1. Metals in dentistry
Dental material

2. General information Alloy: a mixture of two or more metals
Pure metals are rarely used in dentistry because they are weaker than they are when mixed with other metals.

3. All metal casting Classification of cast restorations:
Intra-coronal (e.g. inlay)
Extra-coronal (e.g. crown)
Cast metal alloys can be used for bridges, partial dentures

4. Cast metal restorations

5. NOBLE METALS & ALLOYS
NOBLE METALS ARE ELEMENTS WİTH A GOOD METALLİC SURFACE THAT RETAİN THEİR SURFACE İN DRY AİR. THEY HAVE A GOOD RESİSTANCE TO OXİDATION , TARNİSH AND CORROSION DURİNG HEATİNG.
Group A
Ruthenium 2310c
Rhodium 1966c
Palladium 1553c
a.w. 100
12/13 g/cm3
Group B
Osmium
Iridium
Platinium
Gold
a.W 190
19-23 g/cm3
GOLD
PLATİNUM
PALLADİUM
IRIDIUM
RHODIUM
OSMIUM
RUTHENIUM

6. GOLD Soft, malleable, ductile Yellow.
İt must alloyed with silver or palladium
Small amounts of impurities have a pronounced effevt on the mechanical properties of gold and its alloys.
%0.2 lead = brittle
Calcium = improves the mechanical prop., of gold foil.
It can be produced as foil by a process known as gold beating mm

7. Platinum Bluish white metal Ductile and melleable
Has a widw using area in dentistry
as ametal for metal reinforced ceramics
As posts and pins
Adda greatly to the hardness and elastic qualities of gold.

8. Palladium White metal but darker than platinum
Its density little more than half that of platinum and gold
Is not used in the pure state in dentistry

9. Classification of dental casting alloy (ADA)
High noble alloys: What does noble mean?
Gold-platinum Does not corrode readily
Gold-palladium
Gold-copper-silver High noble: at least 60% noble
Noble alloys: (Au, Pd, Pt). 40% of which is gold.
Silver-gold-copper The remaining 40% is base metal
Palladium-copper (precious metals)
Silver-palladium Noble: at least 25% noble (no gold
Base metal alloys requirements). 75% base metal
Ni-based (semiprecious)
Co-based
Ti-based

10. Gold alloys (Au) Most corrosion resistant
Pure gold is 24 karat, 100%, or 1000 fine (percentage * 10)
Pure gold is too soft, so, gold alloys were mostly used
Gold alloys classified:
Hardness (resistance to penetration)
Malleability (ability to be shaped by tapping)
Ductility (ability to be elongated)
The higher the gold content in gold alloys, the more burnishing can be accomplished.

11. Platinum is not used much because:
Too expensive
High melting point
Difficult to mix with gold
Palladium is used more widely because:
Good corrosion resistance
Increases hardness of alloy
Silver is precious but not noble because it corrodes.

12. Base metal alloys < 25% noble metal
Primary base metals (non-precious):
Copper
Silver
Nickel
Tin
Zinc: added to decrease oxidation
Titanium
Stiffer than gold alloys, higher stress resistance
Added to gold alloy to increase hardness

13. Base metal alloys Drawbacks: Difficult to finish and cut
More equipment to manufacture
Higher casting temperature
Biocompatibility issues

14. Crystal formation
Alloys start to form crystals as they cool down after being poured into molds.
Small crystals produce better qualities than larger ones
Some alloys such as gold maybe reheated (annealing) to improve properties
Reheating base metal alloys is not recommended.

15. Porcelain bonded alloys
High noble
Noble
Base metal
Composition is slightly modified to make them more compatible with porcelain. How?
Blended and mixed to withstand high temperature when porcelain is fired ( °C)
Small amounts of indium and tin are added to form oxides on metal surface to which porcelain is bonded
Silver and copper is not used to avoid green staining of porcelain

16. Porcelain bonding alloy
When PFM restorations are constructed, layers of porcelain are fired in an oven on the metal base to cover the metals’ dark color
Body and incisal porcelain are added in layers to simulate enamel and dentine colors and translucency.
Porcelain and metal should have compatible rates of thermal expansion or porcelain will crack.

17. Removable prosthetic casting alloys
Base metals used
Cobalt
Iron
Titanium
Beryllium
*Chromium
Gallium
*Nickel
Carbon
Aluminium
molybdenum
Vanadium

18. Continue,
Components are attached to prosthesis (precision and non precision attachments, bars) made from metal alloys :
High noble
Noble
Base metal

19. Biocompatibility
Noble metals are more biocompatible than base metals because they corrode less (corrosion products can cause allergy):
Nickel is associated with allergy (9-12% of population), especially in women
Seen on free gingival tissue in contact with metal
Mostly more sever with fixed prosthesis
Skin response may occur

20. Continue,
Beryllium, added to Ni-Cr to reduce fusion temperature and create smaller crystals:
Can also cause allergy.
Inhalation can cause lung disease called berylliosis

21. Solders Gold solders Silver solders Join bridge units
Alloys that are used to join metals together or repair cast restorations
Gold solders
Silver solders
Join bridge units
Used in ortho., paedo.
Add contacts
Solder fixed space maintainer components
Correct marginal deficiencies
Close holes from occlusal adjustment
Solder wire components to removable ortho. appliances

22. Solders
The solder alloy should have a lower melting temperature than the cast restoration.
For gold solders, the higher the gold content the lower the melting range.
For silver solders, tin is added to lower melting temperature and improve flow. Silver solders produce stronger joints and need lower heat to melt so they do not weaken the wire adjacent to solder joint.
Soldering procedure: the components to be joined are invested in a special soldering investment gypsum in the proper relationship. A flux is added to remove oxides and improve flow of solder alloy. (containing borax). Alloys are heated until red, then solder is added until it melts and flows to cover exposed area.

23. Welding
Process of fusing two or more metal parts through the application of heat, pressure, or both, with or without a filler metal, to produce a localized union across an interface between the parts.
The welded point is susceptible to corrosion
In soldering no fusion occurs, the gap between the two joint parts is filled with molten metal.

24. Wrought metal alloys
Are alloys that have been mechanically changed into another form (can be shaped as a flat plate, or wire).
The resulting alloy, is harder and has a greater yield strength (point at which a force produces permanent deformation).
Resistance to deformity can be modified by heating, annealing.

25. Wire
Is a wrought metal which can be soft and easily shaped or may resist bending as does as spring.
Used for clasps in partial dentures
Stainless steel (iron, carbon and traces of Mn, Cr, Ni to resist tarnish and rust)
Platinum-gold-palladium (PGP)
Arch wires and ligature used in orthodontic appliances
Arch bars and ligature wires used in oral surgery for fracture stabilization

26. Endodontic files and reamers
Example of wrought metal alloy which have been twisted to produce cutting edges
Stainless steel
Nickel-titanium (more flexible)
Reamers are similar to files but with fewer twists and cut faster

27. Endodontic files

28. Metals used in orthodontics
Wires:
composed of base meta, stainless steel, cobalt-chrome-nickel, titanium, titanium-nickel.
Able to resist deformity. This resistance creates ‘memory’ in the wire, so it tries to reassume its original shape. That enables the wire to move teeth.
Wires have different diameters (gauge), the thicker the wire the smaller the gauge

29. Brackets and bands Cemented on teeth with bonding resin
Retain the arch wire that has been shaped by the orthodontists to guide the teeth into new position. The wire is held to brackets and bands by ligature wire or elastics
Made from stainless steel, the bracket has a slot into which the wire fits and 4 wings to hold the ligature or elastics

31. Lingual retainer:
Used to maintain the position of teeth after orthodontic treatment
Adapted to the lingual surface of anterior teeth and bonded with composite.

32. Implant materials
Used as anchors for prosthetic replacement of missing teeth
One or more single units as crowns or bridges
Support for dentures
Three main types:
Subperiosteal
Transosteal
Endosseous

34. A: Subperiosteal
B: Transosteal
C: Endosseous

35. Continue,
These implants are made of titanium or titanium alloy, used for its biocompatibility:
Pure titanium is not as rigid as the alloy
These implants are retained by intimate contact with bone (osseointegration)
Some implants are coated with Calcium phosphate (hydroxyapatite) or plasma proteins to improve osseointegration

36. Placement and restoration
Incision and bone exposure
A hole is drilled that is slightly smaller than implant cylinder size so when implant is placed it will have a frictional fit with bone. Excessive heat should be avoided
Permanent restoration is attached to implant core with a screw made of gold alloy

38. Maintenance

39. Endodontic posts Posts are metal or nonmetal rods placed in root canal
The purpose of a post is to retain the core build up over which the crown is placed
Classification:
Active, engages canal surface with threads
Passive post, cemented into the canal space
Classification by shape:
Parallel
Tapered

40. Classification by material:
Metal
Nonmetal
Classification by manufacturing method:
Custom made: made from a wax or resin pattern made directly on tooth or indirectly in lab. Using lot wax technique. Core attached
Preformed:
They rely for retention on shape, diameter, length, and cementation.
Come in kits with drills specific to size of post
Core not attached, need to be made from amalgam, composite, hybrid GIC

42. Lectures included in the midterm exam next Thursday
Amalgam
Composite
Glass ionomer cements
Adhesives in dentistry
Dental cements

43. End of part one References: Chapter 8 metals in dentistry
Dental materials, clinical applications for dental assistants and dental hygienists