Casting alloys can be used to fabricate what 4 things?
inlays
onlays
crowns
bridges
Properties of casting alloys is determined by what?
components
Casting alloys are classified as precious or non-precious based on _______.
composition
Which type of metals resist tarnish and corrosion?
noble metals (in precious alloys)
precious alloys contain _______ metals.
noble
What are 3 noble metals used in dentistry?
gold
palladium
platinum
Which type of metal has base metals that tarnish and corrode, and may be allergenic causing gingival inflammation?
base metals (non-precious alloys)
non-precious alloys contain ______ metals
base
What are 5 base metals used in dentistry?
silver
copper
nickel
tin
zinc
How is gold polished intraorally?
with tin oxide
Occlusal wear is often caused by what?
opposing porcelain restorations
Know conversions for gold:
pure gold = _____; ____ = 1000 fine; 1000 fine = __________
therefore: 500 fine = ____% = ___ karat
100%
100%
24 karat
50%
12 karat
ADA classifies dental casting alloys according to their noble metal content and divides them into 3 categories which are what?
high-noble alloys: contain 60% by weight noble alloys of which gold makes up 40%
noble alloys: don't require gold, but must contain atleast 25% noble metals by weight
base-metal alloys: don't require gold and require less than 25% by weight of noble metals
Name 3 noble metals.
gold: Au
platinum: Pt
palladium: Pd
What is the most corrosive resistant noble metal?
gold (Au)
What are each of the classifications of gold?
karat:
%:
fine:
24
100
1000
What are 3 ways that dental gold casting alloys are classified?
hardness: resistance to penetration
malleability: ability to be shaped
ductility: ability to be elongated by stretching or pulling
The more ductile the alloy, the more the margins can be ________.
burnished
What are 3 reasons that Platinum is not used much in dentistry?
expense
high melting point
difficulty mixing with gold
true or false. Platinum is used often in dentistry.
FALSE. It is NOT used often in dentistry
What are 3 reasons that Palladium is used widely in dentistry?
good corrosion resistance
increases hardness of the alloy
less expensive than gold: although prices have greatly increased because of shortages in the supply of palladium
true or false. Palladium is widely used in dentistry.
TRUE
Silver is considered to be a precious metal, but is it considered noble as well? Why or why not?
NO
because of high tarnish and corrosion in the oral cavity
What metal is added to base-metal dental casting alloys to reduce oxidation DURING CASTING?
zinc (Zn)
What metals are added to base-metal dental casting alloys to increase hardness?
copper and silver
Which metal used in base-metal alloys has the highest incidence of allergic responses?
nickel (Ni)
Why are is Iridium or Ruthenium added to gold-base alloys?
to keep the crystals from growing too large
What are 4 metals (or substructures) that are added to porcelain bonding alloys to form oxides on the metal to bond the porcelain?
indium
iron
gallium
tin
Why are the substructures of porcelain bonding alloys heated at high temperature?
to form oxides on the surface; which forms an oxide layer that the porcelain CHEMICALLY fuses to
How thick is the 'coping' metal that is covered with layers of porcelain? And why must it be this thick?
0.3-0.5 mm thick
to prevent distortion at high temperatures
Why must the 'coping' layer of PFM crowns be convex with no sharp angles?
sharp angles would create stress areas in the overlying porcelain
to make room for a thin metal substructure and layers of porcelain that are at least _________ mm thick in areas under function, these crowns require what?
1.5 mm
requires a greater reduction of the tooth than all-metal crowns
true or false. noble metals are more biocompatible with oral tissues and corrode less than base materials.
both are true
_________ products are responsible for allergenic responses.
corrosion
What metal has the highest incidence of allergenicity?
nickel
The ratio of allergy to nickel is women 10:1, why is this the case?
it is thought that it is related to a prior exposure to nickel in jewelry
Where is the allergic response to nickel most often seen?
in crowns
around free gingival tissues
true or false. Some responses to nickel cause skin reaction even though the source is in the mouth
true
What type of solders are used more often in orthodontics and pediatric dentistry to solder fixed-space maintainer components, and to solder wire components to removable ortho appliances?
SILVER
the ___________ the fineness number, the higher is the gold content, and the _________ the melting point of the solder
HIGHER
LOWER
What is added to both gold and silver solders to lower the melting point range?
tin
Which type of alloy is formed after the metal is cast, is harder and has greater yield strength, and MAY BE ANNEALED (HEAT MODIFIED)?
wrought metal alloys
What material is used for clasps for removable prosthesis?
Wrought wire
How is arch wire (used in orthodontics) held to ortho brackets? (2)
ligature wire
elastics
What are 2 features of REAMERS that differentiate them from files?
fewer twists than files
cut faster
What is the material called that is used to fill and seal root canals so that bacteria will not grow in the space?
gutta percha
What is the purpose of an endodontic post?
to retain the core build up
Which type of post transmits less stress to the root, tapered or parallel?
