2 Glass iono!Der ceroe~ts lGICs) ( ) h · cal bonding to tooth tissue, chemical

Mtcromec ani . developed by Smith and resulted in the

bonding was . . d · f polycarboxylate cement. The basic bonding intro ucuon o .

} · was an ionic attraction between two carboxyl mec 1arusm . (COO-) groups in the cement to the calc1u~ (~a++) in enamel and dentine. Further work by Wilson s team resulted in the introduction of glass-ionomer (glass

polyalkenoate) cements.

Glass-ionomer cements have a particular role in adhesive dentistry because of their reliable chemical adhesion to enamel and dentine, and because of their apparent ability to promote the re-mineralization of

'affected' dentine.

Composition and types:

The original glass-ionomer cements (GICs) were water­based materials which set by an acid-base reaction between a 50% aqueous solution of polyalkenoic acid (as a liquid) and fluro-aluminosilicate glass (as a powder). Many attempts were made to enhance the physical properties of the material as by the addition of either:

✓ Metal particles (silver or gold), by a fusion process

r~sulting in a 'cennet' (ceramic-metal) e.g.: Ketac­silver. _This improves the wear property but in the

same hme silver particles produce discoloration in the adjacent tooth structure.

✓ Addition of a I . , d · ·') . . ma gam alloy particles ( a mix which improve the strength properties and decrease

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solubility. But the metal particles are not bonded to the set material resulting in increased surface wear

✓ Other modification is done by changing the size and

loading of fillers as "highly-filled, high viscosity GICs. This type of glass ionomer has high strength

properties.

✓ The most important modification of G!Cs is the resin-modified glass ionomer RMGI in which resin is incorporated into the conventional G!Cs. RMGI

shows significant improvement of the physical and

mechanical properties and also reduces the

sensitivity to water balance of the conventional

GICs. ✓ Recently introduced GIC is the Nano-ionomer

restoration that used nano-si2ed filler to enhance the optical and physical properties.

Classification of the GI Cs:

► Type I GICs: luting cements that characterized by

low film thickness and rapid set

► Type II GICs: restorative cements, with sub-types

I and 2. Type 11-1 GICs: are aesthetic cements (available

in both conventional and resin-modified presentations)

Type 11-2 GICs: are 'reinforced' types as Admix and Cermet

► Type LIi GI Cs: lining cements and fissure sealants.

characterized by low viscosity and rapid set.

Sttlli]~ reaction:

t. nal GICs set by a complex reaction between Conven 1o . . the (acidic) liquid and the (basic) ~owder. Setting reaction of GI Cs consists of three overlappmg phases.

Phase 1: (Ion leaching phase) on mixing powder and liquid, the acid attacks the glass resulting in SUrface degradation of the glass and release of metal ions ( e.g., strontium, calcium, aluminium), fluoride ions and silicic acid. At this stage, the mix appears glossy and the placement of glass ionomer should be completed in this phase because the maximum amount of the free carboxylic ions is available for chemical adhesion to the tooth structure.

Phase n: Hydrogel phase (initial set) it starts 5-lO minutes after mixing. At this phase Ca ions are released and cross-linked with the polyacid chains producing the initial setting of the GICS. The cement appears rigid and opaque and at this stage GICs should be protected from moisture and desiccation.

Phase m: polysalt gel (final set) aluminum ions released more slowly and form polysalt hydrogel to surround unreacted particles causing final setting. Continuing 'maturation' phase occurs over subsequent months. This is predominantly due to the slow reaction of the aluminium ions and is the cause of the set material's sens,itivity to

water balance. The set material needs to be protected frotll r · th( sa ivary contamination for several hours, otherwise .

surface becomes weak and opaque, and from water toss for several 1nonths.

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_.---::::::;:::~~ --

GI~ \ rb<>xyllc acld M : •

potyca r e,a11ons /--~ co-

- --- ~ o r.,1• 01 o- r., :• !'1j( • .,,.._ / -=- .!ii:11' oio-co- ~ -.... o~ --- 1ncorP4ratad glas~

partl~\~s

. f lass ionomer cement . (9 J)· settino reaction o g

Figure · · 0

Advantages: . din to tooth structures: .

1) Chemical bon g b l (COO-) ions Ul b tween the car oxy

An ionic bond occurs e . Ca++) ions in enamel and the cement acid and the calcium ( . l GIC is placed

·tine. When freshly mixed conventiona

\ dentire d ,c; ... " , .. . 1 of any smear layer occurs

-name or · · · th - 1nioimal since the too

:;~roxyapatite buffers the acid, and polyalkenoic is q~ite

weak. Phosphate ions (negatively charged) and calcium ~1.. " h:\rged) are displaced from the

.!d into the unset cement.

This forms an intennediate layer between the 'pure' GIC and the 'pure' hydroxyapatite that is called 'ion-enriched' layer (zone of interaction', 'inter-diffusion zone). The ion­

exchange layer appears to consist of calcium and phosphate

ions from the tooth, and aluminium, silicic, fluoride and

calcium and/or strontium ions ( depending on glass

composition) from the GIC. The thickness of the ion­

exchange layer appears to be in the order of a few . micrometres and merges into the GIC on one side and into

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Vd tine on the other. Measurement of the bo the ename en d . . nd

f GIC to enamel and enttne 1s complicated 1-,, strength o b "1 the brittle nature of t~e GIC. Laboratory ond strength tests

d hesive failure of the GIC, rather than failure reporte co . h' the 1· on exchange layer. Wtt lD

,--~ , ·.~ \ / .,

I •

◄ ~ --, ~.!\ \. .,,. Al '-

◄

,-"\ . \ Glm l ><>. i ... I ~:),_

✓ ..

◄ 0 ~ ✓ '.,

◄ ~J ' J Figure (10.3): adhesion of GI Cs to tooth structure

2) Fluoride release and recharge: The release of fluoride ions is one of the notable advantages of GI Cs. The mechanism of release is complex and not fully understood. However, the maximum release is in the first few days and decreases rapidly to a lower level over weeks, and maintains a low level over months. It has also been shown that GIC can be 'recharged' with

fluoride by subsequent professional application of topical fluoride, resulting in a prolonged substantial release. Most of the fluoride is released as sodium fluoride, which is ~t

critical to the cement matrix, and thus does not result Ul

weakening or disintegration of the set cement.

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fluoride release provides:

✓ Sufficient protection against recurrent caries .

✓ help in re-mineralization of caries affected denim

✓ make bacterial plaque fails to survive on the surface

✓ ~fhg~::a~~:~:::tic effect on streptococcus mutans

3) Biocompatibility of the GICs: . . . The term 'biocompatibility ': it is the ab1hty of a matenal to

elicit an appropriate biological response in a specific application. GICs are a biocompatible material due to:

✓ Its anti-cariogenic effect ✓ It is biocompatible to the tooth structure (dentin and

pulp) as polyacrylic acid is weak, high viscosity and high molecular weight. This limits its diffusion to the dentinal tubules and pulp tissue

✓ The pH of GIC increases as the cement sets ✓ Sealing potential of GICs that desensitize dentin,

sedate the pulp and eliminate the micro-leakage at tooth/restoration interface

4) Good thermal insulator: so use as base and liner material

5) Radiopacity: due to presence of radio-opaque material similar to amalgam restoration

6) Dimension stability: due to low setting contraction and the thermal coefficient of expansion and contraction ofGIC is close to that of tooth structure

Disadvantages:

I) Low strength properties: GIC is brittle material.

low rigidity and low fracture toughness. But the

recent modifications of GICs may improve its mechanical properties

l) Moisture sensitivity: con:entional ?I C is sensitive to hydration and dehydration especially in the earl stage of setting that . may decreases its strenJ properties and make it more opaque less esthetic material

3) Low wear and abrasion resistance: that increase the surface roughness by time

4) Questionable esthetic properties: it provides initial color matching but translucency talces several days to developed in the chemical cured type of GIC

Indications:.

Generally; GIC is indicate in high caries index patients, patient with bad oral hygiene, non-cooperative patients (old age, children) and medically compromised patients.

l) Restoration of class III and class V especially if cervical wall is in dentin or sub-gingival

2) Cervical non-carious lesion (abrasion, erosion) 3) Root caries

4) Caries control restoration: in patient with high caries index and multiple acute carious lesions. Caries control is an intermediate step in the treatment plan

of such case until the reasons behind this acute condition are dealt with

5) As Atraumatic Restorative Treatment (ART rest0ration): in under developed countries wbere_tbe

. . possible routine dental treatment is not accessible or . . b iscd to so restorative treatment using GIC could e \

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. of acute lesion. it includes, stop the progression d h 'sel used to remove the excavation of canes an ~I~ owder and liquid is undermined enamel the p . hand mixed then applied directly to the cavity.

6) Base and liner material unde_r any restorations

7) Pit and fissure sealant matenals

8) Luting cement . 9) Core build up for crown and bndges crown and 10) Minor repair of restorations,

bridges Contraindications:

\) G\C is not used in stress bearing areas as class II and

class \V 2) Not used if highly esthetic property is required

Clinical steps of application:

► Selection of G/Cs in,e: as it will be used as liner and base materials or will be used as restorative

material. Also we should decide if we need high fluoride release (conventional GIC), high esthetic properties (RMGI, nano-ionomer) or high strength in stress bearing area (highly-filled viscous GIC)

► Field isolation: it is essential step as GIC is sensitive to water intake during setting. Proper isolation of field is obtained by using rubber dam, saliva ejector, cotton rolls and retraction cord in cervical cavities

► Application of liner: if needed, we applied liner material as Calcium Hydroxide under GIC for pulp protection in very deep cavity

► Conditioning of the tooth: by using 1 concentration polyacrylic acid 10-25% is appliedow

. . d' bl to enamel and dentin using 1sposa e brush wait for 10-15 seconds then washed thoroughly by water (it will remove smear layer but leave the smear plugs and increase the surf ace energy of the tooth surface so increase the wettability)

► Application of matrix if needed ► Proportion, mixing and placement of GIC: proper

proportioning is very essential to obtain the required properties. The P:L ratio is 1.5: 1. The GIC is available commercially in two forms:

✓ Encapsulated for mechanical mixing ✓ Or supplied in two separate bottles for hand

ffiJXtng The capsules are preferred as it provides consistent

powder/liquid ratio also it used as syringe for placement of mixed material. For hand mixing, is applied over dry, cool glass slab or paper pad and mixing is done by Teflon· plated instruments

► Maintenance of water balance and finishing and polishing: GIC should be covered immediately with

layer of low viscosity, light activated resin bond or varnish. Then excess restoration is trimmed wilh

sharp blade. Finishing and polishing is carried out by · d' added using 1amond points or rubber tips then we f

another layer of resin bond to provide a water-proo seal.

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(3) Hybrid materials . b een resin composite and glass

They are m_atenals .~::-'the benefits of both materials. ionomer trymg to g . to have intermediate However, these mat~nals see~ lass ionomer that

erties between resm composite and g . d ~;;i~ composite still has the ~ighest esth~tic propert1~:e glass ionomcr still has the highest fluonde release.

materials era includes:

1) Resin modified glass ionomer (RMGI) . 2) Compomer (poly-acid modified resin composite)

3) Fluoride containing composite Resin- modified glass ionomer (RMGI):

ComposWon and setting reaction:

It is a hybrid material consists of powder which is the same

as conventional GIC and liquid that contain aqueous

solution of polyacrylic acid and water -soluble monomer

as HEMA. Their initial setting is classic acid base reaction

and then followed by polymerization reaction for resin that

cou ld be: Ligth-activated, chemically- activated or dual

curing (both of them). The set RMGI has two connecting matnces:

✓ Ionic matrix from acid/base reaction

✓ Polymerized matrix from the free radical reaction Clinical steps of application:

► Similar to GIC as applied with conditioner but some

RMGI applied with adhesive system as composite

but it hinder the fluoride diffusion into the tooth

structure. ► Light cured RMGI should be packed in increments

of 2-3 mm in thickness then light curing is applied

for each increments

Advantages:

► Improved strength properties ► High wear resistance ► Shows high wettability to dentin, as it contain

hydrophilic monomer (HEMA)

► Bonding to resin composite restoration so facilitate its placement in sandwich technique under resin composite

► Command fast setting by light-induced polymerization resulting in long working time

► Immediate stabilization of water balance Disadvantages:

► Less fluoride release than conventional GIC ► Although it provides initial good esthetic properties

but it may discolored by time Compomer (poly-acid modified resin composite):

It is a polymer-based composite that has been modified 10

take the advantage of fluoride release of GIC. It is made up filler/resin system that uses alumino-fluoro-silicate glass as fille~ and Setting occurs only by polymerization reaction. But 1t showed:

► L ess fluoride release as GIC or RMGI ► God· · · 0 initial esthetic but not stable

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► Decreased physical and mechanical properties fluoride-containing composite:

These arc composite that containing glass ionomer fillers but do not contain polyacrylic acids. They reported less fluoride release, un capable of fluoride-recharge, unstable esthelic and decreased strength properties.

G'.omer: it is an example of fluoride-containing composite. It mcludes pre-reacted glass ionomer particles into the resin besides, fluoro-alumino-silicate filler so ii shows high tluonde release and recharging.