Metals Used Flashcards
What are the three base metal alloys (conventional)
cobalt-chromium
nickel-chromium
cobalt-chromium-nickel
This metal can be processed at some dental labs for RPD frameworks; their densities are much lower than conventional base metal alloys, and they have a high strength: weight ratio
titanium and titanium alloys
What was the first base metal allow in dentistry
vitallium
The important difference between hardened gold and base metal RPD alloys is what property
modulus of elasticity; the amount of deflection for RPD framework at the same force will be about half as much for base metal alloys compared to gold alloys
What are four advantages of base metal alloys for RPD framework
cost (lower than gold)
density (much less than gold)
high elastic modulus and yield strength
excellent corrosion resistance
What is meant by the high elastic modulus and yield strength of base metal alloys
minimizes bending deflection over long spans and minimizes permanent deformation
What are four concerns with base metal casting alloys
limited ductility and rapid work hardening can cause fracture during clasp adjustment
greater hardness than enamel
high speed finishing equipment needed
induction melting may be required
Why do base metals require a high temperature investment
there is greater casting shrinkage than gold alloys, which require compensation by the greater investment expansion due to a high melting point
Which will have more casting defects, base metal alloys or gold alloys
base metal alloys
Dominant microstructure of RPD alloys is this, which is showing different types of parallel or approximately parallel features
dendritic
Fracture typically occurs where, cause of variations in ductility
at a weaker boundary regions between dendrites
True or False
dendritic microstructure is not desirable
True
For uniform beams (in regards to clasps), deflection at given force is directly proportional to what and inversely proportional to what
directly proportional to length and inversely proportional to elastic modulus
*high modulus = less deflection
Which is more flexible, gold alloys or chromium cobalt alloys; for both the bar and CC clasps
gold alloys
What is the approximate permitted flexibility of gold alloy compared to base metal alloy
twice that
What is the elastic modulus of gold alloy compared to base metals
gold alloy elastic modulus is about half of that as base metals, which is why gold is twice as flexible with permanent deformation
Noble wrought allows were classified according two types according to what three things
noble metal content
fusion temperature
mechanical properties
The strength is higher (about 25%) for which kind of clasps; wire clasps of clasps cast with framework
wire
To achieve desirable mechanical properties, wrought (wire) microstructure must be retained during what
heating for soldering or when casting RPD framework; must avoid overheating that causes recrystallization and loss of wire structure, which degrades mechanical properties of clasp
Noble metal wire partial dentures cannot be what to improve mechanical properties
heat-treated
What is an example of noble meal wires
platinum-gold-palladium
What is the composition of base metal wire clasps
ticonium wire with cobalt, chromium, tungsten, and nickel are major composition components
True or False
base metal wire clasps cannot be heat-treated to improve mechanical properties
True
This is considered the most biocompatible metal (surface oxide) and has half the density of base metal RPD alloys
titanium
What is required to use titanium in RPDs
special and expensive dental casting machines and only available in a few dental labs; arc-melting in vacuum or inert atmosphere employed because high tendency to undergo oxidation in air
This type of burnout is needed to minimize reaction with titanium and formation of very hard surface region (ɑ case)
low-temperature
Which has a lower density, titanium or Co-Cr alloys
titanium
Co-Cr alloys have comparable strength to what
hardened gold alloys
This metal causes skin irritation, and its important to check medical history of the patient (knowledge about skin irritation from eyeglasses or jewelry)
nickel
This metal can cause severe problems with the respiratory system and its important for adequate ventilation in the dental laboratory to remove dust from finishing and fume from casting
beryllium
What is beryllium used for
its added to allow composition to reduce melting temperature of Ni-Cr alloys and make easier to cast
This technology is much labor intensive and use biocompatible Co-Cr alloy which avoids the Ni allergy, also aids in the difficultly of casting higher melting Co-Cr alloys
laser sintering (3D printing, CAD/CAM)
How does laser sintering work
CAD or STL image files from scanned part used with high-power laser to fuse particles layer-by-layer on powder bed of allow and build up part rapidly
