dental luting agents

Question 1

luting agent

Answer 1

dental cement

Question 2

properties of a luting agent

Answer 2

Viscosity and film thickness
Ease of Use
Radiopaque
Marginal seal
Aesthetics
Solubility
Cariostatic
Biocompatible
Mechanical properties

Question 3

viscosity and film thickness

Answer 3

depends on the size of powder or filler particles

must be low to allow seating of the restoration without interference.

viscosity increases as material sets -> must seat restoration quickly and maintain pressure.

Question 4

ease of use

Answer 4

easy to mix
long working time

Question 5

radiopaque

Answer 5

Some ceramic crowns are radiolucent
Makes it easier to see marginal breakdown

Question 6

marginal seal

Answer 6

Ideally the luting agent should bond chemically to the tooth and the indirect restoration with a permanent and impenetrable bond.

Question 7

solubility

Answer 7

low

Question 8

cariostatic

Answer 8

Fluoride releasing
Antibacterial

This is important in preventing secondary caries around crown margins.

Question 9

biocompatible

Answer 9

Not toxic
Not damaging to the pulp
Inappropriate pH
Heat on setting
Low thermal conductivity

Question 10

mechanical properties

Answer 10

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

No luting agent gets close to tooth values for more than one or two physical properties

Question 11

types of dental luting materials

Answer 11

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 12

zinc phosphate facts

Answer 12

In use for 100+ years
Acid base reaction -> followed by a hydration reaction
Powder and liquid
Excellent clinical service
Easy to use
Cheap

Powder
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

Liquid
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

Problems with this material
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 13

zinc polycarboxylate cement

Answer 13

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.

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

Question 14

glass ionomer cement

Answer 14

Chemistry of the luting cement is exactly the same as the filling material
The main difference is particle size of the glass which is less than 20um to allow for suitable film thickness
Acid base reaction between Glass and Acid
Glass is SiO2, Al2O3 and CaF2.
Poly acid mixture of Acrylic, Maleic and Itaconic acid and their copolymers.
The reaction goes through the same dissolution, gelation and hardening stages.

Cement bonds to tooth surface 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 bond to the tooth.
There is no chemical bond to the restoration surface.
The surface of the restoration should be sandblasted to allow mechanical adhesion.

Clinically easy to use and durable cement
Low shrinkage
Long term stability.
Relatively insoluble once fully set.
Aesthetically better than ZnPhos.
Self adhesive to tooth substance.
Fluoride release.
Cheap.

Question 15

resin modified glass ionomer

Answer 15

Chemistry is the same as RMGI filling material
Glass particle size is smaller to allow acceptable film thickness
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)

Light activation causes polymerisation of the HEMA and any copolymers in the material leading to a rapid initial set.

Incorporation of resin improves some material properties.
Shorter setting time
Longer working time
Higher compressive and tensile strengths
Higher bond strength to tooth
Decreased solubility

Potential problems with RMGI
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 16

composite luting agents

Answer 16

e.g. NX3

variants on composite filling materials

can be light cured or dual cured

better physical properties, lower solubility and better aesthetics
BUT
technique sensitive.

Question 17

bonding to indirect composite

Answer 17

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 18

bonding to porcelain

Answer 18

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 19

etched porcelain surface silane coupling agent

Answer 19

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 20

bonding to porcelain

Answer 20

Strong durable bond
Only use a light cured composite luting agent if the porcelain restoration is thin.
You must increase your curing time.
If the restoration is thick use a dual cured composite.
Remove as much of the luting resin as possible before curing.

Question 21

bonding to metal

Answer 21

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

Etching metal
Electrolytic etching removes the different phases of the alloy at different rates
This gives a very retentive surface
BUT
Technique sensitive

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

e.g. MDP and 4-META

Question 22

bonding to precious metal

Answer 22

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 23

self adhesive composite resin

Answer 23

e.g. panavia

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

Anaerobic self cured material
Good film thickness
Opaque
Moisture sensitive
Expensive

Question 24

self etching composite resin cements

Answer 24

e.g. rely x unicem

combination of a Composite resin cement and a
Self etching dentine bonding agent.

Sound like a great idea as it should stick to everything and it is easy to use.
However as with all dentine bonding it requires good moisture control. There is also doubt about the bond strength to enamel due to inadequate etching. The pH of the carboxylic monomer doesn’t stay low for long enough to give a good etch.

Question 25

self etching composite resin luting agents

Answer 25

Attaches like a self etching primer(sort of)
Limited removal of smear layer or significant infiltration into the tooth surface. (only a couple of microns)
Good bond strength to dentine

Mechanical properties
Compressive Strength
Tensile strength
Hardness
Wear resistance

All slightly lower than conventional Resin luting agents but better than ‘cements’

Bonding to Enamel
Lower than to dentine: should be etched with acid prior to application
Bonding to Dentine
Better than to enamel: should not be etched with acid prior to application
Bonding to Ceramics
Brand specific. RelyX unicem seem to bond quite well to sandblasted Zirconia
Bonding to Metal
Better to non-precious
Not good enough to cement ortho brackets

Question 26

temporary cements

Answer 26

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 27

types of temporary cements

Answer 27

Two main types those with and those without eugenol
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.