Dental luting agents Flashcards
What is luting agent another word for?
- Dental cement
What is the ideal film thickness of luting agent?
- 25um or less
What is the ideal viscosity for luting agent?
- Must be low to allow seating of restoration without interference
- Viscosity increases as material sets therefore must seat restoration quickly and maintain pressure
What ease of use properties should luting agents have?
- Easy to mix i.e via clicker system in encapsulated ones
- Working time long to allow for seating of restoration
- Setting time short
Why must luting agents be radiopaque?
- Some ceramic crowns are radiolucent
- Makes it easier to see marginal breakdown
Ideally how should a luting agent bond to tooth and indirect restoration?
- Bond chemically to tooth and indirect rest with a permanent and impenetrable bond
What is the ideal aesthetics of luting agents?
- Tooth coloured with variation in shades and translucency
- Non staining
What is the ideal solubility of luting agent?
- Low
What is the ideal cariostatic properties of luting agents?
- Fluoride releasing
- Antibacterial
- Important in preventing secondary caries around crown margins
What is the ideal biocompatibility of luting agents?
- Non toxic
- Not damaging to the pulp (inappropriate pH and heat on setting)
- Low thermal conductivity
What are the ideal mechanical properties of luting agents?
- High compressive strength (dentine 275MPa)
- High tensile strength (dentine 50MPa)
- High hardness value (dentine 70K and enamel 400k)
- Young modulus similar to tooth (dentine 15GPa)
- No luting agent gets close to tooth values for more than one or two physical properties*
What are the types of dental cement?
- Zinc phosphate
- Zinc polycarboxylate
What are the types of glass ionomer cement?
- Conventional
- Resin modified
What are the types of composite resin luting agents?
- Total etch for use with DBA
- Self etch
- Requires etch but has own bonding agent incorporated
What is zinc phosphate?
- In use for 100+years
- Acid base reaction
- Powder and liquid
- Excellent clinical service
- Easy to use
- Cheap
What is the constituents of zinc phosphate powder?
- Zinc oxide >90% (main reactive ingredient)
- Magnesium dioxide <10%
- Other oxides (alumina and silica)
What is magnesium dioxide used for in zinc phosphate powder?
- Gives white colour
- Increases compressive strength
What are alumina and silica used for in the powder of zinc phosphate cement?
- Improves physical properties
- Alter shade of set material
What are the constituents of zinc phosphate liquid?
- Aqueous sol of phosphoric acid (approx 50%)
- Aluminium oxide that ensures even consistency of set material
- Zinc oxide slows the reaction giving better working time
What are the reactions of the zinc phosphate cement?
- Initial acid base reaction
- Followed by hydration reaction
- Results in formation of crystallised phosphate matrix
What does the aluminium oxide prevent in Zinc phosphate?
- Prevent crystallisation leading to amorphous glassy matrix of acid salt surrounding unreacted ZnO powder
What happens when zinc phosphate cement matures?
- Matrix originally insoluble but it is porous and contains free water from setting reaction
- When it matures it binds the water
- Leads to stronger, less porous material
What are the disadvantages of zinc phosphate cement?
- Low initial pH approx 2
- Exothermic setting reaction (release heat)
- Not adhesive to tooth or restoration
- Not cariostatic
- Final set takes 24hrs
- Brittle
- Opaque
What can a low pH lead to?
- Pulpal irritation
How is zinc phosphate retained in tooth?
- Works like grout on tiles and fills spaces
- Retention slightly micromechanical due to surface irregularities on prep and restoration
What are the constituents of Zinc Polycarboxylate cement?
- Aqueous sol of polyacrylic acid (approx 50%)
- Aluminium oxide
- Zinc oxide
- Zinc oxide >90% (main reactive ingredient)
- Magnesium dioxide <10%
- Other oxides (alumina and silica)
What are some negatives of Zinc Polycarboxylate cement?
- Difficult to mix
- Difficult to manipulate
- Soluble in oral environment at lower pH
- Opaque
- Lower modulus and compressive strength than Zinc phosphate
How does the glass ionomer cement bond to tooth surface?
- Ion exchange with calcium in enamel and dentine
- Hydrogen bonding with collagen in dentine
- Results in fairly strong, durable bond to tooth
- No chemical bond to restoration surface
What are the advantages of glass ionomer cements?
- Clinically easy to use and durable cement
- Low shrinkage
- Long term stability
- Relatively insoluble once fully set
- Aesthetically better than Zinc phosphate
- Self adhesive to tooth substance
- Fluoride release
- Cheap
What monomer does the RMGI cement liquid have in addition to conventional GIC powder?
- Hydrophillic monomer
- Must be hydrophilic as GIC is water based material
- HEMA (Hydroxyethyl methacrylate)
How is the RMGI set?
- Light activation causes polymerisation of HEMA and any copolymers = rapid initial set
- Acid base reaction continues for some time
- Some materials have secondary cure via REDOX
- Allows Dark curing
What is Dark curing?
- Material not exposed to light will cure
What are some advantages of RMGI?
- Shorter setting time
- Longer working time
- Higher compressive and tensile strengths
- Higher bond strength to tooth
- Decreased solubility
What are some potential problems with RMGI?
- HEMA is cytotoxic (can damage pulp if any remain)
- HEMA swells (expands in wet environment so can’t use conventional porcelain crowns as may crack
- No bond to indirect restoration
What are the advantages and disadvantages of composite luting agents?
- Can be light or dual cured
- Better physical properties, lower solubility and better aesthetics
- But technique sensitive
What are the advantages and disadvantages to bonding to indirect composite?
- Composite bonds to composite
- Bond strength lower to inlay fitting than new composite
- Bond is micromechanical to rough internal surface of inlay
- Bond is chemical C=C bonds on fitting surface of inlay
- Use dual curing cement as light penetration through inlay is poor
Why does porcelain need to be treated with 10% HF in order to bond to tooth?
- Porcelain is brittle and needs to be bonded to tooth to prevent fracture
- Untreated porcelain is smooth and non retentive
- Treated with HF to etch surface (toxic)
- Leads to rough retentive surface
- Allows silane bonded coupling agent to adhere
What is a silane coupling agent and how does it bond?
- Gamma-methacryoxypropyltrimothoxysilane
- Applied to etched porcelain surface as monolayer
- Strong bond between oxide groups on porcelain surface and silane
- Other end of silane molecule has C=C bond which reacts with composite resin luting agent
- Works same manner as dentine bonding agent
When curing a composite luting agent to porcelain what should you do?
- If porcelain restoration is thin use light cured
- If thick use dual cure
- Remove as much of the luting resin as poss before curing
How does composite materials bond to metal?
- Does not bond directly to metal
- Metal surface to be roughened by etching
- Usually done by sandblasting
What does etching metal lead to?
- Electrolytic etching removes diff phases of alloy at different rates
- Gives very retentive surface
- But technique sensitive
- Beryllium alloy works best
- Can’t etch precious metals at all
What is required after sandblasting a metal?
- Sandblasting roughen surface
- Does not give undercut surface of etching
- Chemical bonding required to strengthen bond
How are non-precious metals bonded?
- MDP and 4-META
- Molecules have acidic end and C=C end
- Acidic end of molecule reacts with metal oxide and surface is now hydrophobic
- Use dual cure as light doesn’t penetrate metal
How are precious metals bonded?
- Change precious alloy composition to allow oxide formation
- Increase copper content and heat 400oC in air
- Tin plate
- Sulphur based chemistry of bonding agent
- Complicated and technique sensitive
What are the advantages of self adhesive composites resins?
- Good film thickness
- Opaque
- Moisture sensitive
- Expensive
What is a self adhesive composite resin?
- Metal coupling agent incorporated into composite resin
- Simplifies bonding process
What are the advantages and disadvantages of Self etching composite resin cements (Rely X Unicem)?
- Stick to everything
- Easy to use
- Requires good moisture control
- Potential inadequate bond strength to enamel due to inadequate etching
- pH of carboxylic monomer doesn’t stay low enough enough for good etch
How do Self etching composite resin luting agents work?
- Acidic group binds with calcium in hydroxyapatite
- Forms stabilising attachment between tooth and resin
- Ions from dissolution of filler neutralise remaining acidic groups
- Forms chelate reinforced methacrylate network
- Limited removal of smear layer or sig infiltration into tooth surface
- Good bond strength to dentine
What are the properties of Self etching composite resin luting agents?
Mechanical
- Compressive strength
- Tensile strength
- Hardness
- Wear resistance
*Slightly lower than conventional resin luting agent’s but better than cements
When using a MCC what luting agent should you use?
- Glass ionomer cement
- RMGI
When using metal post what luting agent should you use?
- GIC
When using a fibre post what luting agent should you use?
- Dual cure composite and DBA
- Self adhesive composite
When using veneer what luting agent should you use?
- Light cure composite and DBA
When using adhesive bridge what luting agent should you use?
- Anaerobic cure composite
When using zirconia crown what luting agent should you use?
- GIC
- RMGIC
- Dual cure composite and DBA
- Anaerobic cure composite
- Self adhesive composite
When using composite inlay what luting agent should you use?
- Dual cure composite and DBA
- Self adhesive composite
When using porcelain inlay what luting agent should you use?
- Dual cure composite and DBA
- Self adhesive composite
When using gold restoration what luting agent should you use?
- GIC
- RMGIC
What are temporary cements used for?
- Cement temporary restorations in place whilst permanent restoration is fabricated
- Soft for easy removal and some don’t even set
- Prep must be physically retentive or doesn’t work
What are temporary cements made of?
- Two paste system (base and catalyst/accelerator)
- Base = ZnO, Starch and mineral oil
- Accelerator = resins, eugenol or ortho-EBA and carnauba wax
What is the wax for in temporary cements?
- Weakens structure of set cement
- Makes it easier to remove
- Can be made even weaker with petroleum jelly
What are the two types of temporary cements?
- With and without eugenol
What can’t eugenol containing temporary cements be used for?
- Not used to cement provisional restoration where permanent restoration will be cemented with resin cement
- Any eugenol residue can interfere with setting of resin cement
