Glass Ionomer cement – II
The clinical development and use of GIC was first described by McLean & Wilson (1977).
Certain properties, such as their:
ü Hydrophilic nature.
ü Adhesion to tooth structure.
ü Ability to release fluoride ions.
Made them very attractive materials as “preventive restorations” or for lining and luting purposes.
Classification of plastic direct filling materials based on GI & resin composite
(no water added)
Resin-modified (hybrid ionomer)
No acid-base bonding
(requires resin-dentin bonding)
High acid base bonding
(Only need a conditioner)
More shrinkage on setting
Less shrinkage on setting
Less fluoride release
High fluoride release
(after water immersion)
Increased thermal expansion
Low thermal expansion
Higher tensile strength
Low tensile strength
Low susceptibility to desiccation
high susceptibility to desiccation
Indications for use:
1. Restorative materials
2. Fast-setting lining cement and bases
3. Luting cements
1. Restoration of erosion/abrasion lesions w/o cavity preparation.
2. Sealing & filling of occlusal pits & fissures.
3. Restoration of deciduous teeth.
4. Restoration of class V carious lesions.
5. Restoration of class III carious lesions (lingual approach).
6. Repair of defective margins in restorations.
7. Minimal cavity preparations; approximal lesions B & Occ approach (tunnel preparations).
8. Core buildup.
9. Provisional restorations.
10. Restoration of root caries. Sealing of root surfaces for overdentures.
Lining and bases:
1. Lining of all types of cavities where a biological seal & cariostatic action are required.
2. Replacement of carious dentin for the attachment of composite resins using the acid-etch technique.
3. Sealing and filling of occlusal fissures showing early signs of caries.
Fine-grain versions of the GIC are available for luting purposes.
· Fl leach.
· GIC are brittle materials w/ a low tensile strength. (cohesive failure)
· Must be used in bulk & in low-stress-bearing cavity preparations.
· Have insufficient translucency & lack polishability.
1. Class IV carious lesions or fractured incisors.
2. Lesions involving large areas of labial enamel where aesthetic is of major importance.
3. Class II carious lesions where conventional cavities are prepared; replacement of existing amalgam restorations.
4. Lost cusp areas.
They are capable, under moist conditions, of permanently adhering to reactive or polar substrates (E, D & base metals). Ion-Exchange Adhesion
They are able to adhere to unconditioned D surfaces.
Because freshly cut D is covered by a rather structureless smear layer, fixation or removal of that layer is recommended.
Dentine surface condioning
Adhesion to both E & D can be improved if first treated & cleaned w/ agents as aqueous solutions of tannic acid, poly acrylic acid. (mild effect: reveal D tubules)
When bonding conventional GIC to E, etching w/poly acrylic acid cleans the substrate, creates a rough surface, reduces its surface energy, allowing both micromechnical & chemical bonding.
Early water contamination & protection
GIC is impervious to oral fluids when fully hardened.
But it is vulnerable to moisture while setting & hardening.
This occurs while cement-forming ions (Ca²+, Al³+) from the glass are being transferred to the poly acid, where they are locked up in a resistant gel.
Hydration of early setting cement:
The ions will be washed out & lost.
Absorption of water & expansion. This damage is permanent.
Clinically: loss of translucency & erosion of its weakened surface.
Dehydration of early setting cement:
Loss of water needed for cement formation.
Clinically: fissuring, crazing & cracking of cement surface.
There is a critical water balance at the interface between water needed for cement formation & excess water absorbed from saliva.
Protection of setting cement:
Immediate application (after matrix removal) of a coat of:
A special varnish (Ketac-Glaze).
A low-viscosity, light-curing bonding resin.
It is largely controlled by the manufacturer.
Type II restorative cement is the most translucent.
Dry mixes will appear more opaque because of increased porosity.
Accurate proportioning of the powder & liquid will also ensure a mix which produces both optimum strength & translucency.
One of the reasons for the limited use of GIC for ant restorations in the past has been its poor color match to enamel. Arising from poor translucency.
All cements tend to shrink on setting, except under conditions of high humidity, when they pick up water & expand.
Slight expansion is preferred. (normal)
The coefficient of thermal expansion for GIC is similar to that for tooth & its thermal diffusivity is low. So microleakage is minimal compared w/ other types of direct restorations.
To reproduce the physical characteristics of E & D, 2 different restorative materials are needed:
One must be hard & rigid like E, another resilient like D.
The material used to replace lost D can serve as a lining. The ideal lining must be sufficiently flexible to completely absorb mechanical & thermal stress in order to maintain bonding at the tooth structure-restoration interface.
GIC can reduce setting stress. Because of their low & delayed shrinkage rates, GIC flow during their pre-gel phase.
In the post-gel phase, their flow capacity decreases & they harden slowly. The longer the setting time the better the restoration can adapt to shrinkage.
The presence of intrinsic porosity permits the volume & form of the restoration to change during setting, allowing for load compensation.
These microcracks (porosities) are repaired through chemical reaction or if sufficient water is available, the material swells rapidly, closing the cracks.
To act as a stress-absorbing liner/base, the GI material should be applied in a substantial thickness.
N.B. other materials as flowable composites & RMGIC also can be used as linings.
Fluoride release & uptake
Very high upon comparison w/ other types of GIC.
Conventional GIC contain 12% to 18% of fluoride as F.
Studies have shown that F is released continuously for at least 18 months.
The translucency of GIC dose not reach its maximum for about a day after insertion.
Experience is vital.
Dispensing & mixing techniques
In all dental cements manipulation time is at a premium.
For restorations, mix the paste as thickly as possible.
Follow the manufacturer’s recommended powder/liquid ratio.
Mixing on a chilled slab can significantly prolong working & setting time.
Good adhesion of GIC is very dependent on sufficient wetting of the tooth structure, which can only be achieved if the cement is glossy & provides free surface poly acid for ion-displacement at the E/D interface.
The ideal hand–mixed cement should be a stiff paste that has retained its gloss & packing consistency.
Capsulated cements are preferable.
The best surface obtainable is that produced when the cement is allowed to set against the matrix.
Carving the cement external to the cavity margins w/ sharp knives after initial set is the best technique for finishing, thus preserving gel surface.
Gross finishing of bulk surfaces w/ rotary instruments after initial set is strongly deprecated.(next visit)
It should never be finished under dry conditions.
Clinical procedures for placement
1. Select the appropriate shade of cement.
2. Isolate the tooth w/ a rubber dam.
3. Prepare the cavity:
a. Erosion-abrasion lesion: clean only.
b. Carious lesion: conventional instrumentation. No bevel
4. Where there is <0.5mm of remaining dentin, line the cavity w/ a setting Ca(OH)2.
5. Place the matrix.
6. Apply a surface conditioner to the cavity for 10 seconds.
7. Dispense the cement on a refrigerated glass slab & mix quickly:
30 sec for hand mixing
10 sec for machine mixing
8. Wash & lightly dry the cavity. Do not dehydrate the dentin because this will tend to reduce wettability. Insert the cement, preferably using a syringe.
9. Allow to set for the recommended setting time, at least 4min from the start of mix.
10. Remove the matrix & immediately apply a waterproof varnish or light cured bonding agent. (critical point)
11. Trim any excess material external to the cavity w/ sharp scalpel blades or excavators. Do not use rotary instruments at this stage of setting.
12. Reapply varnish.
13. If the marginal adaptation is good the final polishing of the restoration should be delayed until the patient’s next visit. The modern fast-setting GI may be finished w/n 10-15 min. Fuji IX
14. Reapply varnish after polishing.
Class V restorations
Rubber dam (avoid dehydration)
A. The erosion/abrasion/abfraction lesions:
Any plaque, pellicle or stain in the lesion should be removed by scrubbing lightly for 10 sec w/ slurry of fine pumice flour in water on a soft rubber cup.
Don’t use polishing paste. (contaminants)
Due to poor dietary habits. (Fluoride)
Cavity prep w/butt joint margins to avoid fracture of thin marginal areas of filling.
Retention improved by small undercuts in D.
Place calcium hydroxide if deep.
Apply a solution of 25% poly acrylic acid for 10 sec. wash off & lightly dry the tooth. Do not dehydrate.
Protect the cement during setting.
Allows pressure to be applied to the cement to bring it into intimate contact with D & reduce porosity. (smoothest)
Hawe matrices are soft-metal type useful for class V.
Insertion of the cement
The tip of the syringe should be placed into the base of the cavity & withdrawn slowly while still syringing.
It varies according to material selection, mixing technique, temp, & P/L ratio.
About 5min from start of mix is adequate for capsulated type.
Removing matrix & protecting cement
Critical procedure (moisture).
Apply varnish. (crazing)
Accurate contouring of the cervical matrix should make gross trimming unnecessary. (avoid rotary)
Use sharp carving instruments.
Next visit: these surfaces can be polished w/soft abrasive rubber cups & slurry of fine-grained alumina.
Class III restorations:
GIC are still not as translucent as composite.
A lingual approach to the restoration is preferred.
It involves replacing the lost D w/ GIC & the E w/ a resin composite.
This clinical procedure involves using a base of either chemically set or light-cured GI. Which is then covered w/ composite to improve the physical & aesthetic characteristics.
Ideally, the restorative material & tooth structure should undergo similar changes to avoid mismatch at the interfaces. This could result in microleakage.
It can be used in restoring class V & class II lesions.
Select the shade if GI is used as a liner in Cl V.
Apply in appropriate thickness of at least 0.4mm in Cl V & 1.5 to 2mm in Cl II. (to act as an elastic buffer)
When the Cl V cavity is due to abrasion or erosion, occlusion must be checked.
The eccentric loads applied to the occlusal surfaces can concentrate the stress in the cervical region provoking detachment of the restorations.
When abfraction lesions are present, careful lining & nightguard use are indicated.
The closed sandwich tech.
It consists of restoring the cavity w/GIC & few days-2, 3 weeks later, repreparing the restored tooth, leaving a thick GI base & creating a sufficient space to make a composite veneer. (or can be done in one visit)
All margins should be on enamel.
The open sandwich tech.
The clinician fills the interproximal box w/ GIC & completes the occlusal restoration w/ resin composite. When gingival margin is deep on root surface i.e. on dentine.
Acid etch & apply an E-D bonding agent after the GIC is completely hardened.
The bond between conventional GIC & composite is mainly micromechanical.
Class V (sandwich technique)
Standard Class V cavity & any cavosurface margin involving D is finished to a butt joint.
E margins should be beveled to increase surface area for bonding of the composite resin.
Only where a near-exposure w/less than 0.5mm of remaining D should a calcium hydroxide liner be used.
25% Poly acrylic acid for 10 sec.
Insertion of cement
Fast-setting type III GI (opaque) or type II GI applied w/a fine, ball-ended instrument on D only.
Remove any excess cement from E margins.
After setting of the cement, a solution of 37% phosphoric acid is applied to the cement & E.
Wash & thoroughly dry.
Application of bonding resin
Light cure for 20 sec.
Application of bulk composite resin
Use a fluted 12-or 16-bladed carbide burs.
Use an abrasive rubber polishing cups & a slurry of fine aluminum oxide.
Class III (sandwich technique)
Suitable for very large Class III restorations where the optimum properties of both composite & GIC are used to their maximum advantage:
Composite: excellent aesthetics, strong bond to E.
GIC: long-term adhesion, cariostatic action.
Class IV (sandwich technique)
A provisional restoration intended to last for a short period of time (days-few weeks).
1. Emergency replacement of a lost filling.
2. Emergency repair of a fractured tooth fragment or cusp.
3. Restoration of endo access cavity or walking bleach preparation.
4. Treatment of an inflamed pulp. (often in association with a lining of an obtundent material as dycal, Ca (OH)2 in pulp capping)
5. A diagnostic procedure, failing crown margin or a chronically sensitive noncarious cervical lesion.
Transitional & interm restorations
A holding restoration that remains in site until circumstances are suitable for placement of a final restoration.
1. As immediate caries control regimen.
2. Semipermanent restorations while awaiting the out come of a treatment, as pulp capping.
3. For pts receiving radiotherapy Tx to head & neck area.
4. For pts w/ xerostomia.
Sealants & preventive restorations
Limited evidence of their effectiveness.
GIC lack the physical properties of high tensile strength & wear resistance.
It is used in limited situations.
Careful examination of occlusal contacts.
Margins should not be beveled.
Mainly it is used as a base to prevent microleakage & postoperative sensitivity at the D interface.
Approximal lesions )posterior)
a. Occlusal approach
b. Approximal approach
buccal or lingual.
Atraumatic restorative treatment
Used in underdeveloped countries.
The ART concept is based on minimal intervention & minimal cavity preparation.
Core build up
The construction of foundation restoration is necessary prior to crown preparation. (resistance & retention)
Cement too dry at placement.
Poor surface preparation for bonding.
Loss of restoration
Moisture contamination during matrix formation.
Loss of translucency
Dehydration during setting/maturation.
Insufficient bulk of material.
Chipping/fracture of cement
1. Glass-Ionomer Cement by Alan D. Wilson/John W. McLean
Chapters: 9, 10, 11, 12, 13, & 16.
2. Advances in Glass-Ionomer Cements by Carel L. Davidson & Ivar A. Mjor.
Chapters: 7, 12, & 13.
3. Tooth Colored Restoratives Principles and Techniques, Albers 9th edit.