Glass Ionomer Cements

Question 1

two types of glass ionomer cements

Answer 1

1. conventional GI (anhydrous or original)

2. resin modified GI (self cure or light cure)

Question 2

uses of Glass ionomers

Answer 2

• luting (cementing tooth and prosthesis together)
• filling material
• core build up (for under crown)
• lining
• fissure sealant

Question 3

what is conventional glass ionomer made up of

Answer 3

i. liquid acid (polyacrylic and tartartic acid)
ii. glass powder base (silica and alumina primarily)

• gives ross linked polyacid matrix with alumino silicate glass particles surrounded by silica gel

Question 4

phases of conventional glass ionomer setting reaction

Answer 4

1. dissolution (acid added, H+ attacks glass, leaving silica gel around unreacted glass particles)
2. gelation (bivalent Ca ions cause cross linking with polyacid carboxyl groups [calcium polyacrylate], joining molecules together, taking several minutes)
3. hardening (trivalent aluminium ions cause further cross linking [X3], mean increased strength, takes place 30mins in to a week after)

Question 5

issues that can be encountered in the hardening phase of conventional glass ionomer and how to prevent these?

Answer 5

• excessive drying or saliva contact
• aluminium ions diffusing out of material
  - all = weakness and poor aesthetics

how to fix

• varnish
• cover with resin
• vasaline

Question 6

properties of conventional glass ionomers

Answer 6

handling
     - too long working/setting times
     - can add tartaric acid to help this
aesthetics 
     - lacks translucency
fluoride release
     - without damage to structure
     - antibacterial 
     - can recharge with fluoride

Question 7

how does conventional glass ionomer bond to enamel and dentine itself?

Answer 7

chelation between carboxyl groups and Ca of tooth (sometimes conditioned with polyacrylic acid to smooth surface)

Question 8

mechanical negatives of conventional glass ionomer

Answer 8

• worse tensile and compressive strength, wear resistance, hardness and higher solubility than composite
• brittle
• etching for bonding to composite may damage material

Question 9

mechanical positives of conventional glass ionomer

Answer 9

• good thermal properties
• no contraction on setting
• less likely to stain than composite

Question 10

reason for resin modified glass ionomer cement

Answer 10

• fix short comings of conventional with composite tech (aesthetics, physical properties and light curing) while keeping positives (F- release and bonding)

Question 11

chemical make up of resin modified glass ionomer

Answer 11

• powder = fluro-alumino-silicate glass etc.

- liquid = photoinitiators, HEMA (resin), tartaric acid etc.

Question 12

setting reaction of RMGIC

Answer 12

• more complicates acid base reaction than conventional
• dual curing = occurs as usual but with the addition of light curing (free radical methacrylate initiates polymerisation of resin matrix)
• tri curing = same as conventional (aluminium polyacrylate formation)

Question 13

what is easier to work with RMGIC or Composite

Answer 13

RMGIC

Question 14

negatives of RMGIC compared to conventional

Answer 14

• polymerisation contraction
• exothermic setting
• HEMA (resin) toxicity to pulp if not fully set
• swelling due to HEMA water uptake
• reduced strength if not fully cured and curing slows acid base reaction