Tooth-coloured materials: GICs and their relatives Flashcards
What are the 4 different classifications of materials?
composite
compomer
GIC
RMGIC
What is the technical name for GIC and RMGIC?
glass polyalkenoate cement
resin modified glass polyalkenate cement
What is the technical name for composite and compomer?
composite
poly acid modified resin cement
Why do GIC and RMGIC have good wetting?
they are both hydrophilic
Why do compomer and composite need a bonding system?
they are both hydrophobic so need a bonding system to bond to hydrophilic tooth substrate
have bad wetting
What is the composition of glass polyalkenoates?
Fluoro-alumino-phospho-silicate glass polyacid
Some acids that can be used are polyacrylic acid, polymaleic acid
Some newer materials contain sodium
What are the disadvantages of glass polyalkenoates?
Technique sensitive
Moisture sensitivity (can desiccate or get too wet)
Cannot be placed in stress bearing areas
Low tensile and fracture toughness
Poor wear resistance
Only average aesthetics
What is the setting reaction of glass polyalkenoates?
Polyacid + base -> polysalt + water
What is the setting reaction composed of?
- Decomposition
- Migration
- Gelation
- Post-set hardening
- Maturation
How is the ion depleted layer formed in decomposition?
polyacrylic acid is buried in water
H ions from carboxylic acid come off - makes acidic environment
they attack glass
glass releases its ions
What are the ions released from glass in the ion depleted layer?
calcium
aluminium
iron
come out into the matrix and crosslink the polyacrylate chains
In maturation, there is the continued formation of poly salts via…
hydration of polysalts
expanded gel structure
Why can fluoride be released without upsetting the cement structure?
it doesn’t play an integral part of the matrix
What happens when water slowly hydrates the cross-linked matrix?
increased strength
improved translucency
increased resistance to desiccation
What happens when there is excess water in glass polyalkenoates?
contaminates setting material
increases opacity
reduces strength and hardness
What happens when there is a loss of water in glass polalkenoates?
leads to desiccation
surface of restoration crazes or cracks
to prevent this, place a thin layer of vaseline or varnish over restoration
How does GICs bond to enamel differ from dentine?
stronger bond to enamel - ionic bond
GICs bond to collagen in dentine via hydrogen bonds (10th strength of ionic bond)
What is the 2-step process of fluoride release in GICs?
a rapid initial burst of fluoride
then a second slow and much sustained release of fluoride suitable for long-term release
What is the contradiction of fluoride in GICs?
As fluoride prevents secondary caries as it promotes remineralisation in adjacent area
But the main reason for replacement of GICs are secondary caries
Which microbe do GICs inhibit?
streptococcus mutans
What are the applications of glass ionomer cement?
Cementation of rigid restorations
Restorations of primary teeth
Class III and V carious lesions
Crown margin repair
Temporary dressing – carious cavity
Temporary dressing – fractured tooth
Base under amalgam and composite
How are cermets made?
silver particles fused to glass, mixture is then ground
Why do cermets have limited clinical use?
poor aesthetics
mechanical properties are not better than normal GIC
Why are cermets indicated for core buildup?
low coefficient of thermal expansion
brittle (better results with 2 walls of dentine)
good adhesion
