Metals and Alloys in Dentistry - 2.5 PDF

**[Metals and alloys - 2.5]** Metals - elements that readily lose electrons to form positive ions and have metallic bonds Alloys - mixtures of two or more metals, or metals with non-metals, designed to have enhanced properties **Characteristics of metals** Physical properties - - - Chem...

**[Metals and alloys - 2.5]** Metals - elements that readily lose electrons to form positive ions and have metallic bonds Alloys - mixtures of two or more metals, or metals with non-metals, designed to have enhanced properties **Characteristics of metals** Physical properties - - - Chemical properties - - **Metallic bonding** Delocalised electrons = valence electrons not bound to any specific atom Sea of electrons = atoms can slide over each other - malleable Alloys = combination of metals to achieve desired properties not found in pure metals Types of alloys: 1. 2. **Benefits of dental alloys** Improved mechanical properties Tailored physical properties eg adjusting mpt and thermal expansion Enhanced biocompatibility - reduced allergenic and improved tissue response Common dental metals Gold = v good malleability and corrosion resistance Silver = high thermal conductivity and ductility Used as a component in dental alloys Titanium = high strength to weight ratio and biocompatibility Used for dental implants and ortho wires Common dental metals Amalgam = alloy of mercury with silver, tin, copper Used for fillings Gold alloys = gold with copper, silver, palladium Used for crowns, bridges, inlays Base metal alloys = nickel-chromium, cobalt-chromium alloys Used for partial denture frameworks, orthodontic wires **Fundamental metallurgical principles** **Crystal structure =** ordered arrangement of atoms in a metal , affects mechanical properties eg ductility and strength Types 1. 2. 3. **Phases =** different structural forms of material each with distinct physical properties, predicts how alloys behave under diff conditions Types 1. 2. Phase diagrams are visual representations of phases at different temps and compositions Eutectic point = lowest melting point of an alloy system Solidus and liquidus lines = boundaries between solid and liquid phases **Alloying in dentistry** Purpose: - - - Common alloying elements: - - - - - **Relationship between metallurgy and properties** Crystal structure impact - - Phase influence - - Alloying effects - - **Classification of dental alloys** By composition - - - By structure - - By application - - -  High noble alloys *Composition* - gold (primary component, palladium and platinum added for strength *Characteristics* - v good corrosion resistance (prevents ion release and tarnishing, reduces tissue irrigation), highly compatible with oral tissues *Applications* - crowns, bridges, inlays, onlays Noble alloys *Composition* - gold, palladium, silver *Characteristics* - good corrosion resistance, balanced strength and ductility *Applications* - PFM restorations (compatible with thermal expansion with porcelain) and metal frameworks (for fixed and removable prostheses) Base metal alloys *Composition* - nickel, chromium, cobalt *Characteristics* - higher strength and hardness than noble alloys, more economical but nickel can cause reaction *Applications* - partial denture frameworks (high rigidity) and ortho wires (elasticity and formability) **Noble metals in dentistry** Gold - malleable, ductile, corrosion resistant *Use* - high noble alloys for crowns and bridges Platinum and palladium - increases alloy strength and melting point *Use* - added to gold alloys for durability - - **Base metals in dentistry** Nickel - strengthens alloys but can cause allergy Chromium - corrosion resistance via oxide layer Cobalt - enhances hardness *Advantages* - strong so allows for thinner designs *Limitations* - higher melting point **Corrosion** Types: - - Prevention - - - **Biocompatibility** Allergic reactions - nickel sensitivity affects up to 10% of pop Tissue response - passive oxide layers (Cr and Ti form layers which reduces ion release and tissue irritation) Regulatory standards - ISO (guidelines for composition and safety) **Summary** §Metals and alloys are fundamental materials in dentistry, providing strength and durability. §Metallic bonding and crystal structures (BCC, FCC, HCP) determine metal properties. §Alloying enhances metal properties, making them more suitable for dental applications. §Metallurgical principles influence mechanical and physical properties like strength and corrosion resistance. §Dental alloys are classified by composition (high noble, noble, base metals), structure, and application. §Noble metals (gold, palladium, platinum) offer excellent corrosion resistance and biocompatibility. §Base metals (nickel, chromium, cobalt) provide high strength but may pose allergy risks.