glass ionomer cements

Question 1

what are the uses of GIC?

Answer 1

restorative
core build up
-prior to rest. w/ crown
lining
luting
-cementing indirect rest.

Question 2

what are the 2 materials in GIC?

Answer 2

zinc polycarboxylate cement

silicate cement

Question 3

what happened when silicate & zinc polycarboxylate combined?

Answer 3

glass from silicate was dissolved in polyacrylic acid from zinc cement

Question 4

why was this viewed as a good material?

Answer 4

resulted in a fluoride releasing filing material which had the ability to bond to tooth structure

Question 5

what are the 2 components?

Answer 5

acid
-liquid
base
-glass powder

Question 6

what acids are used?

Answer 6

polyacrylic acid
-usually copolymers of acrylic and itaconic acid or acrylic and maleic acid
tartaric acid
-added to control the setting characteristics of the material

Question 7

what are the powder components?

Answer 7

silica (SiO2) 30-40%
alumina (Al2O3) 15-30%
CaF2 15-35%
aluminium F 2-10%
AlPO 4-20%
NaF 4-10%

Question 8

what ratio alters the translucency and how?

Answer 8

alumina/silica

silica more translucent

Question 9

describe anhydrous material composition

Answer 9

acid is freeze dried and added to powder
liquid is distilled water
easier handling of material, particularly mixing (& storage)

Question 10

describe encapsulated materials?

Answer 10

consistent powder/liquid ratio
easier to use
should be more consistent properties of mixed materials
-this can be a disadvantage as clinically may need more wet/dry composition

Question 11

what are some variations in composition?

Answer 11

due to composition of powders
powder particle size
-smaller = quicker setting + more opaque
molecular weight of acid, higher = better mechanical properties of set material, but more viscous

Question 12

what are the 3 phases of the setting reaction?

Answer 12

dissolution
gelation
hardening

Question 13

what is the basic acid base reaction?

Answer 13

glass + acid -> salt + silica gel

Question 14

describe dissolution

Answer 14

acid into solution
H+ ions attack the glass surface
Ca, Al, NA + F ions are released
leaves silica gel around unreacted glass

Question 15

describe gelation

Answer 15

initial set due to Ca ion crosslinking with polyacid by chelation with carboxyl groups
Ca ions bivalent so they can react with 2 molecules joining them
crosslinking not ideal as the Ca can chelate w/ two carboxyl groups on the same molecule
several minutes
forms calcium polyacrylate
material -> hard

Question 16

describe hardening

Answer 16

trivalent Al ions ensure good crosslinking with an increase in strength
Al polyacrylate formation takes a long time from 30 mins- a week
aluminium reaction causes much higher degree of crosslinking
improves mechanical properties of material

Question 17

what happens if moisture contamination occurs during the setting reaction?

Answer 17

Al ions diffuse out of the material
excessive drying means water will be lost
saliva contaminations causes absorption of water
all lead to a weak material which will be rough, break up and have poor aesthetics

Question 18

what can be used for protection following placement?

Answer 18

varnishes
-copal ether
-acetate
resins
-dentine/enamel bonding agents
-unfilled Bis-GMS resins
greases or gels
-vaseline

Question 19

why is Vaseline not ideal protection?

Answer 19

quickly removed by the action of lips and tongue

Question 20

what other situation is protection required?

Answer 20

is desiccation of a GIC restoration is possible during work on other areas in the mouth
-thin layer applies to prevent surface damage due to excessive drying

Question 21

describe the handling properties

Answer 21

tartaric acid gives ease of use
setting time good
working time too long

Question 22

describe the adhesion properties

Answer 22

can bond to enamel and dentine w/o need for use of an intermediate material
low bond strength
good sealing ability w/ little leakage around margins

Question 23

what is the bonding mechanism?

Answer 23

chelation between carboxyl groups in the cement and Ca on the tooth surface
re-precipitation of complex mixture of Ca phosphate and Ca salts from polyacid onto and into the tooth surface
hydrogen/metallic ion bridging to collagen

Question 24

what is required for a good bond?

Answer 24

a clean surface
conditioned surface
-polyacrylic acid
no etch
little/no tissue removed
clean smooth surface

Question 25

what are the mechanical properties?

Answer 25

poor tensile strength
low compressive strength
poor wear resistance
low hardness
high solubility
good thermal expansion
no setting contraction
less susceptible to staining and colour change
fluoride release
low rigidity modulus

Question 26

how does it act as a fluoride reservoir?

Answer 26

initial release
recharge Fl when conc. around them is higher than in cement
release again when conc. gradient changes

Question 27

what are the uses?

Answer 27

dressing
fissure sealant
endodontic access cavity temporary filling 
luting
orthodontic cement
rest.
deciduous rest. 
base/lining

Question 28

what are the advantages of GIC?

Answer 28

stable chemical bond to enamel and dentine
low microleakage
Fl release
good thermal properties
no setting contraction

Question 29

what are the disadvantages of GIC?

Answer 29

brittle
poor wear resistance
moisture susceptible when first placed
no command set
poor aesthetics
poor handling characteristics
susceptible to acid attack and drying out over time
possible problems bonding to composite
-etching damages surface