DMS - Luting agents Flashcards
what are the ideal properties of a luting agent? (9)
low viscosity and film thickness - 25um or less - doesn’t interfere with soteatingof indirect
easy to use with short setting time
radiopaque
Good marginal seal by chemically bonding to the tooth
Natural aesthetics and non-staining
Low solubility
cariostatic - prevent secondary caries via fluoride and antibacterial properties
biocompatible - doesn’t damage the pulp
good mechanical properties - high = compressive, tensile, hardness
What types of luting agents are available?
dental cement (historic)
- zinc phosphate
- zinc polycarboxylate
GI cement
- RMGI
- GI
composite resin luting agents
What are the advantages of using dental cements as luting agents? (2)
easy to use
cheap
what 2 reactions are involved in zinc PHOSPHATE cements (dental cement)?
acid base
hydration
what are the disadvantages of zinc PHOSPHATE dental cement? (7)
Low initial pH = pulpal irritation
takes 24 hours to fully set
Exothermic setting = pulp damage
not adhesive to teeth/restoration
not cariostatic
brittle
opaque - not natural looking
what are the advantages of using zinc POLYCARBOXYLATE dental cement? (4)
Bonds to the tooth
less of an exothermic reaction
Low initial pH neutralises quickly
cheap
what are the disadvantages of zinc POLYCARBOXYLATE dental cement? (4)
difficult to use - mixing and manipulation
soluble in low pH oral environment
opaque
poorer mechanical properties - lower Youngs modulus and compressive strength
What is the difference between GI cement used for restorations vs used as a luting agent
Glass particle size is different (< 20um) to allow suitable film thickness
What reaction is involved in GI cements?
acid base reaction between glass and acid
How does GI luting agents bond to the tooth? (2)
ion exchange with calcium in enamel and dentine
hydrogen bonding with dentine collagen
what must be done to the surface of restorations to allow them to be luted with GI?
sandblasted
what are the advantages of using gI cement as a luting agent? (7)
self adhesive to the tooth surface
cheap
releases fluoride
long term stability
better aesthetic than dental cement
low shrinkage
relatively insoluble once fully set
what is the difference between GIC luting agents and RMGI luting agents?
In RMGI the the liquid contains a hydrophilic monomer - HEMA (Hydroxyethyl methacrylate)
why does the monomer used in RMGI have to be hydrophilic?
as GIC is a water based material
What causes the initial rapid set of RMGI luting agents?
Light activation = polymerisation of HEMA and other copolymers
What reaction creates the secondary cure in RMGI luting agents and allows dark curing?
REDOX
List the improved properties of the material after adding resin to the luting agent? (5)
shorter setting time
longer working time
Better bond strength to the tooth
decrease solubility
higher mechanical properties - compressive and tensile strength
What are the disadvantages of using RMGI luting agents? (3)
HEMA = cytotoxic = unreacted can lead to pulp irritation
HEMA = expands in wet environment
no bond to indirect restorations
For what types of restorations can RMGI luting agents not be used in and why? (2)
X - Porcelain crowns - can cause cracking when the HEMA expands in wet environments
X - Posts - expansion can split the root
How can we modify temporary cements to make them weaker?
adding petroleum jelly into the mix
What are the 2 types of temporary cements?
Eugenol
Non-eugenol
when should eugenol temporary cements never be used and why?
if the permanent restoration will be cemented with a resin cement
- residual eugenol may interfere with the setting of resin luting agents
Describe the types of bonds between composite and an indirect composite (2)
Micromechanical - to rough internal surface
chemical - to remaining c=c bonds on fittings surface
what type of curing is used when using composite to cement an indirect composite?
dual curing - light doesn’t penetrate the through the inlay very well
