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BDS2; Dental materials > DML2: Cavity lining materials > Flashcards

DML2: Cavity lining materials Flashcards

1
Q

What are cavity lining materials

A
  • Intermediate restorative materials lining the cavity
  • Applied before the placement of the restorative
  • They can remain permanently within deep cavities

They are protective, palliative and therapeutic barriers for penetration through the dentinal tubules for pulp protection

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2
Q

What factors should be taken into account for cavity linings

A
  • cavity position
  • tissue conduction
  • cavity size and depth
  • oral health
  • restorative to use
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3
Q

What are the different options for cavity lining materials (7)

A
  1. Varnishes
  2. Calcium hydroxide cements
  3. Zinc oxide based cements
  4. GICs
  5. Resin modified GICs
  6. Visible light cured resins
  7. Calcium silicate based cements
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4
Q

How do cavity liners protect the pulp

A

Because they can protect the pulp from the leakage of unpolymerised resin at the margin

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5
Q

What can provide the pulp with chemical protection

A

Cavity varnish

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6
Q

What provides the pulp medication

A

Cavity liners

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7
Q

What provides the pulp with thermal and electrical protection

A

Cavity liners or base

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8
Q

What provides the pulp with mechanical protection

A

Cavity base

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9
Q

What is cavity varnish

A

This is the thinnest cavity liner which is painted onto the cut surface and is designed to act as a barrier to penetration of chemicals by doing the following

  • seal dentinal tubules
  • reduce diffusion through dentine
  • reduce microleakage

It doesnt provide added strength because it isnt chemically boned to dentine

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10
Q

What are cavity varnishes composed of

A
  1. Natural resins e.g. copal
  2. Synthetic resins e.g. polystyrene
  3. Solvent e.g. alcohol, acetone, ether
  4. Some contain calcium/zinc hydroxide
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11
Q

Why do cavity varnishes contain solvents

A

Because this allows the varnish to be painted on with a brush onto cut surfaces and the solvent will then evaporate

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12
Q

What is a cavity liner

A

This is thicker than cavity varnish and will seal the exposed dentine = 0.5mm

It promotes health of pulp as it adheres to the tooth structure and has antibacterial action

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13
Q

Give examples of cavity lining materials

A
  1. Calcium hydroxide (for pup capping)
  2. ZOE
  3. Zinc oxide non-eugenol
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14
Q

Why is calcium hydroxide cavity lining used for pulp capping

A

Because it doesn’t contain eugenol which cannot be placed directly onto the pulp

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15
Q

What is a cavity base

A

A thick mix which is placed in bulk and can act as a dentine replacement = >0.75mm

This is used in deep caries as it reduces the bulk of the restorative

It is insulating and of higher strength and blocks out undercuts

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16
Q

Give examples of cavity base materials

A
  1. Reinforced ZOE
  2. Visible light cured resins
  3. Zinc phosphate
  4. Zinc polycarboxylate
  5. Glass ionomer
  6. Resin modified glass ionomer
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17
Q

What is in the powder component of ZOE cements

A
  • ZnO (MgO)
  • SiO2, Al2O3 fillers
  • Dicalcium phosphate, mica or rosin (to improve mixing)
  • Zinc salts (accelerates set)
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18
Q

What is in the liquid component of ZOE cements (4)

A
  • eugenol
  • olive oil (modifying viscosity)
  • acetic acid 1% (accelerates set)
  • water (small amount is essential to setting)
19
Q

What is the ZOE cement setting reaction

A

An acid-base reaction to form zinc eugenolate = chelate complex; this is initiated by water which is also a byproduct of this reaction

20
Q

What is the issue with the zinc eugenolate complex not being stable

A

The setting reaction will reverse in the presence of excess water

21
Q

How is ZOE mixed

A
  • on a glass slab / oil resistant paper
  • incremental powder addition (2)
  • mixing time of 60-90 seconds
  • 2-3 mins working time
  • sets in less than 5 mins
22
Q

What produces a faster and stronger set in ZOE cements

A

A higher powder to liquid ratio and smaller particle size

23
Q

What are the advantages of ZOE cements

A
  • easy to mix an handle
  • fast set in mouth due to temp and moisture which both accelerate set
  • non-irritant pH (close to neutral)
  • obtundant (calming effect on pulp due to eugenol when placed on dentine)
  • good sealing characteristics
  • protects pulp from chemical irritation
  • good thermal insulator
24
Q

What are the disadvantages of ZOE cements

A
  1. Low compressive + tensile strengths 15-25MPa
  2. High water solubility
  3. Eugenol is a potential allergen and mild irritant
  4. Eugenol inhibits vinyl polymerisation (-C=C-) so cannot be used under composites and compomers
25
Q

What is reinforced ZOE

A

e.g. IRM

10-40% of a synthetic resin is

  • added to the powder
  • coated round the powder particles
  • styrene or MMA is added to the liquid
26
Q

What does the addition of powder, coated particles and styrene or MMA result in in reinforced ZOE composites

A
  1. Increased compressive strength 40MPa
  2. Increased tensile strength
  3. Reduced water solubility
27
Q

What are the uses of ZOE cements

A
  • Used where strength isnt important but low irritancy is
  • Not in direct pulpal contact
  • Thermal insulating base = cavity lining
  • Temporary restorations
  • Intermediate restorations
  • Long-term cementation
  • Endodontic useage
28
Q

What is a ZOE cement alternative

A

Ethoxybenzoic acid cement = EBA

29
Q

What is in the powder part of EBA cements

A
  1. ZnO = 60-75%
  2. Filler SiO2, Al2O3 = 20-35%
  3. Hydrogenated rosin = 6% (helps add viscosity)
30
Q

What is in the liquid part of EBA cements

A
  1. 50-60% of the eugenol in ZOE is replaced by ethoxybenzoic acid
  2. 35-50% eugenol
31
Q

Why do EBA cements provide greater strength

A

because it contains carboxyl groups making it more acidic

32
Q

What is an issue with EBA cements

A

Though they are less water soluble than ZOE cements, they are more soluble over time

33
Q

When are zinc oxide non-eugenol cements used

A
  • used with resin composites and compomers formed by polymerisation
  • if patients are allergic to eugenol
34
Q

What is the composition of calcium hydroxide cement

A

Paste 1 = base

  • salicylate ester = acidic component
  • fillers = TiO2, CaSO4, BaSO4 (prove set + radiopacity)

Paste 2 = catalyst

  • Ca(OH)2 = 50%
  • ZnO = 10%
  • Plasticiser = 40% (important for adequate mixing, viscosity and fast setting)
35
Q

Describe the setting reaction of calcium hydroxide cements

A
  • an acid-base reaction

- disalicylate reacts with Ca(OH)2 and ZnO forming calcium and zinc disalicylates

36
Q

Describe the mixing of calcium hydroxide cements

A

Take equal volumes of two pastes on an oil-resistant pad

  • mixing time = 5-30 seconds
  • working time = +30-60 seconds
  • setting time = +1-2 mins
37
Q

What are the advantages of calcium hydroxide cement (8)

A
  1. easy to mix and handle
  2. rapid hardening in thin layers
  3. moisture and temperature accelerates set
  4. good seal to dentine
  5. alkaline pH 9-12 so can neutralise acidic materials
  6. alkalinity makes it antibacterial
  7. stimulates reparative/sclerotic/secondary dentine
  8. compatible with composites
38
Q

How does calcium hydroxide cement stimulate secondary dentine production

A

Contact with pulp causes necrosis layer which will calcify into secondary dentine

39
Q

What are the disadvantages of calcium hydroxide cements (4)

A
  1. low strength
  2. weakened by moisture exposure
  3. can dissolve completely in acidic conditions where marginal leakage can occur
  4. can undergo plastic deformation at mouth temperature (becomes flowable under load)
40
Q

What are the uses of calcium hydroxide cements

A
  • cavity lining; especially deep cavities and pulp capping
  • with composites (as ZOE with inhibit the setting)
  • strong enough to withstand amalgam condensation pressure
  • thermal insulating agent to the pulp

Care must be taken when acid etching because it can wash away the calcium hydroxide layer so bonding wont occur

41
Q

What is a suspension liner

A

Non-setting calcium hydroxide which is 20-25um thick

  • it is a thick solution of calcium hydroxide suspended in water
  • methyl or ethyl cellulose can be added for strength making it more like a gel
42
Q

Why are visible light-cure resins used as cavity liners

A
  1. Because they are tougher and less soluble
  2. Give an increased resistance to etchants
  3. Can have an an alkaline surface pH
43
Q

What are calcium silicate-based or MTA cements used for

A
  • endodontic applications

- they are high strength alkaline and bioactive so help the pulp repair

BDS2; Dental materials (11 decks)

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