dental composite 2

8/2/2019 Dental Composite 2

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Considered as natural tooth composites The reinforcing filler particles are

hydroxyapatite crystals.


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All purpose Condensable

Flowable

Laboratory microfilled


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Anterior restorations Direct aesthetic restorations

Posterior restorations

Pit & fissure sealants

Ceramic veneer bonding Cementation

Provisional restorations

Core buildups Fiber-reinforced posts


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Dental composite is composed of a resin matrix and fillermaterials.

Coupling agents are used to improve adherence of resin tofiller surfaces.

Activation systems including heat, chemical andphotochemical initiate polymerization.

Plasticizers are solvents that contain catalysts for mixture intoresin.

Monomer, a single molecule, is joined together to form apolymer, a long chain of monomers.

Physical characteristics improve by combining more than onetype of monomer and are referred to as a copolymer.

Cross linking monomers join long chain polymers togetheralong the chain and improve strength.


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3 structural components matrix plastic resin material that forms a

continuous phase and binds the filler particles

Filler- reinforcing particles and/or fibers that are

dispersed in the matrix coupling agent- bonding agent that promotes

adhesion between filler and resin matrix


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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 firstBIS-GMA resin. Diluents are added to increase flowand handling characteristics or provide crosslinking for improved strength.

Common examples are: RESIN:- BIS-GMA bisphenol glycidylmethacrylate DILUENTS:- MMA methylmethacrylate

BIS-DMA bisphenol dimethacrylateUDMA urethane dimethacrylate CROSS LINK DILUENTS

TEGDMA triethylene glycoldimethacrylate

EGDMA ethylene glycol dimethacrylate


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Reduces polymerization shrinkageproportionately

Extensive cross-linking which increases thestrength and rigidity of the polymer

Increases viscosity resulting to difficulty inblending and manipulating


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Coupling agents are used to improve adherence of resinto filler surfaces.

Coupling agents chemically coat filler surfaces andincrease strength.

Silanes have been used to coat fillers for over fifty yearsin industrial plastics and later in dental fillers.

Silanes have disadvantages. They age quickly in a bottle and become

ineffective. Silanes are sensitive to water so the silanefiller 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 triethoxysilanemethacryloxypropyltrimethoxysilane


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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 polymerizewhen heat is applied even without initiators.

Resins require stabilizers to avoid spontaneouspolymerization. Stabilizers are also used to control thereaction of activators and resin mixtures.

Hydroquinone is most commonly used as a stabilizer. Common heat based initiators are peroxides such as

benzoylperoxide

t-butylperoxidet-cumythydroxyperoxide


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Early photochemical systems used were benzoin methyl etherwhich is sensitive to UV wavelengths at 365 nm. UV systemshad limited use as depth of cure was limited. Visible lightactivation of diketones is the preferred photochemicalsystems. Diketones activate by visible, blue light to produceslow reactions. Amines are added to accelerate curing time.

Presently, different composites use different photochemicalsystems. These systems are activated by differentwavelengths of light. In addition, different curing lightsproduce various ranges of wavelengths that might not matchcomposite activation wavelengths. This can result in no cureor partial cure. Composite materials must be matched tocuring lights.

Common photochemical initiators are:CamphoroquinoneAcenaphthene quinoneBenzyl


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Light curing can be accomplished with:-

1) Quartz-Tungsten-Halogen

2) Plasma Arc Curing

3) Light Emitting Diode


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Chemical activation of peroxides produces free

radicals. Chemical accelerators are often not color stable andhave been improved for this reason.

The term self cure or dual cure (when combined with photochemical initiation) describes chemical cure materials.

Chemical composites mix a base paste and a catalyst pastefor 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-toludineN,N-bis(hydroxy-lower-alkyl)-3,5-xylidine


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Fillers are placed in dental composites to reduce shrinkageupon curing.

Physical properties of composite are improved by fillers,however, composite characteristics change based on fillermaterial, surface, size, load, shape, surface modifiers, opticalindex, filler load and size distribution.

Materials such as strontium glass, barium glass, quartz,borosilicate glass, ceramic, silica, prepolymerized resin, orthe like are used.


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Primary purpose to strengthen a compositeand to reduce the amount of matrix material Greatly improves material properties, provided that

the filler particles are well bonded to the matrix

with the use of an effective coupling agent.


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Reinforcement of the matrix resin results inincreased hardness, strength, anddecreased wear

Reduction in polymerization shrinkage Reduction in thermal expansion &

contraction Closer to tooth tissue hence less interfacial stress

Improves workability by increasing viscosity Reduction in water sorption, softening, and

staining


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Increased radiopacity and diagnosticsensitivity through the incorporation ofstrontium (Sr) and barium (Ba) glass & other

heavy metal compounds that absorb x-rays. Curing shrinkage is offset in proportion to

the volume fraction (loading) of filler. Increase in the volume fraction of well-bonded filler

particles enhances physical and mechanicalproperties to levels comparable with those of toothtissue, thereby increasing clinical performance anddurability.


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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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FINE FILLERS Quartz, lithium aluminum silicate, barium,

strontium, zinc, ytterbium glasses

MICROFINE FILLERS

Colloidal silica RADIOPAQUE FILLERS

Fine fillers containing barium, strontium, zinc,ytterbium atoms

RADIOLUCENT FILLERS Quartz (crystalline silica), lithium aluminum

silicate


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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 umNANOFILLERS ----- 0.005 TO 0.01 um


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Visible light-cured system Intense blue light wavelength 468nm

Camphorquinone (CQ)

photosensitizer

Dimethylaminoethyl methacrylate (DMAEMA)

Amine initiator

Self-cured system Organic peroxide (benzoyl peroxide) initiator & an

organic amine accelerator (N, N-dimethyl-p-toluidine)


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Added to minimize or prevent spontaneousor accidental polymerization of monomers.

Have a strong reactivity potential with freeradicals

Butylated hydroxytoluene

Function of inhibitor Extend the storage lifetime for all resins

Ensure sufficient working time


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Dimethacrylate + Initiator + accelerator + treated

inorganic or reinforced filler Dental composite


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Optical Modifiers 10 or more shades covering the normal range

of human teeth (yellow to gray)

Consists minute amounts of metal oxideparticles Titanium oxide & aluminum oxide

Highly effective opacifiers


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Chemical activation Cold curing or self curing

Problems incorporation of air, no control over theworking time

Light activation Photocuring with visible (blue) light

Curing lamps

LED lamps

QTH lamps PAC lamps

Argon laser lamps


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Mixing is not required Less porosity, staining and increased strength

An aliphatic amine can be used instead of thearomatic amines required with chemical

curing Enhances color stability

Command polymerization on exposure toblue light Provides control of working time


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Limited curing depth Requires buildup layers of 2mm or less

Relatively poor accessibility in certain posterior andinterproximal locations

Variable exposure times because of shade (hue,value and chroma) differences

Results in longer exposure times for darkershades and/or increased opacity

Sensitivity to room illumination May lead to formation of a skin or crust when an

opened tube is exposed too long to room light


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LED lamps Light-emitting diodes

Emits radiation only in the blue part of the visiblespectrum between 440 & 480nm(nanometer)

Do not require filters Require low wattage

Can be battery-powered

Generate no heat

quiet


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QTH lamps Quartz-tungsten-halogen

Quartz bulb with a tungsten filament

Irradiates both UV and white light that must befiltered to remove heat and all wavelength exceptthose in the violet-blue range( 400 to 500 nm)

The intensity of the blue diminishes with use

A calibration meter is required


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PAC lamps Plasma arc curing

Uses a xenon gas that is ionized to produce a

plasma

The high-intensity white light is filtered to removeheat and to allow blue light to be emitted

Argon laser lamps Have the highest intensity Emits a single wavelength


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Depth of cure and Exposure time Curing depth is limited to 2-3mm unless

excessively long exposure times are used

regardless of lamp intensity

D l i


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Dual-cure resins Consists of 2 light-curable pastes

Benzoyl peroxide

Aromatic tertiary amine light curing is promoted by the amine/CQ

combination

Chemical curing is promoted by the amine/BPinteraction

Intended for any situation that does not allowsufficient light penetration to produce adequatemonomer conversion

Problems air inhibition & porosity


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Extraoral curing To promote a higher level of cure

For inlays or onlays


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Dental composite is composed of a resin matrix and fillermaterials.

Coupling agents are used to improve adherence of resin tofiller 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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Following are the important 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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It is the ratio of the bonded surfaces to the unbonded or freesurfaces in a tooth preparation.

The higher the C-Factor, greater is the potential for bonddisruption from polymerisation effects.


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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 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. Apackable composite is firm and hard to displace.


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One of the requirements of using a composite as a posteriorrestorative is that it should be radiopaque.

In order for a material to be described as being radiopaque,the International Standard Organization (ISO) specifies that itshould 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 radiopacityto be equivalent to 2 mm of aluminium, which isapproximately equal to natural tooth enamel.

A majority of the composites described as all-purpose oruniversal have levels of radiopacity greater than 2 mm of

aluminium


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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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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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1) Esthetics 2) Conservative tooth preparation.

3) Insulative.

4) Bonded to the tooth structure.

5) repairable.


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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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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 teethwith composite:


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A dentist must understand proper smile design so compositerestoration can achieve a beautiful smile. This is true forextensive veneering and small restorations.

Factors which are considered in smile design include:-A. Smile Form which includes size in relation to the face, sizeof 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, incisaledge, surface contours, line angles, contact areas, embrasureform, height of contour, surface texture, characterization,and tissue contours within an overall smile design.C. Tooth Color of gingival, middle, incisal, and interproximalareas and the intricacies of characterization within an overallsmile design.


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Colour is a study in and of itself. In dentistry, the effect ofenamel rods, surface contours, surface textures, dentinallight absorption, etc. on light transmission and reflection isdifficult to understand and even more difficult replicate.

The intricacies of understanding matching and replicatinghue, chroma, value, translucency, florescence; lighttransmission, reflection and refraction to that of a naturaltooth under various light sources is essential but far beyondthe scope of this article.


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Analysis of colour variation within teeth is improved by anunderstanding of how teeth produce color variation.

Enamel is prismatic and translucent which results in a bluegray color on the incisal edge, interproximal areas and areasof increased thickness at the junction of lobe formations.

The gingival third of a tooth appears darker as enamel thinsand 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 orexternal staining, enamel wear and cracking, caries, acute

trauma and dentistry.


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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 resultof aging, disease, trauma and wear.

Knowledge of anatomy allows a dentist to reproduce naturalteeth. For example, a craze line is not a straight line as oftenis produced by a dentist, but is a more irregular form guidedby enamel rods.


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Knowledge ofnormal position and axial tilt of teeth within ahead, lips, and arches allows reproduction of natural beautifulsmiles.

Understanding the goals of an ideal smile and compromisesfrom limitations of treatment allows realistic expectations ofa dentist and patient.

Often, learning about tooth position is easily done throughdenture esthetics.

Ideal and normal variations of tooth position is emphasized inremovable prosthetics so a denture look does not occur.


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The results of esthetic dentistry are limited by limitations ofideals and limitations of treatment.

Ideals of the golden proportion have been replaced bypreconceived 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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Esthetic dentistry is an art form. There are different levels ofappreciation so individual dentists evaluate results of estheticdentistry differently. Artistically, dentists select compositesbased on their level of appreciation, artistic ability andknowledge of specific materials.

Factors which influence composite selection

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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Tooth preparation often defines restoration strength.

Small tooth defects which receive minimal force requireminimal tooth preparation because only bond strength isrequired to provide retention and resistance.

In larger tooth defects where maximum forces are applied,mechanical retention and resistance with increased bond areacan be required to provide adequate strength.


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Understanding techniques to bond composite to dentin andenamel provide strength, elimination of sensitivity andprevention of micro-leakage.

Enamel bonding is a well understood science. Dentinalbonding, however, is constantly changing as more research is

being done and requires constant periodic review.

Micro-etching combined with composite bonding techniquesto old composite, porcelain, and metal must be understood todo anterior composite repairs.


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Understanding techniques which allow ease of placement,minimize effects of shrinkage, eliminate air entrapment andprevent material from pulling back from tooth structureduring instrumentation determine ultimate success or failureof a restoration.

It is important to incorporate proper instrumentation to allowease of shaping tooth anatomy and provide color variationprior to curing composite.

In addition, a dentist must understand placement of various

composite layers with varying opacities and color to replicatenormal tooth structure.


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Composite sculpture of cured composite is properly done ifappropriate use of polishing strips, burs, cups, wheels andpoints is understood.

In addition, proper use of instrumentation maximizes

esthetics and allows minimal heat or vibrational trauma tocomposite resulting in a long lasting restoration.


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Polishing composite to allow a smooth or textured surfaceshiny produces realistic, natural restorations.

Proper use ofpolishing strips, burs, cups, wheels and pointswith water or polish pastes as required minimizes heat

generation and vibration trauma to composite material for along lasting restoration.


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Tooth preparation requires adequate access to


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p p q qremove caries, removal of caries, elimination ofweak tooth structure that could fracture, bevelingof enamel to maximize enamel bond strength, andextension into defective areas such as stainedgrooves and decalcified areas.

Matrix systems are placed to contain materialswithin the tooth and form proper interproximalcontours and contacts. Selection of a matrixsystem 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 mustbe layered to minimize negative forces.

Generally, any area thicker than two millimeters

requires layering. In addition, cavity preparationproduces 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


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Composite built in layers replicate tooth structureby placing dentin layers first and then enamellayers.

Final contouring with hand instruments is ideal tominimize the trauma of shaping with burs.

Matrix systems are removed and refined shaping

and occlusal adjustment done with a 245 bur and aflame shaped finishing bur. Interproximal buccaland lingual areas are trimmed of excess with aflame shaped finishing bur.

Final polish is achieved with polishing cups, points,sandpaper disks, and polishing paste.


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Indirect laboratory composite is indicated on teeth that requiredlarge restorations but have a significant amount of toothremaining. It is used when a tooth defect is larger than indicatedfor direct composite and smaller than indicated for a crown. Acommon situation is fracture of a single cusp on a molar or athin cusp on a bicuspid. Force analysis is critical to success ashigh force will fracture composite, tooth structure or separatebonded interfaces. High force is indicated on teeth furthest backin the mouth for example, a second molar receives five timesmore force than a bicuspid. Orthodontic low angle cases andlarge masseter muscles generate high force. Sharp pointcontacts from opposing teeth create immense force and areoften altered with enameloplasty.

Indirect composite restorations are processed in a laboratoryunder heat, pressure and nitrogen to produce a more thoroughcomposite cure. Pressure and heat increase cure while nitrogen

eliminates oxygen that inhibits cure. Increased cure results instronger restorations. Strength of laboratory processedcomposite is between composite and crown strength andrequires adequate tooth support.


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Tooth preparation requires removal of existing restorationsand caries. Thin cusps and enamel are removed incombination of blocking out undercuts with composite, glassionomer, flowable composite or the like.

Tooth preparation requires adequate wall divergence to bondand cement the restoration and ideally, margins should finishin enamel. The restoration floor is bonded and light cured.

Bonding agent is light cured to stabilize collagen fibers andavoid collapse during restoration placement. A base of glassionomer or composite is used if thermal sensitivity isanticipated.

Restoration retention is judged by bonded surface area,number and location of retentive walls, divergence ofretentive walls, height to width ratio and restoration internaland external shape.

Resistance form, reduction of internal stress and conversionof potential shear and tensile forces is accomplished bysmoothing sharp areas and creating flat floors as opposed toexternal angular walls.


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Impressions are taken of prepared teeth, models poured andcomposite restorations constructed at a laboratory. Temporariesare placed and a second appointment made.

At a second appointment, temporaries are removed and a rubberdam placed. Restorations are tried on the teeth andadjusted. Manufacturers directions are followed. In general,bonding is completed on the tooth surfaces and bonding resinprecured.

Matrix bands are placed prior to etching to contain etch withinprepared areas. Trimming of excess cement where no etchinghas occurred is easier.

Composite surfaces are silinated and dual cure resin cementapplied. Restorations are seated, excess resin cement is wipedaway with a brush and then facial and lingual surfaces are lightcured. Interproximal areas are flossed and then lightcured. Excess is trimmed with hand instruments and finishingflame shaped burs.

The rubber dam is removed and occlusion adjusted. Surfaces arefinished and polished.


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There are several mechanisms of composite wearincluding adhesive wear, abrasive wear, fatigue,and chemical wear.

Adhesive wear is created by extremely smallcontacts and therefore extremely high forces, oftwo opposing surfaces. When small forces release,material is removed. All surfaces have microscopic

roughness which is where extremely small contactsoccur between opposing surfaces. Abrasive wear is when a rough material gouges out

material on an opposing surface. A harder surfacegouges a softer surface. Materials are not uniform

so hard materials in a soft matrix, such as filler inresin, gouge resin and opposing surfaces. Fatiguecauses wear. Constant repeated force causessubstructure deterioration and eventual loss ofsurface material. Chemical wear occurs whenenvironmental materials such as saliva, acids or

like affect a surface.


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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 resinto expand more with heat. When fracture occurs, a crackpropagates and strikes a filler particle. Resin pulls away from fillerparticle surfaces during failure. This type of failure is moredifficult with larger particles as surface area is greater. A macrofillcomposite is stronger than a microfill composite.

Coupling agents are used to improve adherence of resinto filler surfaces. Modification of filler physical structure on the surface or

aggregating filler particles create mechanical locking to improveinterface strength. Coupling agents chemically coat filler surfacesand increase strength. Silanes have been used to coat fillers forover fifty years in industrial plastics and later in dentalfillers. Today, they are still state of the art.


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RECENT ADVANCES


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Hierarchical microstructures - Dr H-X Peng The properties of composite materials can be tailored

through microstructural design at different lengthscales suchas the micro- and nano-structural level.

At the micro-structural level, our novel approach createsmicrostructures with controlled inhomogeneousreinforcement distributions.

These microstructures effectively contain more than onestructural hierarchy. This has the potential to create wholenew classes of composite materials with superior singleproperties and property combinations.

Research also involves tailoring the nano-structures of micro-wires/ribbons for macro-composites.


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- Dr Ian Bond Impact damage to composite structures can result in a drastic

reduction in mechanical properties. Bio-inspired approach isadopted to effect selfhealing which can be described asmechanical, thermal or chemically induced damage that isautonomically repaired by materials already contained within thestructure.

Efforts are undergoing to manufacture and incorporate

multifunctional hollow fibres to generate healing and vascularnetworks within both composite laminates and sandwichstructures.

The release of repair agent from these embedded storagereservoirs mimics the bleeding mechanism in biologicalorganisms.

Once cured, the healing resin provides crack arrest and recoveryof mechanical integrity.

It is also possible to introduce UV fluorescent dye into the resin,which will illuminate any damage/healing events that thestructure has undergone, thereby simplifying the inspectionprocess for subsequent permanent repair.


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- Dr Bo Su An electrospinning technique has been used to produce

polymer, ceramic and nanocomposite nanofibres for woundaddressing, tissue engineering and dental compositesapplications.

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 dopedalginate nanofibres and alginate/chitosan core-shellnanofibres, have also been investigated for antimicrobials andtissue engineering scaffolds.

Zirconia and silica nanofibre/epoxy composites are currently

under investigation for dental fillings and aestheticorthodontic archwires.


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- 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 exploringtheir application to composite propellers and blades.

These tailored materials also have potential applications inlightning 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 sensorapplications.


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- 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 maintainingstructural performance.

This has been achieved by filling hollow fibres with asuspension of magnetic materials after manufacture of thecomposite component.

Research is continuing to tailor the magnetic properties of thecomposite to other applications.

In another approach, magnetic microribbons and microwiresare being tailored and embedded into macrocompositematerials to provide magnetic sensing functions.


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- 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 foraerospace, maritime and ergonomics applications.

The use of smart material technologies and negativePoissons ratio solids has also led to the development ofsmart auxetics for active sound management, vibroacousticsand structural health monitoring.


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- 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 fibrereinforced composites.

The diamond fibres are made by coating thin (100 mmdiameter) tungsten wires with a uniform coating of

polycrystalline diamond using hot filament chemical vapourdeposition.

The diamond-coated wires are extremely stiff and rigid, andcan be embedded into a matrix material (such as a metal orplastic) to make a stiff but lightweight composite materialwith anisotropic properties. Such materials may haveapplications in the aerospace industry.


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- Professor Steve Mann New types of composites with a combination of strength,

toughness and functionality are being prepared by combiningresearch in the synthesis of inorganic non-particles with thatin the synthesis of organic polymers.

This interdisciplinary approach has been used to produceflexible fibres of magnetic spider silk as shown in thephotograph (left). Silk fibres are coated by a dippingprocedure using dilute suspensions of inorganic nano-particles that are prepared with specific surface properties.

Similar methods are being investigated with swellablepolymer gels and bacterial supercellular fibres to producenovel hybrid composites.

dental composite 2

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