Partial Denture Alloys Flashcards Preview

BDS2 CLINICAL Dental Materials > Partial Denture Alloys > Flashcards

Flashcards in Partial Denture Alloys Deck (67)
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1

What are the ideal properties of a partial denture alloy

▪ Rigid (Young's Modulus)
▪ Strong (ultimate tensile strength and elastic limit)
▪ Hard
▪ Ductile
▪ Precise casting (shrinkage)
▪ Melting point (investment material)
process
Density

2

Why is melting point important for partial denture alloys

Partial denture alloys are produced using the casting technique - one of the challenges with this method is that the melting point will dictate the type of investment material that will be used in that casting process

3

What are the partial denture alloys

ADA type IV gold
White gold (Ag-Pd)
Co-Cr
Titanium

4

What properties do we want a denture base to have

a HIGH YOUNG'S MODULUS to withstand forces and maintain its shape in use and a HIGH ELASTIC LIMIT to avoid plastic deformation

5

What properties do we want the denture clasp to have

a LOW YOUNG'S MODULUS to allow flexure over the tooth and can disengage and a HIGH ELASTIC LIMIT to maintain its elasticity over a wide range of movement

6

To compromise the properties we want for a denture base and clasp what do we do

we use THICK SECTIONS for a rigid base and THIN SECTIONS for a flexible clasp

7

What are the ADA specifications of gold alloys

Type I: simple alloys
Type II: larger (2-3 surface) inlays
Type III: crown and bridge alloys
Type IV: partial dentures

8

What is the composition of type 4 gold

Gold (60-70%)

Silver (4-20%)

Copper (11-16%)

Zinc (1-2%)

Palladium (0-5%)

Platinum (0-4%)

9

What does the phase diagram for Au-Cu show

the liquidus and solidus are CONTINUOUS meaning that we can have all sorts of combinations for gold and copper

10

What are the effect of copper as an alloying element in a gold alloy

Solid solution in all proportions
Solution hardening
Order hardening - if 40-80% Gold and correct heat treatment
Reduced melting point
No coring - solidus is close to the liquidus
Imparts red colour (if sufficient quantity)
Reduces density
Base metal so copper is more likely to make it corrode

11

What does the phase diagram for Au/Ag show

This phase diagram shows that any combination of gold and silver can coexist in the same grain structure

12

What are the effect of using silver as an alloying element in a gold alloy

Solid solution in all proportions
Solution hardening
Precipitation hardening with COPPER and heat treatment and this can be used to improve the properties of the materials
Downside is that it can allow tarnishing
Molten silver absorbs gas (CO2) - porosities during casting
It whitens the alloy

13

What does molten silver absorbing gas result in

it creates porosities during the casting process

14

Why is silver whitening the alloy an advantage

compensates for the presence of copper

15

What is the phase diagram for Ag-Cu

shows that it has partial solid solubility
has solubility limit lines

16

Because the Ag-Cu is partially soluble solid solution what can it suffer from

precipitation hardening

17

What is the phase diagram for Au-Pt

straight forward

18

What is the effect of using platinum as an alloying element in a gold alloy

Solid solution with Gold
Solution hardening
Fine grain structure
Coring can occur (wide liquidus-solidus gap)

19

What is the effect of using palladium as an alloying element in a gold alloy

Similar to Pt but less expensive
Less coring than Pt
Coarser grains than Pt
Absorbs gases when molten - porous casting

20

What is the function of zinc in type 4 gold

scavenger

21

What is the function of nickel in type 4 gold

increase hardness and strength

22

What is the function of indium in type 4 gold

fine grain structure

23

Describe the heat treatment for type 4 gold

1) Quench after casting (fine grains)

2) Homogenising anneal (700 degrees Celsius for ten minutes)

3) If cold worked then stress relief annealing is required

4) Heat harden - (order and precipitation) at 450 degrees and then cool slowly through 15-30 minutes to 200 degrees then quench it

24

What are the properties of type 4 gold (heat treated) more suitable for

Its properties more suitable for clasps
You need thickness for the base

25

What are the uses for cobalt chromium

Wires
Surgical implants
Cast partial dentures (connectors)

26

In thick sections what are the properties of COCr

high EL
high YM

27

In thin sections what are the properties of CoCr

High EL, low YM

28

What is the composition of CoCr

Cobalt (35-65%)

Chromium (25-30%)

Nickel (0-30%)

Molybdenum (5-6%)

Carbon (0.2–0.4%)

29

What are the effects of cobalt on the alloy

Forms solid solution with chromium
Increased strength, hardness, rigidity
CORING possible

30

What are the effect of chromium on the CoCr alloy

Forms solid solution with cobalt
Increased strength, hardness, rigidity
Coring possible
Forms passive oxide layer, corrosion resistance