cons imp points

8/13/2019 Cons Imp Points

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-the forces that the dental material will be

subjected to

Compressive: crushing like biting forces ( upper on lower teeth)

Tensile: biting force stretches a material

Shear: e.g. an incisor used for cutting.

-tarnish : that the amalgam become dark because of surface reaction with

oxygen, chloride, sulfides.-corrosion : that the amalgam become dark because of surface reaction and

weaker because of inner reactions.

*Percolation: gap formation between a filling and the tooth because of

deferent ( CTE ).

Microleakage: Occurs when the restoration does not completely seal thesurrounding margins of the cavity preparation.the harmful materials through the gap between tooth and restoration. Can

cause:

Staining

Recurrent cariesSensitivity.

-micromechanical: a term used to describe how composite is bonded to

tooth surface by creating a ruff surface in enamel and dentin by makingsmall holes .

Affected by:Viscosity

Film thicknessSurface characteristics: cleanliness, moisture

contamination, texture, energy.

-acid etch with phosphoric acid; to remove mineral, create porosity,

wettability.-adhesion; the force that binds two dissimilar materials together when they arebrought into intimate contact.

the adhesion affected by;

-Wettability of the substrate surface-The viscosity of adhesive


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-The morphology or surface roughness.

-Surface energy: the attraction of atoms to a surface (directed inward). Inliquids, it is called surface tension.

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Enamel etching

Etching time: 10-30 seconds (around 15 seconds)Primary teeth and fluoride treated teeth require more timeEtched enamel looks frosty white when driedEtching produces a rough surface (pits) into which resin flows and forms resintags = micromechanical retention.

The depth of penetration depends on:Etching timeRinsing time

These two actors determine how effective etching was, and how well debriswere removed from enamel surface.

-Without etching, bonding is weakened and this leads tomicroleakage.

In amalgam corrosion products may seal any spaces between cavity andrestoration, in GIC the release of fluoride provides protection but in composite,good bonding is essential.

-Liquid or gel (the gel is made by adding colloidal silica to the acid)phosphoric acid 30-50% (usually 37%).

-If contamination occurs enamel should be re-etched for 10 seconds.

-When the bonding resin is apply to etched dentin, it penetrate theexposed collagen matrix and dentinal tubule. An intermingling of resin


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with etched dentin forms a hybrid layer. This layer provide a resinrich layer for bonding with other resins such as composite resin.

-PRR: minimal cavity preparation, resin composite placement, sealantplacement on top.---------------------------------------------------GIC; Self-cured, tooth colored, fluoride releasing restorative materials that bond to toothstructure without an additional bonding agent.

Composition:-Glass(Silica, Alumina, Calcium fluoride), Polyacid, Water, Tartaric acid.Different types and combinations of polyacid and glass create different versionsof GIC.

Properties:

Fluoride release:high initial fluoride release, then lower continuous releasefor long time. F-antibacterial, remineralization

Biocompatibility: Tolerated by surrounding tissue & kind to pulp. However,theyve been associated with postoperative sensitivity, acid pH initially thenneutral

Strength: Moderate compressive strength, low tensile strength. not suitable forstress bearing areas

Thermal expansion: similar to that of tooth structure.

-GIC should be protected with a varnish (resin dissolved in a volatilesolvent) to avoid moisture contamination and dehydration.

Clinical uses of GIC: restorative material in non-stress bearing areas;Root cariesOcclusal lesions in primary teethTemporary restorationsCervical cavities (abrasion and erosion lesions)Anterior class III when color matching is not an issueLiners and bases: used to protect the pulp from:Temperature changes


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Chemicals from other restorative materialsAcid etchantsGIC bases are used to rebuild missing tooth structure, stronger than liners andhave a higher powder: liquid ratio.

-Lamination or sandwich technique: GIC is used as a base underneath

composite restorations, in deep proximal cavities where the gingival floor ison the root.

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Amalgam;

-Why amalgam: Inexpensive, Ease of use, Proven track record>100 years,Familiarity.

-Drawbacks:EstheticsMercury content.

Constituents in amalgam:Basic: silver, tin, copper, mercury.Others: zinc, indium, palladium.

-Creep: usually seen with low-copper amalgam. It involves a change in theshape of the restoration due to compression from chewing and opposing teeth.

Physical properties of amalgam:Strength: High compressive strength 400-450 MPa, but low tensile strength(12% of C.S) and low shear strength, therefore enough bulk of amalgam isneeded to provide enough strength.

High copper amalgam have higher strength values after the first hourof placement than low copper amalgams.

Over trituration; sticks to capsuledecreases working / setting timeslight increase in setting contractionUndertrituration;

grainy, crumbly mix.


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Burnishing; maybe done before carving to further condense amalgam andremove excess mercury.

Carving is done soon after amalgam is placed in cavity

Finishing and polishing is done after 24 hours.

Amalgam bonding

Using resin bonding agents:Etching of cavity preparationBonding is done with one or two bonding resins:1sttechnique: bonding agent applied to enamel and dentine, followed bychemical cured resin. Amalgam is condensed against the wet resin

.

2ndtechnique: a single chemical cure bonding agent is applied beforeplacement of amalgam

Composite resin:

Composition: Resin matrix, Fillers, Coupling agents (silane)join filler andmatrix, Pigments.

-Resin matrix: bis-GMA (bisphenol A-glycidyl methacrylate). UDMA (Urethanedimethacrylate)These resins are made of oligomers (organic molecules) and low molecular

weight monomers.

-Fillers: silica, quartz, glasses

Why add fillers:

-Add strength-Increase wear resistance-Reduce polymerization shrinkage.---------------------------------------------Light curing units:


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Halogen light bulbs are used as a light source. Light delivery probe or tip is glassor glass encased in metal or plastic casing. Should be covered in a disposablecover.

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Compomers:

Composites modified with polyacid (polyacid-modified resin).

The resin contains MMA and polycarboxylic acid.Light activation chemicals are included and also fluoride containing glasses.

Fluoride release is small compared to conventional GIC due to resin bindingthe glass fillers after light activation.


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cons imp points

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