A dental crown is a tooth-shaped cap used in restorative dentistry to cover a damaged or decayed tooth, restoring its shape, strength, and appearance. Crowns are cemented onto the existing tooth, completely encasing the visible portion that sits above the gum line. The term “gold crown” refers to a highly durable, biocompatible restoration material chosen for its longevity and excellent performance under chewing forces.
Why Pure Gold Is Not Used in Dentistry
Pure gold, known as 24-karat gold, is too soft and malleable to withstand the immense and constant pressure of chewing, or mastication, within the mouth. If a crown were made from this pure form, it would quickly deform or wear down, compromising the structural integrity of the restoration. Dental materials require a high degree of tensile strength and hardness to resist distortion over many years of use.
To achieve the necessary mechanical properties, gold must be combined with other metals to create an alloy. This alloying process significantly increases the hardness of the material, making it resistant to wear against the opposing teeth. The resulting gold alloy also maintains gold’s natural resistance to corrosion and tarnish in the oral environment, ensuring the crown remains stable and non-reactive.
Classification of Gold Dental Alloys
The term “gold crown” is actually a common way to describe a crown made from a gold-containing alloy, which is a specialized mixture of metals. Dental alloys are classified based on their noble metal content, which includes elements like gold, palladium, and platinum that resist corrosion and oxidation. Silver, while often called a precious metal, is not considered noble in the oral cavity due to its tendency to tarnish.
High Noble Alloys
These alloys represent the highest quality classification, requiring a minimum of 60% noble metal content by weight. At least 40% of the total alloy must be pure gold. The high concentration of gold and other noble metals, such as palladium and platinum, provides superior corrosion resistance and excellent biocompatibility. These alloys are considered the most desirable for dental restorations due to their proven durability and low potential for adverse reactions.
Noble Alloys
Noble Alloys must contain a total noble metal content of 25% or more by weight. While they contain less gold than High Noble Alloys, they still offer good resistance to tarnish and corrosion, making them a reliable option for crowns. The remaining composition often includes silver, copper, or palladium, which are added to enhance the material’s strength and manage costs.
Predominantly Base Metal Alloys
Predominantly Base Metal Alloys contain less than 25% noble metal content, often including only trace amounts of gold, if any. These alloys rely heavily on non-noble metals like nickel, chromium, or cobalt for their strength and structure. Nickel and chromium are often used to provide high stiffness and hardness, allowing for thinner crown walls. While these alloys are significantly less expensive, they may possess a higher potential for corrosion compared to the noble classifications. The non-noble metals included in all dental alloys serve specific purposes to optimize the crown’s performance. Copper is a common additive that provides increased hardness, while zinc is frequently incorporated as an oxygen scavenger during the casting process.