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BDS2 CDS DMS > 3. Cavity Lining Materials > Flashcards

3. Cavity Lining Materials Flashcards

1
Q

Disadvantages of restorative materials (3)

A

May not make intimate contact with the tooth surface (any gaps may allow ingress of fluids and bacteria)
Heat released during setting or curing
Release of chemicals (pulpal irritants and lead to pain or pulpal damage)

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2
Q

Function of lining materials (2)

A

Prevents gaps

Acts as a protective barrier

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3
Q

Features of cavity base (3)

A

Thick mix placed in bulk
Dentine replacement used to minimise the bulk of the material of block out undercuts
More common in metal restorations

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4
Q

Features of cavity lining (2)

A 
Thin coating (<0.5mm) over exposed dentine
A dentine sealer able to promote the health of the pulp by adhering to the tooth structure or by an antibacterial action
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5
Q

Purpose of cavity liner (5)

A

Pulpal protection from chemical stimuli from unreacted chemicals in the filling material/initial pH of filling
Pulpal protection from thermal stimuli - exothermic setting reaction of composite or heat conducted through metal fillings
Pulpal protection from bacteria and toxins - micro leakage - the penetration of oral fluids and bacteria and their toxins between the restorative and the cavity walls
Therapeutic - to calm down inflammation within the pulp and promote pulpal healing prior to/at the time of a permanent restoration being placed
Palliative - to reduce patient symptoms prior to definitive treatment being carried out. Most commonly in patients with irreversible pulpitis

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6
Q

Properties of lining materials (9)

A 
Easy to use
Thermal properties
Mechanical properties
Radiopaque
Marginal seal
Solubility
Cariostatic
Biocompatible
Compatible with restorative materials
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7
Q

Ideal easy to use properties of lining materials (3)

A

Easy to mix
Long working time for easy placement
Short setting time - ideally command set

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8
Q

Ideal thermal properties of cavity lining materials (3)

A

Thermal conductivity should be low
Thermal expansion coefficient should be similar to dentine
Thermal diffusivity should be similar to dentine or lower

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9
Q

Definition of thermal conductivity

A

How well heat energy is transferred through a material (heat flow through a cylinder of unit cross-sectional area and unit length, with a temperature difference of 1C between the ends)
Units are Wm-1C-1

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10
Q

Examples of thermal conductivity (3)

A

Denture base should be high
Restorative material should be low
Cavity lining should be as low as possible

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11
Q

Definition of thermal expansion coefficient

A

Change in length per unit length for a temperature rise of 1C
Units are ppmC-1

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12
Q

Thermal expansion coefficient of enamel

A

8.3ppmC-1

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13
Q

Thermal expansion coefficient of dentine

A

11.4ppmC-1

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14
Q

Thermal expansion coefficient of GIC

A

11ppmC-1

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15
Q

Thermal expansion coefficient of RMGIC

A

20ppmC-1

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16
Q

Thermal expansion coefficient of composite

A

25ppmC-1

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17
Q

Thermal expansion coefficient of amalgam

A

25ppmC-1

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18
Q

Definition of thermal diffusivity

A

Similar to thermal conductivity but measured in cm2s-1

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19
Q

Thermal expansion coefficient of enamel

A

0.0042cm2s-1

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20
Q

Thermal expansion coefficient of dentine

A

0.0026cm2s-1

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21
Q

Thermal expansion coefficient of cavity liners

A

Similar/lower than enamel

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22
Q

Thermal expansion coefficient of amalgam

A

1.7cm2s-1

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23
Q

Ideal mechanical properties of cavity lining materials (2)

A

High compressive strength

YM/rigidity similar to dentine

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24
Q

Why is a high compressive strength required

A

To allow placement of filling without it breaking

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25
Compressive strength of dentine
275MPa
26
YM of dentine
15GPa
27
Advantages of radiopaque cavity lining material (3)
Easy to see difference between lining and tooth Easy to check for leakage Easy to check for secondary caries
28
Ideal chemical properties of cavity lining material (2)
Should form a chemical bond to dentine | This bond should be permanents and impenetrable (marginal seal)
29
Ideal solubility of cavity lining material
Low
30
Ideal cariostatic properties of cavity lining material (2)
Fluoride releasing | Antibacterial
31
Advantages of cariostatic properties of cavity lining material
Help to prevent secondary caries around restoration
32
Ideal biocompatible properties of cavity lining material (5)
``` Non-toxic Not damaging to pulp Neutral pH No excessive heat during setting Low thermal conductivity ```
33
Types of cavity lining materials (4)
Setting CaOH (liner) ZnO-based cements (base) GIC and RMGIC (base/liner) Palliative cements (base - rarely used)
34
Constituents of CaOH liner base (2)
Base - CaOH, ZnO filler, Zn stearate filler, N-ethyl toluene sulphonamide plasticiser Catalyst - butylene glycol disalicylate reactive element, TiO2 filler, CaSO4 filler, Ca tungstate filler and radiopaque
35
CaOH setting reaction (2)
Chelation reaction between the ZnO and the butylene glycol disalicylate Results in cement with initial pH around 12
36
Mode of action of CaOH liner (2)
Bactericidal to cariogenic bacteria (alkaline pH kills bacteria) Irritation (to odontoblast layer --> necrosis) --> reparative tertiary dentine formation
37
Good CaOH liner properties (3)
Quick setting time Radiopaque Easy to use
38
Bad CaOH liner properties (3)
Low compressive strength Unstable Soluble
39
Types of ZnO-based cements (5)
``` Zinc phosphate Zinc polycarboxylate Zinc oxide eugenol (ZOE) Resin modified ZOE Ethoxybenzoic acid (EBA) ZOE ```
40
ZnPO4 cement initial reaction (2)
Acid base reaction between powder and liquid ZnO + 2H3PO4 --> Zn(H2PO4)2 + H2O
41
ZnPO4 secondary reaction (2)
Hydration reaction resulting in the formation of a crystallised phosphate matrix: ZnO + Zn(H2PO4)2 + 2H2O --> Zn3(H2PO4).4H2O (hopiete)
42
Components of ZnPO4 (2)
Powder - ZnO, MgO2 (increase compressive strength), other oxides (improve physical properties) Liquid - aqueous phosphoric acid, oxides (buffer solution), ZnO (slows reaction, better working time)
43
Purpose of AlO in ZnPO4 (3)
Prevents crystallisation leading to an an amorphous glassy matrix of the acid salt surrounding unreacted ZnO powder The matrix is almost insoluble, but it is porous and contains free water from the setting reaction The cement subsequently matures, binding this water leading to a stronger, less porous material
44
Good ZnPO4 properties (2)
Cheap | Easy to use
45
Bad ZnPO4 properties (7)
``` Low initial pH (pH 2) can cause pulpal irritation as the pH takes 24 hours to return to neutral Exothermic setting reaction Not adhesive to tooth or restoration Not cariostatic Final set takes 24 hours Brittle Opaque ```
46
ZnPO4 retention
Retention may be slightly micromechanical due to surface irregularities of cavity
47
Benefit of Zn polycarboxylate over ZnPO4 (2)
Similar material, but phosphoric acid is replaced by polyacrylic acid There is less heat of reaction and the pH is low to begin with but returns to neutral more quickly and longer chains do not penetrate dentine as easily This material had the advantage of bonding to tooth surfaces in a similar way to glass ionomer cements
48
Good Zn polycarboxylate features
Cheap
49
Bad Zn polycarboxylate features (5)
``` Difficult to mix and manipulate Soluble in oral environment at lower pHs Opaque Lower YM than ZnPO4 Lower compressive strength than ZnPO4 ```
50
Uses of ZOE, zinc oxide eugenol (4)
Linings/bases in deep cavities (under amalgam restorations) Temporary restorations Root canal sealer Periodontal dressings
51
ZOE setting reaction (3)
Acid base reaction ZnO + eugenol --> salt + water Chelation reaction of ZnO with eugenol to form Zn eugenolate matrix. This matrix bonds the unreacted ZnO particles
52
Good ZOE properties (3)
Adequate working time Relatively rapid setting time Radiopaque
53
Bad ZOE properties (2)
``` Low thermal conductivity Low strength (20MPa) - weak H bonds between eugenolate - would fracture if amalgam packed on top High solubility (eugenol constantly released) ```
54
Features of eugenol release (5)
Eugenol is replaced by water which leads to disintegration of the material Eugenol, when liberated, has an obtundent effect on the pulp and can reduce pain The released eugenol inhibits the set of resin-based filling materials It softens them and can cause discolouration ZOE materials should not be used under composite resin materials
55
Function of resins in RMZOE (2)
Added to the powder and the liquid | Do not take part in the reaction, but give a stronger backbone to the set material
56
Good RMZOE properties (2)
Increases the compressive strength to >40MPa making it suitable as a cavity lining Greatly decreases the solubility
57
Components of EBA ZOE cement (2)
Powder (ZnO, quartz/alumina, hydrogenated rosin) | Liquid (eugenol, ethoxybenzoic acid)
58
Function of EBA (2)
Reactive | Encourages a crystalline structure which imparts greater strength to the set material
59
Function of quartz and alumina in EBA ZOE
Reinforcing components
60
Setting of EBA ZOE
Similar to ZOE
61
Good EBA ZOE properties (2)
``` Decreased solubility Increased strength (60MPa) ```
62
Good GI lining material properties (11)
Can bond and seal dentine Can bond to the composite resin Releases fluoride over time Can be cariostatic Easy to use (two paste clicker system - light-cured/command set - long working time and conveniently short setting time) Thermal conductivity and diffusivity lower than dentine Thermal expansion similar to enamel Compressive strength is >170MPa (higher than any ZnO-based material) Radiopaque (varies between materials) Marginal seal is better than any of the other materials as there is a chemical bond to enamel and dentine Predictability seals dentine tubules, decreasing micro leakage and helps prevents post-treatment sensitivity
63
Solubility of GIC and RMGIC (2)
GIC > RMGIC | Greatest initially
64
Cytotoxic effects of GIC lining materials (2)
Benzoyl iodides and benzoyl bromides are released during the polymerisation reaction of RMGICs These are cytotoxic and can be effective against residual cavity bacteria
65
Why is complete cure of RMGIC required
As any unreacted HEMA may damage the pulp
66
GIC and RMGIC specific features (4)
Only lining able to bond restorative materials Some conventional GI materials may require to be etched prior to bonding RMGICs require no surface treatment May be possible to bond amalgam to tooth using RMGIC
67
Use of lining materials in GDH (3)
For cavities in dentine (consider use of a lining of RMGIC for amalgam and for larger cavities to be filled with composite) CaOH should only be used when the cavity approaches the pulp (either as a direct or indirect pulp cap over the deepest part of the cavity) CaOH should be covered with RMGIC prior to a final restoration being placed

BDS2 CDS DMS (15 decks)

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