Tooth-coloured Filling Materials 2: Glass-ionomer Cements and their Relatives Flashcards
Technical terms for…
- Glass ionomer cement
- Light cured glass ionomer cement
- Compomer
- Composite
- Glass polyalkenoate cement
- Resin modified glass polyalkenoate
- Polyacid modified resin cement
- Composite
Which are hydrophilic or hydrophobic?
- Glass ionomer cement
- Light cured glass ionomer cement
- Compomer
- Composite
Composite based are hydrophobic hence they need a bonding system
- Hydrophilic
- Hydrophilic
- Hydrophobic
- Hydrophobic
Poly glass alkenoate what are they and how are they formed?
Formed as a result of an acid-base reaction between a fluoride containing glass and a poly acid (poly acrylic acid)
Adhesive, cariostatic
- Used because they’re naturally adhesive to enamel and dentine
- Glass contains fluoride so potential for fluoride release (suggests may have a role in preventing secondary / recurrent caries)
Glass polyalkenoate composition ?
Fluoro - alumino -phospho - silicate glass
- Silicone forms the back bone of glass
- Fluorine for fluoride release
- Aluminium in the glass network for support
- Calcium and sodium ions sit in holes of the glass network to maintain a network charge neutrality
- Glass is specifically formulated to release ions in the presence of acid
Polyacid eg,
- poly acrylic acid
- polymaleic acid
Disadvantages of glass poly alkenoate
- technique sensitive
- moisture sensitivity
- cannot be placed in stress bearing areas
- low tensile and fracture toughness
- poor wear resistance
- only average aesthetic
Advantages of glass poly alkenoate
- adhesive
- potentially cariostatic
Setting reaction of glass polyalkenoate
Acid + base = salt + water
Poly acid + base (glass) =
Poly acid + base (glass) = Poly salt + water
Glass polyalkenoate Setting reaction - what are the steps?
- Decomposition
- Migration - of ions from the decomposing glass
- Gelation - formation of gel around the glass particles
- Post set hardening of the matrix
- Maturation (long term)
Glass polyalkenoate chemical structure
Glass particle
Poly acrylic acid
- carboxylic acid functional group along the polymer backbone
- by varying the molecular weight of the polymer, you can vary the properties
Glass polyalkenoate - how does it act in water?
- In water the hydrogen ion comes off and forms an acidic environment which attacks the glass particles
- The glass particle then releases its own ions (calcium, aluminium, silicon, phosphorus, fluorine) therefore there is an ion depleted layer on the surface of the glass
- The ions come out into the matrix and cross link the poly acrylate chains
(calcium 2+ ion will cross link 2 poly acrylate chains… Aluminium 3+ ion will cross link 3 poly acrylate chains and so on..) - Final material consists of matrix (poly salt) with glass particles sitting in the matrix with an ion depleted layer
What occurs during maturation
Precipitation of Ca2+ salts initially
Precipitation of Al3+ salts added and continue for 24 hours
The setting process continues thereafter but at a very slow pace for up to 1 year
Calcium and aluminium release over time
Continued formation of poly salts
- hydration of the poly salts
- expanded gel structure
What about the fluoride?
Fluoride sits in the matrix but is not a part of the matrix
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
- the dry materials wont set without the presence of water
- increased strength
- improved translucency - good optical properties (improves over time)
- increased resistance to desiccation
Moisture sensitive - excess water?
Excess water —> Contamination —> =
Increased opacity
Decreased strength / hardness
Moisture sensitive - loss of water
Loss of water —> Desiccation —> =
Increased crazing and cracking
(Requires Vaseline whilst setting to avoid desiccation)
What advantage does the Bonding to tooth structure have?
It bonds directly without the need for an intermediate bonding system
Bonding system is in multiple steps, - its technique sensitive, chemistry between different commercial materials aren’t the same and so its easy to make a misstep and get it wrong
The advantage of this material is it directly bonds to tooth surface structure
The polyalkenoate chains through the carboxylic acid groups bond ionically to the calcium on the tooth surface - strong bond
They also bond to dentine and the collagen in dentine through hydrogen bonds (weaker than ionic bond) and so for glass ionomer cement - they bond better to enamel through ionic bonds than they bond to dentine through hydrogen bonds (although they are adhesive to both)
They are also adhesive to other materials such as metals due to the acid base chemistry of the material
Fluoride release?
- fluoride ions are released form 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
- if released into the mouth, they are washed away by saliva (fluoride release unimportant in the mouth)
- fluoride release is important for the adjacent tooth structure (eg can remineralise caries lesion)
What is the steps of fluoride release?
2 step process
- A rapid initial process responsible for the early burst of fluoride release
- A second slower and much sustained process responsible for the long tern release of fluoride
Benefits and contradictions of fluoride release?
- fluoride prevents secondary caries as it promotes remineralisation in adjacent area
- but main reason for replacement of GIC restoration is secondary caries
Biocompatibility
- Plaque does not thrive on glass ionomer surface
- Streptococcus mutans growth is inhibited by GIC restorations? Due to fluoride presence
- The soft tissue response to GIC is favourable as shown by gingival tissue response to Class V restorations
- Pulpal response is favourable
- freshly mixed cement because its an acid base material… ph initially of poly acrylic acid is of 0.9 to 1.6 but causes a very mild inflammatory response
- direct capping material as it promotes dentine bridge formation
Applications for 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
Cermets
- silver particles fused to the glass - mixture is then re ground
- limited clinical use due to poor aesthetics
- mechanical properties no better than normal GPC
Indications for cermets
Core build up
- low coefficient of thermal expansion
- good adhesion
- brittle (best results with at least 2 walls of dentine)
Fluoride releasing temporary restorations
Alternative cements
DiamondCarve and Diamond90
- Glass polyalkenoates
- Based on glass and a co polymer of
Poly-vinyl-phosphonic acid
Poly-acrylic acid
Viscous glass polyalkenoates
eg, Fuji IX, Ketac molar, Hi dense
- higher powder : liquid ratio
- lower water content
- smaller glass particles
= Packable? Greater strength?
- used in ART technique
Survival times - posterior
Amalgam -
Median survival time 11yrs
Higher fracture toughness (Kic ~ 0.8-1.6 MPam-2)
Survival times - posterior
GIC
Median survival time 6yrs
Lower fracture toughness (Kic ~ 0.2-0.6 MPam-2)
Resin modified GIC
RMGIC’s are glass ionomer cements with the addition of a small quantity of resin components
The resin in set cement = 4.5-6%
RMGIC advantages
- tooth coloured + improved aesthetic
- medium fluoride release
- recharges
- shorter setting / longer working
- decreased moisture sensitivity
- increased tensile strength
- sets on command
- better wear characteristics
- easier to use
- higher bond strength to composite
- fewer steps to composite
- can finish immediately
2 modifications to conventional GIC’s
- less water - it is replaced by water / HEMA mixture (vitremer)
Modification of the Polyacid with side chains the can polymerise by light curing mechanisms (Fuji ii lc & photac-fil)
Resin modified glass polyalkenoates
How is command set achieved
In addition to the acid base reaction, part of the polymer contains polymerisable functional groups
C=C bond in dentistry means its there to be broken
HEMA - hydroxy ethyl methacrylate
- Severely irritating to the eye and is a 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 a no-touch technique is recommended
RMGIC indications
- cervical and root caries
- base
- abfraction lesions
RMGIC advantages
- resistant to desiccation (due to command set)
- can be contoured immediately
Composites
Composition -
Bis-GMA or UDMA
EGDMA (diluent monomer)
Inorganic filler
Silane coupling agent
Uv stabilisers
Inhibitors
Compomers
Composition of dyract
- UDMA resin
- TCB resin
- strontium fluorosilicate glass
- initiators
- stabilisers
Rather than having modification to GIC we have modification to the composite
What do compomers consist of?
Monomers
They have a C=C bond at each end (therefore they’re dimethacrylates)
They have a carboxylic acid group grafted onto the monomers from GIC
Setting mechanism of a compomer
1st stage - light curing induces polymerisation of the resins
2nd stage - after water uptake, the acid base reaction takes place, resulting in further cross linking of the matrix
It is essentially a composite modified to allow an acid-base reaction to occur through the grafting of a carboxylic acid group onto a monomer
pros of compomers
- excellent handling
- command set
- good strength
Cons of compomers
- poor adhesion
- low fluoride release
- needs a bonding agent
In essence a compomer is a ‘poly acid modified resin cement’ composite
Look at lecture for examples
How is chemfil rock different?
- added zinc which makes it stronger, tougher, earlier
- no need to condition cavity
- no need to protect with varnish
New bio active RMGIC
Chemically bonds to teeth, seals against bacterial micro leakage, release more fluoride and is more bio active than glass ionomers and is more durable and fracture resistant than composites
