Noble Metal
A group of precious metals—principally gold, platinum, palladium, and rhodium—characterised by high corrosion resistance, used in dental casting alloys and their classification per ADA/ISO standards.
Full Definition
In dental materials terminology, noble metals are defined by the ADA and ISO standards as those metallic elements (gold, platinum, palladium, rhodium, ruthenium, iridium, and osmium) that resist oxidation and corrosion under oral conditions. This categorisation underpins the ADA classification of dental casting alloys into high noble (≥60 wt% noble metals including ≥40 wt% gold), noble (≥25 wt% noble metals), and predominantly base metal (<25 wt% noble metals). Editors should be alert to the common error of using 'precious metal' and 'noble metal' interchangeably; while all precious metals overlap substantially, the classification systems use specific noble-metal thresholds. Content reporting alloy compositions should adhere to weight-percentage notation.
Usage
Usage note: When reporting alloy classifications, use the ADA three-tier nomenclature (high noble / noble / predominantly base metal) and express compositions in weight percentage (wt%), not volume percentage.
In Context
- "The alloy was classified as 'noble' because its noble metal content reached 38 wt%, falling below the high-noble threshold." — Restorative dentistry product data sheet
- "Editors should not substitute 'precious metal' for 'noble metal' in ADA classification contexts, as the terms carry distinct compositional thresholds." — Editorial style guide for dental journals