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COMPOSITES
By: Naghman Zuberi
Naghman Zuberi 2
Material with two or more distinct substances metals, ceramics or polymers
Dental resin composite soft organic-resin matrix polymer
hard, inorganic-filler particles ceramic
Most frequently used esthetic-restorative material
Leinfelder 1993
COMPOSITE
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COMPOSITE’S CHEMISTRY
Dental composite is composed of a resin matrix and fillermaterials.
Coupling agents are used to improve adherence of resin to fillersurfaces.
Activation systems including heat, chemical and photochemicalinitiate 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 together alongthe 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 withTEGDMA (triethylene glycol dimethacrylate) to form the first BIS-GMA resin. Diluents are added to increase flow and handlingcharacteristics or provide cross linking for improvedstrength. Common examples are:
RESIN:- BIS-GMA bisphenol glycidylmethacrylate
DILUENTS:- MMA methylmethacrylateBIS-DMA bisphenol dimethacrylateUDMA urethane dimethacrylate
CROSS LINK DILUENTSTEGDMA triethylene glycol dimethacrylateEGDMA ethylene glycol dimethacrylate
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COUPLING AGENTS
Coupling agents are used to improve adherence of resin to fillersurfaces.
Coupling agents chemically coat filler surfaces and increasestrength.
Silanes have been used to coat fillers for over fifty years inindustrial plastics and later in dental fillers. Today, they are stillstate of the art.
Silanes have disadvantages. They age quickly in a bottle andbecome ineffective. Silanes are sensitive to water so the silanefiller bond breaks down with moisture.
Water absorbed into composites results in hydrolysis of thesilane bond and eventual filler loss.
Common silane agents are:vinyl triethoxysilanemethacryloxypropyltrimethoxysilane
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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 appliedeven without initiators.
Resins require stabilizers to avoid spontaneouspolymerization. Stabilizers are also used to control the reaction ofactivators and resin mixtures.
Hydroquinone is most commonly used as a stabilizer. Common heat based initiators are peroxides such as
benzoylperoxidet-butylperoxidet-cumythydroxyperoxide
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PHOTOCHEMICAL CATALYST
Early photochemical systems used were benzoin methyl ether which issensitive to UV wavelengths at 365 nm. UV systems had limited use asdepth of cure was limited. Visible light activation of diketones is thepreferred photochemical systems. Diketones activate by visible, bluelight to produce slow reactions. Amines are added to accelerate curingtime.
Presently, different composites use different photochemicalsystems. These systems are activated by different wavelengths oflight. In addition, different curing lights produce various ranges ofwavelengths that might not match composite activationwavelengths. This can result in no cure or partial cure. Compositematerials must be matched to curing lights.
Common photochemical initiators are:CamphoroquinoneAcenaphthene quinoneBenzyl
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LIGHT CURING
Light curing can beaccomplished with:-1) Quartz-Tungsten-Halogen2) Plasma Arc Curing3) Light Emitting Diode
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Camphorquinone most common photoinitiator absorbs blue light 400 - 500 nm range
Initiator reacts with amine activator Forms free radicals Initiates addition polymerization
OCH2CHCH2O-C-C=CH2CH2=C-C-O-CH2CH-CH2O -C-
CH3 CH3
CH3
CH3OH OH
O O
Bis-GMA
VISIBLE LIGHT ACTIVATION
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CHEMICAL CATALYST
Chemical activation of peroxides produces free radicals. Chemicalaccelerators are often not color stable and have been improved for thisreason.
The term self cure or dual cure (when combined with photo chemicalinitiation) describes chemical cure materials.
Chemical composites mix a base paste and a catalyst paste for selfcure.
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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Initiation production of reactive free radicals typically with light for restorative materials
Propagation hundreds of monomer units polymer network 50 – 60% degree of conversion
Termination
Craig Restorative Dental Materials 2002
POLYMERIZATION
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C=C
C=C C=C
C=C C=C C=C C=C
C=C C=C
C=C C=CC=C C=C
C=C C=C
C=C C=C
C=C
C=C
C=CC=C
C=C
C=C
C=C C=C C=CC=C C=C
C=C
C=C
polymerization
Ferracane
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COMPOSITE FILLERS
Fillers are placed in dental composites to reduce shrinkage uponcuring.
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 sizedistribution.
Materials such as strontium glass, barium glass, quartz, borosilicateglass, ceramic, silica, prepolymerized resin, or the likewise are used.
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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.
FILLERS CLASSIFICATION
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Classification According to Size:-MACROFILLERS ---- 10 TO 100 umMIDIFILLERS ----- 1 TO 10 umMINIFILLERS ----- 0.1 TO 1 umMICROFILLERS ----- 0.01 TO 0.1 umNANOFILLERS ----- 0.005 TO 0.01 um
FILLERS CLASSIFICATION
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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 CHARECTERISTICS
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 toothpreparation.
The higher the C-Factor, greater is the potential for bond disruption frompolymerisation effects.
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C- FACTOR
Sealants and Class V have C Factor of 1:5 whereas Class I has a C Factor of 5:1
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C Factor in Class I C Factor in Class II
C Factor in Class IV
Incremental LayeringMinimizes the C Factor
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INTERNAL STRESSES
Internal stresses can be reduced by,1) ‘Self start’ Polymerisation- A Dual Cured System2) Incremental placement3) Use of stress breaking liners such as:-
a)Filled Dentinal Adhesivesb)Resin Modified Glass Ionomer (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 firmand 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 polymerizecomposite.
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RADIOPACITY
One of the requirements of using a composite as a posterior restorativeis that it should be radiopaque.
In order for a material to be described as being radiopaque, theInternational Standard Organization (ISO) specifies that it should haveradiopacity equivalent to 1 mm of aluminium, which is approximatelyequal to natural tooth dentine.
However, there has been a move to increase the radiopacity to beequivalent to 2 mm of aluminium, which is approximately equal tonatural tooth enamel.
A majority of the composites described as all-purpose or universal havelevels 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 rootsurface.
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 COMPOSITERESTORATION 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 ANTERIORCOMPOSITE 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 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,
size of one tooth to another, gingival contours to the upper lipline, 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 smiledesign.
C. Tooth Color of gingival, middle, incisal, andinterproximal areas and the intricacies of characterizationwithin an overall smile design.
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2. COLOUR AND COLOURANALYSIS Colour is a study in and of itself. In dentistry, the effect of enamel rods,
surface contours, surface textures, dentinal light absorption, etc. onlight transmission and reflection is difficult to understand and even moredifficult replicate.
The intricacies of understanding matching and replicating hue, chroma,value, translucency, florescence; light transmission, reflection andrefraction to that of a natural tooth under various light sources isessential.
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3. TOOTH COLOUR
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 blue gray coloron the incisal edge, interproximal areas and areas of increasedthickness at the junction of lobe formations.
The gingival third of a tooth appears darker as enamel thins and dentinshows through.
Color deviation, such as craze lines or hypocalcifications, within dentinor enamel can cause further color variation.
Aging has a profound effect on color caused by internal or externalstaining, enamel wear and cracking, caries, acute trauma and density.
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4. TOOTH SHAPE
Understanding tooth shaperequires studying dental anatomy.
Studying anatomy of teeth requiresrecognition of general form, detailanatomy and internal anatomy.
It is important to know idealanatomy and anatomy as a resultof aging, disease, trauma and wear.
Knowledge of anatomy allows adentist to reproduce natural teeth.For example, a craze line is not astraight line as often is producedby a dentist, but is a more irregularform guided by enamel rods.
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5. TOOTH POSITION
Knowledge of normal positionand axial tilt of teeth within ahead, lips, and arches allowsreproduction of natural beautifulsmiles.
Understanding the goals of anideal smile and compromisesfrom limitations of treatmentallows realistic expectations of adentist and patient.
Often, learning about toothposition is easily done throughdenture esthetics.
Ideal and normal variations oftooth position is emphasized inremovable prosthetics so adenture look does not occur.
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6. ESTHETIC GOALS
The results of esthetic dentistry are limited by limitationsof ideals 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, financialand psychological factors.
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7. COMPOSITE SELECTION
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 influencecomposite 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 oftendefines restoration strength.
Small tooth defects whichreceive minimal force requireminimal tooth preparationbecause only bond strength isrequired to provide retentionand resistance.
In larger tooth defects wheremaximum forces are applied,mechanical retention andresistance with increasedbond area can be required toprovide adequate strength.
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9. BONDING TECHNIQUES
Understanding techniques to bond composite to dentin and enamelprovide 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 andrequires constant periodic review.
Micro-etching combined with composite bonding techniques to oldcomposite, porcelain, and metal must be understood to do anteriorcomposite repairs.
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10. COMPOSITE PLACEMENTTECHNIQUE Understanding techniques which
allow ease of placement,minimize effects of shrinkage,eliminate air entrapment andprevent material from pullingback from tooth structure duringinstrumentation determineultimate success or failure of arestoration.
It is important to incorporateproper instrumentation to allowease of shaping tooth anatomyand provide color variation priorto curing composite.
In addition, a dentist mustunderstand placement of variouscomposite layers with varyingopacities and color to replicatenormal tooth structure.
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11. COMPOSITE SCULPTURE
Composite sculpture of curedcomposite is properly done ifappropriate use of polishing strips,burs, cups, wheels and points isunderstood.
In addition, proper use ofinstrumentation maximizes estheticsand allows minimal heat orvibrational trauma to compositeresulting in a long lastingrestoration.
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12. COMPOSITE POLISHING
Polishing composite to allow a smooth or textured surface shinyproduces realistic, natural restorations.
Proper use of polishing strips, burs, cups, wheels and points with wateror polish pastes as required minimizes heat generation and vibrationtrauma to composite material for a long lasting restoration.
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DIRECT POSTERIORCOMPOSITES Composites are indicated for Class 1, class 2 and class 5 defects on
premolars and molars. Ideally, an isthmus width of less than one thirdthe intercuspal distance is required.
This requirement is balanced against forces created on remaining toothstructure and composite material. Forces are analyzed by direction,frequency, duration and intensity. High force occurs with low anglecases, in molar areas, with strong muscles, point contacts andparafunctional 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 bypreparation design and occlusal contacts can be critical to restorativesuccess.
Failure of a restoration occurs if composite fractures, tooth fractures,composite debonds from tooth structure or micro-leakage andsubsequent caries occurs. A common area of failure is direct pointcontact by sharp opposing cusps. Enameloplasty that creates a threepoint 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 couldfracture, beveling of enamel to maximize enamel bond strength,and extension into defective areas such as stained grooves anddecalcified areas.
Matrix systems are placed to contain materials within the toothand form proper interproximal contours and contacts. Selectionof a matrix system should vary depending on the situation.
Enamel and dentin bonding is completed. Composite shrinkswhen cured so large areas must be layered to minimize negativeforces.
Generally, any area thicker than two millimeters requireslayering. In addition, cavity preparation produces multiple walldefects.
Composite curing when touching multiple walls creates dramaticstress and should be avoided.
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Anterior and Posterior Matrix Systems
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Composite built in layers replicate tooth structure byplacing dentin layers first and then enamel layers.
Final contouring with hand instruments is ideal tominimize the trauma of shaping with burs.
Matrix systems are removed and refined shaping andocclusal adjustment done with a 245 bur and a flameshaped finishing bur. Interproximal buccal and lingualareas are trimmed of excess with a flame shapedfinishing bur.
Final polish is achieved with polishing cups, points,sandpaper disks, and polishing paste.
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Polishing and Polishing Kit
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INDIRECT POSTERIORCOMPOSITES Indirect laboratory composite is indicated on teeth that required large
restorations but have a significant amount of tooth remaining. It is usedwhen a tooth defect is larger than indicated for direct composite andsmaller than indicated for a crown. A common situation is fracture of asingle cusp on a molar or a thin cusp on a bicuspid. Force analysis iscritical to success as high force will fracture composite, tooth structureor separate bonded interfaces. High force is indicated on teeth furthestback in the mouth for example, a second molar receives five timesmore force than a bicuspid. Orthodontic low angle cases and largemasseter muscles generate high force. Sharp point contacts fromopposing teeth create immense force and are often altered withenameloplasty.
Indirect composite restorations are processed in a laboratory underheat, pressure and nitrogen to produce a more thorough compositecure. Pressure and heat increase cure while nitrogen eliminatesoxygen that inhibits cure. Increased cure results in strongerrestorations. Strength of laboratory processed composite is betweencomposite and crown strength and requires adequate tooth support.
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Indirect Composite Restoration
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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 outundercuts with composite, glass ionomer, flowable composite or thelikewise material.
Tooth preparation requires adequate wall divergence to bond andcement 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 avoidcollapse during restoration placement. A base of glass ionomer orcomposite is used if thermal sensitivity is anticipated.
Restoration retention is judged by bonded surface area, number andlocation of retentive walls, divergence of retentive walls, height to widthratio and restoration internal and external shape.
Resistance form, reduction of internal stress and conversion of potentialshear and tensile forces is accomplished by smoothing sharp areas andcreating flat floors as opposed to external angular walls.
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TOOTH PREPARATION
Impressions are taken of prepared teeth, models poured and compositerestorations constructed at a laboratory. Temporaries are placed and asecond appointment made.
At a second appointment, temporaries are removed and a rubber damplaced. Restorations are tried on the teeth andadjusted. Manufacturers directions are followed. In general, bonding iscompleted on the tooth surfaces and bonding resin precured.
Matrix bands are placed prior to etching to contain etch within preparedareas. Trimming of excess cement where no etching has occurred iseasier.
Composite surfaces are silinated and dual cure resin cementapplied. Restorations are seated, excess resin cement is wiped awaywith a brush and then facial and lingual surfaces are lightcured. Interproximal areas are flossed and then light cured. Excess istrimmed with hand instruments and finishing flame shaped burs.
The rubber dam is removed and occlusion adjusted. Surfaces arefinished and polished.
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COMPOSITE WEAR
There are several mechanisms of composite wear including adhesivewear, abrasive wear, fatigue, and chemical wear.
Adhesive wear is created by extremely small contacts and thereforeextremely high forces, of two opposing surfaces. When small forcesrelease, material is removed. All surfaces have microscopic roughnesswhich is where extremely small contacts occur between opposingsurfaces.
Abrasive wear is when a rough material gouges out material on anopposing surface. A harder surface gouges a softer surface. Materialsare not uniform so hard materials in a soft matrix, such as filler in resin,gouge resin and opposing surfaces. Fatigue causes wear. Constantrepeated force causes substructure deterioration and eventual loss ofsurface material. Chemical wear occurs when environmentalmaterials such s saliva, acids or similar agents affect a surface.
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COMPOSITE FRACTURE
Dental composite is composed of a resin matrix and fillermaterials. The resin filler interface is important for most physicalproperties.
There are three causes of stress on this interface including: resinshrinkage pulls on fillers, filler modulus of elasticity is higher than resin,and filler thermo coefficient of expansion allows resin to expand morewith heat. When fracture occurs, a crack propagates and strikes a fillerparticle. Resin pulls away from filler particle surfaces duringfailure. This type of failure is more difficult with larger particles assurface area is greater. A macrofill composite is stronger than amicrofill composite.
Coupling agents are used to improve adherence of resin to fillersurfaces. Modification of filler physical structure on the surface oraggregating filler particles create mechanical locking to improveinterface strength. Coupling agents chemically coat filler surfaces andincrease strength. Silanes have been used to coat fillers for over fiftyyears in industrial plastics and later in dental fillers. Today, they are stillstate of the art.
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SILANE COUPLING AGENT
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REPAIRING CHIPPED PORCELAIN BRIDGE
Chipped Edge of Porcelain Pontic Porcelain is Etched with HF Acid
Silane and Bonding is Applied Repaired in Light Cured Composite
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