7 - Luting agents Flashcards
What are examples of luting agents?
- dental cements
- composite resin
- self adhesive composite resin
- surface modifying chemicals
Describe the ideal film thickness of a luting agent.
- film thickness is dependant on the filler particle size
- film thickness must be low to allow seating of the restoration without interference
- ideally 25um or less
Describe the ideal viscosity of a luting agent.
- low viscosity prevents interference with the seating o the restoration
- the viscosity increases as the material sets, so restoration should be placed quickly and pressure maintained during set
Describe the ideal working time of a luting agent.
Long, to allow for seating of restoration
Describe the ideal setting time of a luting agent.
Short
How are luting agents mixed?
- some are encapsulated
- some use a clicker system
Describe the ideal radiopacity of a luting agent.
- ideally radiopaque
- some ceramic crowns are radiolucent so it make it easier to see the margin and any breakdown
Describe the ideal bond of a luting agent.
- marginal seal ideally chemically bonds to both the tooth and the restoration
- should be permanent and impenetrable
Describe the ideal aesthetics of a luting agent.
- tooth coloured (prevents metal restoration shining through)
- non staining (may shine through tooth)
Describe the ideal solubility of a luting agent.
LOW
Describe the cariostatic properties of a luting agent.
- fluoride releasing
- antibacterial
- helps to prevent secondary caries in crown margins
Describe the ideal biocompatibility of a luting agent.
- non toxic
- not damaging to pulp, ie neutral pH and low heat release on setting
- low thermal conductivity
Describe the ideal mechanical properties of a luting agent. (4)
- high compressive strength
- high tensile strength
- high hardness value
- similar Youngs modulus to tooth (15GPa)
Name a dental cement.
- zinc phosphate
- zinc polycarboxylate
What are the different types of GI cement?
- conventional
- resin modified
What are the different types of composite resin luting agent?
- total etch for use with DBA
- self etch
- requires etch but has own bonding agent incorporated
Describe zinc phosphate cement.
- dental cement
- acid base reaction
- powder and liquid
- easy to use
- cheap
What are the components of zinc phosphate? (3+3)
POWDER
- zinc oxide
- magnesium dioxide
- alumina and silica oxides
LIQUID
- phosphoric acid
- aluminium oxide
- zinc oxide
What are the components of zinc polycarboxylate?
POWDER
- zinc oxide
- magnesium dioxide
- alumina and silica oxides
LIQUID
- polyacrylic acid
- aluminium oxide
- zinc oxide
What are the negatives associated with zinc phosphate cement?
- low pH (2) which can cause pulpal irritation
- exothermic setting reaction
- not adhesive to tooth or restoration (acts like grout)
- not cariostatic
- final set 24hrs
- brittle
Describe zinc polycarboxylate cement.
- dental cement
- similar to zinc phosphate, phosphoric acid replaced by polyacrylic acid
- bonds to tooth surfaces
- less exothermic reaction
- low pH is for less time, therefore less pulpal irritation
- cheap
What are the negatives associated with zinc polycarboxylate cement?
- difficult to mix
- difficult to manipulate (jelly like consistency)
- soluble in oral environment
- lower modulus and compressive strength than zinc phosphate
Describe GI cement.
- particle size smaller than that of the filling material
- acid base reaction between glass and acid
- same dissolution, gelation and hardening reaction
- bonds to tooth via ion exchange from calcium and hydrogen bonding with collagen
- no chemical bond to restoration
- cheap
Describe the physical properties of GI cement. (6)
- low shrinkage
- long term stability
- relatively insoluble after set
- aesthetic
- self adhesive to tooth
- fluoride release
Describe RMGIC.
- same acid base reaction as GIC
- HEMA added to cause polymerisation resulting in rapid set
How does RMGIC properties differ from GIC?
RMGIC has
- shorter setting time
- longer working time
- higher compressive and tensile strength
- higher bond strength to tooth
- decreased solubility
What are the negatives associated with RMGIC?
- HEMA is cytotoxic and can damage pulp
- HEMA swells in a damp environment, can crack crowns or tooth (do not use to cement posts as may split root)
- no bond to restoration
Describe composite luting agents.
- variant on filling material, with smaller filler particles
- used in conjunction with DBA
- light or dual cured
- better physical properties but technique sensitive
- can chemically bond to indirect composite restorations
How do composite luting agents bond to porcelain restorations?
- hydrofluoric acid (lab use) etches the surface of porcelain to allow for micro-mechanical bonds to form
- wetting agent is required as composite luting agent and porcelain are not compatible (porcelain is hydrophilic and composite is hydrophobic)
What is silane coupling agent?
- applied to etched porcelain surface as a monolayer
- very strong bond between oxide groups on porcelain surface and silane
- other end of silane has C=C bond which bonds with composite
How do you bond to an indirect metal restoration?
- surface needs to be roughened by sandblasting for mechanical bond
- bond strengthened by chemical bonding
- requires dual curing as light does not penetrate metal
- can be used to cement most indirect restoration including posts
What material can be used to bond to a non-precious metal?
Materials with carboxylic or phosphoric acid derived resin monomers
How do you bond to a precious metal?
- change the alloy composition to allow oxide formation (eg increase copper)
- tin plate
- very technique sensitive
Describe self adhesive composite resin.
- metal coupling agent is incorporated
- anaerobic self cured material
- good film thickness
- opaque (prevents shine through of metal)
- moisture sensitive
What type of dental cement should you use for a metal ceramic crown?
GIC
What type of dental cement should you use for a metal post?
GIC
What type of dental cement should you use for a fibre post?
Dual cure composite and DBA
What type of dental cement should you use for a veneer?
Light cure composite and DBA
What type of dental cement should you use for an adhesive bridge?
Anaerobic cure composite
What type of dental cement should you use for a zirconia crown?
GIC
What type of dental cement should you use for a composite inlay?
Dual cure composite and DBA
What type of dental cement should you use for a porcelain inlay?
Dual cure composite and DBA
What type of dental cement should you use for a gold restoration?
GIC
What are temporary cements?
- used to hold temporary restorations in place whilst a permanent one if constructed
- soft for easy removal
- prep must be physically retentive
What are the components of temporary cement? (3+3)
BASE
- ZnO
- Starch
- mineral oil
ACCELERATOR
- resin
- eugenol
- carnauba wax (prevent set)
When are eugenol temporary cements contraindicated?
When the permanent restoration contains resin
