Composites by Varsha

8/6/2019 Composites by Varsha

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COMPOSITES

S.VARSHA VARDHINI,

C.R.I


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DEFINITION

COMPOSITE RESIN IS A THREE DIMENSIONAL

COMBINATION OF TWO OR MORE CHEMICALLY

DIFFERENT MATERIALS WITH A DISTINCTINTERPHASE BETWEEN THEM.

IN COMBINATION, THE PROPERTIES ARE

SUPERIOR TO THOSE OF INDIVIDUAL

COMPONENTS.


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COMPOSITION

The basic components of composite resins include the following

1.Resin matrix.2.Fillers. 3.Coupling agent. 4.Activator-initiator system.

5.Inhibitors.6.Optimal modifiers/ coloring agents.


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RESIN MATRIX

The resin matrix is the continuous phase to which the otheringredients are incorporated,

resin matrix composed of monomers which are aromatic or

aliphatic diacrylates. COMPOSITE RESINS CONTAINS

-BisGMA Bisphenol-A-glycidyl methacrylate.

-UDMA urethane dimethacrylate.-combination of BisGMA and UDMA. Both these chemicals have reactive carbon double bond at each

end that can under go addition polymerization


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FILLERS

Fillers in the composite resins are usually a type of glass suchas quartz,silica, borosilicate

glass,barium,strontium,zinc,zirconium

They are added to improve the physical,mechanical and optical properties of the resin.

The filler contain in the composite resin ranges from 30% to 70%.


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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 stillstate of the art. Silanes have disadvantages. They age quickly in a bottle and

become ineffective. Silanes are sensitive to water so the silane fillerbond breaks down with moisture.

Water absorbed into composites results in hydrolysis of the silanebond and eventual filler loss.

Common silane agents are:vinyl triethoxysilane

methacryloxypropyltrimethoxysilane


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l

silane moleculehydrolysis

silonol group bonds with the filler particles.methacrylate group

covalent bond

resin


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ACTIVATOR-INITIATOR SYSTEMS

Type of composites Activator Initiator

Chemically cured

composites

N.N.dimethyl-p-

toluidine

Benzoyl peroxide

Light-curedcomposites

1.Ultrviolet lightTertiary amine

Benzoin methylether


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Chemically cured composites Light;-cured composites

Polymerization is towards the

centre

Polymerization is towards the

light sourceBulk placement is possible Incremental placement is recommended

Rapid setting occurs Command setting occurs which is

under the operators controlReduce working time so insertionand contouring should be quicklydone

Adequate working time is possibledue to command set.

Voids can be incor erated durin No voids as there is no mixin so


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ULTRAVIOLETLIGHT

VISIBLE LIGHT

Wavelength is360-400nm Wavelength is 450-480nm

Harmful to the dentist andpatient Notinjurious

Intensity of the light fails withtime

Intensity of the light remains thesame

Limited de th o curin Greater de th o curin is


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INHIBITORS

These are added to prevent spontaneous poly merization of themonomers by inhibiting the free radical.

butylated hydroxytoluene 0.01% is added as inhibitor incomposite resin.


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Optical modifiers/colouring

agents Metal oxides in minute ammounts are added to the composite resinsto produce different shades of composites.

Aluminium oxide and titaniumoxide in small amounts provideopacity to composite resin.


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CLASSIFICATION

BASED ON THE MEAN PARTICLE

SIZE OF THE MAJOR FILLER

1.Traditional composites,8-12m. 2.small particle composites 1-5m. 3.Microfilled composites 0.04-0.4m. 4.Hybrid composites 0.6-1 m.


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BASED ON THE FILLER PARTICLE

SIZE AND DISTRIBUTION.

1.Megafilled composites very large fillers2.macrofilled composites 10-100m 3.midifilled composites 1-10m 4.minifilled composites 0.1-1m

5.microfilled composites 0.01-0.1m6.nanofilled composites 0.005-0.01m


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BASED ON THE METHOD OF

POLYMERIZATION:

Light-cured composites1.ultraviolet light-cured composite2.visible light-cured composite

Dual-Self cured, auto-cured or chemically cured composites .cured composites-both self curing and light curing mechanismsStaged-curing composites initial soft-start polymerization

followed by complete polymerization.


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BASED ON MODE OF

PRESENTATION:

Two paste system Single paste system Powder liquid system.


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BASED ON USE Anterior composite.

Posterior composite. Core buildup composite.

Luting composite.


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BASED ON CONSISTENCY: Light body composite- flowable composite

Medium body composite- medium viscosity composites likemicrofilled, hybrid,microhybrid composites. Heavy body composites- packable composites.


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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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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 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 withcomposite:


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1. SMILE DESIGN

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

Factors which are considered in smile design include:-

A. Smile Form which includes size in relation to the face, size of onetooth to another, gingival contours to the upper lip line, incisal edgesoverall 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 ofcontour, surface texture, characterization, and tissue contours withinan overall smile design.C. Tooth Color of gingival, middle, incisal, and interproximal areasand 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 understandand 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. TOOTHCOLOUR

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

color on 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

dentin shows through.

Color deviation, such as craze lines or hypocalcifications, withindentin 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 ofaging, 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 producedby 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 andpatient. Often, learning about tooth position is easily done through denture

esthetics.

Ideal and normal variations of tooth position is emphasized inremovable 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 idealsand limitations of treatment.

Ideals of the golden proportion have been replaced by preconceivedperceptions.

Limitations of ideals are based on physical, environmental andpsychological 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 composites basedon their level of appreciation, artistic ability and knowledge ofspecific 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 provideretention 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 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 old

composite, porcelain, and metal must be understood to do anteriorcomposite 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 materialfrom pulling back from tooth structure during instrumentation

determine ultimate success or failure of a restoration. It is important to incorporate proper instrumentation to allow easeof shaping tooth anatomy and provide color variation prior to curingcomposite.

In addition, a dentist must understand placement of variouscomposite layers with varying opacities and color to replicate normaltooth structure.


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11.COMPOSITE SCULPTURE

Composite sculpture of cured composite is properly done ifappropriate use of polishing strips, burs, cups, wheels and points isunderstood.

In addition, proper use of instrumentation maximizes esthetics andallows 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 shinyproduces realistic, natural restorations.

Proper use of polishing strips, burs, cups, wheels and points with

water or polish pastes as required minimizes heat generation andvibration 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 onpremolars 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 anglecases, in molar areas, with strong muscles, point contacts andparafunctional forces such as grinding and biting finger nails.

Failure of a restoration occurs if composite fractures, tooth fractures,composite debonds from tooth structure or micro-leakage and subsequentcaries occurs. A common area of failure is direct point contact by sharpopposing 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, removalof caries, elimination of weak tooth structure that could fracture,

beveling of enamel to maximize enamel bond strength, and extensioninto defective areas such as stained grooves and decalcified areas.

Matrix systems are placed to contain materials within the tooth andform 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 whencured 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 dramaticstress and should be avoided.


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Composite built in layers replicate tooth structure by placingdentin 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 occlusaladjustment 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, sandpaperdisks, and polishing paste.


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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 forces

release, material is removed. Abrasive wear is when a rough material gouges out material on anopposing surface. A harder surface gouges a softersurface. Materials are not uniform so hard materials in a softmatrix, such as filler in resin, gouge resin and opposingsurfaces. Fatigue causes wear. Constant repeated force causessubstructure deterioration and eventual loss of surfacematerial. Chemical wear occurs when environmental materialssuch s saliva, acids or like 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 toexpand more with heat. When fracture occurs, a crack propagatesand strikes a filler particle. Resin pulls away from filler particlesurfaces 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 fillersurfaces. Modification of filler physical structure on the surfaceor aggregating filler particles create mechanical locking to improveinterface strength. Coupling agents chemically coat filler surfacesand increase strength. Silanes have been used to coat fillers for over


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