DENTAL COMPOSITES

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DENTAL COMPOSITES
dr shabeel pn

• REVIEW

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DEFINITION
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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.

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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

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  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 

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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             

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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

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LIGHT CURING

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

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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

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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.

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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.

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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

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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.             

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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

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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.

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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.

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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.

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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.

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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

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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.

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CONTRAINDICATIONS

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

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ADVANTAGES

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

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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.

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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.

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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

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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.

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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.

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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.

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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.

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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.

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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.

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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

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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.

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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.

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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.

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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.

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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.

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 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.  

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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.

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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.

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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.  

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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.

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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.

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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.

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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.

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• RECENT ADVANCES

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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.

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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.

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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.

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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.

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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