The black filling was first introduced in United States in the 1830s where it has been the primary restorative material for more than 150 years. It has also been the subject of intense research and has been found to be safe, beneficial, and cost-effective. Scientifically known as Amalgam Restoration, where I will be using the term Amalgam instead of black filling in this article.
Dental Amalgam is a metallic restorative material composed of a mixture of silver-tin-copper alloy and mercury. Its used to restore a tooth that has been exposed to caries under certain mechanical principles, bringing the tooth back to its form and function.
The popularity nowadays of Amalgam has been decreased due to reduction in caries rate and esthetic concerns due to the introduction of composite restoration (tooth-colored fillings) later on, which has a good esthetic appearance than the silver colored fillings. In addition, mercury toxicity has been attributed to the decrease in popularity of dental amalgams although it has been known for its safety through multiple intensive researches. Unfortunately, it has been phased out in Japan, Denmark, Canada, Sweden, and Germany as a result of mercury toxicity.
There are many types of dental amalgams that has been used through out the years, I will just list these types & speak about the current Amalgam that is used in our modern world.
Types of Amalgam:
- Low-Copper Amalgam
- High-Copper Amalgam
- Spherical Amalgam
- Admixed Amalgam
Although many other types have been introduced in our modern world. The most widely used nowadays is the High-Copper Amalgam.
- High-Copper Amalgams
These kinds of fillings have a high a compressive strength that is similar to the tooth structure, but the tensile strength is low, making amalgam restorations prone to fracture. Because amalgam is brittle in thin sections and have a low edge strength, it requires a significant amount of tooth structure to be removed to satisfy its strength. It should have a sufficient bulk and 90 degree or greater marginal configuration. Keep this in your mind as I will explain it in pictures for easy understanding.
Since amalgam is a metallic restoration, its also a good thermal conductor. That’s why it shouldn’t be placed close to the pulpal tissues in order to avoid their irritation. In such cases, a liner or a base shall be placed in the cavity before placing amalgam. These liners and bases will protect the pulp from any irritants that might cause pain later on.
- Mechanical Principles
Certain major mechanical principles has to be met in order to qualify for Amalgam restoration:
- Possess a uniform specified minimum thickness for strength.
- Produce a 90-degree amalgam angle at the margin.
- Be mechanically retained in the tooth.
There are other mechanical principles but these are the major ones of which mainly without them, the amalgam could possibly dislodge or fracture. Even after the introduction of Bonded amalgams of which they will chemically be glued to the tooth structure, you will still need to provide the mechanical principles for any cavity, because the amount of retention produced by bonded amalgams is minimal.
There are certain points toward which the Amalgam restoration must be used:
- Occlusal Factors: Amalgam has a greater wear resistance than does Composite (Tooth-Colored Filling). Its also used in situations where there is a heavy occlusal functioning like in the back teeth.
- Isolation Factors: All fillings no matter what they are require isolation. Isolation means isolating the tooth from the oral cavity & saliva by the use of a rubber dam (See Figure) for proper & successful restoration.
Since there indications, there are also contraindications. Amalgam shall not be used in patients who are allergic to their components. It shall not be used in areas where esthetic is going to be compromised like in Incisors, or Canines.
- Advantages of Amalgam
Some of the advantages of amalgam has already been discussed. To summarize it, I will write in points:
- High strength
- Excellent wear resistance
- Favorable long-term clinical research results
- Lower cost than for composite restorations (tooth-colored fillings)
- Disadvantages of Amalgam
- Noninsulating: This means they a good thermal conductor so they have to not be placed near pulpal tissues as this will lead to their irritation and subsequent pain.
- Non-Esthetic: Due to their silvery color.
- Less conservative (more removal of tooth structure is required to satisfy its strength and may end up weakening the tooth).
- Clinical Technique
Your dentist will have make a complete examination, diagnosis, and treatment plan written before you are admitted for restoration. A local anesthesia might be needed for smooth operation and without interruption and usually results in a marked temporary reduction of salivation. An isolation of the tooth with a rubber dam or cotton rolls has to be done. A cavity preparation has to be formed by the dentist which will remove all caries and defects and provide the specific dimensions and characteristics required for the success of amalgam restoration. Amalgam has to be condensed really heavy in a force of 2-5 Kg which you might have your face being moved, of which your dentist will need to stabilize it. After finishing of placement, condensation & burnishing (to give it a shiny surface), occlusion will have to be checked by closing your mouth very gently on an articulating paper placed by your dentist. This paper contain ink that will mark high points on the restoration and your dentist will need to reduce it.
- Safety of Amalgam Restoration
A number of independent health agencies have extensively reviewed the issues of safety and efficacy of amalgam in recent years and have all concluded that available data does not justify either the discontinuance of use of amalgam or the removal of existing amalgam restoration. These agencies include the U.S Food and Drug Administration (FDA) in 1991 and 2002; the World Health Organization (WHO) along with the FDA in 1997; The National Institutes of Dental Research (NIDR) in 1991; and the U.S Public Health Fraud (USPHS) in 1993. The National Council Against Health Fraud (NCAHF) warns consumers about dentists recommending unnecessary removal of serviceable amalgam restorations and states: ‘Promoting a dental practice as mercury free is unethical because it falsely implies that amalgam fillings are dangerous and that mercury-free methods are superior.’
An analysis of available data leads to the conclusion that mercury in amalgam restorations poses absolutely no problem for dental patients. This conclusion has been reached by experts in the field, by consumer interest groups, and by thorough reviews by governmental agencies.
Amalgam is safe and effective restorative material. An amalgam restoration is relatively easy to accomplish, and adherence to tooth preparation and material handling requirements results in clinical success.
Reference: ‘Sturdevant’s Art & Science of Operative Dentistry, Sixth Edition.’
So, do you have an amalgam filling? For how many years did it stay? & are you complaining of any problems?
I would love to read your comments. If my article does help you, please let me know as this makes my day. I will read each & Every comment.
Haider Maitham, DDS