Cavity bases Flashcards
Bases, liners, varnish - why we use them (22 cards)
What are intermediate restorative materials?
Materials applied to dentine to protect the pulp prior to placing the main restorative material may be collectively termed intermediate restorative materials (IRMs)
Why may you need to protect the pulp when placing a direct restorative material?
The pulp chamber is sensitive and can be affected by a range of chemical/physical stimuli and/or microbial invasion
Properties of an ideal cavity base or liner?
- Safe and biocompatible.
- Forms effective dentine seal against chemicals, bacteria, and other stimuli.
- May encourage dentine regeneration in pulp chamber (reparative dentine, may also be referred to as secondary, tertiary or reactionary).
- Chemically and mechanically compatible with other restorative materials.
- Tooth coloured, radiopaque and easy to place
What does a cavity base, liner or varnish aim to restore?
Some of the protective functions of dentine
What dental materials are used as IRMs?
- Varnishes
- Calcium hydroxide cements (e.g. Dycal®) or MTA (including Biodentine®) where pulp exposed.
- Zinc oxide cements (commonly zinc oxide-eugenol or ZOE, not popular today)
- Glass-ionomer cements (GICs)*
- Resin modified glass-ionomer cements (RMGICs)*
- Visible light cured resins
How do varnishes work?
polymer resin dissolved in solvent and applied to cavity floor
solvent evaporates leaving thin layer of polymer resin
process can be repeated
barrier against chemical penetration/microleakage/secondary caries
What are the two pastes that are mixed for CaOH cements?
- Calcium hydroxide, zinc oxide and other compounds.
2. Salicylate ester, titanium dioxide and calcium sulphate
What reaction forms zinc and calcium disalicylate and other compounds?
Chelation reaction
How can CaOH cements promote secondary dentine formation?
Alkaline nature due to free Ca(OH)2 may promote secondary dentine formation as well as provide antibacterial properties.
What are CaOH properties?
- low compressive strength but sufficient to withstand condensation of dental amalgam
- inital pH > 11 –> tissue necrosis later mineralises so stimulates and forms reparative dentine
- May be used as a protective base/liner under primary restorative - pulp cap
- slowly soluble in water
What is the mixing, working and setting time for Dycal?
Mixing time 10 s, working time 2 min 20 s,
setting time 2.5 - 3.5 minutes
Why is ZnO increasingly unpopular as an IRM?
risk of pulpal necrosis plus inhibition of composite resin polymerisation.
What is ZnO most commonly used as?
temporary restoration
How is ZnO generally formed?
by an acid-base reaction between a metal oxide and eugenol (to form a metal eugenolate chelate)
Describe the properties of IRM (the actual product)
intermediate restoration designed to remain in place for up to 12 months or for use as a base under a non-resin restoration
- ivory colour, compressive strength around 20MPa
Describe properties of GIC’s
- relatively durable
- adhesive + good marginal seal
- insoluble
- insulating
- fluoride releasing
- aesthetic
What are GIC’s composed of?
Basic fluoroaluminosilicate glass, a polymeric acid, water and tartaric acid
- acid base reaction during mixing
How are GIC’s formed?
From acid-base reactions with 3 phases
- dissolution (acidic attack of glass surface)
- gelation (early cross linking by calcium)
- hardening (substitution of calcium by aluminium)
What factors are predicted to influence biocompatibility?
Bulk compositionn
Surface chemistry
Ion release
How is a resin-modified GIC different to GIC?
Like a GIC but with the addition of a water miscible monomer (HEMA) and a photoinitiator
sets with BOTH an acid-base reaction and photo-polymerisation
What are unfilled resins used for?
May be used to seal the dentine surface in a cavity
Methcrylate monomers and photoinitiator to provide command set via polymerisation
can be layered to increase thickness
What are the clinical benefits of using a base, liner or varnish?
- Seal dentine - reduced microleakage - reduced risk of pulpal inflammation
- thermal insulation
- mechanical protection - resistance to packing or elimination of undercuts - better supported restoration
- widely held belief in stimulation of reparative dentine is sometimes questioned
