DMS - Luting agents

Question 1

what are the ideal properties of a luting agent? (9)

Answer 1

low viscosity and film thickness - 25um or less - doesn’t interfere with soteatingof indirect

easy to use with short setting time

radiopaque

Good marginal seal by chemically bonding to the tooth

Natural aesthetics and non-staining

Low solubility

cariostatic - prevent secondary caries via fluoride and antibacterial properties

biocompatible - doesn’t damage the pulp

good mechanical properties - high = compressive, tensile, hardness

Question 2

What types of luting agents are available?

Answer 2

dental cement (historic)

• zinc phosphate
• zinc polycarboxylate

GI cement

• RMGI
• GI

composite resin luting agents

Question 3

What are the advantages of using dental cements as luting agents? (2)

Answer 3

easy to use

cheap

Question 4

what 2 reactions are involved in zinc PHOSPHATE cements (dental cement)?

Answer 4

acid base

hydration

Question 5

what are the disadvantages of zinc PHOSPHATE dental cement? (7)

Answer 5

Low initial pH = pulpal irritation

takes 24 hours to fully set

Exothermic setting = pulp damage

not adhesive to teeth/restoration

not cariostatic

brittle

opaque - not natural looking

Question 6

what are the advantages of using zinc POLYCARBOXYLATE dental cement? (4)

Answer 6

Bonds to the tooth

less of an exothermic reaction

Low initial pH neutralises quickly

cheap

Question 7

what are the disadvantages of zinc POLYCARBOXYLATE dental cement? (4)

Answer 7

difficult to use - mixing and manipulation

soluble in low pH oral environment

opaque

poorer mechanical properties - lower Youngs modulus and compressive strength

Question 8

What is the difference between GI cement used for restorations vs used as a luting agent

Answer 8

Glass particle size is different (< 20um) to allow suitable film thickness

Question 9

What reaction is involved in GI cements?

Answer 9

acid base reaction between glass and acid

Question 10

How does GI luting agents bond to the tooth? (2)

Answer 10

ion exchange with calcium in enamel and dentine

hydrogen bonding with dentine collagen

Question 11

what must be done to the surface of restorations to allow them to be luted with GI?

Answer 11

sandblasted

Question 12

what are the advantages of using gI cement as a luting agent? (7)

Answer 12

self adhesive to the tooth surface

cheap

releases fluoride

long term stability

better aesthetic than dental cement

low shrinkage

relatively insoluble once fully set

Question 13

what is the difference between GIC luting agents and RMGI luting agents?

Answer 13

In RMGI the the liquid contains a hydrophilic monomer - HEMA (Hydroxyethyl methacrylate)

Question 14

why does the monomer used in RMGI have to be hydrophilic?

Answer 14

as GIC is a water based material

Question 15

What causes the initial rapid set of RMGI luting agents?

Answer 15

Light activation = polymerisation of HEMA and other copolymers

Question 16

What reaction creates the secondary cure in RMGI luting agents and allows dark curing?

Answer 16

REDOX

Question 17

List the improved properties of the material after adding resin to the luting agent? (5)

Answer 17

shorter setting time

longer working time

Better bond strength to the tooth

decrease solubility

higher mechanical properties - compressive and tensile strength

Question 18

What are the disadvantages of using RMGI luting agents? (3)

Answer 18

HEMA = cytotoxic = unreacted can lead to pulp irritation

HEMA = expands in wet environment

no bond to indirect restorations

Question 19

For what types of restorations can RMGI luting agents not be used in and why? (2)

Answer 19

X - Porcelain crowns - can cause cracking when the HEMA expands in wet environments

X - Posts - expansion can split the root

Question 20

How can we modify temporary cements to make them weaker?

Answer 20

adding petroleum jelly into the mix

Question 21

What are the 2 types of temporary cements?

Answer 21

Eugenol

Non-eugenol

Question 22

when should eugenol temporary cements never be used and why?

Answer 22

if the permanent restoration will be cemented with a resin cement

• residual eugenol may interfere with the setting of resin luting agents

Question 23

Describe the types of bonds between composite and an indirect composite (2)

Answer 23

Micromechanical - to rough internal surface

chemical - to remaining c=c bonds on fittings surface

Question 24

what type of curing is used when using composite to cement an indirect composite?

Answer 24

dual curing - light doesn’t penetrate the through the inlay very well

Question 25

How do you achieve cementing porcelain using composite luting agents? (2)

Answer 25

etch the porcelain surface using hydrofluoric acid and use a wetting agent to bond to the luting composite

then use DBA to bond the tooth to the composite luting agent

Question 26

Describe how a silane coupling agent (a wetting agent) helps bond porcelain to the composite luting agent. (2)

Answer 26

strong bond between porcelain oxide groups on the surface and the silane.

The other end of the silane molecule has C=C bond which reacts with the composite resin luting agent.

Question 27

What type of curing is used with a composite luting agent and a thin porcelain restoration?

what type of curing is used in a thicker porcelain restoration?

Answer 27

thin = light cure

thick = dual cure

Question 28

How do you bond composite luting agents to metal? (2)

Answer 28

electrolytic etching metal surface

sandblasting metal surface

Question 29

What type of curing is used in a composite luting agent and a metal restoration?

Answer 29

dual cure as light cannot penetrate the metal