#3 Clinical Skills B > Denture Base polymers > Flashcards

Denture Base polymers Flashcards

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1
Q

define what is meant by denture base

A
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2
Q

list the requirements of denture base materials

A
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3
Q

define what is meant by resiliance of a material

A

Resilience is defined as the amount of energy absorbed by a material up until the point at which it undergoes permanent deformation.

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4
Q

define what we mean by toughness of a material

A

Toughness is the amount of energy absorbed by a material until it breaks. Neither resilience or toughness are included in the standard requirements, however, they are important properties.

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5
Q

in addition to the mandated properties, list the desirable properties of a denture base material

A
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6
Q

before using PMMA, list the denture base materials that we used to make dentures with

A
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7
Q

list the different uses of PMMA in other industries

A
  • bone cement
  • windo/lens
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8
Q

list the 4 stages of polymerisation of PMMA

A
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9
Q

what type of polymerisation reaction does PMMA goes through?

A

addition

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10
Q

what are the 3 ways in which PMMA can be activates?

A

head
light
chemical

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11
Q

heat cured materials:

Q: What is the main initiator used in heat-cured denture base resins?

A

A: Benzoyl peroxide

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12
Q

Q: At what temperature does benzoyl peroxide decompose to form free radicals?

A

A: Above 60 degrees Celsius

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13
Q

Q: What do benzoyl peroxide molecules yield when they decompose?

A

A: Electrically neutral species containing unpaired electrons (free radicals)

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14
Q

Q: What is the role of free radicals in heat-cured materials?

A

A: They initiate the chain growth of polymerization

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15
Q

Q: What is the term used for benzoyl peroxide in the polymerization process?

A

A: Initiator

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16
Q

Q: What is the activator in heat-cured materials?

A

A: Heat

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17
Q

Q: How is heat applied to activate the polymerization process in heat-cured materials?

A

A: By immersing a flask in a water bath

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18
Q

Q: What is the common initiator used in the polymerization of PMMA?

A

A: Benzoyl peroxide

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19
Q

Q: What is the monomer used to form PMMA?

A

A: Methyl methacrylate

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20
Q

Q: What role does heat play in the polymerization of PMMA?

A

A: Heat breaks down benzoyl peroxide into free radicals that initiate polymerization.

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21
Q

Q: How does benzoyl peroxide initiate polymerization?

A

A: It decomposes under heat to form free radicals, which attack the double bonds of monomer molecules.

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22
Q

Q: What type of reaction is involved in the polymerization of methyl methacrylate?

A

A: Free radical polymerization

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23
Q

Q: What happens when a free radical attacks a double bond in methyl methacrylate?

A

A: It opens the bond, allowing the monomer to react and form a polymer chain.

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24
Q

Q: What is the polymer product formed from methyl methacrylate?

A

A: Poly(methyl methacrylate) (PMMA)

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25
Q: What is the similarity between benzoyl peroxide in PMMA polymerization and camphorquinone in composites?
A: Both act as initiators by breaking down into free radicals to start the polymerization process.
26
Q: What is the glass transition temperature (Tg) in polymers?
A: It is the temperature above which an amorphous polymer becomes soft and rubbery.
27
Q: Why does PMMA shrink during polymerization?
A: As monomer molecules join to form polymer chains, the space between them reduces, causing shrinkage.
28
Q: What is the state of methyl methacrylate (MMA) before polymerization?
A: Liquid
29
Q: How does polymerization affect the volume of PMMA?
A: The volume decreases due to the closer packing of polymer chains compared to monomer molecules.
30
Q: What is a major concern with PMMA shrinkage in dental applications?
A: It can lead to dimensional changes and affect the fit of dental prosthetics.
31
hwo do we minimise polymerisation shrinkage?
addition of fillers add pre-polymerised PMM beads
32
if we add pre-polymerised polymethylmethacrelate beads what can we reduce volumetric shrinkage to?
6%
33
if we add pre-polymerised polymethylmethacrelate beads what can we reduce linear shrinkage to?
0.5%
34
Q: What are the two main components of heat-cured acrylic resin?
A: Powder and liquid
35
Q: What is the main polymer used in the powder component of heat-cured acrylic resin?
A: Polymethyl methacrylate (PMMA)
36
Q: What is the function of benzoyl peroxide in heat-cured acrylic resin?
Q: What is the function of benzoyl peroxide in heat-cured acrylic resin?
37
Q: What is the role of pigments and dyes in heat-cured acrylic resin?
A: They provide color vitality, using compounds like cadmium, iron, and organic dyes.
38
Q: What materials are used as optical opacifiers in heat-cured acrylic resin?
Q: What materials are used as optical opacifiers in heat-cured acrylic resin?
39
Q: What is the purpose of plasticizers in heat-cured acrylic resin?
A: They make the dough easier to manipulate.
40
Q: What type of fibers are used in heat-cured acrylic resin for strength?
A: Synthetic fibers such as nylon
41
Q: Why are colored fibers added to heat-cured acrylic resin?
A: To simulate the appearance of blood vessels
42
Q: Why is the liquid component of heat-cured acrylic resin stored in a dark bottle?
A: To prevent contamination and degradation by light exposure.
43
Q: What is the main monomer in the liquid component of heat-cured acrylic resin?
A: Methyl methacrylate (MMA)
44
Q: What is the role of hydroquinone in the liquid component?
A: It acts as an inhibitor to prevent premature polymerization.
45
Q: What is the purpose of a crosslinking agent in heat-cured acrylic resin?
A: It improves the strength and durability of the polymerized resin.
46
Q: Name two common crosslinking agents used in heat-cured acrylic resin.
A: Diethylene glycol dimethacrylate and 1,4 butylene glycol dimethacrylate
47
list all the diff components contained in the powder of heat cured acrylic resin
48
list all the diff components contained in the liquid of heat cured acrylic resin
49
50
Q: What happens to the monomer when the powder and liquid components of heat-cured acrylic resin are mixed?
A: Monomer diffuses and softens the surface of the powder, leading to different gelling stages.
51
Q: What is the typical powder-to-liquid (P/L) ratio in heat-cured acrylic resin? by weight
2/1 by weight (%)
52
Q: What is the typical powder-to-liquid (P/L) ratio in heat-cured acrylic resin? by volume
1.6-1
53
Q: What is the first stage in the setting reaction of heat-cured acrylic resin?
Sandy stage – Initial melting of PMMA beads.
54
Q: What happens during the stringy or sticky stage of the setting reaction?
A: Entanglements form between swollen beads and thickened interstitial monomer.
55
Q: Which stage in the setting reaction is considered the most useful?
A: Dough stage – Gelation occurs, making the material workable.
56
Q: What characterizes the rubbery stage of the setting reaction?
A: Monomer penetrates to the core of beads, plasticizing them.
57
list the stages of the setting reaction
sandy stringy or sticky dough rubbery
58
list the stages of denture processing in order
59
list the 3 types of processing problems in terms of popsity
60
Q: What causes gaseous porosity in heat-cured acrylic resin?
A: Boiling of MMA liquid during the polymerization process. Due to monomer boiling before it polymerises Occurs deep within the thickest parts
61
Q: What is the boiling point of methyl methacrylate (MMA) liquid?
A: 100.3°C
62
Q: Why can temperatures in the mould exceed MMA’s boiling point?
A: The polymerization reaction is exothermic and can reach up to 170°C.
63
Q: Where does gaseous porosity most commonly occur in a denture?
A: In the deepest parts of the denture, as the surface hardens first.
64
Q: Why does the surface of the denture harden before porosity can occur?
A: It is closest to the heat source and solidifies before the temperature rises too high inside.
65
Q: How can gaseous porosity be prevented during denture processing?
A: By heating the MMA very slowly to allow solidification before reaching the boiling point.
66
Q: How long does the denture processing technique typically take to prevent porosity?
A: At least 4 hours of slow warming.
67
Q: What causes contraction porosity in PMMA?
Due to shrinkage during polymerisation Not enough material in the mould or not enough pressure Occurs at the surface as well as in deep areas A: The inherent 6% shrinkage during PMMA polymerization.
68
Q: How can contraction porosity be prevented?
A: By adding a little extra PMMA dough to the mould before heating.
69
Q: Why is high pressure applied during the denture processing procedure?
A: To prevent bubbles from growing in size and causing porosity.
70
Q: What is the key difference between gaseous porosity and contraction porosity?
A: Gaseous porosity is due to MMA boiling, while contraction porosity is due to PMMA shrinkage.
71
what is granular porosity caused by?
Due to drying out of dough before processing
72
what are the advantages of PMMA
73
what are the disadvantages of PMMA
74
Q: What is another name for the glass transition temperature (Tg)?
A: Glass to rubber transition
75
Q: What happens to an amorphous polymer when it reaches Tg?
A: It softens but does not melt, becoming more flexible and rubber-like.
76
Q: How can Tg be compared to wax behavior?
A: Like wax that becomes soft before melting, polymers transition to a rubbery state at Tg.
77
Q: Why must denture base materials have a Tg higher than 70°C?
A: Because liquids consumed in the mouth can reach 70°C, and the denture must stay rigid at this temperature.
78
Q: How does molecular structure affect the glass transition temperature (Tg)?
A: Large pendant groups prevent polymer chains from packing closely, making movement easier and lowering Tg.
79
Q: How does a plasticizer affect Tg?
A: It increases polymer chain mobility, reducing intermolecular forces, and lowers Tg.
80
Q: Which methacrylate material has a Tg higher than 70°C?
A: PMMA (Polymethyl methacrylate)
81
Q: Why is PMMA preferred for dentures?
A: It remains rigid at mouth temperatures, unlike other methacrylates that would soften.
82
Q: When might a lower Tg material be advantageous?
A: For applications like sports mouthguards, where softness at mouth temperature is beneficial.
83
what are the disadvantages of PMMA?
Poor impact strength Poor thermal conductor
84
68% of dentures fracture within the first ........ years
3
85
what sort of dentures break the most?
upper partials
86
why is it that upper partial dentures fracture the most?
as there are often weak areas where small saddles are connected to the major connector
87
in terms of upper denture failures, about half occur where along the denture?
the midline
88
what are the upper complete denture midline fractures that are due to stress concentrations associated with?
Deep fraenal notches Sharp fraenal notches Diastema
89
what are the upper complete denture midline fractures that are due to increased flexing associated with?
Worn teeth Ill fitting dentures Hard bony suture in palatal midline Palatine tori
90
list the diff ways in which we can improve the properties of denture base materials
91
what was found about metal strengtheners when they began being added to strengthen denture base materials
Metal bars and meshes are often added by technicians, but there is little evidence that they actually strengthen a denture and may in fact act as a stress concentrator
92
Co-polymers Graft co-polymer of butadiene styrene is the best solution yet to improving the properties of pmma and creates what is known as “high impact acrylic”, one example of this is the commercial product Lucitone 199. what is its disadvantage?
we add a rubbery component so inc stiffness of the material and make it more flexible
93
besides plastic acrylic teeth, what other teeth material have we got?
- porcelain (high fusing ceramic) - experimental fiber-reinforced teeth
94
Q: Which alternative material is becoming more popular for flexible partial dentures?
A: Nylon
95
Q: What is a potential downside of using flexible materials for dentures?
A: They may increase forces on abutment teeth and bone, leading to faster bone resorption.
96
Q: Why is PMMA still considered the best material for dentures?
A: It offers great aesthetics, adequate physical properties, and remains rigid at mouth temperatures.
97
Q: What is a major weakness of PMMA dentures?
A: They are brittle—so don’t drop them!
98
Q: What are the three main curing methods for denture materials?
A: Chemically cured, Heat cured, and Light cured
99
Q: What is the accelerator in chemically cured resins?
A: Tertiary amine (e.g., dimethyl-p-toluidine or sulfinic acid)
100
Q: What is the initiator in both chemically and heat-cured resins?
A: Benzoyl peroxide
101
Q: What is the role of hydroquinone in chemically cured resins?
A: It acts as an inhibitor to prevent premature polymerization.
102
Q: What are the advantages of heat-cured resins?
Heat and pressure control Avoids porosity Maximizes conversion of monomer to polymer
103
Q: What is the photo-initiator used in light-cured resins?
A: Camphorquinone, activated by blue light
104
Q: Where are light-cured resins commonly used?
A: For record bases, custom trays, and denture repairs
#3 Clinical Skills B
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