Metals Used

Question 1

What are the three base metal alloys (conventional)

Answer 1

cobalt-chromium
nickel-chromium
cobalt-chromium-nickel

Question 2

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

Answer 2

titanium and titanium alloys

Question 3

What was the first base metal allow in dentistry

Answer 3

vitallium

Question 4

The important difference between hardened gold and base metal RPD alloys is what property

Answer 4

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

Question 5

What are four advantages of base metal alloys for RPD framework

Answer 5

cost (lower than gold)
density (much less than gold)
high elastic modulus and yield strength
excellent corrosion resistance

Question 6

What is meant by the high elastic modulus and yield strength of base metal alloys

Answer 6

minimizes bending deflection over long spans and minimizes permanent deformation

Question 7

What are four concerns with base metal casting alloys

Answer 7

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

Question 8

Why do base metals require a high temperature investment

Answer 8

there is greater casting shrinkage than gold alloys, which require compensation by the greater investment expansion due to a high melting point

Question 9

Which will have more casting defects, base metal alloys or gold alloys

Answer 9

base metal alloys

Question 10

Dominant microstructure of RPD alloys is this, which is showing different types of parallel or approximately parallel features

Answer 10

dendritic

Question 11

Fracture typically occurs where, cause of variations in ductility

Answer 11

at a weaker boundary regions between dendrites

Question 12

True or False

dendritic microstructure is not desirable

Answer 12

True

Question 13

For uniform beams (in regards to clasps), deflection at given force is directly proportional to what and inversely proportional to what

Answer 13

directly proportional to length and inversely proportional to elastic modulus
*high modulus = less deflection

Question 14

Which is more flexible, gold alloys or chromium cobalt alloys; for both the bar and CC clasps

Answer 14

gold alloys

Question 15

What is the approximate permitted flexibility of gold alloy compared to base metal alloy

Answer 15

twice that

Question 16

What is the elastic modulus of gold alloy compared to base metals

Answer 16

gold alloy elastic modulus is about half of that as base metals, which is why gold is twice as flexible with permanent deformation

Question 17

Noble wrought allows were classified according two types according to what three things

Answer 17

noble metal content
fusion temperature
mechanical properties

Question 18

The strength is higher (about 25%) for which kind of clasps; wire clasps of clasps cast with framework

Answer 18

wire

Question 19

To achieve desirable mechanical properties, wrought (wire) microstructure must be retained during what

Answer 19

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

Question 20

Noble metal wire partial dentures cannot be what to improve mechanical properties

Answer 20

heat-treated

Question 21

What is an example of noble meal wires

Answer 21

platinum-gold-palladium

Question 22

What is the composition of base metal wire clasps

Answer 22

ticonium wire with cobalt, chromium, tungsten, and nickel are major composition components

Question 23

True or False

base metal wire clasps cannot be heat-treated to improve mechanical properties

Answer 23

True

Question 24

This is considered the most biocompatible metal (surface oxide) and has half the density of base metal RPD alloys

Answer 24

titanium

Question 25

What is required to use titanium in RPDs

Answer 25

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

Question 26

This type of burnout is needed to minimize reaction with titanium and formation of very hard surface region (ɑ case)

Answer 26

low-temperature

Question 27

Which has a lower density, titanium or Co-Cr alloys

Answer 27

titanium

Question 28

Co-Cr alloys have comparable strength to what

Answer 28

hardened gold alloys

Question 29

This metal causes skin irritation, and its important to check medical history of the patient (knowledge about skin irritation from eyeglasses or jewelry)

Answer 29

nickel

Question 30

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

Answer 30

beryllium

Question 31

What is beryllium used for

Answer 31

its added to allow composition to reduce melting temperature of Ni-Cr alloys and make easier to cast

Question 32

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

Answer 32

laser sintering (3D printing, CAD/CAM)

Question 33

How does laser sintering work

Answer 33

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