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dental material science need to know Flashcards

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1
Q

explain gaseous porosity

A

voids in the material occurring when PMMA is cured fast
monomer boils
usually happens in a thicker section of the acrylic

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2
Q

what are the constitutes of gutta-percher?

A

20% GP
65% zinc oxide
10% radiopacifier
5% plasticiser

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3
Q

what are the properties of non-setting calcium hydroxide?

A

high pH- antimicrobial factors
hydrolysis pf LPS reduce inflammatory potential
removal of tissue debris

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4
Q

what are the constitutes of stainless steel?

A

72% iron
18% chromium
8% nickel
1.7% titanium
0.3% carbon

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5
Q

what is work hardening?

A

work done on metal below its recrystallisation temperature causes slip
slip= dislocations collect ar grain boundaries hence stronger, harder material
the hard wire is made by drawing the metal in a cold state through a series of dies of successively smaller diameter
this makes it stronger and gives it spring properties

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6
Q

define springiness

A

can undergo large defelctions without permanent deformation

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7
Q

give disadvantages of self cure PMMA

A

poor mechanical properties
not suitable for pts w residual monomer allergy

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8
Q

What is the use of a cavity base?

A

to minimise bulk of material

blocks out undercuts

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9
Q

what kind of reaction takes place when mixing the base and catalyst for calcium hydroxide?

A

chelation reaction

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10
Q

what is the use of a cavity lining material

A

thin coat of material over the dentine and pulp

has pallative effect

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11
Q

what reaction occurs in ZOE cement

A

acid base reaction

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12
Q

what is the composition of the base for calcium hydroxde lining material?

A
  • calcium hydroxide
  • zinc oxide
  • plasticiser
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13
Q

what chemicals react in ZOE cement and what is formed

A

ZnO and eugenol form zinc eugenolate

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14
Q

what is the strongest ZOE and why

A

EBA ZOE due to addition of quartz and aluminium

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15
Q

what takes part in the chelation reaction when mixing caclium hydroxide?

A

base- zinc oxide
catalyst- butylene glycol disalicylate

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16
Q

what pH is calcium hydroxide?

A

pH 12

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17
Q

what are uses of ZOE cement

A

lining material
temporary restoration
Root canal sealer - slow set 24 hours

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18
Q

what is the advantage of calcium hydroxide being highly alkaline?

A

kills bacteria

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19
Q

what are properties of ZOE

A

rapid set
good working time
low thermal conductivity
radiopaque
High soluble

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20
Q

name 4 properties of calcium hydroxide

A
  • soluble
  • alkaline
  • irritant- stimulate tertiary dentine formation
  • radiopaque
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21
Q

explain advantage and disadvantage of ZOE’s solubility

A

advantage - eugenol is continually released which releives pain

disadvantage - soluble in water so eugenol is released and this inhibits setting of resin materials

eugenol also discolours resin materials

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22
Q

what is a contraindication of using ZOE

A

cannot place under a composite restoration as it affects bonding

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23
Q

when should calcium hydroxide be used?

A

as a direct or indirect pulp cap under deep restorations

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24
Q

why does calcium hydroxide need to be covered with a RMGIC?

A

soluble- prevents dissolution

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25
what kind of bond is formed when etching an GIC?
micromechanical bond
26
What type of ZOE is least soluble resin modified or normal
resin modified so can use under amalgam filling
27
What form of cement is the least soluble
RMGIC
28
What is a contraindication of using GI near the pulp
any unreacted HEMA is cytotoxic to the pulp
29
list ideal properties of lining materials
* pulpal protection * therapeutic * radiopaque * bond to dentine * low solubility * cariostatic * low thermal expansion and conductivity
30
how can a lining material give pulpal protection?
* thermal- exothermic reaction of composite/heat conducted through metal restorations * chemical- unreacted chemicals/pH of restorative materials * bacterial- against microleakage
31
what property of GI makes it bettern than other lining materials
It bonds to enamel and dentine forming a better marginal seal
32
how does RMGI kill bacteria
polymerisation of RMGI releases cytotoxic enzymes
33
what does it mean if a lining material is "therapeutic"?
* reduces inflammation * promotes healing
34
what is the significance of a lining material being radiopaque?
can be viewed radiogrpahically if displaced from tooth allows for microleakage to be seen radiographically
35
explain the thermal properties of GI and their significance
thermal conductivity is less than dentine (RMGI and GI) thermal expansion is similar to dentine (GI) during exposure to heat the GI will react similarly to dentine which will maintain seal of material
36
give an example of how a lining material can be cariostatic?
release fluoride
37
Explain GI interaction with dentine tubules and its significance
GI seals dentine tubules this decreases micro-leakage and decreases sensitivity
38
what is the reason for using a lining material in a pt with reversible pulpititis?
pallitave care- eases the pts symptoms
39
What is an advantage of using GI over other cements
it releases fluoride = CARIOSTATIC
40
What does the initial gradient on a graph show
young's (elastic) Modulus
41
what type of alloy is stainless steel?
wrought alloy- can be cold worked
42
What is indicated by the change in gradient on the stress strain curve
the proportional limit
43
what are the components of stainless steel?
* 72% iron * 18% chromium * 8% nickel * 1.7% titanium * 0.3% carbon
44
what is the role of chromium in stainless steel?
corosion resistance
45
what is the role of nickel in stainless steel?
corosion resistance increase strength
46
What is proportional limit and explain it
The stress applied before a material behaves inelastically >proportional limit will result in deformation < proportional limit - the material will return to the original shape
47
what is the role of titanium in stainless steel?
prevents precipitation of chromium carbide at grain boundaries
48
what does the end of a line in the stress strain curve show?
fracture stress
49
What is translucency
Ability for light to pass through a material but be scattered, at one of the surfaces or internally, leading to blurring of transmitted light
50
give 3 properties of stainless steel
* springiness * ductile * corrosion resistant
51
how does weld decay affect stainless steel?
makes it brittle
52
What is opalescence
the ability of translucent material to appear blue in reflected light and orange/yellow in transmitted light
53
define springiness
the ability to undergo large deflection WITHOUT deformation
54
what makes steel classed as "stainless" steel?
contians at least 12% chromium
55
Define cold working
Shaping a material below its recrystallisation temperature
56
Define slip
Defects in a grain move to grain boundaries this results in fewer defects in the lattice structure
57
what does it mean by classing iron as 'allotropic'?
undergoes 2 solid state changes due to temperature
58
What is an alloy
2 or more metals that form a common lattice structure and are soluble in one another
59
define creep
repetitive small forces that cause gradual dimensional change
60
define Fatigue
Repetitive small stresses that because fracture
61
what are the 2 types of acrylic used in dentistry?
self cure heat cure
62
give an advantage of heat cure PMMA
has a higher molecular weight than self cure this means better mechanical properties
63
what are ideal properties of luting agents
low viscosity - increases as it sets low film thickness - <25 um easy to use Radiopaque Good marginal seal Low solubility Cariostatic Non-toxic High compressive strength High hardness
64
give a disadvantage of heat cure PMMA
gaseous porosity occurs if cured too fast results in process taking far to long to avoid this
65
What does dual cure material mean
cured by: - light - cures on its own by REDOX reaction
66
what are the ideal properties of acrylic?
* non-toxic * non-irritant * unaffected by oral fluids * high softening temperature * low density- lightweight * low thermal conductivity
67
What are issues with HEMA
- cytotoxic to the pulp - swells
68
when can you not use RMGI as a cement
for porcelain - it swells cracking the crown for posts - it will swell and split the root
69
give an advantage of self cure PMMA
polymerisation doesnt require heat- less thermal contraction means a better fitting denture
70
RMGI does not bond to indirect restorations so what chemical is needed
composite luting agent
71
how does dentine bonding agent bond composite luting agent to the tooth
hydrophilic end bonds to tooth hydrophobic end bonds to composite
72
give 2 disadvantages of self cure PMMA
polymerisation is less efficiant, meaning there are more unreacted monomers irritant/allergy issues lower molecular weight= reduced transverse strength
73
how can self cure PMMA dentures become oversized?
they absorb water and expand
74
what is free radical polymerisation?
chemical union of 2 molecules to form a larger molecule without elimination of the smaller molecule
75
How does composite luting agent bond to indirect restorations
chemical bond forms between C=C micro-mechanical bond forms between composite luting agent and the rough inside surface of indirect restoration
76
what type of bonds are present in the molecules that undergo free radical polymerisation?
C=C
77
How do you improve bonding to porcelain
etch the surface with hydrofluric acid
78
what are the 4 stages of free radical polymerisation?
activation initiation propagation termination
79
What is required to bond composite luting agent to porcelain/ceramics
Silane coupling agent
80
How does silane coupling agent bond to composite luting agent and porcelain/ceramics
C=C bonds from silane coupling agent react with similar groups in the composite luting agents hydroxyl groups in the silane coupling agent react with oxide groups on the porcelain surface
81
What is needed to bond composite luting agent to metal
Metal bonding agent
82
What are examples of metal bonding agents
MDP and 4-META
83
What is important when using compoosite luting agent to bond to metal
must use a self cure composite as light cannot penetrate through metal
84
How does metal bonding agent bond metal to composite luting agent
C=C bonds in metal bonding agent react with similar groups in the composite luting agent Acid end of metal bonding agent reacts with metal oxide
85
What is a self adhesive composite resin
composite luting material with metal bonding agent in it
86
What is an example of a Self adhesive composite resin luting agent
Panavia
87
How do you bond an indirect retention to the tooth
Tooth DBA Composite luting Agent Indirect retention
88
How do you bond porcelain/ceramic to the tooth
Tooth DBA Composite luting agent Silane coupling agent Porcelain/Ceramic
89
How do you bond metal to the tooth
Tooth DBA Composite luting agent Metal bonding agent Metal

Need to Know (21 decks)

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