BDS2 > Cavity lining materials > Flashcards

Cavity lining materials Flashcards

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1
Q

Which materials are placed in tooth cavities?

A

amalgam, composite resin, glass ionomer, precious metal, ceramic

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2
Q

What are the disadvantages of restorative materials?

A
  • may not make intimate contact with the tooth surface (especially dentine)
  • release heat during setting / curing
  • release chemicals
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3
Q

Why is it a problem if restorative materials do not make intimate contact with the tooth surface?

A

any gap may allow ingress of bacteria and fluids (microleakage) which can lead to pulpitis

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4
Q

Why is it a problem if restorative materials release chemicals?

A

the chemicals may be pulpal irritants and lead to pain or pulpal damage

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5
Q

What can you do to prevent microleakage (e.g. due to composite shrinkage)?

A

use an intermediate restorative material OR a lining material

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6
Q

What is the function of a lining material?

A

prevents gaps and acts as a protective barrier

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7
Q

Why is it especially important to use a lining material in a deep cavity?

A

dentine closer to the pulp is more permeable because there is less intratubular dentine so the tubules are wider. So lining material required to protect the pulp and ease symptoms.

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8
Q

What is a cavity base material?

A

a thick mix placed in bulk that is used as a dentine replacement

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9
Q

What is the function of a cavity base material?

A
  • protect the pulp by providing thermal insulation and absorbing occlusal forces
  • used to block out undercuts for indirect restorations
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10
Q

Which type of restorations would you more commonly use a cavity base material for?

A

metal restorations (indirect or direct)

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11
Q

What is a cavity lining material?

A

a thin coating placed over exposed dentine

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12
Q

How thin is a coating of a cavity lining material?

A

<0.5mm

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13
Q

What are the functions of a cavity lining material?

A
  • dentinal sealing
  • pulpal protection
  • therapeutic effects
  • palliative effects
  • stimulation of tertiary dentine
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14
Q

What does a cavity lining material protect the pulp from?

A
  1. chemical stimuli (unreacted chemical or initial pH of restoration)
  2. Thermal stimuli (exothermic setting reaction of composite or heat conducted through metal restorations)
  3. bacterial and endotoxins (microleakage)
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15
Q

What is microleakage?

A

penetration of oral fluids and bacteria and their toxins between the restorative and cavity walls

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16
Q

How do cavity liners have a therapeutic effect?

A

calm down inflammation within the pulp and promote pulpal healing (prior to or at the time of placing a permanent restoration)

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17
Q

Which condition are cavity liners used most commonly for their palliative effect?

A

patients with reversible pulpitis - reduced patient symptoms prior to definitive treatment

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18
Q

What are the properties of lining materials?

A
  • ease of use
  • thermal properties
  • mechanical properties
  • radiopaque
  • marginal seal
  • solubility
  • cariostatic
  • biocompatible
  • compatible with restorative materials
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19
Q

What are the ideal properties to make cavity lining materials easy to use?

A
  • easy to mix
  • long working time to allow easy placement
  • short setting time (command set e.g. light cure)
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20
Q

What are the ideal thermal properties for cavity lining materials?

A

low thermal conductivity, thermal expansion coefficient similar to dentine, thermal diffusivity similar to dentine or lower

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21
Q

What is thermal conductivity?

A

How well heat energy is transferred through a material

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22
Q

How is thermal conductivity measured?

A

heat flow through a cylinder of unit cross-sectional area and unit length with a temperature difference of 1 degree between the ends

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23
Q

What are the units for thermal conductivity?

A

watts per meter per degree (W / m degreeC

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24
Q

What should the thermal conductivity of a denture base material be?

A

high so that the patient can feel the temperature of drink / food across the palate

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25
What should the thermal conductivity of a restorative material be?
as low as possible (so heat is not transmitted onto the pulp)
26
What should the thermal conductivity of a cavity lining material be?
as low as possible (so heat is not transmitted onto the pulp)
27
What is the thermal expansion coefficient?
change in length per unit length for a temperature rise of 1 degree C
28
What are the units for thermal expansion coefficient?
ppm / degrees C
29
What should the thermal expansion coefficient of a lining material and restorative material be?
should match the thermal expansion coefficient of the tooth structure
30
What are the thermal expansion coefficients for enamel and dentine?
enamel 8.3 ppm / C dentine 11.4 ppm / C
31
Which restorative material has a thermal expansion coefficient closest to a tooth?
glass ionomer cement (GIC) - 11 ppm / C
32
What is the thermal expansion coefficient of RMGIC (resin modified glass ionomer cement)?
20 ppm / C
33
What is the thermal expansion coefficient of composite and amalgam?
25 ppm / C
34
What is thermal diffusivity?
how heat spreads through a material (similar to thermal conductivity)
35
What are the units for thermal diffusivity?
cm2 / s - centimetre squared per second
36
What should the thermal diffusivity of cavity liners and restorative materials be?
ideally at least as low as tooth (enamel 0.0042 cm2/s, dentine 0.0026cm2/s) - all available liners have similar or lower thermal diffusivity than tooth enamel
37
What is the thermal diffusivity of amalgam?
1.7 cm2/s - much greater than enamel
38
What are the ideal mechanical properties of a cavity lining material?
high compressive strength and similar modulus of elasticity to dentine (how material deforms when force applied)
39
Why is it important for a restorative material to have a high compressive strength?
to allow placement of filling without it breaking
40
What is the compressive strength of dentine?
around 275 MPa
41
What is the modulus of elasticity of dentine?
around 15 GPa
42
Why is it advantageous for a lining material to be radiopaque?
so you can easily see the difference between lining and tooth to identify if there is any leakage or secondary caries
43
What are the ideal qualities of the marginal seal of a cavity lining material?
chemical bond to dentine that is permanent and impenetrable
44
What should the solubility of a cavity lining material be?
low solubility (material exposed to saliva and dentinal fluid as dentine is moist)
45
What properties of a cavity lining material make it cariostatic?
fluoride releasing and antibacterial
46
Why is it important to have a cariostatic lining material?
to prevent secondary caries around the restoration
47
What characteristics of a cavity lining material make it biocompatible?
non-toxic, not damaging to the pulp, low thermal conductivity
48
What are the different types of materials for cavity liners?
setting calcium hydroxide Ca(OH)2, glass ionomer and resin modified glass ionomer cements (liner or base)
49
What are the different types of materials used for cavity bases?
zinc oxide based cements, GI or RMGI cements (base or liner), palliative cements (historic)
50
In what form does setting calcium hydroxide liner come in?
two pastes - one is a base, the other is a catalyst
51
Examples of brand names for setting calcium hydroxide liner
Life, Dycal
52
What are the constituents of setting calcium hydroxide liner?
base and a catalyst
53
What makes up the base of a setting calcium hydroxide liner?
calcium hydroxide 50%, zinc oxide (filler) 10%, zinc stearate (filler) <1%, N-ethyl toluene sulphonamide (plasticiser) 40%
54
What makes up the catalyst of a setting calcium hydroxide liner?
butylene glycol disalicylate (reactive element) 40%, titanium dioxide (filler) 13-14%, calcium sulphate (filler) 30%, calcium tungstate (filler and radiopaquer) 15%
55
What is the setting reaction of setting calcium hydroxide liner?
chelation reaction between ZnO and butylene glycol disalicylate
56
What is the initial pH of setting calcium hydroxide liner?
approx pH 12 (encourages reactionary dentine formation)
57
What are the modes of action of Ca(OH)2 liner?
bactericidal to cariogenic bacteria and acts as an irritant to stimulate tertiary dentine formation (reactionary)
58
How does Ca(OH)2 liner act as a bactericidal to cariogenic bacteria?
cariogenic bacteria survive in an acidic environment so the highly alkaline liner (pH 12) kills the bacteria
59
How does Ca(OH)2 liner stimulate the formation of tertiary (reactionary) dentine?
irritates the odontoblast layer causing necrosis (pulp shrinks way) which in turn results in production of a layer of tertiary dentine. This forms a calcified bridge walling off the base of the cavity from the pulp
60
Where is the calcium of the tertiary / reparative dentine (produced as a result of Ca(OH)2 liner irritation) sourced from?
the pulp (not the calcium hydroxide liner)
61
What are the properties of Ca(OH)2?
quick setting time, radiopaque, easy to use
62
What are the disadvantageous properties of Ca(OH)2?
low compressive strength (risk of cracking), unstable and soluble (lining will disappear if cavity leaks or just due to contact with moist dentine)
63
What are the different types of zinc oxide based cements?
zinc phosphate, zinc polycarboxylate, zinc oxide eugenol (ZOE), resin modified ZOE, ethoxybenzoic acid (EBA) ZOE
64
How long has zinc phosphate cement been in use for?
+100 years
65
What form does zinc phosphate cement come in?
powder and liquid
66
What are the advantages of zinc phosphate cement?
easy to use and cheap
67
What is the powder component of zinc phosphate cement comprised of?
zinc oxide >90%, magnesium dioxide <10%, other oxides (alumina and silica)
68
What is the purpose of the ingredient zinc oxide in the powder element of zinc phosphate cement?
zinc oxide (>90% of powder) is the main reactive ingredient
69
What is the purpose of the ingredient magnesium dioxide in the powder element of zinc phosphate cement?
magnesium dioxide (<10% of powder) gives white colour and increases compressive strength
70
Why is it beneficial for the cavity lining material to be white?
if removing a restoration, you can tell the difference between the composite and lining material
71
What is the purpose of the other oxides (alumina and silica) present in the powder component of zinc phosphate cement?
improves the physical properties and alters the shade of set material
72
What are the components of the liquid aspect of zinc phosphate cement?
phosphoric acid solution (approx 50%) and oxides (buffer the solution)
73
What oxides are present in the liquid part of zinc phosphate cement?
aluminium oxide and zinc oxide
74
What is the purpose of aluminium oxide in the liquid part of zinc phosphate cement?
ensures the even consistency of set material
75
What is the purpose of zinc oxide in the liquid part of zinc phosphate cement?
slows the reaction giving longer working time
76
What is the initial reaction of the zinc phosphate cement setting?
acid base reaction (2 H3PO4 + ZnO -> Zn(H2PO4)2 + H2O)
77
What reaction follows the acid base reaction in zinc phosphate setting?
hydration reaction resulting in formation of a crystalised phosphate matrix (Hopiete) - ZnO + Zn(H2PO4)2 + 2H2O -> Zn3(H2PO4)2.4H2O
78
What is the name of the crystalised phosphate matrix in zinc phosphate cement formed by the hydration reaction following the acid base reaction?
Hopiete
79
What are some problems with zinc phosphate cement?
low initial pH (approx pH 2) that takes 24hrs to return to neutral, exothermic setting reaction, not adhesive, not cariostatic, final set takes 24h, brittle, opaque
80
Why is it problematic that zinc phosphate has a low initial pH that can take 24hr to return to neutral?
can cause pulpal irritation (pH 2 for 24hrs is a long time for pulp to be irritated)
81
How is zinc phosphate cement retentive as it is not adhesive?
retention may be slightly micromechanical due to surface irregularities of cavity
82
What is the difference in the materials of zinc phosphate cement and zinc polycarboxylate cement?
phosphoric acid replaced by polyacrylic acid
83
What is the advantage of using zinc polycarboxylate cement over zinc phosphate cement?
zinc polycarboxylate bonds to tooth surface in similar way to GIC, less heat of reaction, initial low pH but returns to neutral more quickly and longer chain acids do not penetrate dentine as easily
84
What are the disadvantages of zinc polycarboxylate cements?
difficult to mix and manipulate, soluble at lower pH, opaque, lower modulus and compressive strength than zinc phosphate
85
Example of brand name of zinc polycarboxylate cement
Poly-F
86
Which zinc oxide based cements are rarely used as linings anymore?
zinc phosphate and zinc polycarboxylate
87
What are zinc oxide eugenol (ZOE) cements used for?
linings/base in deep cavities, temporary restorations, root canal sealer, periodontal dressings
88
Under which type of restorations are zinc oxide eugenol (ZOE) cements used as a liner/base?
under amalgam restorations
89
Which type of zinc oxide eugenol (ZOE) cement is used as a temporary restoration?
resin modified ZOE (Kalzinol) or EBA ZOE (ethoxybenzoic acid)
90
Example of a brand name of ZOE cement used as a root canal sealer
Tubli-seal
91
How long does it take root canal sealer (e.g. Tubli-seal) to set?
slow setting 24hrs
92
How long does it take for periodontal dressings to set?
fast setting - 5 min
93
Example of a brand name of ZOE cement used as a periodontal dressing
Coe-Pak (a zinc oxide cement but is eugenol free)
94
What type of reaction is the setting reaction for zinc oxide eugenol cement?
acid base reaction
95
What is the general equation for an acid base reaction?
acid + base -> salt + water
96
What is the base in zinc oxide eugenol cement?
ZnO
97
What is the acid in ZOE cement?
eugenol
98
What is the product of the chelating reaction of zinc oxide with eugenol?
zinc eugenolate matrix
99
What does the zinc eugenolate matrix bond to?
unreacted ZnO particles
100
What are the properties of ZOE?
adequate working time, relatively rapid setting time, low thermal conductivity, low strength, radiopaque, high solubility
101
Why does ZOE set faster in the mouth?
due to moisture and heat
102
How can the setting time of ZOE be modified?
by the addition of accelerators
103
Why does ZOE have a low strength (around 20MPa)?
due to the weak hydrogen bonds between the eugenolate molecules
104
What are the implications of the low strength of ZOE?
ZOE not strong enough to be used as a base beneath amalgam as the packing pressure would damage it
105
What is the cause of the high solubility of ZOE?
Eugenol is constantly released making the material porous
106
What is the disadvantage of the high solubility of ZOE?
eugenol is replaced by water which leads to the disintegration of the material
107
What is the advantage of the high solubility of ZOE?
eugenol when liberated has an obtundent effect on the pulp and can reduce pain
108
Under which restorative material should ZOE materials not be used?
ZOE materials should not be used under composite resin materials
109
Why should ZOE cements not be used under composite resin materials?
the release of eugenol inhibits the set of resin-based materials which softens them and causes discolouration
110
What are resin modified ZOE cements?
resin added to the powder and liquid to improve the ZOE properties
111
Examples of brand names of resin modified ZOE
IRM and Kalzinol
112
Which resin is added to ZOE in IRM?
polymethylmethacrylate
113
Which resin is added to ZOE in Kalzinol?
polystyrene
114
What is the purpose of adding resins to ZOE?
do not take part in the reaction but resins increase the compressive strength to >40MPa making it suitable as a cavity lining and greatly decreases solubility
115
Examples of modified ZOE
resin modified ZOE and ethoxybenzoic acid (EBA) ZOE cement
116
What components make up the powder element of (ethoxybenxoic acid) EBA cement?
ZnO 65%, quartz or alumina (filler particles) 35%, hydrogenated resin ~6%
117
What components make up the liquid element of EBA ZOE cement?
eugenol 37%, ethoxybenzoic acid (EBA) 63%
118
In EBA cement, which material is reactive with ZnO?
EBA (ethoxybenzoic acid)
119
What is the difference between the setting reaction of ZOE and EBA cement?
EBA encourages crystalline structure which imparts greater strength to the set material
120
What are the properties of ethoxybenzoic acid (EBA) cement?
stronger than ZOE or resin modified ZOE (around 60MPa) and less soluble
121
What is the most widely used lining materials?
glass ionomer lining materials
122
How does glass ionomer work as a lining material?
the glass ionomer bonds to and seals the dentine and can in turn bond to the composite resin filling placed over it
123
What feature of glass ionomers may make them cariostatic?
release fluoride over time
124
How does the appearance of glass ionomer differ from zinc oxide cements?
glass ionomer is more yellow like dentine whereas ZnO is white
125
What features make glass ionomer lining materials easy to use?
simple mixing and the materials are generally light cured
126
How are most glass ionomer lining materials mixed?
most GI liners come as two pastes in a 'clicker' dispensing system
127
What is the benefit of glass ionomer lining materials being light cured?
gives a long working time and short setting time (30s)
128
Example of a common brand of glass ionomer lining material used
Vitrebond (RMGIC)
129
What are the advantageous properties of glass ionomer lining materials with regards to its thermal conductivity, diffusivity and expansion?
both GIC and RMGIC have thermal conductivity and diffusivity lower than dentine. GIC has a similar thermal expansion to dentine
130
What is the advantage of the compressive strength of glass ionomer lining materials?
compressive strength is >170MPa which is higher than any of the ZnO based materials (therefore GIC used as filling material)
131
Is GIC radiopaque?
most are radiopaque - but varies between materials
132
What is the marginal seal like with glass ionomer lining materials?
marginal seal is better than any of the other materials as there is a chemical bond to enamel and dentine
133
What is the only material that predictably seals dentinal tubules?
glass ionomer lining materials
134
What is the advantage of GI lining materials sealing dentinal tubules?
decreases microleakage and helps prevent post treatment sensitivity
135
Which out of RMGIC and GIC has the greatest solubility?
solubility is greater for GIC than RMGIC
136
When is solubility of glass ionomer lining materials greatest?
greatest initially
137
What is the order of solubility of the lining materials?
RMGI (least soluble) < Zinc phosphate < GI < others (ZOE/ZO/Ca(OH)2)
138
What makes RMGICs cytotoxic?
polymerisation reaction of RMGICs releases benzoyl iodides and benzoyl bromides which are cytotoxic
139
Why is cytotoxicity an advantageous characteristic of RMGICs?
kills any residual cavity bacteria
140
Why is it important that RMGICs are completely cured?
any unreacted HEMA (resin) may damage the pulp - so make sure not to cure too thick of a layer
141
Which is the only lining that is able to bond to restorative materials?
glass ionomer cements
142
What surface treatment may be required prior to bonding some conventional glass ionomer materials?
etching
143
What surface treatment may be required prior to bonding resin modified glass ionomer cements?
no surface treatment - resin penetrates the dentinal tubules
144
What method may make it possible to bond amalgam to tooth?
using RMGIC
145
What are the dental hospital guidelines for using liners in cavities in dentine?
use RMGIC (e.g. Vitrebond) as a lining for amalgam and larger cavities that are to be filled with composite
146
What material does the dental hospital recommend using when the cavity approaches the pulp?
calcium hydroxide (as a direct or indirect pulp cap over the deepest part of the cavity) which should then be covered with RMGIC prior to placing of final restoration - 2 lining materials
147
Why is it necessary to cover calcium hydroxide with RMGIC?
calcium hydroxide is very soluble
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