Luting Agents Flashcards
What are the 4 different materials that can be considered luting agents?
- dental cements
- composite resins
- self-adhesive composite resins
- surface modifying chemicals
What are the properties that must be considered for luting agents?
- viscosity and film thickness
- ease of use
- radiopacity
- marginal seal
- aesthetics
- solubility
- cariostatic ability
- biocompatibility
- mechanical properties
Discuss the importance of viscosity and film thickness in luting agents
- viscosity and film thickness should be low to allow seating of the restoration without interference
- viscosity must increase as the material sets
- film thickness should be as thin as possible (<25um)
How do filler particles differ in luting agents and filling materials?
- smaller filler particles in luting agents
- viscosity and film thickness dependant on the size of the filler particles
Discuss the importance of ease of use of luting agents
- should be easy to mix
- encapsulated with clicker system
- working time should be long to allow seating
- setting time should be short
Discuss the importance of radiopacity of luting agents
- highlights crown-tooth margin
- makes marginal breakdown easier to identify
Discuss the importance of marginal seal of luting agents
- should chemically bond to tooth and restoration
- bond should be permanent and impenetrable
Discuss the importance of aesthetics of luting agents
- should be tooth coloured
- variations of shade and translucency should be available
- if not translucent can affect the veneer on top
- some material may be visible so should match the colour of the restoration
- non-staining
Discuss the solubility of luting agents
- must be low solubility
Discuss the importance of cariostatic behaviour in luting agents
- prevents secondary caries around crown margins
- can be fluoride releasing or antibacterial
Discuss the importance of biocompatibility of luting agents
- must be non-toxic
- must not damage the pulp
- inappropriate pH (especially low)
- heat on setting
- low thermal conductivity
- indirect restorations are often metal based
- heat must not reach pulp
Discuss the desired mechanical properties of luting agents
- high compressive strength
- high tensile strength
- high hardness value
- Young’s modulus similar to tooth
Give two examples of dental cements
- zinc phosphate
- zinc polycarboxylate
Give two examples of glass ionomer cement
- conventional
- resin modified
Give three examples of composite resin luting agents
- total etch for use with DBA
- self-etch
- bonding agent incorporated
What are the advantages of zinc phosphate?
- excellent clinical service
- easy to use
- cheap
What are the components of zinc phosphate cement powder?
- zinc oxide
- > 90%
- main reactive ingredient
- magnesium dioxide
- <10%
- provides white colour
- increases compressive strength
- metal oxides
- e.g. alumina and silica
- improve physical properties
- alter shade of material once set
What are the components of zinc phosphate cement liquid?
- phosphoric acid
- aqueous solution around 50%
- oxides
- buffer solution
- aluminium oxide (ensures even consistency)
- zinc oxide (slows reaction)
Describe the reaction that takes place in zinc phosphate cement
- acid base reaction:
ZnO + 2H3PO4 —-> Zn(H2PO4)2 + H2O - hydration reaction:
ZnO + Zn(H2PO4)2 + 2H2O
—->
Zn3(H2PO4)2.4H2O
Discuss the setting of zinc phosphate cement after the acid-base and hydration reactions
- aluminium oxide prevents crystallisation resulting in an amorphous glassy matrix of acid salt surrounded by ZnO powder
- matrix is insoluble but porous
- hydration reaction fills spaces with free water
- cement matures and binds water leading to a stronger less porous material
Discuss the disadvantages of zinc phosphate cement
- low initial pH
- around pH2
- can cause plural irritation
- low pH for around 24 hours
- exothermic setting reaction
- heat generated
- not adhesive to tooth or restoration
- retention may be slightly micro mechanical
- best for non-retentive cavities
- removed with ultrasonic scaler
- not cariostatic
- final set takes 24 hours
- brittle
- opaque
- yellow/white in colour
What is the component that varies between zinc phosphate cement and zinc polycarboxylate cement?
the phosphoric acid is replaced with poly acrylic acid
What are the advantages of zinc polycarboxylate cement?
- bonds to tooth surface in a similar way to glass ionomer cements
- reduced exothermic reaction
- less time at low pHs
- long chain acids do not readily penetrate dentine
- cheap
What are the disadvantages of zinc polycarboxylate cement?
- difficult to mix
- difficult to manipulate, jelly like material
- soluble in the oral environment at lower pHs
- opaque
- lower modulus and compressive strength than zinc phosphate
Are zinc phosphate and zinc polycarboxylate used now?
No - mainly historic
- materials with chemical bonding more valuable
What is the difference between glass ionomer cement and glass ionomer filling material?
- the particle size of the glass particles
- less than 20um in cement
- allows for suitable film thickness
- crown can be fitted completely
Describe the acid base reaction between acid and glass which occurs in glass ionomer cement
- glass (SiO2, Al2O3, CaF2)
- polyacid mixture of acrylic, malice and itaconic acid (+copolymers)
- reaction goes through dissolution, gelation and hardening stages
Describe the bond between glass ionomer cement and tooth tissue
- ion exchange with the calcium in enamel and dentine
- hydrogen bonding with collagen in dentine
- family strong and durable bond with tooth
- no chemical bond with restoration
- restoration must be sandblasted to allow for mechanical adhesion
Describe the clinical ease and durability of glass ionomer cement
- no shrinkage
- long term stability
- relatively insoluble once set (7 days)
- aesthetically better than Zinc Phosphate
- self adhesive to tooth substance
- fluoride releasing
- cheap (£15 per bottle)
What is the additional component contained in resin modified glass ionomer cement compared to conventional?
- HEMA
- hydrophilic monomer in liquid
- HydroxyEthyl MethAcrylate
What is the effect of light activation on HEMA?
polymerisation of HEMA and copolymers leading to a rapid initial set
What are the three setting reactions for resin modified glass ionomer
- light activation
- acid base reaction
- redox
What properties are positively affected by the addition of resin?
- shorter setting time
- longer working time
- high compressive and tensile strengths
- higher bond strength to tooth tissue
- decreased solubility
- command setting
What are the potential disadvantages of resin modified glass ionomer cements
- HEMA is cytotoxic
- must be no monomer released
- can damage pulp
- HEMA swells due to moisture
- water soluble
- 1-2% expansion experienced
- not suitable for porcelain crowns (crack)
- not suitable for post crowns (root fracture)
- no bond to restoration
What must be used with composite luting agents?
a suitable dentine bonding agent
What are the disadvantages of composite luting agents?
- technique sensitive
- reduced physical properties in some cases
- for dual cure that isn’t light cured
- light cannot penetrate crowns/onlays/etc.
Give an example of a brand of composite luting agent
NX3
- Nexus Third Generation
Describe the bond between composite luting agents and indirect composites
- micro mechanical
- touch internal surface of restoration
- chemical
- remaining C=C bonds on fitting surface
dual cure must be used as light penetration will not be adequate
How do dentine bonding agents bond tooth tissue to composite luting resins?
They have hydrophobic and hydrophilic ends
- hydrophobic to composite
- hydrophilic to tooth
Why is the bond between porcelain and tooth important?
porcelain is brittle and requires a bond to prevent fracture
Describe the way in which porcelain is bonded to tooth tissue
- untreated porcelain is smooth/non-retentive
- treated with HF/HCl to etch surface
- roughened surface but is not hydrophobic
- surface wetting agent required
- phosphoric acid cannot be used to etch surface as interacts with oxide groups in the porcelain
What is the purpose of a silane coupling agent?
Gamma-methacryoxypropyltrimothoxysilane
- applied to porcelain as a monolayer
- double ended molecule with oxide and C=C
- forms strong bond with oxide on porcelain
- C=C bond with the composite resin
- same way in which DBA acts with tooth/composite
Describe bonding between composite luting agents and metal
- no bond between composite and metal
- metal must be roughened
- can be done by etching or sandblasting
- chemical bonding is required for strength
What does the process of etching metal involve?
- electrolytic etching removes the different phases of the alloy at different rates
- retentive surface produced
- technique sensitive
- Beryllium (in alloys) is carcinogenic
- precious metals cannot be etched
- rarely used technique
How is bonding to non-precious metals achieved?
- MDP and 4-META
- carboxylic and phosphoric derived
- resin monomers
- acidic end and C=C end
- acidic end reacts with metal oxide
- creates hydrophobic surface
What are the necessary considerations for bonding to metal?
- dual curing material must be used
- light cannot penetrate metal
- crowns/bridges/posts possible
- technique sensitive
- moisture control
- glass ionomer
- dissolution where wet
- less strong in areas
- composite luting agents
- dissolution where wet
- no bond in these areas
How is bonding to precious metals achieved?
- composition must be changed to allow oxide formation
- increase copper content (heat 400 degrees)
- tin plate fitting surface (oxide rich)
- sulphur based chemistry in bonding agent
What is a self-adhesive composite resin?
- metal coupling agent incorporated into resin
- simplified bonding process
- anaerobic self cured material
What are the advantages and disadvantages of self-adhesive composite resins
Advantages:
- consistent results over many years
- good film thickness
Disadvantages
- opaque (only used under metal)
- moisture sensitive
- expensive
Describe the key features of Panavia composite resin
- phosphoric acid gel, DBA, cement
- MDP used in Panavia cement
- edges covered with oxiguard or vaseline
What are self etching composite resin cements?
- combination of composite resin cement and self etching dentine bonding agent
- Rely X Unicem
- contain metal bonding agent
- good moisture control required
- questionable bond strength
- not excellent properties but multi-functional
How do self etching composite resins work?
- acidic groups bind to calcium
- ions from dissolution of filler neutralise remaining acidic groups forming chelate
- chelate reinforced methacrylate network
- limited removal of smear layer
- limited infiltration to tooth surface
- good bond strength to dentine
How do self etching composite resin luting agents compare to composite luting cements
all mechanical properties are lesser than composite luting cements
Describe the bonding capabilities of self etching composite resin luting agents
- bonding to enamel
- lower than to dentine
- acid etch required prior to application
- bonding to dentine
- better than to enamel
- no acid etch recommended
- bonding to ceramics
- brand specific
- RelyX Unicem good with sandblasted Zirconia
- bonding to metal
- better to non-precious
- not used for ortho brackets
- good for crowns
- not good for resin retained bridgework
what can be used to cement MCCs?
Yes:
- GIC
- RMGIC
Maybe:
- Dual cure composite +DBA
- Anaerobic cure composite
- Self adhesive composite
No:
- Light cure composite +DBA
what can be used to cement metal posts?
Yes:
- GIC
Maybe:
- Dual cure composite +DBA
- Anaerobic cure composite
- Self adhesive composite
No:
- RMGIC
- Light cure composite +DBA
what can be used to cement fibre posts?
Yes:
- Dual cure composite +DBA
- Self adhesive composite
Maybe:
- Anaerobic cure composite
No:
- GIC
- RMGIC
- Light cure composite +DBA
what can be used to cement veneers?
Yes:
- Light cure composite +DBA
Maybe:
- Dual cure composite +DBA
- Self adhesive composite
No:
- GIC
- RMGIC
- Anaerobic cure composite
what can be used to cement adhesive bridges?
Yes:
- Anaerobic cure composite
Maybe:
- Dual cure composite +DBA
- Self adhesive composite
No:
- GIC
- RMGIC
- Light cure composite +DBA
what can be used to cement Zirconia crowns?
Yes:
- GIC
- RMGIC
- Dual cure composite +DBA
- Anaerobic cure composite
- Self adhesive composite
No:
- Light cure composite +DBA
what can be used to cement composite inlays?
Yes:
- Dual cure composite +DBA
- Self adhesive composite
No:
- GIC
- RMGIC
- Light cure composite +DBA
- Anaerobic cure composite
what can be used to cement porcelain inlays?
Yes:
- Dual cure composite +DBA
- Self adhesive composite
No:
- GIC
- RMGIC
- Light cure composite +DBA
- Anaerobic cure composite
what can be used to cement gold restorations?
Yes:
- GIC
- RMGIC
Maybe:
- Dual cure composite +DBA
- Self adhesive composite
- Anaerobic cure composite
No:
- Light cure composite +DBA
What properties are desirable for temporary cements?
- soft, for easy removal
- potentially non-setting
- retentive prep required
What are the components of temporary cements?
- two paste systems
- base
- catalyst/accelerator
- base
- ZnO
- starch
- mineral oil
- catalyst/accelerator
- resins
- eugenol (not used for resin cements)
- ortho-EBA
- carnauba wax (prevents full set)
- vaseline can be mixed into the material to reduce the retention
