Tooth coloured filling materials 2 - GICs Flashcards
Name different types of cements
- Glass polyalkenoate cement
- Resin modified glass polyalkenoate
- Polyacid modified resin cement
- composite
How do we measure wetting of cements
measure contact angle between droplet and surface
how are glass polyakenoates formed
- result of acid-base reaction between fluoride containing glass and a poly acid
- adhesive, cariostatic
what is the composition of glass polyakenoates
fluroro- alumina- phosphor- silicate glass
- poly acid eg.
poly acrylic acid
polymaleic acid
what is the setting reaction of GIC involve?
Poly acid + base > poly salt +water
- decomposition
- migration
- gelation
- post set hardening
- maturation
what are the disadvantages of GICs
- technique sensitive
- moisture senstivity
- cannot be placed in stress bearing areas
- low tensile and fracture toughness
- poor wear resistance
- only average aesthetics
describe the process of setting reactions
Hydrogen comes off carboxylic acid and attacks glass particles
the glass particles then releases ions and then releases fluorine
- Ions come out into matrix and cross lining polyacrylate chains
- final material consists of matrix and glass particles sitting in matrix have ion efficient depleted layer
what happens In maturation of GICs
- precipitation of aluminium salts continues for 24 hours
- the setting process continues thereafter but at a very slow pace for up to 1 year
- continued formation of polysalts
- hydration of poly salts
- expanded gel structure
what about fluoride in the setting reactions?
Fluoride is not an integral part of the matrix and can be released without upsetting the structure of the cement
What role does water play?
- slowly hydrates the mature cross linked matrix
- increased strength
- improved translucency
- increased resistance to desiccation
what is sensitive tot the setting reaction
- moisture sensitve
- excess water increases risk of contamination
- more opacity and strength/hardness decreases
- loss of water can lead to desiccation which can increase grazing and cracking
How does the GIC bond to the tooth
- bonds directly to the tooth
- bonds better to enamel but can bond to collagen
How are the fluoride ions released?
- Fluoride ions are released from the glass by the acid attack
- the ions lie free within the matrix and can be released from the restoration into the surrounding tooth structure
- this contributes to the biocompatibility of the material and also the capacity to inhibit recurrent caries
they are released:
- a rapid initial process responsible for the early burst of fluoride release
- second slower and much sustained process responsible for the long term release of fluoride
what does fluoride help in caries
- prevents secondary caires as it promotes remineralisation in adjacent area
- main reason for replacement of GIC restoration is secondary caries
How is GICs biocompatible
- plaque does not thrive on glass ionomer surfaces
- Streptococcus mutant growth is inhibited by GIC restorations due to fluoride present
- the soft tissue response to GIC is favourable as shown by gingival tissue response to class V restorations
- plural response is favourable
- freshly mixed cement pH of 0.9 to 1.6 but very mild inflammatory response
- direct capping material as it promotes dentine bridge formation
describe the applications for glass ionomer cement?
- cementation of rigid restorations
- restorations of primary teeth
- Class III and V carious lesions
- Crown margin repair
- temporary dressing -c various cavity
- temporary dressing - fractured tooth
- base under amalgam and composite
what are CERMETS
- silver particles fused tot eh glass. Mixture is then re ground
- limited clinical use due to poor aesthetics
- mechanical properties no better than normal GPC
what are indications for cermets
- core build up
- low coefficient of thermal expansion
- good adhesion
- brittle
- F- releasing temporary restorations
what are some alternative cements?
- diamond carve and diamond 90
- glass polyalkenoates
- based on glass and co-polymer of
polyvinylphosphonic acid
poly acrylic acid
what are some viscous glass polyalkeonates?
e.g fuji IX, Ketch molar, Hi dese
higher powder: liquid ratio
- Low water content
- smaller glass particles
-= packable? greater strength
- used in ART technique
what are posterior survival times of amalgam and GIC?
amalgam - 11 years median
GIC- 6 years median
what are RMGICs and what amount of resin is found in set cement?
- RMGICS are glass ionomer cements with the addition of a small quantity of resin components
- the resin in set cement = 4.5 -6%
Name soem advantages of RMGICs
- tooth coloured
- improved aesthetics
- medium fluoride release
- ’ recharges’
- short setting/ longer working
- decreased moisture sensitvity
- improved tensile strength
- sets on command
- better wear characteristics
- easier to use
- higher bond strength to composite
- fewer steps than composite
- can finish immediately
what are 2 modifications to conventional GICs
- less water - replaced by a water/ HEMA mixture (vITREMER)
- modification of the poly acid with side chains that can polymerise by light curing mechanism
what else does the polymer contain aswell as acid base reaction
- polymerisable functional groups
what is HEMA?
Hydroxyl Ethyl Methacrylate
- severely irritating to the eye and is known contact allergen. A small percentage of the population is known to have an allergic response to acrylate resins.
- to reduce the risk of allergic response , minimise exposure to these materials. In particular exposure to uncured resin should be avoided
- Use of protective gloves and no touch technique is recommended
why are indications for RMGIC and advantages?
Indications
- cervical and root caries
- base
- abfraction lesions
Advantages
- resistant to desiccation
- can be contoured immediately
what is the composition of composites
bis -GMA or UDMA
- EGDMA
inorganic filler
silage coupling agent
U. v stabilisers
inhibitors
what is the composition of dytract
- UDMA resin
TCB resin
strontium fluorosilicate glass
ignitors
stabilisers
how are compomers formed?
- formed from new monomers which contain acidic and acrylate groups
what is the 1st stage of the setting mechnism
- light curing induces polymerisation of the resins
what is 2nd stage of setting mechanisms
after water uptake, the acid- base reaction takes place, resulting in further corsslinking of matrix
what are the pros and cons of composite
- excellent handling
- command set
- good strength
- poor adhesion
- low fluoride release
- needs a bonding agent
