Glass polyalkyenotes

Question 1

Glass polyalkenoates

Answer 1

Glass polyalkenoates are derived from polycarboxylate cements.

These are based upon zinc oxide that reacts with polycarboxylate- when it sets, it is adhesive to tooth surfaces however have a poor apperance and poor mechanical properties

Question 2

What does glass polyalkenoate powder and liquid contain

Answer 2

Powder- contains sodium aluminosilicate glass with 20% CaF

Liquid- aqueous solution of acrylic/ Itaconic acid plus tartaric acid

Question 3

What type of reaction is the setting reaction

Answer 3

Acid base reaction- siliceous hydrogel plus water. Unreacted glass cores surrounded by a silaceous hydrogel

Question 4

What increases the porosity of the setting reaction- hand or mechanical mixing

Answer 4

Mechanical mixing as it is more likely to froth

Question 5

What occurs in the setting reaction

Answer 5

Ions of the glass particles liberate poly acid chains that are involved in cross linking. At the initial calcium dominates but the final set aluminium.

Question 6

Why are there more calcium ions in the initial set compared to the final set

Answer 6

Initial set- As a solvent, calcium is more mobile than aluminium- due to its ionic radii-

Aluminium wants to cross link with 3 chains whereas calcium with 2- statistically more likely for 2 chain cross linkage to happen

Question 7

What are the implications of two sets

Answer 7

Material is not fully set until 24 hours after placement- material is sensitive to moisture until the final set is complete e.g. with the application of varnish

Question 8

What are the properties of GI

Answer 8

1|) fluoride release- from the glass itself

2) tooth coloured and translucent
3) biocompatibile
4) brittle and relatively poor abrasion resistance
5) cross link with calcium ions and collagen- boost with tooth cleanser (citric acid removes smear layer)
6) thermal diffusivity is close to dentine- chemical set is exothermic

Question 9

RMGIC

Answer 9

Resin modified glass ionomer

Question 10

What are RMGIC- modified composites

Answer 10

These are similar to resin composite- but the filler is replaced by aluminosilicate glass- the aim of it is to encourage fluoride release.

Acid base reaction occurs- resin is modified to contain acidic groups- once the water is set- it undergoes an acid base reaction

Setting by light cured free radical polymerisation

Question 11

What are GIomers

Answer 11

Composition of modified composite- aluminisilicate glass is pre-reacted with poly acid to form pre-reacted polyalkenoate complex.

it has a surface reaction (reaction only at the surface particles and a full reaction (reaction is of all the particles with the expense of properties)

Question 12

what are resin modified glass ionomer cements

Answer 12

Powder and liquid where the mixing initiates the acid base reaction-

Question 13

What do these resin modified products do

Answer 13

They cause significant shrinkage

PS: resin modified glass ionomer- can expand in water and help seal the cavity.

Question 14

What are the properties of resin modified products

Answer 14

1) adhesion is limited to the presence of active acid species therefore may need to provide additional chemical agents to the tooth to promote bonding.
2) fluoride release occurs but at the expense of the product disintegrating.

Question 15

What are the advantages of composite and glass polyalkelnoate

Answer 15

composite- strong, tongue, insoluble, radiopaque with quick setting.

glass polyalkenoate- little shrinkage. causes fluoride release and does inherent adhesion.

Question 16

What are the disadvantages of composite and glass polyalkelnoate

Answer 16

There is no inherent adhesion, shrinkage and no fluoride release with composite.

Glass polyalkenoates- brittle, soluble, not radiopaque, wear prone, water sensitive and has a slow set.