Cavity Linings Flashcards
(112 cards)
1
Q
What are examples of materials that are placed into tooth cavities? (5 points)
A
- Composite resin
- Glass ionomer
- Amalgam
- Precious metal
- Ceramic
2
Q
One disadvantage of restorations is that they may not make intimate contact with the tooth surface (especially dentine). What can this lead to?
A
- Any gap may allow ingress of fluids and bacteria
3
Q
A disadvantage of restorations is that heat may be release during setting/curing. What can this have an effect on?
A
- Potentially detrimental effect on the pulp
4
Q
A disadvantage of restorations is that there may be a release of chemical. What my this lead to?
A
- They may be pulpal irritants and lead to pain or pulpal damage
5
Q
What are the functions of a lining material? (2 points)
A
- Prevents gaps
- Acts as a protective barrier
6
Q
What is a cavity base?
A
- A thick mix placed in bulk
7
Q
What is a cavity base used for?
A
- Dentine replacement used to minimise the bulk of material or block out undercuts
8
Q
Where are cavity bases more common?
A
- In metal restorations (direct of indirect)
9
Q
What is a cavity lining?
A
- A thin coating (<0.5mm) over EXPOSED dentine
- Van Noort ‘A dentine sealer able to promote the health of the pulp by adhering to the tooth structure of by an anti-bacterial action’ - RMGI does this to a certain extent
10
Q
One purpose of a liner is for pulpal protection. What is the protection from? (3 points)
A
- Chemical stimuli from unreacted chemicals in the filling material or the initial pH of the filling
- Thermal stimuli e.g. exothermic setting reaction of composite or heat conducted through metal fillings
- Bacteria and exotoxins. Microleakage - the penetration of oral fluids and bacteria and their toxins between the restorative and the cavity walls
11
Q
What is microleakage?
A
- The penetration of oral fluids and bacteria and their toxins between the restorative material and the cavity walls
12
Q
One purpose of a liner is to have a therapeutic effect. What does this mean?
A
- To calm down inflammation within the pulp and promote pulpal healing
- Prior to or at the time of a permanent restoration being placed
13
Q
One purpose of a liner is to have a palliative effect. What does this mean?
A
- To reduce patient symptoms prior to definitive treatment being carried out. Most commonly in patients with reversible pulpitis
- More insulation before placing a final restoration
14
Q
What are the properties of lining materials? (9 points)
A
- Ease of use
- Thermal properties
- Mechanical properties
- Radiopaque
- Marginal seal
- Solubility
- Cariogenic
- Biocompatible
- Compatible with restorative materials
15
Q
What makes lining materials easy to use?
A
- Easy to mix
- Working time should be long to allow easy placement
- setting time short - ideally command set
16
Q
What should the thermal properties of lining materials be? (3 points)
A
- Thermal conductivity should be low
- Thermal expansion coefficient should be similar to dentine
- Thermal diffusivity should be similar to dentine or lower
17
Q
What is thermal conductivity?
A
- How well heat energy is transferred through a material
18
Q
What is the thermal expansion coefficient?
A
- Change in length per unit length for a temperature rise of 1 degree
- Units are ppm/degree celcius^-1
19
Q
Ideally what should the thermal expansion coefficient of a lining material be?
A
- Ideally a liner should match the thermal coefficient of a tooth
- Enamel = 8.3
- Dentine = 11.4
- GIC - 11
- RMGIC - 20
- Composite - 25
- Amalgam - 25
20
Q
What is thermal diffusivity?
A
- The thermal conductivity of a substance divided by the product of its density and its specific heat capacity
- IT is similar to conductivity
21
Q
What unit is thermal diffusivity measured in?
A
- cm^2/sec
22
Q
Ideally what should the thermal diffusivity of a lining material be?
A
- Ideally at least as low as the tooth
- Enamel = 0.0042cm^2/sec
- Dentine = 0.0026cm^2/sec
23
Q
What is the thermal diffusivity of liners like compared to toot h enamel?
A
- All commercially available liners have similar or lower thermal diffusivity than tooth enamel
24
Q
What is the thermal diffusivity of amalgam?
A
- 1.7cm^2/sec
- Amalgam is 500x more than dentine
25
What are the mechanical properties of lining materials? (2 points)
- High compressive strength
| - Modulus is similar to dentine
26
Why do lining materials need a high compressive strength?
- To allow the placement of a filling on top without it breaking
- Dentine is about 275MPa
27
Why does the modulus of elasticity of a lining material have to be similar to dentine?
- If the tooth bends and flexes, want the lining material to do the same
- Want it to be around 15MPa
28
Why do lining materials need to be radiopaque? (2 points)
- As it should be easy to see the difference between the lining and the tooth
- Makes it easier to see if there is any leakage or secondary caries
29
Ideally a lining material should form a chemical bond to dentine. What properties do you want from the bond? (2 points)
- The bond should be permanent and impermeable
30
What should the solubility of a lining material be like ?
- Solubility should be low
31
What does cariostatic mean?
- Tending to inhibit the formation of dental caries
32
What are the cariostatic properties of lining materials and why are they important? (3 points)
- Fluoride releasing
- Antibacterial
- Important in preventing secondary caries around the restoration
33
Why are cariostatic features of lining materials important?
- They are important in preventing secondary caries around the restoration
34
Are lining materials toxic to the pulp?
- No
35
lining materials are not damaging to the pulp. What 3 factors ensure this?
- They have a neutral pH
- There is no excessive heat during setting
- They have a low thermal conductivity
36
Is setting calcium hydroxide a base or a liner?
- A liner
37
Are zinc oxide based cements a base or a liner?
- A base
38
Are GI and RMGIC's bases or liners?
- Can be a base or a liner
39
Are palliative cements bases or liners?
- A base (seldom used nowadays, mainly historic)
40
How many pastes are setting calcium hydroxide liners composed of?
- 2 pastes
41
What are 2 examples of setting calcium hydroxide liners?
- Life
| - Dycal (used most of the time in the dental hospital)
42
What are the 2 constituents of a setting calcium hydroxide liner?
- A base
| - A catalyst
43
What are the 4 components of the base in a setting calcium hydroxide liner?
- Calcium hydroxide 50%
- Zinc oxide (filler) 10%
- Zinc Stearate (filler) <1%
- N-ethyl toluene sulphonamide (plasticiser) 40%
44
What are the 4 components of the catalyst in 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%
45
What is the setting reaction of setting calcium hydroxide liner?
- A chelation reaction between the ZnO and the butylene glycol disalicylate
46
The setting reaction of setting calcium hydroxide liners results in a cement with an initial pH of around 12. Why is this good? (2 points)
- As all of the microbes that cause caries like to live in acidic conditions
- It also causes a degree of irritation in the pulp which causes the lay down of tertiary dentine so increases the distance between where the cavity was and where the pulp starts
47
Why is a CaOH liner bactericidal to cariogenic bacteria?
- Cariogenic bacterial suirvive in an acidic environment. The highly alkaline liner kills the bugs
48
Why does irritation of the pulp by CaOH liners result in reparative dentine formation?
- The cement causes irritation to the odontoblast layer
- Necrosis follows which in turn results in a layer of tertiary dentine being produced
- This eventually forms a calcified bri dge walling the base from the pulp. (The calcium comes from the pulp not the cement)
49
What are 3 advantageous properties of CaOH?
- Quick setting time
- Radiopaque
- Easy to use
50
What are 2 disadvantageous properties of CaOH?
- Low compressive strength (if try to pack amalgam filling in top of it, it will probably break)
- It may even disappear just because it if in contact with moist dentine
51
What are 5 examples of Zinc Oxide based cements?
- Zinc phosphate
- Zinc Polycarboxylate
- Zinc Oxide Eugenol (ZOE)
- Resin modified ZOE
- Ethoxybenzoic acid (EBA) (ZOE)
52
How long has Zinc Phosphate cement been used for?
- In use for 100+ years
53
Zinc phosphate cement is produced by an acid base reaction with a powder and a liquid. What is the powder and liquid components?
Powder = Zinc Oxide
Liquid = Phosphoric acid
54
What are 3 advantages of using Zinc Phosphate cement as a lining material?
- Excellent clinical service
- Easy to use
- Cheap
55
What is the powder in Zinc Phosphate cement composed of? (3 points)
- Zinc Oxide >90% (main reactive ingredient)
- Magnesium dioxide <10%
- Other Oxides (alumina and Silica)
56
What 2 things does the magnesium dioxide component of the powder in Zinc Phosphate cements do?
- Gives white colour
| - Increases compressive strength
57
What 2 things does the Oxide components (Alumina and Silica) of the powder in Zinc Phosphate cements do?
- Improves physical properties
| - Alters the shade of the set material
58
What is the liquid component of Zinc Phosphate cements composed of? (2 points)
- Aqueous solution of phosphoric acid (approx. 50%)
- Oxides which buffer the solution:
* aluminium oxide = ensures even consistency of set material
* Zinc oxide = slows the reaction giving better working time
59
What does the aluminium oxide component of the liquid in Zinc oxide cements do?
- Ensures even consistency of set material
60
What does the zinc oxide component of the liquid in Zinc oxide cements do?
- Slows the reaction giving better working time
61
What reactions are involved in producing Zinc Phosphate cement? (5 points)
- The initial reaction is acid base
- This is followed by a hydration reaction resulting in the formation of a crystallised phosphate matrix
- The aluminium oxide prevents crystallisation leading to an amorphous glassy matrix of the acid salt surrounding unreacted ZnO powder
- This 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
62
One problem with Zinc Phosphate cement is that it has a low initial pH of approx. 2. Why is this a problem?
- It can cause pulpal irritation as pH can take 24 hours to return to neutral
63
Is Zinc phosphate cement an endothermic or exothermic reaction?
- Exothermic
64
One problem with Zinc Phosphate cement is that it is not adhesive to the tooth or restoration. Why is this a problem?
- Retention may be slightly micromechanical due to the surface irregularities of the cavity
65
Is Zinc phosphate cement cariostatic?
- No
66
How long does it take for Zinc phosphate cement to completely set?
- Final set takes 24 hours
| - It is reasonably hard within 5 minutes
67
Is Zinc phosphate cement brittle?
- Yes
68
Is zinc phosphate cement opaque?
- Yes
69
Zinc polycarboxylate is similar to Zinc phosphate. What is the difference?
- Phosphoric acid is replaced by polyacrylic acid
70
What are the advantages of Zinc polycarboxylate cement as a liner? (4 points)
- Bonds to tooth surfaces in similar way to GIC's
- Less heat of reaction
- pH is low to begin with but returns to neutral more quickly and longer chain acids do not penetrate dentine as easily
- Cheap
71
What are the disadvantages of Zinc Polycarboxylate cement as a lining? (5 points)
- Difficult to mix
- Difficult to manipulate
- Soluble in oral environment at lower pH
- Opaque
- Lower modulus and compressive strength than Zinc phosphate
72
What are Zinc Oxide Eugenol (ZOE) cements used for? (4 points)
Linings/base in deep cavities
- Under amalgam restorations
Temporary restorations
- Resin modified or EBA ZOE
Root canal sealer
- Slow setting 24hrs
Periodontal dressings
- Fast setting, 5 mins
73
Zinc Oxide Eugenol cement is a base acid reaction. What is the base and what is the acid?
Base = ZnO
Acid = Eugenol
Base + Acid --> Salt + Water
74
What is the setting reaction of Zinc Oxide Eugenol?
- Chelation reaction of Zinc Oxide with the eugenol to form zinc eugenolate matrix
- This matrix bonds the unreacted ZnO particles
75
What is the working time of ZOE like?
- Adequate working time
76
What is the setting time of ZOE like?
Relatively rapid setting time
- Sets quicker in the mouth due to moisture and heat
- Can be modified by the addition of accelerators
77
What is the thermal conductivity of ZOE like?
- Low thermal conductivity
78
What is the strength of ZOE like?
Low strength, around 20MPa
- Weak hydrogen bonds between the eugenolate molecules
- Not strong enough to use as a base beneath as amalgam filling. The packing pressure would damage it.
79
Is ZOE radiopaque?
- Yes
80
What is the solubility of ZOE like?
- Highly soluble
- Eugenol is constantly released:
This is good and bad:
- Eugenol is replaced by water which -> disintegration of the material BUT
- Eugenol when liberated has an obtundent effect on the pulp and can reduce pain
81
Why should ZOE materials NOT be used under composite resin materials?
- As the release of eugenol inhibits the set of resin based filling materials. It softens them and can cause discolouration
82
Resins can be added to the powder and liquid of ZOE to make resin modified ZOE. What resins are added to IRM and Kalzinol?
- IRM = Polymethylmethacrylate
| - Kalzinol = Polystyrene
83
Resins added to ZOE do not take part in the reaction. What do they do?
- They give a stronger backbone to the set material
84
Adding resins to ZOE increases the compressive strength to >40MPa. What does this make ZOE suitable for?
- Suitable as a cavity lining
85
What does adding resins to ZOE do to the solubility of it?
- Greatly decreases the solubility
86
Ethoxybenzoic acid (EBA) cement is a modified ZOE. What is the composition of the powder component of this? (3 points)
- ZnO 65%
- Quartz or Alumina 35%
- Hydrogenated rosin (around 6%)
87
Ethoxybenzoic acid (EBA) cement is a modified ZOE. What is the composition of the liquid component of this? (2 points)
- Eugenol 37%
| - Ethoxybenzoic acid EBA 63%
88
What does the inclusion of quartz and alumina in EBA do?
- Makes the cement stronger
| - It is reinforcing
89
The setting reaction of EBA is similar to that of ZOE. What is the difference?
- EBA encourages a crystalline structure which imparts greater strength to the set material
90
EBA is stronger than ZOE or Resin modified ZOE. What is the strength of EBA?
Around 60MPa which is more than strong enough to place an amalgam filling onto it
91
Is EBA more or less soluble than ZOE?
- Less soluble
92
What are the most widely used lining materials?
- Glass ionomer lining
93
Can glass ionomer bond to dentine?
- Yes, can bond to and seal dentine
94
Can glass ionomer bond to composite?
- Yes
95
Is glass ionomer cariostatic?
- Yes, as it releases fluoride over time
96
Are glass ionomer lining materials easy to use?
- Yes, mixing is simple and many materials come as a two paste 'clicker' system
97
Glass ionomer lining materials are generally light cured and so are command set. What does this allow?
- Gives a ling working time and a conveniently short setting time (30 seconds)
98
What is the thermal conductivity and diffusivity of glass ionomer lining materials like compared to dentine?
- Lower than dentine for both GIC and RMGIC
99
What is the thermal expansion of GIC and RMGIC's like compared to dentine?
- Similar to dentine
| - RMGIC is a little bit less so
100
What is the compressive strength of GIC's?
- >170MPa, higher than any of the ZnO based materials
| - Not quite as high as dentine though
101
Are GIC's radiopaque?
- Yes, most of them are, but the radiopacity varies between materials
102
What is the marginal seal of GIC's to dentine like?
- Better than any other materials as there is a chemical bond to enamel and dentine
103
What feature of GIC's decreases microleakage and helps to prevent post treatment sensitivity?
- As GIC's are the only material to predictably seal dentinal tubules
104
What is the solubility of GIC and RMGIC's like compared to other lining materials? (3 points)
- Solubility is greater for GIC than RMGIC and is greatest initially
- However, GIC materials are less soluble than any of the other liners apart from Zinc phosphate cement
- RMGIC is less soluble than any other cement
105
Benzoyl iodides and benzoyl bromides are released during the polymerisation reaction of RMGIC's. What does this lead to?
- These are cytotoxic and can be effective against residual cavity bacteria
106
Why is complete cure of RMGIC's required?
- As any unreacted HEMA may damage the pulp
107
Which lining material id the only one able to bond to restorative materials?
- GIC's
108
What do some conventional glass ionomers require prior to bonding?
- Some require to be etched
109
Do RMGIC's require any surface treatment?
- No
110
Is it possible to bond amalgam to a tooth using RMGIC?
- Yes
111
What are the dental hospital guidelines for cavities in dentine?
- Consider the use of a lining RMGIC (such as Vitrebond) for amalgam and for larger cavities to be filled with composite
112
What are the dental hospital lining guidelines for calcium hydroxide? (2 points)
- It 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
- Calcium hydroxide should be covered with RMGIC prior to the final restoration being placed
