Dental casting alloy's, Study notes of Dentistry

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DENTAL CASTING

ALLOYS

Dr. Sanket Jadhav

Metal restorations and prostheses are an integral part of dentistry. Metals and its alloys are among the strongest materials and provide strength and durability to any structure.

• (^) Terminologies NOBLE METALS-
• (^) Resistance to corrosion.
• (^) Used for inlays, crowns and FDPs.
• (^) Gold, platinum, palladium, rhodium, ruthenium, iridium, osmium, and Silver PRECIOUS METALS-
• (^) The term precious indicates the intrinsic value of the metal.
• (^) The eight noble metals are also precious metals and are defined so by major metallurgical societies and federal government agencies, e.g. National Institute of Standards and Technology and National Material Advisory Board.

Gold Pure gold is a soft and ductile metal with a yellow ‘gold’ hue. It has a density of 19.3 g/cm3 and a melting point of 1063 °C. Gold has a good luster and takes up a high polish. It has good chemical stability and does not tarnish and corrode under normal circumstances. Silver Sometimes described as the ‘whitest’ of all metals. It has the lowest density (10.4 g/ cm3 ) and melting point (961°C) among the precious casting alloys. Its CTE is 15.7 × 10-6/°C which is comparatively high. ( In large amounts, it increases tarnish) Palladium Density is 12.02 g/cm3. Palladium has a higher melting point (1552°C). It hardens and whitens the alloy. Platinum It has the highest density (21.65 g/cm3 ) highest melting point (1769°C) and the lowest CTE among the four precious metals. Increases strength and corrosion resistance.

CLASSIFICATION OF DENTAL CASTING

ALLOYS

According to use

a. Alloys for all metal and resin veneer restorations eg. Inlays,posts,resins(acrylic) and composite veneered crowns b. Alloys for metal ceramic restorations eg. PFM crowns & FDPs c. Alloys for removable dentures

Based on yield strength and percent elongation a. Type I Soft b. Type II Medium c. Type III Hard d. Type IV Extra Hard This 1934 classification was originally intended for gold alloys and were based on hardness.Types I and II are known as ‘inlay alloys’ and Types III and IV are known as ‘crown and bridge alloys’. Type IV is occasionally used for RPD frames)

Based on mechanical properties a. Type 0 – Intended for low stress bearing single tooth fixed restorations eg. Small veneered one-surface inlays , veneered crowns b. Type 1 – Intended for low stress bearing single tooth fixed restorations eg. Veneered or unveneered one-surface inlays, veneered crowns c. Type 2 – Intended for single tooth fixed restorarions eg. Crowns or inlays without restorations on no. of surfaces d. Type 3 – Intended for multiple unit fixed restoration eg, bridges e. Type 4 – Intended for appliances with thin sections that are subject to very high forced eg. Removable partial dentures, clasps, wide span bridges implant retained superstructures. f. Type 5 – Intended for appliances in which parts require the combination of high stiffness and strength eg. Thin removable partial dentures

According to major elements a. Gold alloys b. Silver alloys c. Palladium alloys d. Nickel alloys e. Cobalt alloys f. Titanium alloys

According to the number of alloys present a. Binary- two elements b. Tertiary- three elements c. Quaternary- four elements

CLASSIFICATION ACCORDING TO USE

OF DENTAL CASTING ALLOYS

1. Alloys for all metal and resin veneer restorations: - High noble
   • Noble
   • Predominantly base metal
   • Base metal
2. Alloys for metal-ceramics restorations
   • High noble
   • Noble
   • Predominantly base material
   • Base metal
3. Alloys for casting large structures
   • High noble
   • Noble
   • Predominantly base material
   • Base material

According to use a. Alloys for all metal and resin veneer restorations eg. Inlays,posts,resins(acrylic) and composite veneered crowns b. Alloys for metal-ceramic restorations eg. PFM crowns & FDPs c. Alloys for removable dentures

a. Alloys for all metal and resin veneer restorations These alloys were among the earliest alloys available to dentistry. The early alloys were mostly gold alloys. Since they were intended for all-metallic and later for resin/acrylic veneered restorations, they just had to meet the basic requirements. Currently, the use of these alloys are slowly declining because of

• (^) Increased esthetic awareness has reduced the trend for metal display.
• (^) Increasing popularity of all-ceramic and metal-ceramic restorations. Reducing popularity of resin and composite as veneering material.

a. Alloys for all metal and resin veneer restorations USES:

• (^) Inlays and onlays
• (^) Crowns and FDPs
• (^) Partial denture frames
• (^) Post-cores

a. Alloys for all metal and resin veneer restorations

• (^) High noble — Gold alloys
• (^) Noble — Silver palladium alloys
• (^) Base metal — Nickel-chrome alloys Cobalt-chrome alloys Titanium and its alloys Aluminum-bronze alloys