lecture 3 & 4- composites (slides)

8/4/2019 Lecture 3 & 4- Composites (Slides)

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en a

materials

Direct and indirect esthetic

restorative materials


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Midterm exam

15/11/2011 Tuesday 12.15 pm

Location: 10H3,4, N2


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Direct placement restorativematerials

Esthetic materials are those materials thatare tooth colored.

Direct placement materials, are placeddirectly by the clinician in prepared teethwithout the need for extra-oral construction

of the restoration


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Replacement

o f amalgam

Re-contour ing

a p ig shapedla te ra l


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Uses

Maybe used forcosmetic purposes

Out of necessity


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Direct restorative materials

Composite

Glass ionomer cements (GIC)

Resin modified-GIC

Compomers


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Composite resin

Composite: mixture of two or morecomponents.

Major components:

Resin matrix

Fillers

Coupling agents (silane), join filler and matrix Pigments


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Components Resin matrix:bis-GMA (bisphenol A-glycidyl

methacrylate).

UDMA (Urethane dimethacrylate)

These resins are made of oligomers(organic molecules) and low molecularweight monomers


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Fillers: silica, quartz, glasses composed ofbarium, strontium etc.

Why add fillers:

Add strength Increase wear resistance

Reduce polymerization shrinkage

Size of filler?Ratio or weight of filler to resin matrix?

Coupling agent: silane, binds filler to matrix

and reduces wear. Pigments: to produce different colors and

shades.


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Varity of filler size, A, Macrofilled.

B, Microfilled. C, Hybrid


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Polymerization Monomers join polymers

Initiators and activators cause the reaction to begin.

Side chains on polymers cross-link to form strongermaterial


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Polymerization1. Chemical cure (self-cure): 2-paste

system:

Base: composite and benzoyl peroxideas initiator

Catalyst: composite and tertiary amineactivator

Require manual mixing which may leadto air bubbles incorporation.


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Polymerization2. Light cure: blue light (400-500 nm) is

used to harden the composite. These

light curable composites containcomponents that start to react oncesubjected to the light:

1. Diketone2. Organic amines

Depth of cure? Depends on color and

location of restoration


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Polymerization

3. Dual cure: 2-paste system containingboth types of initiators and activators.Advantage: light starts thepolymerization rxn and the chemical

reaction continues in areas were lightcant reach them.


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Classification of composites

1. Macrofilled2. Microfilled

3. Small-particle composite4. Hybrid5. Flowable6. Pit and fissure sealant7. Packable composite8. Smart composite9. Core build up composite


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Macrofilled composites

First generation Filler particle size 10-100 m

Difficult to polish Stronger than composites with smaller

particles


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Microfilled composites

Filler particle size 0.04 m in diameter

Volume of filler is 35-50% (smallercompared to other composites due to the largervolume of several small particles as opposed to

one large particle of the same weight) Lower physical properties


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Small particle composite Particle size 1-5 m

Used to be used for posterior restorationsbut have been replaced by hybrid

composite


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Hybrid composite Mixture of macro and microfillers (75-80% by

weight)

Microhybrid composite: contains 2 particle sizes,small 0.5-3 m and microfine fillers 0.04 m

Hybrids have high polishability and strength sothey can be used for anterior and posterior

restorations


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Flowable composites Low-viscosity, light cured

Can be lightly filled (40%),or more heavily filled (70%)

Particle size 0.07-1 m

Delivered into cavity using

a syringe

Weaker and wear morecompared to hybrids

Used for PRR

Pit and fissure sealing

Liners (cushion stress

caused by polymerizationshrinkage of overlyingcomposite)

Class V


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Pit and fissure sealants

Range from no filler to more heavily filledcomposites similar to flowable composites

Low viscosity

Preventive material


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Packable composites

Highly viscous Heavily filled

Stiff and strong Posterior restorations (as a substitute for

amalgam)

Shrink less due to higher filler content


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Smart composites

Combat caries by having the ability torelease fluoride, calcium, hydroxyl ionswhen acidity increases

Effectiveness has not yet been proven


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Core buildup composites

Heavily filled Replace lost tooth structure in teeth

needing crowns

Colored to distinguish then from naturaltooth structure


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Provisional restorative composites

Replace acrylic resin in constructingprovisional onlays, crowns and bridges

More expensive than acrylic, but wear

less, and shrink less, and produce lessheat when polymerized. Easier to repair

with flowable composite However, they are more brittle than acrylic


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Physical properties

Biocompatibility Polished composites are tolerated by softtissue. Bonding agents protect pulp by

sealing tubules

Strength Larger filler composites are stronger intension and compression

Wear Lower filler content increases wear.Composites wear more than amalgams

Polymerization

shrinkage

Composite shrink away from cavity walls

Minimized by incremental placement.

Can cause postoperative sensitivity, &pressure on tooth


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Shrinkage outcomes


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Thermal conductivity Low thermal conductivity, close to that

of natural tooth structure

Coefficient of thermalexpansion (CTE)

Greater than tooth structure, causesdebonding & leakage. Filler content

CTE

Elastic modulus Determined by amount of filler. Fillerincreases stiffness. Important in

selection for anterior & posteriorrestorations

Water sorption resin content water sorption

Radiopacity Barium, strontium radiopacity. Quartz(radiolucent) used as filler in anteriorcomposites to improve shade


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Clinical handling of composites Composite is used for all sorts of

restorative procedures from class I toclass IV.

Selection criteria:Esthetic demands: ability to match tooth color

and achieve high polishability. Microfills and

microhybrids are suitedStrength demands: in posterior teeth and

stress bearing areas, hybrids are more suited


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Shade guide: Some practitioners apply aportion of composite on tooth surface andcure it to observe the appropriate shade.

The tabs in the shade guide should bemoist and held adjacent to the tooth and

observed under different lights Shelf life: follow manufacturer instructions

but as a general rule, avoid heat and light.

Average shelf life 2-3 years.


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Dispensing and cross-contamination:composites are usually dispensed insyringes. Disposable small containers are

used to avoid cross-contamination. Oncecomposite is dispensed, it should be

covered with a light-protected container


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Isolation


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Single paste, light activated composite

Instruments for placing composite

Syringe for injecting composite

Self-cure 2 paste composite,and bonding agent bottle


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Matrix strips/ bands: Mylar strip is used in class III,IV. Metal matrix bands are used for class II cavities(curing is from an occlusal direction then after the bandis removed, light is directed from facial and lingual

aspects). Clear crown forms are used for build uprestorations. A wedge is also used to seal gingivally.

Incremental placement: 2 mm thick isrecommended:

To minimize polymerization shrinkage

Allow curing light to properly penetrate and cure


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Etching and bonding:Etching is achieved using phosphoric acid (

34-37%). After etching, tooth surface iswashed and gently dried, etched enamel willappear frosty white.

Bonding agent is applied in a thin layer andlight-cured according to manufacturerinstructions. (remember micromechanical

retention).

Etching and bonding


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Etching and bonding

Bonding

and

light

curing

Etch ing


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Acid etched enamel


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Resin to resin bonding:proper isolation, nocontamination is

necessary for properbonding of successivecomposite layers. Thesurface layer is a thinlayer of unpolymerized

composite (air-inhibited), is removedby polishing

Enamel etching

Bonding agent

Composite (bonds chemicallyto bonding agent)

2nd layer of composite, etc.


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Contaminants: After etching and bonding, dentinesurface should be kept contaminant free. Otherwise re-etching for 10-15 seconds is necessary. Eugenolcontaining cements should be avoided. Bonding agentcan be used to prevent sticking of composite toinstrument during filling.

Light-curing: Should be held as closely as possible to composite

20-40 seconds for thin layers

Thicker layers, darker shades, deeper locationsrequire more time


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Finishing and polishing: sandpaper discs,fine, ultra-fine diamonds. For gingival orinterproximal areas, scalpel knife, abrasive

strips and needle-shaped diamond bursare used. Polishing pasts can also beused.

Surface sealers: unfilled resin maybeadded after cleaning and etching the

surface. It is thought to be useful to resealmargins opened by polymerizationshrinkage, or surface porosities.


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Light curing units

Halogen light bulbs are used as a light source.Light delivery probe or tip is glass or glassencased in metal or plastic casing. Should becovered in a disposable cover

Cordless curing units Plugged into an electric outlet

High intensity light units: curing time

Plasma arc curing units (PAC) Argon laser units

Precautions for light curing


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Precautions for light curing

1. Inadequate light output: monthly check on lightsource, to examine output (using radiometers), any

scratches on light probes or darkening due todisinfection.

2. Premature set of composites: caused by operatory

light which should be moved away during placement ofcomposite.

3. Eye protection: light-shielding protective device,

glasses for patient.

4. Heat generation: may cause pulp irritation in deepcavities (1 mm or less of dentine).


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Light curing unit, protective glasses and shield


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Compomers

Composites modified with polyacid (polyacid-modifiedresin). The resin contains MMA and polycarboxylic acid.

Light activation chemicals are included and also fluoridecontaining glasses. Fluoride release is small comparedto conventional GIC due to resin binding the glass fillers

after light activation. Setting rxn occurs in 2 stages

Same as light-cured composite

Acid-base rxn Bonding to tooth structure occurs as in composites


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Indirect esthetic materials Inlays

Onlays Veneers

PFM All-ceramic

Crowns with composite resin facing Indirect composites

I di t it


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Indirect compositerestorations

Veneers: can beporcelain or composite.Veneers are used to treatstaining, close diastemas,lighten teeth color,reshape crooked teeth.


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Indirect composites:inlays, onlays, veneers.Preparation is done inthe clinic, followed by an

impression andconstruction of therestoration on a die,

then cementation in thepreparation. With resincements and bonding

agent.


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Laboratory processed composites

Procedure:Preparation is performed by dentist

Impression and bite registration

Restoration constructionCementation

Shrinkage occurs outside the cavity,therefore less stress is created asopposed to direct restorations

R t ti t i l d


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Restorative materials used:

Conventional composite

Fiber reinforced composite. Fiber source is

carbon Kevlar, glass fiber, polyethylene ( toimprove strength).

Particle-reinforced composite: heavily filled

(70-80% by weight) with ceramic particles toimprove wear resistance.


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Indirect chair-side technique Tooth preparation

Alginate impression

Poured in fast setting die stone or PVS die

material (sets in 2 minutes) Composite restoration is made and light

cured

Adjustment and cementation

Sh d t ki


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Shade taking

Patient

Dentist Assistant

1. Hue

2. Chroma

3. value


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Guidelines for taking the shade: Group effort by dentist, assistant and patient

Should be taken before preparation

Taken before rubber dam placement Teeth should be clean, free of stains and moist

Two different lights should be used (Metamerism):

dental offices usually have fluorescent light (blue), orincandescent light (yellow). Natural light is a goodsource except in morning or late afternoon (more

yellow and orange, and less green and blue)

Continue


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Continue,

A neutral background should be used (e.g.

blue apron)Female patients should be asked to remove

lipstick, and colorful clothes should be

coveredSeveral tabs are held close to patients teeth

and kept moist. Separate shades for cervicalpart of the tooth might be necessary.


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Characterizing the shade Surface texture (affects light scatter from

tooth) and luster (the degree to which thesurface appears shiny) should be noted.These two properties affect how the toothreflects light and scatter it.

The amount of translucency (especially

near the incisal edge) should also benoted.


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Reference Dental materials, clinical applications for

dental assistants and dental hygienists

Chapter 6

lecture 3 & 4- composites (slides)

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