Dental crowns are caps placed over a damaged tooth to restore its shape, strength, and appearance. They are fabricated from various materials, including ceramics, porcelain-fused-to-metal, and metal alloys. Gold alloys are valued for their durability and biocompatibility within the mouth. Determining the true gold content of an existing crown requires knowledge of dental materials and specific analysis methods.
Understanding Gold Dental Alloys
The term “solid gold” in dentistry does not refer to pure 24-karat gold, which is too soft and malleable to withstand the immense forces of biting and chewing. Instead, a gold dental crown is made from an alloy, a blend of gold and other metals engineered for superior strength and hardness. These alloys typically range from 16 to 22 karats, meaning the gold content is generally between 67% and 92% of the material.
Gold is intentionally mixed with metals such as palladium, platinum, silver, or copper to enhance its mechanical properties. For example, the addition of copper increases the alloy’s strength and hardness, making it suitable for molars which bear the heaviest chewing load. Common yellow-colored gold crowns are often around 16-karat, offering an optimal balance of resilience and precious metal value.
Dental alloys are formally categorized based on their noble metal content, which includes gold, platinum, and palladium. A “High Noble” alloy, the highest quality classification, must contain at least 60% noble metal, with a minimum of 40% of the total composition being gold. Alloys with a lower precious metal percentage, such as “Noble” (at least 25% noble metal) or “Base Metal” (less than 25% noble metal), are also used, but quality and corrosion resistance decrease with less noble metal content.
Visual and Preliminary Indicators
Before resorting to specialized equipment, several preliminary, non-invasive observations can provide strong indications of a crown’s gold content. The most immediate indicator is the crown’s color and luster, which should be a rich, warm yellow for high-karat gold alloys. Low-karat gold or gold-plated items often possess a duller hue or may show signs of discoloration due to base metals.
The exceptional density of gold alloys is another reliable sign, as gold is significantly heavier than most other metals used in dentistry. A genuine high noble crown will feel noticeably heavy for its size when held, offering a sense of substantial density. Pure gold has a specific gravity of 19.3, and the high-karat alloys used in crowns maintain a high density compared to non-gold alternatives.
A simple magnetic test can help rule out certain non-gold alloys, as high noble alloys containing gold, platinum, and palladium are non-magnetic. If a small, strong magnet attracts the crown, it strongly suggests the presence of magnetic base metals like iron or nickel, which are commonly found in lower-quality, non-noble alloys. This immediate attraction is a quick way to disqualify the material from being a high noble gold alloy.
The way the crown has worn over time is telling, as high noble gold alloys exhibit superior corrosion and tarnish resistance in the oral environment. Gold crowns tend to wear smoothly and evenly, at a rate similar to natural tooth enamel, without chipping or fracturing. A crown that displays significant pitting, dark tarnishing, or signs of flaking is likely a gold-plated or base metal crown.
Professional Verification Methods
To definitively determine the gold content and karat value of a dental crown, professional, laboratory-grade testing methods are necessary. The gold standard for non-destructive analysis is X-Ray Fluorescence (XRF) testing, which uses specialized equipment often referred to as an XRF gun. This device directs X-rays at the crown’s surface, causing the atoms in the metal to emit secondary X-rays with unique energy signatures.
The XRF analyzer precisely measures these energy signatures to identify every element present in the alloy, providing an exact, quantitative breakdown of the composition. This analysis yields the exact percentage of gold, palladium, silver, and other elements, allowing for a verified calculation of the crown’s karat value. This method is highly valued because it delivers immediate and accurate results without causing any damage to the crown.
Another highly accurate verification technique is Specific Gravity Testing, which measures the precise density of the crown by comparing its weight in air to its weight when fully submerged in water. By calculating the crown’s density and comparing it to the known density values for various gold alloys, the gold content can be confirmed. This method is often performed in a laboratory setting and may require the crown to be removed from the mouth for a precise measurement.
The most straightforward method of verification involves reviewing the original paperwork from the dental laboratory that fabricated the crown. Dentists typically receive a laboratory slip or a certificate of authenticity detailing the exact alloy used, including its composition and noble metal classification. Consulting dental records and obtaining this documentation provides a primary, verifiable source for the crown’s material composition.