Journal of Restorative Dentistry

REVIEW ARTICLE
Year
: 2016  |  Volume : 4  |  Issue : 2  |  Page : 25--30

Silver amalgam: A clinician's perspective


Treville Pereira 
 Department of Oral and Maxillofacial Pathology and Microbiology, School of Dentistry, D. Y. Patil University, Navi Mumbai, Maharashtra, India

Correspondence Address:
Dr. Treville Pereira
Department of Oral and Maxillofacial Pathology and Microbiology, School of Dentistry, D. Y. Patil University, Sector 7, Nerul, Navi Mumbai - 400 706, Maharashtra
India

Abstract

Caries persists throughout the world, and patients have multiple restorations that are likely to need replacement throughout the remainder of their lives. The selection of the best restorative material that can be used in the oral cavity is a challenging job for both the dentist and the manufacturer. While material properties and clinical performance are critically important, local economies, health care systems, will be important determinants of whether and where new materials can be easily adopted. Challenges exist not only in specifying how the material should be manipulated and perform clinically but also in understanding and incorporating implications of the skill of the operator placing the restoration. Many restorative materials currently exist like amalgam, composites, glass ionomers, and resin ionomers. It is important that the dentist must make the selection of the material with great care because, in future years, those restorations needing replacement will result in the loss of increasing amounts of tooth structure. Amalgam has a lot of disadvantages such as lack of adhesion, toxicity, poor esthetics, and marginal leakage; however, the advantages score better over other materials.



How to cite this article:
Pereira T. Silver amalgam: A clinician's perspective.J Res Dent 2016;4:25-30


How to cite this URL:
Pereira T. Silver amalgam: A clinician's perspective. J Res Dent [serial online] 2016 [cited 2019 Jul 17 ];4:25-30
Available from: http://www.jresdent.org/text.asp?2016/4/2/25/181000


Full Text

 Introduction



Operative dentistry has been considered to be the entirety of the clinical practice of dentistry, however, today many of the past subject areas in operative dentistry have become specialty areas. Operative dentistry has been recognized as the foundation of dentistry and the base from which most other aspects of dentistry evolved.[1]

Dentistry originated in the United States in the 17th century when several “barber-dentists” were sent from England. The practice then consisted mainly of tooth extractions. It was in 1896 that G.V. Black developed a standard for cavity preparation and experimented with various mixtures of amalgam thus contributing immensely to the dental profession. Black's son, Authur Black (1870–1937) continued the legacy of his father through dental research.[2]

In recent times, there has been astonishing progress in materials and methods of restoring teeth. Dental materials, as ever before, are available in a great number and variety to the dental profession. Faced with a surfeit of choices, a dental surgeon must necessarily know what to choose and how to choose it.

Intense environmental concerns recently have prompted dentists to evaluate the performance and environmental impact of existing restoration materials. Doing so entices us to explore the “what if?” innovation in materials science to create the best restorative material. Articulating a specification for the design and evaluation methods is proving to be more complicated than originally anticipated. Challenges exist not only in specifying how the material should be manipulated and perform clinically but also in understanding and incorporating implications of the skill of the operator placing the restoration, economic considerations, expectations patients have for their investment, cost-effectiveness, influences of the health care system on how and for whom restorations are to be placed, and global challenges that limit the types of materials available in different areas of the world. The quandary is to find ways to focus on future directions on the creation of more ideal restorative materials that can be available throughout the world.

The “Holy Grail” for dentistry is to eliminate dental caries entirely. Unfortunately, caries remains ubiquitous. A major proportion of the population needs or already has restorations. Once restorations are placed, their lifetimes are influenced by an array of factors and vary enormously. To decide which material is the best, one must know the properties of different materials available.

 A Brief Review of Currently Available Materials



Four classes of direct-placement restorative materials currently exist amalgam, composites, glass ionomers, and resin ionomers.[3] Advantages and disadvantages of each class are summarized in [Table 1]. Together, they present interesting choices.{Table 1}

 Selection of a Dental Restorative Material



The selection of the type of dental restorative material is dependent on many factors, among them the characteristics of the tooth itself, the patient, the dentist, and the material. The dentist must make this selection with great care because, in future years, those restorations needing replacement will result in the loss of increasing amounts of tooth structure. This sets up a cycle where the increasing cavity size limits the selection of the materials that may be used effectively. There are numerous factors to consider when restoring a tooth, for example, the extent of the lesion, the strength of the remaining tooth structure, the preference of the dentist in using the material, and the financial cost of the procedure, both out-of-pocket costs borne directly by the patient and those covered by insurance.[4] In considering the characteristics of an ideal restorative material, it is apparent that no single material can fulfill all of the clinical needs.

Factors which govern the success of a restoration are diagrammatically represented in [Figure 1].{Figure 1}

 Factors Which Influence the Performance of a Material



These include:

Physical properties (thermal, electrical, optical, and mass properties)Chemical properties (water adsorption, chemical corrosion, and biodegradation)Mechanical properties (toughness, fracture resistance, fatigue resistance)Biological properties (especially existence of any ingredients worrisome for adverse patient reactions or environmental impact)Clinical manipulation (minimum isolation, bulk placement, bulk cure, low shrinkage, minimal recycling, minimal waste, minimal packaging, operator skill)Clinical properties (no recurrent caries, good wear resistance, fracture resistance, and retention).

Three items on this long list are most influential in defining the performance of the material/restoration: Crack tolerance, ease of delivery, and clinical performance.[5]

 Challenges That Assess the Performance Properties of a Material



In vitro laboratory research, while important, has not yet been shown to correlate highly with short-term (2–5 years) or long-term (10–20 years) clinical performance. There are numerous reasons for this. In vitro laboratory tests tend to evaluate a single property representing physical, chemical, mechanical, or biological properties and generally are unable to account for variables that influence clinical performance, such as dentist skill, recurrent caries, ever-changing oral environment, and loading.In vitro laboratory testing, while important, is also vulnerable to differences in results based on the operator, research design, materials tested, interfaces, environment, and specimen geometry.[5]

Assessing clinical outcomes is even more challenging. Here, 5 interacting categories of factors complicate the understanding and ability to predict outcomes:

The operator (his/her skill – not judgment)Design (operator judgments relative to cavity preparation features for the restorative material being evaluated)Material (laboratory properties)Intra-oral location (variations in saliva, stress, temperature, and other effects relating to anterior vs. posterior, maxillary vs. mandibular arches, and primary vs. permanent tooth) andPatient factors (caries risk, fluoride history, diet, bites force, etc.).[6]

Interestingly, the operator is considered to have the most influence on clinical performance (at least 50% of the risk for outcomes). The material itself contributes the least to risk. A skilled operator can make even a poor material work relatively well. An unskilled operator cannot make even the best material work well.[7] Thus, operator skill is critically important. Consequently, an ideal material should be as simple to use as possible!

Restorative filling materials are used to “fill the hole” that is left in a tooth after your dentist removes decay from the tooth. Silver amalgam, composite resins, and glass ionomers are commonly used. They are usually placed in one visit.

Dental amalgam was probably first introduced by Monsieur Travaux of Paris in the year 1826. At that time, dental amalgam was usually made by triturating fillings from silver coins, with mercury. Dr. G.V. Black of the USA is credited with the introduction of a dental amalgam alloy in the year 1895, with a silver tin composition which is the precursor of modern day dental alloys. This is in the form of fine particles, which when mixed with a specific amount of pure mercury, forms a plastic mass in its initial stage of the reaction, and gradually hardens, as the reaction progresses. Because of its initial plastic behavior, the amalgam at this stage, can be molded to any form and allowed to harden. In dentistry, amalgam is extensively used to restore tooth structures destroyed by dental caries. In the hands of a competent clinician, it is still the cheapest, most durable and satisfactory material, even today.[8]

 What Is Dental Amalgam?



Dental amalgam is a dental filling material used to fill cavities caused by tooth decay. It has been used for more than 150 years in hundreds of millions of patients. Dental amalgam is a mixture of metals, consisting of liquid mercury and a powdered alloy composed of silver, tin, and copper. Approximately, 50% of dental amalgam is elemental mercury by weight. Dental amalgam fillings are also known as “silver fillings” because of their silver-like appearance.[9] In deciding, what filling material can be used to treat dental decay, a choice must be made by the patient and the dentist.

However, the following points should be kept in mind:

Potential benefits

Dental amalgam fillings are strong and long-lasting, so they are less likely to break than some other types of fillings. It is the least expensive type of filling material.

Potential risks

Dental amalgam contains elemental mercury. It releases low levels of mercury vapor that can be inhaled. High levels of mercury vapor exposure are associated with adverse effects in the brain and the kidneys. Food and Drug Administration (FDA) has reviewed the best available scientific evidence to determine whether the low levels of mercury vapor associated with dental amalgam fillings are a cause for concern. Based on this evidence, FDA considers dental amalgam fillings safe for adults and children ages 6 and above. Even in adults and children ages 6 and above who have fifteen or more amalgam surfaces, mercury exposure due to dental amalgam fillings has been found to be far below the lowest levels associated with harm.[10],[11]

There is limited clinical information about the potential effects of dental amalgam fillings on pregnant women and their developing fetuses, and on children under the age of 6, including breastfed infants. However, the estimated amount of mercury in breast milk attributable to dental amalgam is low and falls well below general levels for an oral intake that the Environmental Protection Agency (EPA) considers safe. FDA concludes that the existing data support a finding that infants are not at risk for adverse health effects from the breast milk of women exposed to mercury vapor from dental amalgam. The estimated daily dose of mercury vapor in children under age 6 with dental amalgams is also expected to be at or below levels that the EPA and the Centers for Disease Control and Prevention consider safe.[12]

Dental amalgam is not inert and small amounts of mercury vapor are released during the functional life of the restoration. Mercury vapor is released in greater amounts when the restoration is mixed and placed or replaced. Such things as number of filled teeth, the number of surfaces per filling, eating habits including gum chewing, tooth brushing, oral breathing habits, and bruxism can influence the amount of mercury released. The World Health Organization and World Dental Federation state, “No controlled studies have been published demonstrating systemic adverse health effects from amalgam restorations.” The World Health Organization issued this consensus statement in March 1997 that dental amalgam is considered to be “safe and effective.”[12]

Allergic reactions to the mercury in amalgam are very rare. Fewer than 100 cases have ever been reported. Mild symptoms of the allergic reaction, similar to typical skin allergies, usually disappear in 2–3 weeks.[13]

Approximately, half of a dental amalgam filling is liquid mercury, and the other half is a powdered alloy of silver, tin, and copper. Mercury is used to bind the alloy particles together into a strong, durable, and solid filling. Mercury's unique properties (it is the only metal that is a liquid at room temperature and that bonds well with the powdered alloy) make it an important component of dental amalgam that contributes to its durability.[14],[15]

There are several different chemical forms of mercury: Elemental mercury, inorganic mercury, and methylmercury. The form of mercury associated with dental amalgam is elemental mercury, which releases mercury vapor. The form of mercury found in fish is methylmercury, a type of organic mercury. Mercury vapor is mainly absorbed by the lungs. Methylmercury is mainly absorbed through the digestive tract. The body processes these forms of mercury differently and has different levels of tolerance for mercury vapor and methylmercury. It is more toxic than mercury vapor.

If the fillings are in good condition, and there is no decay beneath the filling, FDA does not recommend that the amalgam fillings be removed or replaced. Removing sound amalgam fillings results in unnecessary loss of healthy tooth structure, and exposes the patient and the dentist to additional mercury vapor released during the removal process.[12],[16],[17],[18],[19]

 Indications for Silver Amalgam



It seems sensible to restrict the use of amalgam to clinical situations that justify its use.

They may include:

Large Class I and Class II cavities, involving more than the middle 3rd of the occlusal surface of the posterior teeth, where indirect restorations are contraindicatedClass II cavities where the cervical margin of the box finishes subgingivally and is composed entirely of dentinExtensive cores, where the majority of coronal tooth structure is missingWhere definite restorations must be placed but care or moisture cannot be controlledWhere cost is a major patient concern and esthetic unimportant.[20],[21]

 Contraindications for Silver Amalgam



Anterior teeth and clearly visible surfaces of posterior teethRemaining tooth structure requires support or would require extensive preparation to accommodate amalgamTreatment of incipient or early primary fissure caries.[20],[21]

 Disadvantages of Silver Amalgam in Comparison With Tooth Colored Restorative Materials



Lack of adhesion to the tooth structure: Since amalgam does not bond to the tooth structure, microleakage immediately following the insertion of the restoration is inevitable; whereas the tooth colored restorative materials have micromechanical bondEsthetics: The appearance of amalgam is considered to be a drawback hence its use is limited to the posterior teethToxicity: The seemingly constant pronouncements about the toxic effects of mercury and the suggested link between dental amalgam and disease have confused and frightened public. While there is no scientific evidence whatsoever to support these claims they continue to flame the “Antiamalgam fires”Marginal deterioration: The “ditching” around amalgam restorations are considered to be a stress/corrosion dependent defect occurring in areas subject to occlusal loading. The magnitude and extent of ditching are directly proportional to creep properties. Secondary caries is one of the most important factors leading to the replacement of amalgam restoration.[22]

 Advantages of Silver Amalgam



InexpensiveEasy to useStrength under occlusal load and durabilityThe only restorative material existing nowadays in which the marginal seal improves with time due to formation of corrosion products at the tooth-amalgam interfaceQuick to placeStable: Dental amalgam is still considered to be the best direct restorative material for posterior restorations in permanent teeth subject to high occlusal load.[23]

 The Health Care System



It is tempting to assume that treatment decisions are a relatively straightforward decision-making process between dentists and patients. However, the health care system in any given situation may have a profound influence on whether, when, how, and how quickly alternative restorative materials can be introduced. The pressure to lower costs will always be there; however, the pressures may fall in different places, depending on the health care system, and this may determine whether a new material is adopted. This is likely to be a critical factor in the determination of how novel materials are adopted.

For the patient who is willing to pay, there is no issue. However, in a global sense, a costly material or technique will exclude large sections of the population, raising a question of equity around the availability of very routine dental care.[24] Put simply, a costly technique or material may eliminate large sections of the global population from simple dental care.

 Can a Single Material “do it All”?



The answer to this question is complicated. As a first priority, the exquisite need for care in underdeveloped and poor countries and areas that lack infrastructure must be addressed with any material that is available in that area. At the other extreme, existing materials, when properly used, are seemingly adequate in developed, affluent areas served by highly skilled dentists. Notably, though, the general perception is that amalgam is still the “best” material, and that is not likely to remain a choice in many settings. Hence, a compelling question remains: Should the objective be to define one over-engineered material that is highly fracture resistant; extremely forgiving, permitting relatively unskilled operators to place it quickly; and that seals (perhaps even heals) the remaining tooth structure, eliminating concern for recurrent caries around the restoration margins, and can be used in all locations in the mouth in both primary and permanent teeth while providing excellent esthetics and long clinical lifetime? If not, what choices should one make, and how does one justify the compromises? Moreover, should the aim be only for long-term solutions, or the identification of both near term and longer term improvements and innovations?

 What Next?



The reality is that caries persists throughout the world, and whole generations of “heavy metal” patients have multiple restorations that are likely to need replacement throughout the remainder of their lives. There are many, many challenges in, first, specifying, and then creating the best restorative material of the future.

While materials properties and clinical performance are critically important, local economies, health care systems, will be important determinants of whether and where new materials can be easily adopted. For new technologies to be globally relevant, managing the cost of the material and technique will be pivotal.

It is self-evident that, if the costs associated with a new material are much higher than for those already present, these costs will need to be met from somewhere. It is also self-evident that high costs will be a barrier to voluntary change while low costs may be a facilitator. Clinicians, materials scientists, and manufacturers need to collaborate to create the design specification for future innovations. Agencies such as International Standards Organization, Federation Dentaire Internationale, and others can work toward harmonization of global testing protocols and factors that influence the availability of materials. Most importantly, however, leaders of health care systems and third-party payers need to consider how preventive care can become more cost-effective and incentivizing for practitioners. Until then, undoubtedly the clinician can safely rely on amalgam as the best restorative material.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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