Study Guide for Chapter 13 Amalgam.docx

**[Study Guide for Chapter 13 Amalgam]** \*\*\*Know the Key terms for the Chapter 1. An alloy is a mixture of two or more metals. For an alloy to be used as one of the ingredients in producing a dental amalgam material, the principal alloy must be a combination of silver and tin with the...

**[Study Guide for Chapter 13 Amalgam]** \*\*\*Know the Key terms for the Chapter 1. An alloy is a mixture of two or more metals. For an alloy to be used as one of the ingredients in producing a dental amalgam material, the principal alloy must be a combination of silver and tin with the highest percentage being silver -- per the American Dental Association (ADA) guidelines. This silver-based alloy is used to create dental amalgam. Dental Amalgam is a restorative material made up of silver-based alloy that contains other metals mixed with liquid mercury. an alloy of mercury with one or more other metals. Most dental amalgams are called silver [amalgams](https://ec.europa.eu/health/scientific_committees/opinions_layman/en/dental-amalgam/glossary/def/dental-amalgam.htm) since silver is the principal constituent that reacts with mercury. The kinetics of reactions between mercury and silver are not appropriate for clinical use, so that the silver is provided as an alloy with other [elements](https://ec.europa.eu/health/scientific_committees/opinions_layman/en/dental-amalgam/glossary/def/elements.htm). There are several types of dental amalgam alloy, all involving tin and silver and most having some copper and, to a lesser extent, zinc. Some of the dental amalgam alloys themselves contain a little mercury to facilitate the amalgamation reaction. A conventional dental amalgam alloy will contain between 67% and 74% silver, with 25-28% tin, and up to 6% copper, 2% zinc and 3% mercury. The so-called dispersion type amalgam alloys have around 70% silver, 16% tin and 13% copper. A further, quite different, group of amalgam alloys may contain up to 30% copper and are known as high-copper content amalgam alloys. 2. Copper content of 12% or greater designates an amalgam as a high-copper type. The advantage of the added copper is that it responds positively with tin thereby reducing the rate of corrosion. However, enough corrosion occurs at the amalgam--tooth interface to help seal the restoration which helps reduce microleakage. These materials may provide satisfactory clinical performance for more than 12 years. High-copper amalgams are available with admixed or spherical alloy structure. 3. Admixed amalgam contains irregularly shaped and sized alloy particles, sometimes combined with spherical shapes, which are mixed to form a mass that is placed into the tooth preparation. The irregular shape of the particles requires **greater condensation pressure** (which many dentists prefer) and allows the operator to more easily place the matrix bands to generate proximal contacts. 4. A spherical amalgam contains small, round alloy particles that are mixed with mercury. Because of the shape of the particles, the material is condensed into the tooth preparation with **little condensation pressure**. This advantage is combined with its high early strength to provide a material that is well suited for very large amalgam restorations such as complex amalgams or foundations. 5. Because of the concern about mercury toxicity, new compositions of amalgam have been promoted as mercury-free or low-mercury amalgam restorative materials. Alloys with gallium or indium or alloys using cold-welding techniques have been presented as alternatives to mercury-containing amalgams. None of these new alloys have shown sufficient promise to become a universal replacement for current amalgam materials. 6. Although the compressive strength of high-copper amalgam is similar to tooth structure, the tensile strength is lower, making amalgam restorations prone to fracture during flexure. Usually, high-copper amalgam fracture is a bulk fracture, not a marginal fracture. All amalgams are brittle and have low edge strength. As such, the amalgam restoration must have sufficient bulk (usually 1.5 - 2 mm in any occlusally loaded area, depending on the position within the tooth) and a 90-degree marginal configuration. 7. Operative considerations include: relates to occlusal load on amalgam restorations, high-copper amalgams exhibit no clinically relevant creep or flow. As a metallic material, amalgam is a good thermal conductor, therefore, at minimum, a dentin desensitizer should be used immediately prior to amalgam placement to limit sensitivity in the dentinal tubules caused by thermal changes. A liner or base should be placed in areas of deep caries removal prior to amalgam placement to limit thermal sensitivity. 8. Dental amalgam does not bond to tooth substance. It is dependent on the creation of mechanical undercuts, slots, grooves or, to a lesser extent than practiced previously, dentine pins to gain adequate retention and resistance form, to ensure that it is retained in the cavity. Creation of mechanical features such as **undercuts and grooves** may require undesirable sacrifice of sound tooth substance. 9. Amalgam is effective as a direct restorative material because of its easy insertion into a tooth preparation and, when hardened, its ability to restore the tooth to proper form and function. The tooth preparation not only must remove the fault in the tooth and remove weakened tooth structure, but its form must also allow the amalgam material to function properly. 10. Amalgam restorations initially leak and therefore require steps to protect from pulpal sensitivity until self-sealing can occur. After desensitizing the prepared tooth structure, mixing, inserting, carving, and finishing the amalgam are relatively fast and easy. Three (3) methods to help limit initial pulpal sensitivity after amalgam placement: - placement of a dentinal desensitizer - placement of amalgam bonding (amalgam intermingled with adhesive resin) - placement of a sealer (adhesive resin placed aengthen adjacent tooth structure. 11. Mercury can enter the body through ingestion, through direct contact with the skin, and by inhalation of the vapor. Care should be taken when placing or removing amalgam restorations to prevent the swallowing of amalgam particles or the inhaling of mercury vapor. However, the mercury in swallowed particles is not absorbed well and is usually excreted. Use of the rubber dam and high-volume evacuation will help to minimize both. 12. Although dental offices do not contribute as much mercury to the environment as large companies, their contribution is not insignificant. Special collection devices are available to collect amalgam particles and mercury that might escape into the wastewater and ultimately end up in the water supply, streams, rivers, or ocean. Amalgam scrap that is collected from used capsules, remnants from the amalgam well, and amalgam debris from high-volume evacuation traps should be appropriately recycled and not discarded in the trash that ends up in landfill. Commercial firms are available to provide this service.