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DENTAL COMPOSITES

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Title: DENTAL COMPOSITES


1
DENTAL COMPOSITES
  • REVIEW

2
DEFINITION
3
COMPOSITE CHEMISTRY
  • Dental composite is composed of a resin matrix
    and filler materials. 
  • Coupling agents are used to improve adherence of
    resin to filler surfaces. 
  • Activation systems including heat, chemical and
    photochemical initiate polymerization. 
  • Plasticizers are solvents that contain catalysts
    for mixture into resin.
  • Monomer, a single molecule, is joined together to
    form a polymer, a long chain of monomers. 
  • Physical characteristics improve by combining
    more than one type of monomer and are referred to
    as a copolymer. 
  • Cross linking monomers join long chain polymers
    together along the chain and improve strength.

4
RESIN MATERIALS
  • BIS-GMA resin is the base for composite.  In the
    late 1950's, Bowen mixed bisphenol A and
    glycidylmethacrylate thinned with TEGDMA
    (triethylene glycol dimethacrylate) to form the
    first BIS-GMA resin.  Diluents are added to
    increase flow and handling characteristics or
    provide cross linking for improved strength. 
    Common examples are
  •  RESIN-   BIS-GMA      bisphenol
    glycidylmethacrylate
  • DILUENTS- MMA          methylmethacrylate
  • BIS-DMA   bisphenol dimethacrylate
  • UDMA        urethane dimethacrylate
  • CROSS LINK DILUENTS
  • TEGDMA    triethylene glycol dimethacrylate
  • EGDMA      ethylene glycol dimethacrylate

5
  COUPLING AGENTS
  • Coupling agents are used to improve adherence of
    resin to filler surfaces. 
  • Coupling agents chemically coat filler surfaces
    and increase strength. 
  • Silanes have been used to coat fillers for over
    fifty years in industrial plastics and later in
    dental fillers.  Today, they are still state of
    the art.
  • Silanes have disadvantages.  They age quickly in
    a bottle and become ineffective.  Silanes are
    sensitive to water so the silane filler bond
    breaks down with moisture. 
  • Water absorbed into composites results in
    hydrolysis of the silane bond and eventual filler
    loss. 
  • Common silane agents are
  • vinyl triethoxysilane
  • methacryloxypropyltrimethoxysilane 

6
HEAT CATALYST
  • Polymerization of resin requires initiation by a
    free radical. 
  • Initiation starts propagation or continued
    joining of molecules at double bonds until
    termination is reached. 
  • Heat applied to initiators breaks down chemical
    structure to produce free radicals, however,
    monomers may polymerize when heat is applied even
    without initiators.
  • Resins require stabilizers to avoid spontaneous
    polymerization.  Stabilizers are also used to
    control the reaction of activators and resin
    mixtures.
  • Hydroquinone is most commonly used as a
    stabilizer. 
  • Common heat based initiators are peroxides such
    as
  • benzoylperoxide
  • t-butylperoxide
  • t-cumythydroxyperoxide             

7
PHOTOCHEMICAL CATALYST
  • Early photochemical systems used were benzoin
    methyl ether which is sensitive to UV wavelengths
    at 365 nm.  UV systems had limited use as depth
    of cure was limited.  Visible light activation of
    diketones is the preferred photochemical
    systems.  Diketones activate by visible, blue
    light  to produce slow reactions.  Amines are
    added to accelerate curing time. 
  • Presently, different composites use different
    photochemical systems.  These systems are
    activated by different wavelengths of light.  In
    addition, different curing lights produce various
    ranges of wavelengths that might not match
    composite activation wavelengths.  This can
    result in no cure or partial cure.  Composite
    materials must be matched to curing lights.
  • Common photochemical initiators are
  • Camphoroquinone
  • Acenaphthene quinone
  • Benzyl

8
LIGHT CURING
  • Light curing can be accomplished with-
  • 1) Quartz-Tungsten-Halogen
  • 2) Plasma Arc Curing
  • 3) Light Emitting Diode

9
CHEMICAL CATALYST
  •    
  • Chemical activation of peroxides produces free
    radicals.  Chemical accelerators are often not
    color stable and have been improved for this
    reason.
  • The term self cure or dual cure (when combined
    with photo chemical initiation) describes
    chemical cure materials. 
  • Chemical composites mix a base paste and a
    catalyst paste for self cure. 
  • Bonding agents mix two liquids. 
  • Mixing two pastes incorporates air into the
    composite. 
  • Oxygen inhibits curing resulting in a weaker
    restoration.
  • Chemical accelerators include
  • Dimethyl p-toludine
  • N,N-bis(hydroxy-lower-alkyl)-3,5-xylidine

10
COMPOSITE FILLERS
  • Fillers are placed in dental composites to reduce
    shrinkage upon curing. 
  • Physical properties of composite are improved by
    fillers, however, composite characteristics
    change based on filler material, surface, size,
    load, shape, surface modifiers, optical index,
    filler load and size distribution.
  • Materials such as strontium glass, barium glass,
    quartz, borosilicate glass, ceramic, silica,
    prepolymerized resin, or the like are used.

11
FILLERS CLASSIFICATION
  • Fillers are classified by material, shape and
    size.
  • Fillers are irregular or spherical in shape
    depending on the mode of manufacture.
  • Spherical particles are easier to incorporate
    into a resin mix and to fill more space leaving
    less resin.
  • One size spherical particle occupies a certain
    space.
  • Adding smaller particles fills the space between
    the larger particles to take up more space.
  • There is less resin remaining and therefore, less
    shrinkage on curing the more size particles used
    in proper distribution.

12
FILLERS CLASSIFICATION
  • Classification According to Size-
  • MACROFILLERS ---- 10 TO 100 um
  • MIDIFILLERS ----- 1 TO 10 um
  • MINIFILLERS ----- 0.1 TO 1 um
  • MICROFILLERS ----- 0.01 TO 0.1 um
  • NANOFILLERS ----- 0.005 TO 0.01 um

13
PLASTICIZERS
  • Dental composite is composed of a resin matrix
    and filler materials.
  • Coupling agents are used to improve adherence of
    resin to filler surfaces.
  • Plasticizers are solvents that contain catalysts
    for mixture into resin.
  • They need to be non reactive to the catalyst
    resin.             

14
Physical Characteristics
  • Following are the imp physical properties-
  • 1) Linear coefficient of thermal expansion (LCTE)
  • 2) Water Absorption
  • 3) Wear resistance
  • 4) Surface texture
  • 5) Radiopacity
  • 6) Modulus of elasticity
  • 7) Solubility

15
C- FACTOR
  • It is the ratio of the bonded surfaces to the
    unbonded or free surfaces in a tooth preparation.
  • The higher the C-Factor, greater is the potential
    for bond disruption from polymerisation effects.

16
INTERNAL STRESSES
  • Internal stresses can be reduced by,
  • 1) Self start Polymerisation
  • 2) Incremental placement
  • 3) Use of stress breaking liners such as-
  • a)Filled Dentinal Adhesives
  • b)RMGI.

17
COMPOSITE CLASSIFICATION
  • Composite is classified by initiation techniques,
    filler size, and viscosity.
  • Laboratory heat process fillings are processed
    under nitrogen and pressure to produce a more
    thorough cure.
  • Core build up materials are commonly self cure.
  • Dual cure composite is commonly used as a
    cementing medium under crowns. 
  • Viscosity determines flow characteristics during
    placement.  A flowable composite flows like
    liquid or a loose gel.  A packable composite is
    firm and hard to displace.

18
Composite is classified by initiation techniques,
filler size, and viscosity
  • Heat cured composites are polymerized by
    application of heat.
  • Self cured composite means chemical initiation
    converting monomer to polymer takes place.
  • Light cured composite means photochemical
    initiation causes polymerization
  • Dual cure means chemical initiation is used and
    combined with photochemical initiation so either
    and both techniques polymerize composite.

19
Radiospacity
  • One of the requirements of using a composite as a
    posterior restorative is that it should be
    radiopaque.
  • In order for a material to be described as being
    radiopaque, the International Standard
    Organization (ISO) specifies that it should have
    radiopacity equivalent to 1 mm of aluminium,
    which is approximately equal to natural tooth
    dentine.
  • However, there has been a move to increase the
    radiopacity to be equivalent to 2 mm of
    aluminium, which is approximately equal to
    natural tooth enamel.
  • A majority of the composites described as
    all-purpose or universal have levels of
    radiopacity greater than 2 mm of aluminium

20
INDICATIONS
  • 1) Class-I, II, III, IV, V VI restorations.
  • 2) Foundations or core buildups.
  • 3) Sealant Preventive resin restorations.
  • 4) Esthetic enhancement procedures.
  • 5) Luting
  • 6) Temporary restorations
  • 7) Periodontal splinting.

21
CONTRAINDICATIONS
  • 1) Inability to isolate the site.
  • 2) Excessive masticatory forces.
  • 3) Restorations extending to the root surfaces.
  • 4) Other operator errors.

22
ADVANTAGES
  • 1) Esthetics
  • 2) Conservative tooth preparation.
  • 3) Insulative.
  • 4) Bonded to the tooth structure.
  • 5) repairable.

23
DISADVANTAGES
  • 1) May result in gap formation when restoration
    extends to the root surface.
  • 2) Technique sensitive.
  • 3) Expensive
  • 4) May exhibit more occlusal wear in areas of
    higher stresses.
  • 5) Higher linear coefficient of thermal expansion.

24
STEPS IN COMPOSITE RESTORATION
  • 1) Local anaesthesia.
  • 2) Preparation of the operating site.
  • 3) Shade selection
  • 4) Isolation of the operating site.
  • 5) Tooth preparation.
  • 6) preliminary steps of enamel and dentin
    bonding.
  • 7) Matrix placement.
  • 8) Inserting the composite.
  • 9) Contouring the composite.
  • 10) polishing the composite.

25
PRINCIPLES OF ANTERIOR COMPOSITE RESTORATION
  • 1. Smile Design
  • 2. Color and Color Analysis
  • 3. Tooth Color
  • 4. Tooth Shape
  • 5. Tooth Position
  • 6. Esthetic Goals
  • 7. Composite Selection
  • 8. Tooth Preparation
  • 9. Bonding Techniques
  • 10. Composite Placement
  • 11. Composite Sculpture and
  • 12. Composite Polishing to properly restore
    anterior teeth with composite

26
1. SMILE DESIGN
  • A dentist must understand proper smile design so
    composite restoration can achieve a beautiful
    smile. This is true for extensive veneering and
    small restorations.
  • Factors which are considered in smile design
    include-
  • A. Smile Form which includes size in relation to
    the face, size of one tooth to another, gingival
    contours to the upper lip line, incisal edges
    overall to the lower lip line, arch position,
    teeth shape and size, perspective, and midline.
  • B. Teeth Form which includes understanding long
    axis, incisal edge, surface contours, line
    angles, contact areas, embrasure form, height of
    contour, surface texture, characterization, and
    tissue contours within an overall smile design.
  • C. Tooth Color of gingival, middle, incisal, and
    interproximal areas and the intricacies of
    characterization within an overall smile design.

27
2. COLOUR AND COLOUR ANALYSIS
  • Colour is a study in and of itself. In dentistry,
    the effect of enamel rods, surface contours,
    surface textures, dentinal light absorption, etc.
    on light transmission and reflection is difficult
    to understand and even more difficult replicate.
  • The intricacies of understanding matching and
    replicating hue, chroma, value, translucency,
    florescence light transmission, reflection and
    refraction to that of a natural tooth under
    various light sources is essential but far beyond
    the scope of this article.

28
3. TOOTH COLOUR
  • Analysis of colour variation within teeth is
    improved by an understanding of how teeth produce
    color variation.
  • Enamel is prismatic and translucent which results
    in a blue gray color on the incisal edge,
    interproximal areas and areas of increased
    thickness at the junction of lobe formations.
  • The gingival third of a tooth appears darker as
    enamel thins and dentin shows through.
  • Color deviation, such as craze lines or
    hypocalcifications, within dentin or enamel can
    cause further color variation.
  • Aging has a profound effect on color caused by
    internal or external staining, enamel wear and
    cracking, caries, acute trauma and dentistry.

29
4. TOOTH SHAPE
  • Understanding tooth shape requires studying
    dental anatomy.
  • Studying anatomy of teeth requires recognition of
    general form, detail anatomy and internal
    anatomy.
  • It is important to know ideal anatomy and anatomy
    as a result of aging, disease, trauma and wear.
  • Knowledge of anatomy allows a dentist to
    reproduce natural teeth. For example, a craze
    line is not a straight line as often is produced
    by a dentist, but is a more irregular form guided
    by enamel rods.

30
5. TOOTH POSITION
  • Knowledge of normal position and axial tilt of
    teeth within a head, lips, and arches allows
    reproduction of natural beautiful smiles.
  • Understanding the goals of an ideal smile and
    compromises from limitations of treatment allows
    realistic expectations of a dentist and patient.
  • Often, learning about tooth position is easily
    done through denture esthetics.
  • Ideal and normal variations of tooth position is
    emphasized in removable prosthetics so a denture
    look does not occur.

31
6. ESTHETIC GOALS
  • The results of esthetic dentistry are limited by
    limitations of ideals and limitations of
    treatment.
  • Ideals of the golden proportion have been
    replaced by preconceived perceptions.
  • Limitations of ideals are based on physical,
    environmental and psychological factors.
  • Limitations of treatment are base on physical,
    financial and psychological factors.

32
7. COMPOSITE SELECTION
  • Esthetic dentistry is an art form. There are
    different levels of appreciation so individual
    dentists evaluate results of esthetic dentistry
    differently. Artistically dentists select
    composites based on their level of appreciation,
    artistic ability and knowledge of specific
    materials. Factors which influence composite
    selection include
  • A- Restoration Strength,
  • B- Wear
  • C- Restoration Color
  • D- Placement characteristics.
  • E- Ability to use and combine opaquers and tints.
  • F- Ease of shaping.
  • G- Polishing characteristics.
  • H- Polish and colour stability

33
8. TOOTH PREPARATION
  • Tooth preparation often defines restoration
    strength.
  • Small tooth defects which receive minimal force
    require minimal tooth preparation because only
    bond strength is required to provide retention
    and resistance.
  • In larger tooth defects where maximum forces are
    applied, mechanical retention and resistance with
    increased bond area can be required to provide
    adequate strength.

34
9. BONDING TECHNIQUES
  • Understanding techniques to bond composite to
    dentin and enamel provide strength, elimination
    of sensitivity and prevention of micro-leakage.
  • Enamel bonding is a well understood science.
    Dentinal bonding, however, is constantly changing
    as more research is being done and requires
    constant periodic review.
  • Micro-etching combined with composite bonding
    techniques to old composite, porcelain, and metal
    must be understood to do anterior composite
    repairs.

35
10. COMPOSITE PLACEMENT TECHNIQUE
  • Understanding techniques which allow ease of
    placement, minimize effects of shrinkage,
    eliminate air entrapment and prevent material
    from pulling back from tooth structure during
    instrumentation determine ultimate success or
    failure of a restoration.
  • It is important to incorporate proper
    instrumentation to allow ease of shaping tooth
    anatomy and provide color variation prior to
    curing composite.
  • In addition, a dentist must understand placement
    of various composite layers with varying
    opacities and color to replicate normal tooth
    structure.

36
11. COMPOSITE SCULPTURE
  • Composite sculpture of cured composite is
    properly done if appropriate use of polishing
    strips, burs, cups, wheels and points is
    understood.
  • In addition, proper use of instrumentation
    maximizes esthetics and allows minimal heat or
    vibrational trauma to composite resulting in a
    long lasting restoration.

37
12. COMPOSITE POLISHING
  • Polishing composite to allow a smooth or textured
    surface shiny produces realistic, natural
    restorations.
  • Proper use of polishing strips, burs, cups,
    wheels and points with water or polish pastes as
    required minimizes heat generation and vibration
    trauma to composite material for a long lasting
    restoration.

38
 DIRECT POSTERIOR COMPOSITES
  • Composites are indicated for Class 1, class 2 and
    class 5 defects on premolars and molars.
    Ideally, an isthmus width of less than one third
    the intercuspal distance is required.
  • This requirement is balanced against forces
    created on remaining tooth structure and
    composite material. Forces are analyzed by
    direction, frequency, duration and intensity.
    High force occurs with low angle cases, in molar
    areas, with strong muscles, point contacts and
    parafunctional forces such as grinding and biting
    finger nails.
  • Composite is strongest in compressive strength
    and weakest in shear, tensile and modulus of
    elasticity strengths.  Controlling forces by
    preparation design and occlusal contacts can be
    critical to restorative success. 
  • Failure of a restoration occurs if composite
    fractures, tooth fractures, composite debonds
    from tooth structure or micro-leakage and
    subsequent caries occurs.  A common area of
    failure is direct point contact by sharp opposing
    cusps.  Enameloplasty that creates a three point
    contact in fossa or flat contacts is often
    indicated.  

39
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  • Tooth preparation requires adequate access to
    remove caries, removal of caries, elimination of
    weak tooth structure that could fracture,
    beveling of enamel to maximize enamel bond
    strength, and extension into defective areas such
    as stained grooves and decalcified areas.
  • Matrix systems are placed to contain materials
    within the tooth and form proper interproximal
    contours and contacts. Selection of a matrix
    system should vary depending on the situation
    (see web pages contacts and contours in this
    section).
  • Enamel and dentin bonding is completed.
    Composite shrinks when cured so large areas must
    be layered to minimize negative forces.
  • Generally, any area thicker than two millimeters
    requires layering. In addition, cavity
    preparation produces multiple wall defects.
  • Composite curing when touching multiple walls
    creates dramatic stress and should be avoided.

41
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  • Composite built in layers replicate tooth
    structure by placing dentin layers first and then
    enamel layers.
  • Final contouring with hand instruments is ideal
    to minimize the trauma of shaping with burs.
  • Matrix systems are removed and refined shaping
    and occlusal adjustment done with a 245 bur and a
    flame shaped finishing bur. Interproximal buccal
    and lingual areas are trimmed of excess with a
    flame shaped finishing bur.
  • Final polish is achieved with polishing cups,
    points, sandpaper disks, and polishing paste.

43
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44
INDIRECT POSTERIOR COMPOSITES
  • Indirect laboratory composite is indicated on
    teeth that required large restorations but have a
    significant amount of tooth remaining. It is
    used when a tooth defect is larger than indicated
    for direct composite and smaller than indicated
    for a crown. A common situation is fracture of a
    single cusp on a molar or a thin cusp on a
    bicuspid. Force analysis is critical to success
    as high force will fracture composite, tooth
    structure or separate bonded interfaces. High
    force is indicated on teeth furthest back in the
    mouth for example, a second molar receives five
    times more force than a bicuspid. Orthodontic
    low angle cases and large masseter muscles
    generate high force. Sharp point contacts from
    opposing teeth create immense force and are often
    altered with enameloplasty.  
  • Indirect composite restorations are processed in
    a laboratory under heat, pressure and nitrogen to
    produce a more thorough composite cure. Pressure
    and heat increase cure while nitrogen eliminates
    oxygen that inhibits cure. Increased cure
    results in stronger restorations. Strength of
    laboratory processed composite is between
    composite and crown strength and requires
    adequate tooth support.  

45
TOOTH PREPARATION
  • Tooth preparation requires removal of existing
    restorations and caries. Thin cusps and enamel
    are removed in combination of blocking out
    undercuts with composite, glass ionomer, flowable
    composite or the like.
  • Tooth preparation requires adequate wall
    divergence to bond and cement the restoration and
    ideally, margins should finish in enamel. The
    restoration floor is bonded and light cured.
  • Bonding agent is light cured to stabilize
    collagen fibers and avoid collapse during
    restoration placement. A base of glass ionomer
    or composite is used if thermal sensitivity is
    anticipated.  
  • Restoration retention is judged by bonded surface
    area, number and location of retentive walls,
    divergence of retentive walls, height to width
    ratio and restoration internal and external
    shape.
  • Resistance form, reduction of internal stress and
    conversion of potential shear and tensile forces
    is accomplished by smoothing sharp areas and
    creating flat floors as opposed to external
    angular walls.

46
TOOTH PREPARATION
  • Impressions are taken of prepared teeth, models
    poured and composite restorations constructed at
    a laboratory.  Temporaries are placed and a
    second appointment made.
  • At a second appointment, temporaries are removed
    and a rubber dam placed.  Restorations  are tried
    on the teeth and adjusted. Manufacturers
    directions are followed.  In general, bonding is
    completed on the tooth surfaces and bonding resin
    precured.
  • Matrix bands are placed prior to etching to
    contain etch within prepared areas.  Trimming of
    excess cement where no etching has occurred is
    easier. 
  • Composite surfaces are silinated and dual cure
    resin cement applied.  Restorations are seated,
    excess resin cement is wiped away with a brush
    and then facial and lingual surfaces are light
    cured.  Interproximal areas are flossed and then
    light cured.  Excess is trimmed with hand
    instruments and finishing flame shaped burs.
  • The rubber dam is removed and occlusion
    adjusted.  Surfaces are finished and polished.

47
COMPOSITE WEAR
  • There are several mechanisms of composite wear
    including adhesive wear, abrasive wear, fatigue,
    and chemical wear.
  • Adhesive wear is created by extremely small
    contacts and therefore extremely high forces, of
    two opposing surfaces.  When small forces
    release, material is removed.  All surfaces have
    microscopic roughness which is where extremely
    small contacts occur between opposing surfaces.
  • Abrasive wear is when a rough material gouges out
    material on an opposing surface.  A harder
    surface gouges a softer surface.  Materials are
    not uniform so hard materials in a soft matrix,
    such as filler in resin, gouge resin and opposing
    surfaces.  Fatigue causes wear.  Constant
    repeated force causes substructure deterioration
    and eventual loss of surface material.   
    Chemical wear occurs when environmental materials
    such s saliva, acids or like affect a surface.

48
COMPOSITE FRACTURE
  • Dental composite is composed of a resin matrix
    and filler materials.  The resin filler interface
    is important for most physical properties.
  • There are three causes of stress on this
    interface including  resin shrinkage pulls on
    fillers, filler modulus of elasticity is higher
    than resin, and filler thermo coefficient of
    expansion allows resin to expand more with heat. 
    When fracture occurs, a crack propagates and
    strikes a filler particle.  Resin pulls away from
    filler particle surfaces during failure.  This
    type of failure is more difficult with larger
    particles as surface area is greater.  A
    macrofill composite is stronger than a microfill
    composite.
  • Coupling agents are used to improve adherence of
    resin to filler surfaces. Modification of filler
    physical structure on the surface or aggregating
    filler particles create mechanical locking to
    improve interface strength.  Coupling agents
    chemically coat filler surfaces and increase
    strength.  Silanes have been used to coat fillers
    for over fifty years in industrial plastics and
    later in dental fillers.  Today, they are still
    state of the art.

49
  • RECENT ADVANCES

50
Multifunctional Composites and Novel
Microstructures
  • Hierarchical microstructures
  • - Dr H-X Peng
  • The properties of composite materials can be
    tailored through microstructural design at
    different lengthscales such as the micro- and
    nano-structural level.
  • At the micro-structural level, our novel approach
    creates microstructures with controlled
    inhomogeneous reinforcement distributions.
  • These microstructures effectively contain more
    than one structural hierarchy. This has the
    potential to create whole new classes of
    composite materials with superior single
    properties and property combinations.
  • Research also involves tailoring the
    nano-structures of micro-wires/ribbons for
    macro-composites.

51
Shaped fibres
  • - Dr Ian Bond, Dr Paul Weaver
  • Research has shown that shaped fibres can be an
    effective means of improving the through
    thickness properties.
  • A set of guidelines for fibre shape and a
    preferred family of fibres have been generated
    from qualitative analysis for the role of
    reinforcing fibres in composites.
  • Methods have also been developed to produce such
    shaped fibres from glass in order to form
    reinforced laminates in sufficient quantity for
    materials property testing using standard
    methods.
  • Fibre shape has been shown to play a key role in
    contributing to the bonding force between fibre
    and matrix, with significant increases in
    fracture toughness possible. Results suggest that
    the shaped fibre specimens have a greater
    throughthickness strength than the circular fibre
    composites that are currently used.

52
Self healing
  • - Dr Ian Bond
  • Impact damage to composite structures can result
    in a drastic reduction in mechanical properties.
    Bio-inspired approach is adopted to effect
    selfhealing which can be described as mechanical,
    thermal or chemically induced damage that is
    autonomically repaired by materials already
    contained within the structure.
  • Efforts are undergoing to manufacture and
    incorporate multifunctional hollow fibres to
    generate healing and vascular networks within
    both composite laminates and sandwich structures.
  • The release of repair agent from these embedded
    storage reservoirs mimics the bleeding mechanism
    in biological organisms.
  • Once cured, the healing resin provides crack
    arrest and recovery of mechanical integrity.
  • It is also possible to introduce UV fluorescent
    dye into the resin, which will illuminate any
    damage/healing events that the structure has
    undergone, thereby simplifying the inspection
    process for subsequent permanent repair.

53
Fibre Reinforced Dental Resins
  • - Dr Ian Bond and Professor Daryll Jagger
  • The material most commonly used in the
    construction of dentures is poly (methyl
    methacrylate) and although few would dispute that
    satisfactory aesthetics can be achieved with this
    material, in terms of mechanical properties it is
    still far from ideal.
  • Over the years there have been various attempts
    to improve the mechanical properties of the resin
    including the search for an alternative material,
    such as nylon, the chemical modification of the
    resin through the incorporation of butadiene
    styrene as in the "high impact resins" and the
    incorporation of fibres such as carbon, glass and
    polyethylene.
  • The use of self-healing technology within dental
    resins is a novel and exciting approach to solve
    the problems of the failing dental resins.
  • Methods are currently being developed to
    translate the self healing resin technology into
    dental and biomaterials science.

54
Nanofibres and Nanocomposites
  • - Dr Bo Su
  • An electrospinning technique has been used to
    produce polymer, ceramic and nanocomposite
    nanofibres for wound addressing, tissue
    engineering and dental composites applications.
  • The electrospun nanofibres have typical diameters
    of 100-500 nm. Natural biopolymers, such as
    alginate, chitosan, gelatin and collagen
    nanofibres, have been investigated.
  • Novel nanocomposites, such as Ag nanoparticles
    doped alginate nanofibres and alginate/chitosan
    core-shell nanofibres, have also been
    investigated for antimicrobials and tissue
    engineering scaffolds.
  • Zirconia and silica nanofibre/epoxy composites
    are currently under investigation for dental
    fillings and aesthetic orthodontic archwires.

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Nanocomposites
  • - Dr H-X Peng
  • Carbon fibre composite components are susceptible
    to sand and rain erosion as well as cutting by
    sharp objects.
  • The use of nanomaterials in coating formulations
    can lead to wear-resistant nanocomposite
    coatings.
  • Work is developing novel fine-particle filled
    polymer coating systems with a
  • potential step-change in erosion resistance and
    exploring their application to composite
    propellers and blades.
  • These tailored materials also have potential
    applications in lightning strike protection and
    de-icing.
  • The nano-structure of magnetic micro-ribbons/wires
    is being investigated and optimised to obtain
    the Giant Magneto-Impedance (GMI) effect for high
    sensitivity magnetic sensor applications.

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Composites with Magnetic Function
  • - Dr Ian Bond, Prof. Phil Mellor and Dr H-X Peng
  • The main aim of this work is to examine methods
    ofincluding magnetic materials within a composite
    whilst maintaining structural performance.
  • This has been achieved by filling hollow fibres
    with a suspension of magnetic materials after
    manufacture of the composite component.
  • Research is continuing to tailor the magnetic
    properties of the composite to other
    applications.
  • In another approach, magnetic microribbons and
    microwires are being tailored and embedded into
    macrocomposite materials to provide magnetic
    sensing functions.

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Auxetics
  • - Dr Fabrizio Scarpa
  • Auxetic solids expand in all directions when
    pulled in only one, therefore exhibiting a
    negative Poissons ratio.
  • New concepts are being develope for composite
    materials, foams and elastomers with auxetic
    characteristics for aerospace, maritime and
    ergonomics applications.
  • The use of smart material technologies and
    negative Poissons ratio solids has also led to
    the development of smart auxetics for active
    sound management, vibroacoustics and structural
    health monitoring.

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Diamond Fibre Composites
  • - Dr Paul May and Professor Mike Ashfold
  • Researchers in the CVD Diamond Film Lab based in
    the School of Chemistry are investigating ways to
    make diamond fibre reinforced composites.
  • The diamond fibres are made by coating thin (100
    mm diameter) tungsten wires with a uniform
    coating of polycrystalline diamond using hot
    filament chemical vapour deposition.
  • The diamond-coated wires are extremely stiff and
    rigid, and can be embedded into a matrix material
    (such as a metal or plastic) to make a stiff but
    lightweight composite material with anisotropic
    properties. Such materials may have applications
    in the aerospace industry.

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Novel Multifunctional Fibre Composites
  • - Professor Steve Mann
  • New types of composites with a combination of
    strength, toughness and functionality are being
    prepared by combining research in the synthesis
    of inorganic non-particles with that in the
    synthesis of organic polymers.
  • This interdisciplinary approach has been used to
    produce flexible fibres of magnetic spider silk
    as shown in the photograph (left). Silk fibres
    are coated by a dipping procedure using dilute
    suspensions of inorganic nano-particles that are
    prepared with specific surface properties.
  • Similar methods are being investigated with
    swellable polymer gels and bacterial
    supercellular fibres to produce novel hybrid
    composites.

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COMPILED PRESENTED BY,
  • Dr. Amol A. Khapare
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