Dental Luting Agents Flashcards
Why is luting agent a better term than dental cement?
Because all dental cements are luting agents but not all luting agents are dental cements
Give 4 examples of forms of luting cements?
- Dental Cements
- Composite Resins
- Self adhesive composite resins
- Surface modifying chemicals
What are the properties we look at in a luting cement? (9)
- Viscosity and film thickness
- Ease of use
- Radiopaque
- Marginal seal
- Aesthetics
- Solubility
- Cariostatic
- Biocompatible
- Mechanical properties
What is viscosity and film thickness dependent on?
- Dependent on the size of powder or filler particles in the material as well as the flow characteristics of the material itself
What do we want the film thickness to be like in luting agents?
- Must be low to allow seating of the restoration without interference
- The cement must allow the restoration to seat fully on your preparation
- Film thickness should be as thin as possible ideally 25um or less
What do we want the viscosity to be like in luting agents?
- Viscosity increases as material sets -> must seat restoration quickly and maintain pressure during the setting process
How do we make luting agents easy to mix? (2)
- Many products are encapsulated
- Clicker system
How do we make luting agents easy to use? (3)
- Easy to mix
- Working time should be long to allow for seating of the restoration
- Setting time should be short
Do we want luting agents to be radiopaque or radiolucent?
- Some are radiolucent but we want them to be radiopaque
- Makes it easier to see marginal breakdown or secondary caries
What do we want the marginal seal to be like for a luting agent?
- Ideally the luting agent should bond chemically to the tooth and the indirect restoration with a permanent and impenetrable bond
- Some of the newer materials approach this but nothing quite reaches it yet
What do we want the aesthetics of luting agents to be like? (2)
- Tooth coloured (variation in shade and translucency)
- Non staining
What do we want the solubility of luting agents to be like?
- Low (don’t want the material to be washed away)
How are luting agents cariostatic? (2)
- Fluoride releasing
- Antibacterial
- This is important in preventing secondary caries around crown margins
In order to be biocompatible, what properties should luting agents have? (3)
- Non toxic
- Not damaging to the pulp (inappropriate pH or heat on setting)
- Low thermal conductivity to protect the pulp
What are the ideal mechanical properties of a luting agent? (4)
- High compressive strength
- High tensile strength
- High hardness value
- Young’s modulus similar to tooth
- We want the mechanical properties to be similar to that of a tooth
- No luting agent gets close to tooth values for more than one or two physical properties
Give examples of dental cements? (2)
- Zinc phosphate
- Zinc polycarboxylate
- More historic
Give examples of 2 glass ionomer cements?
- Conventional
- Resin modified
Give examples of composite resin luting agents? (3)
- Total etch for use with DBA
- Self etch
- Requires etch but has own bonding agent incorporated
Look at slides on the components of zinc phosphate cements.
Better to look at slides
What are 3 positives of zinc phosphate cements?
- Excellent clinical service
- Easy to use
- Cheap
What is the role of zinc oxide >90% in the powder of zinc phosphate cements?
- Main reactive ingredient
What is the role of magnesium dioxide <10% in the powder of zinc phosphate cements? (2)
- Gives white colour
- Increases compressive strength
What is the role of other oxides (Alumina and Silica) in the powder of zinc phosphate cements? (2)
- Improve physical properties
- Alter shade of set material
What is the role of aluminium oxide in the liquid of zinc phosphate cements?
- Ensures even consistency of set material
What is the role of zinc oxide in the liquid of zinc phosphate cements?
- Slows the reaction giving better working time
What is the initial reaction of zinc phosphate cement?
- It is acid base
What is the second reaction of zinc phosphate cements?
- A hydration reaction resulting in the formation of a crystallised phosphate matrix
Look at zinc phosphate cement reaction slide
:)
What does the aluminium oxide in zinc phosphate cements do?
- It prevents crystallisation leading to an amorphous glassy matrix of the acid salt surrounding unreacted ZnO powder
- This matrix is almost insoluble, but it is porous and contains free water from the setting reaction
- The cement subsequently matures binding this water leading to a stronger, less porous material (once it sets it is a really hard material)
List the problems with zinc phosphate cements? (7)
- Low initial pH approx. 2 (can cause pulpal irritation as pH can take 24 hours to return to neutral)
- Exothermic setting reaction (not good from a pulpal point of view)
- Not adhesive to tooth or restoration (retention might be slightly micromechanical due to surface irregularities on prep and restoration)
- Not cariostatic
- Final set takes 24 hours
- Brittle
- Opaque
Zinc polycarboxylate is a similar material to zinc phosphate. What is the difference?
- Phosphoric acid is replaced by polyacrylic acid
Why does zinc polycarboxylate have an advantage over zinc phosphate? (4)
- This material bonds to tooth surfaces in a similar way to glass ionomer cements
- There is less heat of reaction
- The pH is low to begin with but returns to neutral more quickly and longer chain acids do not penetrate dentine as easily
- Cheap
What are negatives of zinc polycarboxylate cement? (5)
- Difficult to mix
- Difficult to manipulate
- Soluble in oral environment at lower pH
- Opaque
- Lower modulus and compressive strength than Zinc Phosphate
Are dental cements used much anymore?
- These materials are mainly historic. They are seldom used nowadays. All of the more modern materials utilise chemical bonding to the tooth surface. Many of these materials can also bond to the indirect restoration as well
What is the difference between a GI louting cement and a GI filling material?
- The main difference is particle size of the glass which is less than 20um to allow for sustainable film thickness
- Because if they were bigger then there is a possibility of them interfering with the ability of the restoration to seat in the mouth
Look at reaction for GI cement in slides?
:)
One advantage of glass ionomer cements is that they bond to the tooth surface. How do they do this? (2)
Do this through:
- Ion exchange with calcium in enamel and dentine
- Hydrogen bonding with the collagen in the dentine
- This results in a fairly strong, durable and possibly dynamic bone to the tooth
- There is no chemical bone to the restoration surface
- The surface of the restoration should be sandblasted to allow mechanical adhesion
Give examples of positive characteristics of GI cements? (8)
- Clinically easy to use and durable cements
- Low shrinkage
- Long term stability
- Relatively insoluble once fully set
- Aesthetics better than zinc phosphate
- Self adhesive to tooth substance
- Fluoride release
- Cheap
What is the difference between RMGI filling material and RMGI cement?
- In cement the glass size is smaller to allow acceptable film thickness
In RMGI cements in addition to conventional GIC powder and liquid what else does the liquid contain?
- A hydrophilic monomer
- The monomer must be hydrophilic as GIC is a water based material
What is the monomer in RMGI cements?
- HEMA (hydroxyethyl methacrylate)
Explain the reaction for an RMGI cement? (5)
- The same acid base reaction occurs
- Light activation causes polymerisation of the HEMA and any copolymers in the material leading to a rapid initial set
- The acid base reaction then continues for some time
- Some materials have a secondary cure via a REDOX reaction
- This allows ‘dark curing’ where material not exposed to light will cure
Incorporation of resin in GI dental cements improvs some material properties. Give examples of these? (5)
- Shorter setting time
- Longer working time
- Higher compressive and tensile strengths
- Higher bond strength to tooth
- Decreased solubility
What are possible problems with RMGI dental cements? (3)
HEMA is cytotoxic
- Very important that no monomer remains as t can damage the pulp
HEMA swells, it expands in a wet environment
- It cannot be used to cement conventional porcelain crowns as they may crack
- It shouldn’t be used to cement posts as it may split the root
No bond to indirect restoration
What is the purpose of temporary cements?
Made to cement temporary restorations in place while permanent restoration is fabricated
What are some properties of temporary cements? (3)
- Soft for easy removal - some do not set at all
- Prep must be physically retentive or they will not work
- Can be used for trial lute of permanent restoration to allow assessment by patient or clinician
Temporary cements are supplied as a two paste system with a base and catalyst or accelerator. What do their things contain?
- Base contains ZnO, starch and mineral oil
- Accelerator contains resins, eugenol or ortho-EBA and carnauba wax (the wax makes it easy to remove)
- The wax weakens the structure of the set cement and makes it easier to remove
- Material can be modified to make it weaker still by incorporating petroleum jelly into the mixture
What are the 2 main types of temporary cement?
- Those with and those without eugenol
When should eugenol containing temporary cements not be used?
- Should not be used to cement the provisional restoration where the permanent restoration will be cemented with a resin cement
- Any residual eugenol may interfere with the setting of this type of luting agent
- Irrespective of the type used complete removal of the temporary cement is essential
What are composite luting agents?
- The simplest of these materials are variants on composite filling materials with suitable viscosity and filler particle size (reduced)
What must composite luting agents be used in conjunction with?
A suitable DBA (dentine bonding agent)
How are composite luting agents cured?
- They can be light cured or dual cured
Give 3 positives of composite luting agents over other dental cements?
- Better physical properties
- Lower solubility
- Better aesthetics
Give 1 negative of composite luting agents over other dental cements?
- They are technique sensitive
Although composite luting agents can be dual cures, what % reduction in the physical properties is there if they are not light cured?
- 25%
Not making flashcards for third part of lecture
Just read this
