What are disadvantages of restoratives?
- May not make intimate contact with the tooth surface (especially dentine)
– Any gap may allow ingress of fluids and bacteria (microleakage) - Heat released during setting/curing
- Release of chemicals
– These may be pulpal irritants and lead to pain or pulpal damage
What is the solution for the disadvantages?
Intermediate
A lining material
- Prevents gaps
- Acts as a protective barrier
Cavity Base Vs Lining
- Cavity Base
– Thick mix placed in bulk
– Dentine replacement used to minimise the bulk of the material or block out undercuts
– More common in metal restorations (direct or indirect) - Cavity lining
– 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 anti- bacterial action’
What is the pulpal purpose of liner?
- Pulpal Protection from
a) Chemical Stimuli from unreacted chemicals in
the filling material or the initial pH of the filling
b) Thermal Stimuli. eg. exothermic setting reaction of composite or heat conducted through metal fillings
c) Bacteria and Endotoxins. Microleakage – the penetration of oral fluids and bacteria and their toxins between the restorative and the cavity walls.
What are the general purposes of liner?
- Therapeutic. To calm down inflammation within the pulp and promote pulpal healing. Prior to or 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 reversible pulpitis.
What should the properties of lining materials be?
- Easy to mix, long working time and short setting time.
- Thermal expansion similar to dentine, Thermal diffusivity & conductivity LOW.
- High compressive strength. To allow placement of filling without it breaking (Dentine is around 275MPa)
- Elastic modulus similar to dentine (15-25 Gpa)
- Provide a marginal seal by chemically bonding to dentine.
- Radiopaque (easy to see on radiographs).
- Cariostatic = Prevents secondary caries - Fluoride releasing and Anti-bacterial.
- Biocompatible = Non-toxic and not damaging to the pulp.
What materials are bases and what materials are liners?
- Setting calcium hydroxide: Liner
- Zinc Oxide based cements: Base
- Glass Ionomer and Resin Modified Glass Ionomer cements: Base or Liner
- Palliative cements: Base (seldom used nowadays, mainly historic)
What is the setting reaction of calcium hydroxide liner and what is the pH?
Chelation (setting) reaction between a base (Calcium Hydroxide) and a catalyst
This results in a cement with an initial pH of around 12.
What is the CaOH liner highly alkaline and how does it use irritation?
- Bactericidal to cariogenic bacteria
– Cariogenic bacterial survive in an acidic
environment. The highly alkaline liner kills the bugs. - Irritation > 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 bridge walling the base of the cavity off from the pulp. (The calcium comes from the pulp not the cement).
What are the properties of CaOH liner?
good v bad
- Quick setting time
- Radiopaque
- Easy to use
But
- Low compressive strength
- Unstable and soluble
– If the cavity leaks then the lining will disappear
– It may even disappear just because it is in contact with moist dentine - Does not bond
What are examples of zinc oxide based cements?
- Zinc Phosphate
- Zinc Polycarboxylate
- Zinc Oxide Eugenol (ZOE)
- Resin Modified ZOE
- Ethoxybenzoic acid (EBA) ZOE
What is the liquid/ powder components of zinc phosphate cement?
why is good?
*Liquid
– phosphoric acid
*Power
- zinc oxide
insoluble - does not become porous
What are disadvantages of zinc phosphate cement?
Low initial pH + setting reaction is exothermic and slow - can cause pulpal irritation (for first 24 hours)
NOT Adhesive or Cariostatic
What is zinc polycarboxylate cement similar to and why is it better?
- Similar material to zinc phosphate but phosphoric acid replaced by polyacrylic acid.
- bonds to tooth surfaces
- releases less heat
- pH neutralises quicker
What are the disadvantages of zinc polycarboxylae cement?
- Difficult to mix and manipulate
- Soluable in oral environment at lower pH
- Lower modulus and compressive strength than Zinc Phosphate.
Are zinc phosphate and zinc polycarboylate used as linings nowadays?
no
Where is ZOE (zinc oxide eugenol) used?
- 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 minutes
How does zoe set?
– Chelation reaction of zinc oxide with the eugenol
to form zinc eugenolate matrix.
– This matrix bonds the unreacted ZnO particles
What are the properties of ZOE?
Low thermal conductivity & diffusivity
Sets Rapidly
High solubility
Low strength
What does the high solubility of ZOE mean?
Why is this not good for under composite resin materials?
– Eugenol is constantly released causing disintegration
of the material BUT eugenol effect on the pulp and can reduce pain
Released Eugenol inhibits the set of resin based filling materials. It softens them and can cause discoloration.
What are advantages of resin modified ZOE?
Increases the compressive strength to >40MPa making it suitable as a cavity lining. (The resin makes crack propagation more dificult as the cracks must go AROUND the resin.)
Greatly decreases solubility
How does EBA ZOE set and why is it better than resin modified ZOE?
Same as ZOE
Makes the cement less soluble and increases the strength.
(60MPa)
What is the most commonly used lining material and how does it work?
glass ionomer lining
the glass ionomer can bond to and seal the dentine
It then in turn can bond to the composite resin filling placed over it
It releases fluoride over time and can be cariostatic.
What are the properties of glass ionomer?
Thermal conductivity, diffusivity & expansion is lower than dentine.
Cariostatic - releases fluoride.
Bonds to tooth tissue & composite
Compressive strength is high (150-170MPa) - when compared to any other Zinc Oxide based cement.
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Intro22
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Bonding Systems47
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Amalgam29
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Cavity Lining Materials34
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Glass Ionomer32
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Composite 123
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Composite 224
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PMMA29
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Impression Materials20
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Gypsum22
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DMS Tutorial12
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Elastomeric Impression Materials13
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Metals & Alloys 125
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Metals & Alloys 222
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Partial Dentures15
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Luting Agents40
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Dental Ceramics48
