Dental Materials I. Unit X. Direct and Indirect Metals

Transcription

1 Dental Materials I Unit X Direct and Indirect Metals

2 Indirect Metal - Gold Direct In the mouth Indirect outside the mouth, fabricated in lab or in office

3 Indirect Metal - Gold Advantages most complete restoration available margin adaptability expands & contracts same as tooth structure

4 Indirect Metal - Gold Disadvantages expense to pt esthetics - obvious metallic appearance vanity vs. best function

5 Indirect Metal - Gold Composition pure gold is 100% or 24 karat other metals added for strength copper for hardness silver balances red copper appearance platinum increases strength zinc reduces oxygen content by 0.5%

6 malleable will not tarnish or have pitting in presence of saliva (aka Corrosion) maintains own high polish most ideal restorative produced microleakage minimal very high density compresses very solid and hard Indirect Metal - Gold Properties

7 Indirect Metal - Gold Classifications of Gold/Casting Metals Class I soft for simple inlays Class II medium for multiple surface inlays

8 Indirect Metal - Gold Classifications (cont) Class III hard for crown and bridge Class IV extra hard for partials or Maryland bridge construction chrome cobalt or platinum for strength

9 Indirect Metal - Gold Casting Metals metals used for casting crowns, bridges, inlays or onlays are made of variety or combination of metals Combined 2 or more metals = alloy

10 Indirect Metal - Gold Noble Metals Gold = Au Palladium =Pd Platinum = Pt

11 Indirect Metals Base Metals - Nonprecious base metals contain less than 25% noble metals relatively inexpensive inferior properties: lack resistance to corrosion (pitting and tarnishing)& tarnish in oral environment Iron, tin, zinc & nickel are most common

12 Indirect Metal - Gold Casting Metals - Noble High Noble At least 60% of combined alloy must be noble metal Should consist of 40% gold 20% other noble metals remaining 40% can be base metals

13 Indirect Metal - Gold Casting Metals - Noble Low Noble 25% of combined metals must be noble metals % of gold is not fixed required noble metals can be 1 or a combination of up to 3 noble metals remaining 75% can be base metals

14 Direct Metal Direct Technique - Gold all pure gold must be heated before being inserted into prepared tooth manufacturers place a layer of ammonia gas before shipping does not react with gold protects gold from contamination gold sold as cohesive or non-cohesive

15 Direct Metal Direct Technique - Gold Cohesive Gold gold that welds itself together has protective layer of ammonia keeps out gasses protects it from contamination heat is needed to burn off ammonia will not stick to itself otherwise

16 Direct Technique - Gold Noncohesive Gold Direct Metal not protected with a layer of ammonia Has excess air gas cheaper than cohesive gold will not adhere as easily as cohesive has pits and fibers usually placed in the bottom of preps with cohesive gold on top

17 Direct Metal Direct Technique - Gold Gold Foil Formats for Direct Restorations Foil Mat Powder

18 Direct Metals Gold for Direct Restorations - Foil 4 squares thin sheets 22K or 24K welds to itself to form a bond cohesive most expensive of the three

19 Direct Metal Gold for Direct Restorations - Mat fine gold powder compressed together to form sheet just below melting point compressed into narrow or medium strips 2 long & packaged in cylinders Non-cohesive used in bottom of preps

20 Direct Metal Gold for Direct Restorations - Powder tends to fall apart when handled draws moisture from hands compressed into pellet then - wrapped in sheet of foil least expensive Non-cohesive used in bottom of preps

21 Direct Metal Placement of Gold Foil Annealing (degassing) heating gold removes surface gas (ammonia) & impurities cleans surface

22 Direct Metal Placement of Gold Foil alcohol flame run through flame bright red gold glow immediately into prep Over annealing: gold becomes hard & rigid

23 Direct Metal Placement of Gold Foil Under annealing: makes gold flaky will not stick together not heated long enough to drive off ammonia or impurities

24 Direct Metal Placement of Gold Foil Gold foil trays - electrical units heat 700F for 8-12 minutes Cold welding = 2 clean gold portions heated to lose ammonia condensed

25 Direct Metal Placement of Gold Foil Gold Foil - Condensing three most common methods: 1. pneumatic condensers-handpiece w/ compressed air 2. automatic mallet condenser - spring loaded 3. hand mallet and condenser- mallets taps end of condenser

26 Direct Metal Gold Foil - Finishing gold is condensed into prep compressive strength applied more it is packed, harder it gets Gold foil hardens by welding to itself

27 Direct Metal Gold Foil - Finishing Technique 1) burnish margins 2) use gold files to remove excess 3) finish margins with green stones 4) use brownie or greenie points 5) slurry mix with flour of pumice 6) silicone dioxide for luster

28 Direct Metal Gold Foil - Prognosis Used for Class I, III &V, has long life expectancy

29 Functions of the Commercial Dental Lab Steps in Crown & Bridge Construction 1-5 Principles of Preparing Cases for the Lab Recording: patients name and age, shade, today s date and return date Checking Rx for Completeness Disinfecting & Packaging