Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BDS3 DMS > BDS2 Acrylic Resin > Flashcards

BDS2 Acrylic Resin Flashcards

1
Q

What are denture bases often made of?

A

Acrylic resin (PMMA)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Often dentures done fit the patient first time, what sources of error might there be?

A

Production: -initial impression is flawed - material and method not 100% -curing process: several poten tial error sources

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What error sources might lead to an acrylic resin (PMMA) denture not fitting the patient over time?

A

-fracture due to trauma -uncomfortable -becomes warped -surface suffers wear and becomes uncomfortable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the basic requirements for a denture base?

A

-replaces the function of natural teeth -goes into the patients mouth -is aesthetically pleasing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What can be done at chairside if an acrylic resin denture doesn’t fit first time?

A

minor adjustments/ refinement but must have a reasonable fit to start off with

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the ideal properties of PMMA as a denture base?

A

-Dimensionally accurate and stable in use -high softening temperature (T g ) -unaffected by oral fluids over time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What does ‘dimensionally accurate and stable in use’ mean?

A

-must fit the patients mouth AND be retained

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What does a high softening temperature mean?

A

-must not distort during ingestion of hot fluids, or during cleaning (P’s sometimes use boiling water)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the elastic limit of a material?

A

represents the stress beyond which the material will become deformed (slightly) - when stress is relieved the material will not return to original shape

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the ideal mechanical properties for PMMA as a denture base?

A

-High Young’s (Elastic) Modulus i.e. - is rigid and requires large stresses to produce small strain (small change in shape) -High Proportional Limit/Elastic Limit i.e. - only large stresses will cause permanent deformation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the ideal thermal properties of PMMA as a denture base?

A

-The thermal expansion = that of the artificial teeth -thermal expansion allows avoidance of internal stresses on cooling during manufacture -high thermal conductivity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Why do you want high thermal conductivity?

A

-for the transmission of thermal stimuli to mucosa - avoid scalding of back of throat or oesophagus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What other properties are ideal for a denture base?

A

-low density -colour/translucency to match the natural tissues -non-toxix -non-irritant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Why do we want a denture base to have a low density?

A

-lower density aids retention of upper denture (the heavier the material - the greater the gravity pull)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What type of reaction takes place to forma acrylic resin (PMMA)?

A

Free-radical addition polymerisation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the definition of a free radical addition polymerisation reaction?

A

Chemical union of TWO molecules either the same or different to form a larger molecule WITHOUT the elimination of a smaller molecule Note: crucial part = WITHOUT ELIMIN ATION (no small molecules relesased)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What do free-radical addition polymerisation reactions involve molecules with?

A

Molecules with C=C bonds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What monomer is used in the formation of PMMA?

A

Methacrylate monomer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are the steps in acrylic polymerisation?

A

-activation -initiation -propagation -termination

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What happens in the activation step?

A

Activation of the initiator to provide free radicals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the initiator in this reaction?

A

Benzoyl peroxide C 6 H 5 COO-OOCH 5 C 6 Note: it is symmetrical

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

How is the initiator (benzoyl peroxide) activated?

A

a) by heating to >72degrees if heat cured b) can be a self-curing material

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What does activation of the initiator give rise to?

A

2 free radicals (R*): C 6 H 5 COO*

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What happens in the initiation stage?

A

The free-radicals break C=C bond in monomer and transfer free radical

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What happens in the propagation step?

A

Growing polymer chain due to cross-linking with other molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What happens in the termination step?

A

The propagation is terminated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What do you end up with at the end of the termination?

A

https://s3.amazonaws.com/classconnection/589/flashcards/19203589/png/pmma-170074C03FA7DE11F6A.png

28
Q

What are the 2 components of heat cured acrylic?

A

Powder and liquid

29
Q

What is in the powder component of heat cured acrylic?

A

-initiator (Benzoyl Peroxide, 0.2-0.5%) -PMMA particles (pre-polymerised beads) -Plasticiser -pigments -co-polymers

30
Q

What is the purpose of the PMMA particles in the powder?

A

Speeds up the reaction

31
Q

What is the function of the plasticiser in the powder?

A

Allows quicker dissolving in monomer liquid (imp roves dissolution process)

32
Q

What is the function of the pigments in the powder?

A

To give a natural colour to the material

33
Q

What is the function of the co-polymers in the powder?

A

To impoive mechanical properties

34
Q

What is found in the liquid component of heat cured acrylic?

A

-methacrylate monomer -inhibitor (hydroquinone, 0.006%)-co-polymers

35
Q

What is the function of the methacrylate monomer?

A

-dissolves PMMA particles - polymerises

36
Q

What is the function of the inhibitor?

A

-Prolongs shelf-life -reacts with any free-radicals produces by heat, UV light (inadvertently) as these would react with the monomer in the liquid too early

37
Q

What is the function of the co-polymers in the liquid?

A

-improve mechanical properties - particularly cross-linking of the polymers

38
Q

Why is a powder/liquid mix produced?

A

-to produce dough-like material that can be handles/mixed easily and customised to desired shape -reduce heat of reaction -minimise polymerisation shrinkage (monomer on own shrinks 21%, with powder 7%)

39
Q

What are the proportion of powder to liquid used?

A

3-3.5/1 (powder to liquid) by volume or 2.3/1 by weight FOLLOW THE INSTRUCTION ON THE PACK

40
Q

Describe what happens to the powder liquid mix.

A

Is packed into a metal vessel that has a mould in it The vessel is then clamped together and then heated to cure to then produce the denture base

41
Q

What are the requirements for acrylic heat curing?

A

-need a high temp for efficient polymerisation to give high molecular weight polymer (which improves the materials mechanical properties) -but if the temp is too high will have porosity in the materia;

42
Q

What are some examples of heating schedules for acrylic resin? (3)

A

1) 7hrs to 70 degrees + 2hrs up to 100degrees and slow cool 2) 72degrees for at least 16 hrs 3) 20-20-20 reverse curing: -flask in boiling water -remove heat for 20misn -heat to 70 for 20 mins -heat to 100 for 20 mins

43
Q

Over what temp will acrylic begin to get porosity?

A

100 degrees celcius Want the heat cycle in blue in the pic

44
Q

Why is how the acrylic is cooled important?

A

-the mould ad acrylic have different thermal expansion coefficients which can cause internal stresses

45
Q

How can you minimise internal stresses when cooling the acrylic?

A

Cool slowly to allow relief

46
Q

What can internal stresses in the material cause?

A

-decrease in strength -decrease in fatigue strength (ability to withstand low level stresses over a period of time) -warping -repair problems (minor crack may end up being bigger fracture)

47
Q

What are internal stresses related to?

A

-shape and size -curing pressure -curing cycle -thermal expansion -cooling rate (highlighting the complexity of the process)

48
Q

What will under-curing of the material lead to?

A

-Free monomers which will act as an irritant to the patient (leeches out) -low molecular weight = poor mechanical properties

49
Q

What can too fast curing lead to?

A

Possibly gaseous porosity

50
Q

What can the incorrect powder monomer ratio cause when there is too much monomer?

A

Contraction porosity

51
Q

What can the incorrect powder monomer ratio cause when there is too little monomer?

A

Granularity on the surface of the material

52
Q

Why is porosity of the material not ideal?

A

-affects strength -affects appearance -rough sensation to the tongue -absorbs saliva - poor hygiene -plaque trap

53
Q

Where and when will porosity occur?

A

-when monomer bpiling exceeeds 100 degrees celcius -occurs in bulkier parts of the material

54
Q

Why do you need to cure the acrylic slowly to avoid reaching above 100 degrees?

A

The reaction is exothermic

55
Q

What is the polymerisation shrinkage of the monomer on its own?

A

21% (by volume)

56
Q

What is the polymerisation shrinkage of the monomer+powder mix?

A

7%

57
Q

What can cause contraction porosity?

A

-too much monomer -insifficient excess materla -insufficient clamp pressure -occurs anywhere where dough is not sufficiently pack ed

58
Q

Describe acrylic resin properties with relation to toxicity, irritability and oral fluid impact?

A

-Is non-toxic -Is a non-irritant provided no monomer is released BUT some patients are allergic -will absorb water but is virtually insoluble in fluids taken orally

59
Q

Describe the thermal properties of acrylic.

A

Thermal expansion compared to artificial tooth: -is OK if acrylic teeth used -significantly higher than porcelain teeth Has low thermal conductivity which is poor

60
Q

Describe the mechanical properties (YM, PL & EL) of acrylic?

A

Are poor (lower than ideal)

61
Q

How can you compensate for the poor mechanical properties of acrylic?

A

Increase the bulk of the material used

62
Q

How is the colour/translucency of acrylic?

A

Is good - natural looking which is an advantage

63
Q

Describe the density of acrylic.

A

-is low which is good BUT -the need to increase the bulk (overcome poor mechanical properties) offsets this advantage

64
Q

Describe the softening temp for acrylic.

A

-is 75 degrees -is OK for ingested hot fluid -CANNOT use boiling water to clean (will warp the acrylic)

65
Q

Is acrylic dimensionally accurate and stable in use?

A

It is ok Linear contraction 0.5% which is acceptable

BDS3 DMS (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions