Cavity bases Flashcards
Define intermediate restorative materials (IRMs)
Materials applied to dentine to protect pulp prior to placing main restorative material
What is a varnish?
A very thin polymer seal to dentine surface
What is a cavity liner?
A layer of protective dentine sealer less than 500 um (0.5mm) thick
What is a cavity base?
A dentine replacement intended to eliminate undercuts or minimise bulk of main restorative material
What do IRMs do?
Most provide some form of protective function in addition to other functions to stop the pulp from getting damaged
What might adversely affect the pulp?
Physical: e.g. T or mechanical forces
Chemical: e.g. acids
may be related to:
-caries, microbial ingress or contamination
-miscellaneous (e.g. thermal or electrical stimuli)
Clinical need for IRMs
Intended to restore some of the protective barrier functions of enamel and dentine
-some direct restorative dental materials may themselves be irritant to the pulp
Properties of an ideal cavity base or liner
- Safe and biocompatible
- Forms effective dentine seal against chemicals, bacteria and other stimuli
- Encourages reparative dentine
- Chemically and mechanically compatible with other restorative materials
- Tooth coloured, radiopaque and easy to place
What materials are used as IRMs?
Varnishes Calcium hydroxide cements Zinc oxide cements GICs Resin modified GICs Visible light cured resins
What is a cavity varnish made out of?
Natural or synthetic polymer resins dissolved in a solvent
How do you apply cavity varnish?
Applied to cavity floor with brush or cotton
What happens after applying cavity varnish?
Solvent evaporates to leave thin layer of resin (process may be repeated)
What is the function of a cavity varnish?
Acts as barrier against chemical penetration of tooth tissue
May protect against microleakage and secondary caries
How are calcium hydroxide cements prepared?
Rigid self-setting material
Two pastes for mixing, chelation reaction forms zinc and calcium disalicyate and other compounds
What pH are calcium hydroxide cements? What does this do
Alkaline nature due to free Ca(OH)2
May promote secondary dentine as well as provide antibacterial properties
Calcium hydroxide cement properties
Low compressive strength (20MPa)
-sufficient to withstand condensation of amalgam
Initial pH > 11
-associated with tissue necrosis that may later mineralise –> reparative dentine
What is the UK’s leading brand of calcium hydroxide cement?
Dycal Mixing time 10s Working time 2min20s Setting time 2.5-3.5 mins Radiopaque, ivory colour Some say stimulation of secondary dentine
How are ZOEs formed?
Generally by acid-base reaction between metal oxide and eugenol
Forms metal eugenolate chelate
What are ZOEs used for?
Most commonly temporary restoration
Some developed for use as base/ liner
Are ZOEs popular as bases or liners?
Increasingly unpopular
Risk of pulpal necrosis
Inhibition of composite resin polymerisation
What is IRM (brand) used for?
Intermediate restoration designed to remain in place for up to 12 months
Or for use as base under non-resin restoration
ZOE
Properties of GICs
Relatively durable (compressive strength >50 MPa) Insoluble Fluoride releasing Aesthetic Adhesion to mineralised tooth tissue
What are GICs composed of?
Basic fluoroaluminosilicate glass
Polymeric acid
Water and
Tartaric acid
How are GICs formed?
After mixing by acid-base reaction
Metal cations form salt bridges with ionised carboxylic acid gps on high molecular weight polyacids
Phases of GIC reaction
Dissolution (acidic attack of glass surface)
Gelation (early cross-linking by CA++) Hardening (substitution of Ca++ by Al +++)
Structure of a GIC
Composite biomaterial of acid-degraded glass particles set in a cross-linked hydrogel matrix
What is a resin-modified GIC?
Like GIC but with addition of water miscible monomer (HEMA) and a photoinitiator
How are RMGICs formed?
Acid-base reaction and photo-polymerisation
Shares chemical bond to untreated dentine
What are unfilled resins used for?
Increasingly popular to seal dentine surface in a cavity
How are unfilled resins formed?
Methacrylate monomers and photoinitiator to provide command set (via polymerisation)
May be layered to increase the thickness of resin seal
Future trends for IRMs
Mineral trioxide aggregate increasingly considered for pulp capping
-claims to stimulate reparative dentine with good preservation of pulp vitality
What is Biodentine from Septodont?
Portland cement which sets through complex dissolution and re-precipitation
-used in pulp capping
What are the potential clinical benefits of Biodentine?
-Seal dentine = reduced microleakage = < sensitivity
-Thermal insulation = < sensitivity
Mechanical protection = better supported restoration
-Maybe reparative dentine formation
