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BDS3 Dental Materials > Caring waxes and loss wax technique > Flashcards

Caring waxes and loss wax technique Flashcards

https://www.youtube.com/watch?v=2OTGeRCScYc

1
Q

What are boxing waxes?

A

used to retain the gypsum when it is poured into the impression

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2
Q

What are beading waxes used for?

A

used to block out undercuts

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3
Q

Qhy are waxes ideal?

A

can be moulded easily to the shape required

can be easily removed after gypsum has set

relatively inexpensive

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4
Q

What temp can boxing and beading waxes retain their shape?

A

35 dc

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5
Q

What are carving (presentation) wax good for?

A

diagnostic wax up, show patient

laid down in pt model

more easily visualised by pt

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6
Q

What 2 material scanbe used for presentation wax?

A

inlay wax and carving wax

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7
Q

Qhat wax is mainly used as the prototype?

A

inlay

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8
Q

What technique is used for inlay wax?

A

lost wax technique

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9
Q

constituents oif inlay wax

A

paraffin (60%)

ceresin

carnaba

candeilla

beeswax

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10
Q

What are the 3 types of inlay waxes?

A

hard
medium
soft

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11
Q

What is a positive of inlay waxes?

A

high level of detail and dimensional accuracy required

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12
Q

What does stress releif lead to?

A

distortion of pattern and final resto will not fit

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13
Q

What temp should you eat wax to?

A

45-50 dc

20 mins

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14
Q

What colour are inlay waxes?

A

green, dark blue, purple

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15
Q

When wold you use pattern waxes?

A

to construct the wax ‘framework’ which then forms the metal skeleton/baseplate

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16
Q

What re the 2 types of inlay waxes?

A

prefabricated - in the shape of clasps etc

uniform thickness for the baseplate for a denture

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17
Q

What are the properties of preformed wax patterns?

A

slightly sticky - can be repositioned on model

need to be very ductile

must burn out with no residue below the casting temp of the alloy used

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18
Q

Why do you need to burn out wax?

A

no residue - no carbon incorporated in

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19
Q

What does a baseplate/modelling wax form?

A

base of a denture

pink in colour

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20
Q

What do you use the lost wax technique for?

A

fixed prosthodontic restorations:

inlays
onlays
crowns
bridges
removable prostheses

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21
Q

What temp is the wax pattern designed to burn out at?

A

below 600dc

22
Q

What is the initial step in the lost wax technique?

A

wax pattern is made which corresponds to the shape of the object

23
Q

What is the goal of the lost wax technique?

A

wax form to metal tooth to be placed in pt mouth or denture

with similar features to the wax

24
Q

Describe what is going on here

A

wax pattern placed over DIE

sprue allows metal to flow in to the mould cavity - under high pressure

25
Q

What is the die?

A

tooth prepped for crown

impression

a model of an individual prepared tooth - DIE

  • this is a positive impression

take impression and take to lab

26
Q

What is the crucible formed?

A

a structure which you place the sprue attached to the wax mould

27
Q

What has been placed over the crucible and wax casting?

A

casting ring

open at top end

28
Q

what is placed inside the casting ring?

A

casting ring liner

29
Q

What gets brined out during burn out process?

A

casting ring liner

wax

30
Q

Purpose of burnout phase?

A

not just a means to remove wax from the investment; it also cures the investment in preparation for the thermal shock of the metal entering the pattern cavity.

31
Q

What is the investment material?

A

form of alloy

poured into casting ring - before burnout phase

32
Q

What is the purpose of the resevoir?

A

compensate of the cooling and contraction of the metal alloy that’s started to cool

33
Q

What is the metal casting ring lined with?

A

piece of lining material

aluminium silicate ceramic or cellulose lining paper liner

34
Q

What is the purpose of the lining material in the casting ring?

A

help to counteract the effects of the expansion of the investment during the heating phases

35
Q

Where should the wax pattern be situated in the casting ring?

A

hottest part of the ring (thermal centre)

longest possible flow time

36
Q

What happens of the wax is to high up in the casting ring?

A

rupture the investment causing casting failure

due to air moving through microporosities in the investment

37
Q

Do you wet the wax before placing in the casting ring?

A

sprayed with a wetting solution to reduce surface tension and prevent inaccuracies due to air entrapment

38
Q

What do you pour the investment into the casing ring on?

A

vibrating plate

39
Q

What are methods the alloy is heated?

A

naked flame e.g. oxyacetylene torch (if less than 1200 dc)

or by using electric induction casting machine

40
Q

What alloys are quenched?

A

noble alloys

becomes granular and causes it to fracture

facilities burnishing and polishing

41
Q

What happens if the golf is left to cool?

A

harder, stronger casting results but this makes the alloy more difficult to finish

42
Q

When do you remove the casting form the alloy?

A

after cooling

43
Q

How do you remove surface oxides form the crown after removing the investment?

A

sandblasting

44
Q

What is the advantage of the lost wax process?

A

high level accuracy

dimensional change less than 0.05%

45
Q

Why can the cast come out smaller than expected?

A

due to the mould not having been heated sufficiently

46
Q

Why may the casting be distorted?

A

can be due to the wax pattern being damaged during the investing process or by incorrect sprue placement preventing the metal flowing to the extremities of the mould

47
Q

How can you prevent distorting\/

A

thickening of the wax margins

48
Q

How would you melt base metal alloys?

A

electric induction heating

melt at 1200-1500 dc

49
Q

What happens if the alloy is cooled quickly?

A

coring

this is variable metals in the same alloy

electrolytic metals and prone to corrosion/weakness

50
Q

How to overcome coring?

A

homogenisation treatment

reheat alloy and cool slowly

51
Q

gaseous porosity?

A

dissolve oxygen when heated

metal voids

oxygen incorporated when alloy is heated/molten

BDS3 Dental Materials (3 decks)

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