Luting Agents

Question 1

What are properties of a luting agent?

Answer 1

 Viscosity and film thickness
 Ease of Use
 Radiopaque
 Marginal seal (impenetrable bond)
 Good Aesthetics
 Low Solubility
 Cariostatic (fluoride releasing, antibacterial)
 Biocompatible (non toxic, low thermal conductivity)
 Mechanical properties

Question 2

How viscous should luting agents be and what is this dependant on?

Answer 2

 Dependant on the size of powder or filler particles in the material.
 Must be low to allow seating of the restoration without interference.
 Viscosity increases as material sets → must seat restoration quickly and maintain pressure.

Question 3

What should film thickness of the luting agent be?

Answer 3

Film thickness should be as thin as possible ideally 25um or less.

Question 4

Why should it be radiopaque?

Answer 4

easier to see marginal breakdown

Question 5

What mechanical properties should the luting agent have?

Answer 5

 High compressive strength
Dentine around 275 MPa
 High tensile strength
Dentine around 50MPa
 High Hardness Value
Dentine around 70K
Enamel around 400K
 Young’s Modulus similar to tooth Dentine around 15 GPa

Question 6

What are the types?

3 main with their subsections

Answer 6

• Dental Cement
   Zinc Phosphate
   Zinc polycarboxylate
• Glass ionomer Cement
   Conventional
   Resin modified
• Composite resin luting agents
   Total etch for use with DBA
   Self etch
   Requires etch but has own bonding agent incorporated.

Question 7

What is zinc phosphate made from and why is it good?

Answer 7

 Acid base reaction (powder and liquid)
 Excellent clinical service
 Easy to use
 Cheap

Question 8

What are the power components of zinc phosphate?

what is their role

Answer 8

Zinc Oxide >90%
- Main reactive ingredient

Magnesium Dioxide <10%
- Gives white colour
- Increases compressive strength

Other Oxides (Alumina and Silica)
- Improve physical properties
- Alter shade of set material

Question 9

What are the liquid components of zinc phosphate?

Answer 9

Aqueous solution of phosphoric acid (approx. 50%)
- Oxides which buffer the solution

Aluminium oxide
- Ensures even consistency of set material

Zinc Oxide
- Slows the reaction giving better working time

Question 10

What are the disadvantages of zinc phosphate?

Answer 10

Low initial pH approx. 2
 Can cause pulpal irritation as pH can take 24hrs to return to neutral

Exothermic setting reaction

Not adhesive to tooth or restoration
 It works like grout on tiles just filling in any spaces.
 Retention may be slightly micromechanical due to surface irregularities on prep and restoration

Not cariostatic

Final set takes 24hrs

Brittle

Opaque

Question 11

What are the advantages of zinc polycarboylate?

Answer 11

 Similar material but phosphoric acid replaced by polyacrylic acid.
 This material had the advantage of bonding 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.

Question 12

What are the disadvantages of zinc polycarboxylate?

Answer 12

 Difficult to mix
 Difficult to manipulate
 Soluable in oral environment at lower pH
 Opaque
 Lower modulus and compressive strength than Zinc Phosphate.

Question 13

What is the main difference between GI used as cement or as a filling material?

Answer 13

The main difference is particle size of the glass which is less than 20um to allow for suitable film thickness

Question 14

How does the GI cement bond to the tooth?

Answer 14

Cement bonds to tooth surface through
 Ion exchange with calcium in enamel and dentine
 Hydrogen bonding with the collagen in the dentine

Question 15

What are the advantages of GI cement?

Answer 15

 Low shrinkage
 Long term stability.
 Relatively insoluble once fully set.
 Aesthetically better than ZnPhos.
 Self adhesive to tooth substance.
 Fluoride release.
 Cheap.

Question 16

What is added to conventional GIC to make it resin modified?

Answer 16

 In addition to conventional GIC powder and liquid the liquid contains a hydrophilic monomer
 The monomer must be hydrophilic as GIC is a water based material.
 HEMA (Hydroxyethyl methacrylate)

particle size is smaller to allow acceptable film thickness

Question 17

What is the reaction of RMGI?

Answer 17

 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.

Question 18

What are the advantages of RMGI?

Answer 18

 Shorter setting time
 Longer working time
 Higher compressive and tensile strengths
 Higher bond strength to tooth
 Decreased solubility

Question 19

What are disadvantages of RMGI?

Answer 19

 HEMA is cytotoxic - Very important that no monomer remains as it 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

Question 20

What are composite luting agents and what must they be used with?

Answer 20

 The simplest of these materials are variants on composite filling materials with suitable viscosity and filler particle size.
 They must be used in conjunction with a suitable DBA.
 They can be light cured or dual cured

Question 21

How are composite luting agents technique sensitive?

Answer 21

Although dual cured the physical properties are reduced by 25% if they are not light cured.

Question 22

How does bonding of CLA occur with indirect composite?

Answer 22

 Composite bonds to composite
 Bond strength is lower to inlay fitting surface than to
new composite
 Bond is micromechanical to rough internal surface of inlay
 Bond is also chemical to remaining C=C bonds on the fitting surface of the inlay
 Use a dual curing cement as light penetration through the inlay will be poor

Question 23

How does bonding of CLA occur with porcelain?

what is required?

Answer 23

 Porcelain is brittle and requires to be bonded to tooth to prevent fracture
 Untreated porcelain is smooth and non retentive.
 It can be treated with HF to etch the surface (v toxic).
 This produces a rough retentive surface but it is still not hydrophobic and compatible with composite resin luting agents.
 A surface wetting agent is required.

Question 24

What is applied to the etched porcelain surface?

how does this help in bonding?

Answer 24

silane coupling agent

 Applied to the etched porcelain surface, ideally as a
monolayer
 Very strong bond between oxide groups on the porcelain surface and the silane.
 The other end of the silane molecule has C=C bond which reacts with the composite resin luting agent.
 This works in the same manner as a dentine bonding agent does with tooth.

Question 25

Is the bond to porcelain with CLA good?

Answer 25

yes dual cured

requires surface wetting agent

Question 26

What does bonding to metal occur with CLA require?

Answer 26

 Like porcelain composite materials do not bond directly to metal
 Metal surface needs to be roughened.
 This can be done by etching
 More usually done by sandblasting

Question 27

What does etching metal do and why is it sometimes inconvient?

Answer 27

 Electrolytic etching removes the different phases of the
alloy at different rates
 This gives a very retentive surface BUT
 Technique sensitive
 Beryllium containing alloys work best  Cannot etch precious metals at all

Question 28

After sandblasting, what is required to strengthen the bond?

Answer 28

 Sandblasting roughens the surface but does not give the undercut surface of etching.
 Chemical bonding is required to strengthen the bond

Question 29

How does bonding to non precious metals occur?

Answer 29

 Materials with carboxylic and phosphoric acid derived resin monomers.
 MDP and 4-META
 These molecules have an acidic end and a C=C end
 The acidic end of the molecule reacts with the metal oxide and renders the surface hydrophobic.
 This is the same as DBA and Silane

Question 30

How is bonding to metal cured?

Answer 30

Must use a dual curing material as light will not penetrate metal.

Question 31

How is bonding to precious metals carried outt?

Answer 31

 Change precious alloy composition to allow oxide formation
 Increase copper content and heat 400oC in air
 Tin Plate
 Sulphur based chemistry of bonding agent
 All complicated and technique sensitive.

Question 32

What is self adhesive composite resin?

Answer 32

 The metal coupling agent is incorporated into the composite resin.
 This simplifies the bonding process

Question 33

What is an example of a self adhesive composite resin?

Answer 33

MDP is used in Panavia

Question 34

What are the advantages of self adhesive composite resins?

Answer 34

 This is an anaerobic self cured material
 Consistent results over many years
 Good film thickness
 Opaque
 Moisture sensitive

Question 35

How do self etching composite resin luting agents work?

Answer 35

Attaches like a self etching primer (sort of )
 Acidic groups bind with calcium in hydroxyapatite forming a stabilising attachment between the tooth and the resin
 Ions from dissolution of filler neutralise the remaining acidic groups forming a chelate reinforced methacrylate network
 Limited removal of smear layer or significant infiltration into the tooth surface. (only a couple of microns)
 Good bond strength to dentine

Question 36

What are temporary cements?

Answer 36

Made to cement temporary restorations in place while permanent restoration is fabricated.
 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.

Question 37

What is the form of temporary cements?

Answer 37

two paste system base and catalyst/accelerator

Question 38

What are the components of temporary cements?

Answer 38

 Base contains ZnO, Starch and mineral oil
 Accelerator contains resins, eugenol or ortho-EBA and
carnauba wax
 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

Question 39

What are the two main types of temporary cements?

Answer 39

those with and those without eugenol

Question 40

When should eugenol temorary cements not be used and why?

Answer 40

 Eugenol containing materials 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.