In restorative dentistry, various materials are used to repair and replace damaged teeth. Among these, metals have historically played a significant role due to their strength and endurance. High noble metals represent a specific category of these materials, valued for their unique properties in creating durable and compatible dental restorations. Understanding their characteristics clarifies their importance in modern dental practices.
What Defines High Noble Metals?
High noble metals are a classification of dental alloys characterized by their specific metallic composition. To be classified as high noble, an alloy must contain at least 60% noble metal elements by weight, with a minimum of 40% of this content being gold. The primary noble metals in this classification are gold, platinum, and palladium. Other noble elements like rhodium, ruthenium, and iridium may also be present.
This classification system for dental casting alloys was proposed by organizations such as the American Dental Association (ADA). The ADA categorizes dental alloys into high noble, noble, and predominantly base metal, based on their noble metal content. Noble alloys require at least 25% noble metals, while base metal alloys contain less than 25%. This standardization ensures consistency and quality in dental materials.
Why Are High Noble Metals Used?
High noble metals are chosen for dental applications due to properties that contribute to restoration longevity and success. They are biocompatible, meaning well-tolerated by the human body. This minimizes the risk of allergic reactions or tissue irritation within the oral environment, as their inert nature promotes healthy interaction with oral tissues.
These alloys also resist corrosion and tarnish. Their chemical stability prevents degradation and the release of ions, ensuring the long-term integrity and appearance of the restoration.
High noble metals possess excellent strength and durability, enabling them to withstand substantial chewing forces. This prevents fracturing or deformation, contributing to long-term functional success. They efficiently absorb and distribute bite forces, further reducing failure risk.
Their casting properties allow for precise margins and an accurate fit. This fit prevents plaque accumulation and reduces secondary decay around the restoration. The malleability of gold, in particular, permits optimal marginal adaptation during cementation.
Dental Uses of High Noble Metals
High noble metals are utilized in various dental restorations where their superior properties are beneficial. Full cast gold crowns are a common application, made entirely from a high noble metal alloy. These crowns offer exceptional longevity, often lasting 20-30 years or more. They are typically used for posterior teeth, where strength and durability are prioritized over aesthetics due to their metallic appearance.
Another application is in porcelain-fused-to-metal (PFM) crowns. Here, a high noble metal substructure provides strength and support, while porcelain is fused to its surface to mimic a natural tooth. This combination balances durability and aesthetics, making PFM crowns suitable for both front and back teeth.
High noble metals are also employed in dental bridges, which replace missing teeth by spanning the gap between existing teeth. The metal framework, often made from high noble alloys, connects artificial teeth (pontics) to crowns placed on adjacent natural teeth. These bridges provide a reliable and stable solution for tooth replacement.
Inlays and onlays, used to repair specific areas of damaged teeth, also utilize high noble metals. An inlay fits within the cusps of a tooth, while an onlay extends over one or more cusps. These restorations are a more conservative approach than full crowns, preserving more natural tooth structure. Precision casting of high noble metals benefits these restorations for a close fit.