with amalgam fillings, but even these are rare. In these rare circumstances, mercury or one of the metals used in an amalgam restoration is thought to trigger the allergic response. Symptoms of amalgam allergy are similar to those experienced in a typical skin allergy and include skin rashes and itching. Patients who suffer amalgam allergies typically have a medical or family history of allergies to metals. Once an allergy is confirmed, another restorative material can be used.

  • Broken filling. There are numerous reasons for why a filling might fail under pressure. If you feel yours has worn down or has fractured, it is important to see your dentist immediately. Small composite resin fractures can be repaired, but amalgam fillings will need to be fully replaced. If the seal between the tooth enamel and the filling breaks down, food particles and decay-causing bacteria can work their way under the filling. You then run the risk of developing additional decay in that tooth. Decay that is left untreated can progress to infect the dental pulp and may cause an abscessed tooth.

It is crucial that you visit your dentist immediately. If your dentist finds that a dental filling needs constant replacing on one tooth, he might recommend getting a dental crown instead.

Dental Crowns
If the decay is too large, dentists recommend crowns over fillings.
Learn more >

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