Luting Agents

Question 1

What are 3 luting material groups?

Answer 1

Dental cements
GIC
Composite resin luting agents

Question 2

Why are DENTAL CEMENTS rarely used nowadays?

Answer 2

All more modern materials utilise chemical bonding to tooth surface which dental cements do not do.

Question 3

What situation would you use a dental cement (e.g. zinc phosphate) for nowadays?

Answer 3

Use as a temporary for an indirect restoration

Question 4

What are the contents of powder and liquid for zinc phosphate cement?

Answer 4

Powder
- Zinc oxide (>90% - main reactive ingredient)
- Magnesium dioxide - increases compressive strength

Liquid - aqeuous solution of phosphoric acid

Question 5

What are some problems with zinc phosphate material?

Answer 5

Low initial pH
Exothermic setting reaction - not good for pulp
Not adhesive to tooth or restoration
Not cariostatic
Final set takes 24 hours
Brittle

Question 6

What is the difference in composition between zinc phosphate and zinc polycarboxylate?

Answer 6

Similar material but in polycarboxylate has POLYACRYCLIC acid

Zinc phosphate - phosphoric acid

Question 7

What size are the glass filler particles in GIC?

Answer 7

less than 20 microns

Question 8

How does GIC bond to the tooth surface?

Answer 8

Bonds to tooth surface through ionic exchange with calcium in enamel and dentine
Hydrogen bonding with the collagen in the dentine

Question 9

Benefits of GI as luting agent

Answer 9

NO shrinkage
Long-term stability
Relatively insoluble once fully set - takes about a week
Aesthetically better than ZnPhos
Self-adhesive to tooth substance
Fluoride-releasing
Cheap

Question 10

What is the difference between composition of resin-modified GI to regular GI?

Answer 10

RMGI contains hydrophilic monomer HEMA
Monomer has to be hydrophilic as GIC is a water-based material

Question 11

What mechanical properties are improved in RMGI compared with GI?

Answer 11

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

Question 12

What are problems with HEMA monomer?

Answer 12

HEMA is cytotoxic
HEMA swells - it expands in wet environment
No bond to indirect restoration

Question 13

Advantages of Composite luting agents over cement materials?

Answer 13

Better physical properties
Lower solubility than cement materials
Better aesthetics

Question 14

Why is bonding to old composite less effective than bonding to new composite?

Answer 14

Old composites do not have free C=C on surface

Question 15

How does a DBA allow for bonding?

Answer 15

Tooth is hydrophilic
DBA makes tooth hydrophobic to allow bonding to oily composite luting resin

Question 16

What is the gold standard luting agent?

Answer 16

GI

Question 17

Why don’t you use RMGI instead of GI even though the mechanical properties are better?

Answer 17

It swells upon setting - can’t be used on porcelain crowns because they will crack.
Cannot cement posts - because it might split the root

Question 18

What is a surface wetting agent?

Answer 18

Decreases surface tension
Obtains mechanical interlocking of the surface roughness of the tooth tissue on a microscopic scale

Question 19

How do you treat the surface of a metal and ceramic in order for a silane coupling agent to bond?

Answer 19

Metal - sandblast the metal

Ceramic - etch with the hydrofluoric acid 10%