glass ionomer cements students

8/22/2019 Glass Ionomer Cements Students

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Direct esthetic

restorative materials

Glass ionomer cements


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DEFINITION

z Self-cured, tooth colored, fluoridereleasing restorative materials that

bond to tooth structure without anadditional bonding agent.


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CLASSIFICATIONz Luting agents

z Restorative material (erosion/abrasionlesions in permanent dentition, and

restorations in primary teeth)z Liners and bases

z Core build-up materials

z Pit and fissure sealants


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Compositionz Main components are:

z Glass

z Polyacid

z WaterzTartaric acid

z Different types and combinations of polyacidand glass create different versions of GIC


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GlasszThree main components:

z Silica SiO2z Alumina Al2O3z Calcium fluoride CaF2z In addition to sodium and aluminium fluorides,

and calcium or aluminum phosphates.

z Components are fused at high temperatures,

shock cooled then ground to a powder. Particlesize depends on application


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Liquidz Liquid: co-polymers of polyacrylic

acid and waterz E.g. of copolymers used:

z Acrylic acid and itaconic acid

z

Acrylic acid and maleic acidz Viscosity of the liquid depends on

molecular weight and polyacidconcentration.

z Tartaric acid influences workingad setting time

Ref. Introduction to dental materials


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DISPENSINGz 2 bottle system hand mixed:

z Powderz Liquid

z Anhydrous cement: powder (glass and freeze dried

polyacid) and distilled waterz Capsules (pre-measured powder and liquid) mixed

using a triturator (mixer). Easy to use, GIC is directly

dispensed into cavity, eliminate errors from manualmixing.


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8Ref. Phillips science of dental materials


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Setting reactionz Acid base reaction. Three overlapping steps:

z Dissolution

z Gelation

z

Hardening


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Polyacid liquid

Silica gel

Glass core

Ca2+

Al3+

F-

Hydrogenions


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1111

Polyacid liquid

Cross-linkedpolyacid

-COOHCa2+

Al3+

F-


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GelationGelation

Calcium ions have more reactivity thanCalcium ions have more reactivity thanaluminium ions.aluminium ions.

This is critical phase of contamination.This is critical phase of contamination.

Loss of aluminum ionsLoss of aluminum ions

Water lossWater loss

The end result is a weak unaestheticThe end result is a weak unaesthetic

materialmaterial


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Polyacid liquid

Cross-linkedpolyacid

-COOHAl3+


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SETTING REACTION

z Powder and liquid are mixed:

z Calcium, aluminium and fluoride from the glass

particles releasedz Calcium will cross-link the polyacrylic acid chains.

z Calcium will be gradually replaced by aluminium

over the next 24 hours.

z Role of water?

z Role of sodium and fluoride?


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Continue,z Gelation of cement: 2-3 minutes after mixing,

cannot be manipulated.z Next minute, the material hardens, but setting

and maturation goes on for several hours.z Finishing is postponed until after 24 hours


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z Dissolution: Acid attacks the glass. This

releases calcium, aluminum, sodium andfluoride. All is left is silica gel.

z Gelation: free calcium react first withcarboxyl groups in the acid leading to initialsetting. At this stage contamination fromouter environment may lead to:

z Loss of aluminum ions

z Water loss

zThe end result is a weak unaestheticmaterial


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Continuez Hardening: can take as long as 7 days.

Aluminum ions provide the final strength ofthe matrix (aluminum salt bridges). Inaddition, water is bound to silica gel.

z End result: glass particles each surroundedby silica gel in a matrix of crosslinked

polyacrylic acid


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SETTING OF GIC

Ref. Introduction to dental materials


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Propertiesz Handling characteristics: previous versions of

GIC had problems with inappropriate workingand setting time. Tartaric acid inclusionresulted in:

z Tartaric acid reacting with calcium as it wasreleased which extends working time toreasonable values

z Enhances rate of formation of aluminumpolyacrylate crosslinks which speeds up setting.


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Propertiesz Adhesion: Chemical bond to enamel &dentine by ion

exchange (displacing calcium and phosphate ions andcreating an intermediate layer of polyacrylate, phosphateand calcium. Or binding with Ca+2 in tooth.


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Continue,z Adhesion: bond to dentine maybe by hydrogen bond

to collagen and ionic bond to apatite crystals indentine. The major type of failure is cohesive withinGIC rather than adhesive with tooth surface. so, GIC

has a low tensile strength (brittle)z To obtain a good bond: tooth surface should be

cleaned, treated with conditioner to remove debris

and improve wettability


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Propertiesz Aesthetics: glass governs the color of the

material. Pigments maybe added such ascarbon black, ferric oxide.

z

The major issue is translucency rather thancolor. GIC translucency is more comparableto dentine.

z Aesthetically, GIC is inferior to composite,appear opaque, dull, lifeless


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Properties

z Solubility: Sensitive to moisture &dehydrationduring setting and maturation (1st 24 hours). Use

varnish (MMA resin, nitrocellulose) finishing after24 hours

z Loss of material from GIC maybe due to:z

Dissolution of immature cementz Abrasion (GIC have low abrasion resistance)

z Erosion

z Loss of material decreases after it fully setswhich usually takes a few days


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Properties

z Fluoride release: high initial fluoride release, thenlower continuous release for long time. F- antibacterial,remineralization

z Biocompatibility:Tolerated by surrounding tissue &kind to pulp. However, theyve been associated withpostoperative sensitivity, acid pH initially then neutral

z Strength: Moderate compressive strength, low tensilestrength. not suitable for stress bearing areas

zThermal expansion: similar to that of tooth structurez Effect of P:L on strength and solubility?


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Clinical application of GICz General notes:

z Tooth surface should be clean and dry but notdesiccated

z Polyacrylic acid should be used if advised by

manufacturer

z GIC should be protected with a varnish (resindissolved in a volatile solvent) to avoid moisturecontamination and dehydration


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CLINICAL USEz Luting cements:

z Advantages:z Fluoride release

z Low film thickness

z

Kind to pulpz Bond to tooth structure

z Their use decreased

after hybrid ionomersand resin cements wereintroduced since they

are stronger


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CLINICAL USEz Restorative materials: used in non-stress bearing

areas:z Root caries

z Occlusal lesions in primary teeth

z

Temporary restorationsz Cervical cavities (abrasion and erosion lesions)

z Anterior class III when color matching is not an issue


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CLINIAL USEz Liners and bases: used to protect the pulp from:

z Temperature changesz Chemicals from other restorative materials

z Acid etchants

z Liners have lower powder: liquid ratio and weak.z GIC bases are used to rebuild missing tooth

structure, stronger than liners and have a higher

powder: liquid ratio


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Ref. Phillips science of dental materials


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Clinical applicationz Cavity preparation: conservative, no

undercuts necessary due to chemicaladhesion quality.

z Isolation: careful and proper isolation isnecessary. Blood and saliva may impairsetting, weaken GIC and lower bond strength

to tooth structure and reduce aesthetics


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Clinical applicationz Preparation of dentinal surface

z Depends on the nature of the tooth surface onwhich GIC will be placed.

z Most importantly, clean surface, use of a

conditioner

z Incase of prepared cavities: no need for cleaningwith pumice and water but a conditioner isneeded to remove smear layer.

z Patients with sensitive teeth?


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Clinical applicationz Pulpal protection: maybe necessary in very

deep cavities, to prevent direct contactbetween GIC with pulp tissue.

zThe liner of choice is calcium hydroxide, butkeep in mind that the maximum area ofdentine is needed to ensure good bond with

GIC.


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Clinical applicationz Dispensing, mixing, insertion:

z For powder liquid system: ensure accurate ratio,and tap powder bottle to loosen up the particles.Gradual incorporation of powder into liquid, and

follow manufacturer instructions in terms of mixingtime.

z Encapsulated: capsule should be shaken first,

then mixed in an amalgamator running at 4000rpm for 10 seconds


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Clinical applicationz Finishing and polishing: a matrix maybe used to

protect the surface until the material sets, then anyexcess GIC should be removed after 24 hours byfinishing and polishing. Removal of gross excessmaybe done using a sharp blade rather than a

carver.z As a general rule: finishing should be delayed

z After 24 hours: using fine diamond bur or 12 bladecarbide bur with water. Polishing is done usingabrasive discs again with water.


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Clinical applicationz Surface protection: varnishes used:

z Solution of natural copal resinz Synthetic resin (cellulose acetate)

z

These two maybe dissolved in an organicsolvent such as ether, acetone, chloroform

z Other varnishes: nail varnish, bonding

agents.


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CLINICAL USEz Lamination or sandwich

technique: GIC is usedas a base underneathcomposite restorations,in deep proximal

cavities where thegingival floor is on theroot.

z GIC in this caseprovides better sealand releases fluoride.

Ref. Dental materials, clinical applications.

Silver cermets


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Silver cermets

z Have metal particles added to them, e.g.silver (particle size 3-4 m) , to improvetoughness strength and abrasion resistance.

z Also contain Titanium oxide.

z Liquid is copolymer of acrylic, maleic and 9%

tartaric acidz Presentation:z Powder liquid system, or capsules

z Clinical use: small occlusal cavities


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CLINICAL USEz Core build up materials: cermet GICs are

usually used for this purpose. They are used:z In locations were esthetics are not important

z To replace missing tooth structure where the

permanent restoration is crown.


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CLINICAL USE


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CLINICAL USE (Reference, Dentalmaterials, clinical applications for dental assistants anddental hygienists, chapter 7)

z Pit and fissure sealants:materials used to sealnoncarious pits and

fissures of deciduousand permanent teeth.

Indications for the use of


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sealantszTeeth with deep pits and fissures.

z Sealants are targeted to young children so

that susceptible pits and fissures areprotected.

z High caries risk patients (poor oral hygiene,high sugar intake, etc)


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Types of sealantsz GIC based

z Resin based sealants:z similar composition to resin composite (based on

Bis-GMA or UDMA)

z Maybe self cure (Two components) or light cure(One component)

z Maybe clear, opaque or tooth colored

z Sealants are not as heavily filled as resincomposite, because they would be tooviscous


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Continue,z The use of GICs as sealants have

been suggested due to:

z Fluoride release.

z Adhesion to moist tooth structure

z Disadvantages:

z Inability to fully penetrate fissures

z Brittleness

z Low wear resistance


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Clinical applicationzThe tooth should be isolated and

20%polyacrylic acid is applied for 10-15seconds (or according to manufacturerinstructions.

z GIC is mixed and applied to pits and fissures.z GIC varnish is applied to protect the sealant

from moisture contamination and

dehydration.z Occlusion is checked and adjusted.


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H brid (resin modified) GIC


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Hybrid (resin-modified) GIC

z Hydroxyethyl methacrylate (HEMA) resin, isadded to GIC to improve physical properties.

z Advantages compared to conventional GIC:z Improved wear resistance

z Stronger

z More polishablez Resin protects the matrix from moisture, which

decreases solubility

z Setting reaction?


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Resin-modified GICz Composition: the liquid component:

z Hydrophilic monomer is added to the liquidpolyacrylic acid (HEMA) or

z Polyacrylic acid with pendent methacryloxy

groups,

z In addition to tartaric acid and photoinitiator


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Setting reactionz Prolonged and slow acid-base reaction. This

will prolong working time. Rapid set isprovided by light curing. If the material is notexposed to light it will eventually set by acid

base reaction in 15 minutes.

z Incremental placement maybe necessary,

issues of polymerization shrinkage maybeencountered.


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Propertiesz Long working time and short setting time

z Finishing and polishing maybe doneimmediately

z

More resistance to acid attack anddehydration


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Clinical applicationsz Direct restorative materials, proved to be

better than conventional GICs in primarydentition

z Liners and bases underneath composites,amalgams

z Luting agents


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