Dental amalgams have been used in dentistry for the past 160 years as restorative fillings. The use of dental amalgams is decreasing nowadays, but it continues to be the material of choice among many dentists in providing inexpensive restoration of posterior teeth.

Dental amalgams are made of metal alloys. Amalgams are prepared from alloys of mercury and metals. These metals are platinum, gold, zinc, cadmium, antimony, and bismuth. A high dispersion copper alloy was developed in 1963. This dispersion copper alloy is more corrosion resistant than earlier copper alloys.

Today the amalgams are made from mercury and alloys that are composed of silver, tin, and copper. Other metals like zinc, indium, and palladium may also be present in small amounts of 1% or less of the alloy. It is believed that zinc improves the clinical performance of the amalgam by the preventing corrosion. This modern amalgam is made by mixing 43% to 50% mercury by weight with the alloy.

Amalgam fillings

Amalgams are available as irregular practices. They are small spheres or a mixture of the two. Handling characteristics of the alloy depends upon its formulation, shape, and size. But the clinical performance remains the same. Spherical alloys are easily adaptable to cavity walls because they are less resistant to condensation. But an actual experience showed that the spherical alloys exhibit microleakage due to poor adaptation.

In order to seal the margin between the tooth and the amalgam, cavity varnishes are needed to reduce the leakage. Before, copal varnishes were used, it lasted only for a few months. Nowadays, the replacement of the traditional varnishes by bonding resins that provide a better initial seal of the cavity walls is happening gradually. The use of varnish is not advised when an amalgam is used with bonding resins.

The major problem with amalgam restorations is recurrent caries. A retrospective survey was done by clinics and private practitioners. The survey showed that in half of the cases of replacement, restoration was done in teeth with recurrent caries. In this study, it was believed that some cases were wrongly identified as recurrent caries and that the first amalgam restoration was not done properly and the caries remained underneath the first filling.

If the tooth is not correctly prepared and cleanded before a filling this often leaves a residual caries that later becomes a bigger problem. In other cases, marginal discrepancies are also wrongly diagnosed as caries, especially when there is debris found in the area.

Recurrent caries can be minimized by the following ways:

• use topical fluoride applications
• good oral hygiene
• careful amalgam placement
• placement of an unfilled resin to seal restoration margins

Improvements and new studies have led to a changed cavity design. Preserving the tooth structures with minimal intervention is the key. The amalgam fillings should be extended to carious fissures and not to adjacent non-carious fissures. Studies have revealed that smaller restorations last longer, and retaining as much sound tooth as possible also reduces the chances of cusp fracture.

When the tooth has been destroyed by caries and/or trauma, large restorations are needed. The retention of large restorations requires further measures such as the use of retentive pins. These retentive pins are not sufficient to combat the pressure exerted during placement. This can cause fractures in surrounding tooth structure. In these cases, dentists create amalgam pins by cutting channels in the teeth and filling them with amalgam. Amalgam pins also require removal of tooth structure in an already weakened tooth.

No long-term studies were made to show how good amalgam bondings are. But short term studies and an increasing evidence showed that amalgams are effective over the years. Only a successful long term bonding can eliminate mechanical bondings like the retentive and amalgam pins. Reducing the chances of more damage to the tooth and enabling better cavity design that would preserve more sound structures is achieved through the elimination of these pins.

Problems with amalgam fillings

Amalgams have adverse effects. Alloy components present in the amalgams can cause oral lesions, although this occurrence is rare. This problem affects not only the patients but also the dental staff involved in restoration. To resolve the problem, removing the offending restoration is done. Patients may show sensitivity or allergies to the resins.

Another disadvantage of amalgams is aesthetic problems, as they can cause tooth discoloration.

Mercury toxicity, neuro toxicity, birth defects, and compromised health are some of the allegations against the use of amalgams. These have no supporting scientific evidence, but should not be taken lightly.

Mercury is one of the metals used in amalgams. Mercury in large amounts can have adverse effects on people.
There are studies that have revealed that the small amount of mercury vapor released by amalgams does not pose a health hazard.

With all these allegations thrown at the use ofamalgams, its ironic that the dental staff, who are most exposed to these amalgams, have higher life expectancies than others have. There is no evidence that dental staff develop diseases or die from coauses that are different from the general population - they are affected by the same diseases seen in the general population.