Tooth Coloured Filling Materials Flashcards
What is composite?
A product with at least two distinct phases, purpose to combine two or more materials to produce one with superior properties. Contains inorganic filler and an organic binder.
Advantages of composite
Aesthetics Conservation of tooth structure Adhesion to tooth structure Low thermal conductivity Alternative to amalgam
Disadvantages of composite
Technique sensitive Polymerisation shrinkage Marginal leakage Secondary caries Postoperative sensitivity Decreased wear resistance
How does composite set?
Free radical addition polymerisation Activation by chemical organic amine and organic peroxide or light camphorquinone and blue light (450-490nm) breaks into free radicals Initiation Propagation Termination
What are polywave light cures?
They have two photo initiators (one at 410nm and 470nm wavelengths)
What is polymerisation shrinkage?
Where the polymer occupies a smaller volume than the monomer.
What are the monomers in composite?
Bis-GMA
UDMA
TEGMA
All have c=c bonds at either end, which is why they are dimethacrylates
What do monomers do?
Bind filler particles together
Provides workability
What are the properties of Bis-GMA?
Extremely viscous (large benzene rings) Lowered by adding TEGDMA - freely movable - increases polymer conversion - increases cross linking - increases shrinkage
What does a light cure do?
Monomer to polymer
Stresses set up at bonding interface, relieved up to gel point
After gel point = unyielding
Stress transferred to tooth
2mm depth recommended to minimise stress transfer
What are fillers for?
Placed to reduce shrinkage upon curing.
Examples of fillers
Strontium glass, barium glass, quartz, borosilicate glass, ceramic, silica, prepolymerised resin.
How are fillers classified?
Material, shape and size
What shapes can fillers be?
Irregular and spherical
What is the preferred shape of filler?
Spherical - easier to incorporate into a resin mix and take up more space leaving less resin.
Adding smaller particles fills the space between the larger particles so takes up more space, less shrinkage on curing.
What do inorganic fillers reduce and increase?
Reduce - polymerisation shrinkage, water sorption, thermal expansion
Increase - compressive/tensile strength, modulus of elasticity, abrasion resistance
What are the different sizes of filler?
Macrofill (old and the biggest)
Microfill (smaller) with prepolymerised filler
Hybrids with 2+ size regime
Nanohybrid 2+ size regime and prepolymerised filler
What is the third phase of composite?
Coupling agent - transfers stresses and provides a bond between filler particle and resin matrix.
Example of coupling agent
Organosilane
Siloxane end bonds to hydroxyl groups on filler
Methacrylate end polymerises with resin
What do coupling agents do?
Improve adherence of filler to resin surfaces
Have chemically coat filler surfaces and increase strength
Disadvantages of coupling agents
Age quickly in a bottle
Sensitive to water so silane filler bond breaks down with moisture
Water absorbed results in hydrolysis of silane bond and filler loss
What are the different types of composite?
Universal, flowable, packable
What are flowable composites and their indications?
Filler content is less than hybrid resins giving them lower viscosity
Class V restorations
Micro preparations
Extended fissure dealings
Adhesive cementation or ceramic restorations
Blocking cavity undercuts
Initial layer
Disadvantages of flowable composites
Lower filler volumes so increased shrinkage and wear with decreased strength
What are packable composites?
Macrofilled hybrids
They are firm and can be packed
Contain larger filler particles or fibres to improve packing
They are more difficult to sculpt due to high viscosity
What does acid etching do?
Preferentially decalcifies portions of enamel rods, exposed interprismatic and prism areas for interlocking tag formation with bonding resin.
Roughens the surface
Purely mechanical bonding, not true adhesion
20mPa
Why is dentine hard to bond to?
Contains type 1 collagen and water, is a moist living tissue, bonding to something hydrophobic.
What is the smear layer?
Created by any mechanical cutting of dentine, which is dentine debris of variable thickness, smear plugs are formed which block tubules.
Why does the smear layer affect bonding?
Protects dentine and pulp from bacteria penetration but impairs bond of composite to dentine, it is only loosely bound and can harbour bacteria.
What are the four strategies for optimum bonding?
Smear layer left alone
Smear layer removed
Smear layer modified
Smear layer partially removed partially modified
What is the mechanism of bonding?
Exchange process involving replacement of minerals by resin monomers which upon setting become micro-mechanically interlocked in created porosities.
What is the dentine hybrid layer?
Mixture of adhesive polymers and dental hard tissues.
What is the purpose of acid etching?
Improves retention of restoration Increases surface area of dentine Removes smear layer Allows for penetration of bonding agent into dentine Protect pulp exposure before using
Method for etching
Phosphoric acid gel or liquid 35-37%
Isolate teeth, apply etchant wait 5-15 seconds
5 secs for dentine
Rinse but don’t desiccate
Second step - priming
Resin monomer, improves wettability, penetrates etched tubules, applied in a thin layer thinned with air and light cure maybe.
Step 3 - bonding agent
In filled or lightly filled resin Adhesive bonds to collagen fibres in dentine and locks in - hybrid layer Applied in thin layer Light cured Then apply composite
What do primers contain to improve its wetting?
Solvents
What are the different types of primers?
Acetone - one step
Ethanol - optibond solo
Water - scotch bond
What is the problem with self etching primers?
They don’t etch enamel quite as well
Why do we shake self etch primers?
Over time components can separate
What are self etch adhesives?
Self etch primer combined with adhesive resin
What is the pathway for successful bonding to dentine?
Wetting, infiltration to provide hybrid zone, mechanical interlocking, stress resistance.
What are the different types of cements?
Glass polyalkenoate, resin modified, poly acid modified resin, composite
Are GIC’s hydrophilic or hydrophobic?
Hydrophilic
What are glass polyalkenoates?
Formed as a result of an acid base reaction between fluoride containing glass and a poly acid.
What is the composition of GIC?
Fluoro-alumino-phospho-silicate glass and poly acid (polyacrylic usually)
Disadvantages of GIC
Technique sensitive Moisture sensitive Cannot be placed in stress bearing areas Low tensile and fracture toughness Poor wear resistance Average aesthetics
What is the setting reaction of GIC
Decomposition Migration Gelation Post set hardening Maturation
What does the final GIC contain?
Ion depleted layer, glass and poly salt matrix
What does the maturation phase of GIC consist of?
Precipitation of Al3+ salts continues for 24 hours
Setting process continues at a slow pace for up to a year
Continued formation of poly salts - hydration and expanded gel structure
What does the role of water play in the setting reaction of GIC?
Hydrates the mature cross linked matrix
Increases strength
Improves translucency - changes colour
Increased resistance to desiccation
If too much water is present in the setting reaction of GIC what may happen?
Contamination, opacity, reduces strength
If too little water is present in the setting reaction of GIC what may happen?
Desiccation
Grazing and cracking
Use Vaseline to protect from this
How does GIC bind to the tooth structure?
Ionic bonding between polyalkenoate chain and ca2+ ions.
How does GIC bind to dentine?
Hydrogen bonding between ions and collagen
What are the two fluoride releases in GIC?
Rapid initial process responsible for early burst
Second slower and sustained process responsible for long term release
What is the biocompatibility of GIC?
Plaque does not thrive on these restorations and strep mutants growth is inhibited. Soft tissue response is favourable as well as pulpal, mild inflammatory response. Is a direct capping material.
Implications for GIC
Cementation of rigid restorations Restorations of primary teeth Class 3 and 5 restorations Crown margin repair Temporary dressing - carious cavity and fractured tooth Base under amalgam and composite
What are cermets?
Silver particles fused to glass, re ground mixture
Indications of cermets?
Low coefficient of thermal expansion
Good adhesion
Brittle
F releasing temporary restorations
What are diamond carve and diamond 90?
Co polymer of polyvinylphosphonic acid and polyacrylic acid
Glass polyalkenoate
What are viscous glass polyalkenoates?
Higher powder to liquid ratio Lower water content Smaller glass particles Packable greater strength Used in ART technique
What is the survival time of GIC?
6 years posteriorly compared to 11 years for amalgam.
What are rmgic’s?
GIC with addition of small quantities of resin
Advantages of rmgic
Tooth coloured better aesthetic Release fluoride Recharges Shorter setting time longer working Decreased moisture sensitivity Improved tensile strength Sets on command Better wear Higher bond strength to composite Fewer steps than composite
What are modifications to conventional GIC
Less water - replaced by water hema mixture
Modifications of poly acid with side chains that can polymerise by light cure (Fuji ii lc)
What are the risks of HEMA?
Irritating
Allergic response
Use gloves, no touch technique
Indications of RMGIC
Cervical and root caries
Base
Abfraction lesions
What is the composition of composers?
UDMA resin Tcb resin Strontium fluorosilicate glass Initiators Stabilisers
Setting mechanism of compomers
Light curing initiates polymerisation of resins
After water uptake acid base reaction takes place resulting in further cross linking
Pros and cons of compomers
Excellent handling Command set Good strength Poor adhesion Low f release Needs bonding agent
