Potential Danger from Metal Dental Crowns

ALL cast alloy restorations contain many substances other than gold, some of which may cause allergic or toxic reactions in patients. Note that cast alloys are not used for other body replacement parts. For example, try a cast hip replacement instead of titanium or zirconia and watch the body reject it.

Since few dentists test patients for allergies or adverse reactions to metals or are on the lookout for them after insertion, a potential danger exists.

Today, inert (means doesn’t react with body) materials such as Emax(TM), Zirconia & Pressed Glass restorations are now available. Perhaps it’s time dentist consider moving away from cast alloys entirely.

Talk with your dentist to discuss what you should do.

Source: Air Force Pamphlet 47-103 Volume 1 15 November 2005

Effect of Constituent Metals. The exact role of a metal varies with the particular alloy system the metal is added to. For example, copper is included in many of the high palladium alloys to help form an oxide layer for porcelain bonding. However, copper is added to the medium silver-palladium alloys to effectively lower their melting range and permit the use of gypsum-bonded investments. The following elements are frequently used in the traditional gold-base alloys: (NOTE: Their descriptions are generalized.)

Aluminum (Al). Aluminum is added to lower the melting range of the alloy. It is also a hardening agent and influences oxide formation.

Beryllium (Be). Like aluminum, beryllium lowers the melting range, improves castability, serves as a hardener, and influences oxide formation. Reportedly, it improves polishability by acting as a lubricant for polishing agents, thus permitting them to work more effectively. Electrolytic “etching” of nickel-chromium-beryllium alloys removes a nickel-beryllium phase to create microretention for the etched-metal resin-bonded retainers (Maryland Bridges).

Boron (B). Boron is a deoxidizer, hardening agent, and element that reduces the surface tension of an alloy and thereby improves castability. In the nickel chromium alloys, boron acts to reduce ductility and to increase hardness.

Chromium (Cr). Chromium acts as a solid solution hardening agent and ensures corrosion resistance by its passivating nature.

Cobalt (Co). Cobalt-base alloys are an alternate to the nickel-base types, but are more difficult to cast.

Copper (Cu). Copper serves as a hardening and strengthening agent, lowers the melting range, and interacts with platinum, palladium, and silver (if present) to provide a heat-treating capability. It helps form oxides for porcelain bonding, lowers the density slightly, and can also enhance passivity.

Gold (Au). Gold provides a high level of resistance to corrosion and tarnish (no associated passivity) and slightly increases the melting range as well as workability and burnishability. Gold imparts an esthetically pleasing color to the alloy while markedly increasing density.

Indium (In). Indium serves as a less volatile scavenging agent, tends to lower the melting range (gold-base alloys), helps form an oxide layer for ceramic alloys, and lowers the density.

Reportedly, an indium content of 20 percent can adversely affect the corrosion resistance of silver base alloys.

Iridium and Ruthenium. These two elements serve as grain refiners to improve the mechanical properties and tarnish resistance.

Manganese (Mn). Like silicon, manganese acts as an oxide scavenger to prevent the oxidation of other elements when the alloy is melted. It is also a hardening agent.

Molybdenum (Mo). Molybdenum is added to adjust the coefficient of thermal expansion and improve corrosion resistance. It also influences the oxides produced for porcelain bonding.

Nickel (Ni). Nickel has been selected as the base for alloys because its coefficient of thermal expansion is close to that of gold and because it possesses a resistance to corrosion. It is easier to cast than the cobalt-base alloys. Nickel is the most common metal allergy. If you allergic to “costume jewelry” then you may have a nickel allergy.

Palladium (Pd). Palladium is added to increase the strength, hardness (with copper), corrosion, and tarnish resistance of an alloy. It increases the melting range and improves the sagresistance of a ceramic alloy. Palladium has a strong whitening effect, which renders metals as white alloys. It has a high affinity for hydrogen, and it lowers the density of the alloy slightly.

Platinum (Pt). Platinum increases the strength, melting range, and hardness while it improves the corrosion, tarnish, and sag-resistance of an alloy. It whitens the alloy and increases its density.

Silicon (Si). Silicon serves as an oxide scavenger to prevent the oxidation of other elements during the melt. It is also a hardening agent.

Silver (Ag). Silver imparts a moderate increase in the strength and hardness of an alloy (with copper), tends to tarnish in the presence of sulfur, possesses a rather high affinity for oxygen absorption, and lowers the density of the alloy. In ceramic alloys, silver lowers the melting range by counteracting the influence of palladium. Ceramic alloys with a high silver content may produce discoloration (green or brown) in many porcelains.

Tin (Sn). Tin serves as a hardening agent, tends to decrease the melting range of the alloy, and helps produce an oxide layer in ceramic systems.

Titanium (Ti). Titanium is added to lower the melting range and improve castability. It also acts as a hardener and influences oxide formation.

Zinc (Zn). Zinc helps lower the melting range and acts as a deoxidizer or scavenger to combine with any oxides present. It improves the castability of an alloy and, when combined with palladium, contributes to its hardness. Zinc is commonly included in gold alloy solders.