glass ionomer metal-modified gic resin-modified gic dental material

GLASS-IONOMER CEMENTAcid-Base Reaction Cements:

Glass-Ionomer Cement The word glass-ionomer is a generic name derived from materials composition

The powder is ion-leachable glass (Calcium-flouro-alumino-silicate) that is able to react with ionomeric acid containing carboxyl groups (e.g. Poly acrylic acid)

Sometimes the name Polyalkenoic cement is used

General ApplicationsFinal cementationCavity base and linerEsthetic Filling material

(in eroded cervical lesions)Bonding agentFissure sealerEndodontic sealerFilling of deciduous teethAmalgam Bonding

Cementation of orthodontic brackets

Classification of G.I. cementsA. According to the useType I: Luting material (P.size < 15 m)Type II: Esthetic Filling material (P.size =20-50 m)Type III: Cavity base and liner

B. According to The curing mechanismChemical-cured: Cement sets via acid-base reactionDual-cured: Cement sets via both polymerization and acid-base reactionsTriple-cured: Cement sets via chemically-activated polymerization, light-activated polymerization and acid-base reactions

Classification of G.I. cementsC. According to the modificationConventional GI: No modification -- Sets via acid-base reactionMetal-modified: Ketac silver and Cermet--Sets via acid-base reactionResin-modified:-- Either dual or triple-cured

Presentation forms1. Powder-liquid- To be mixed using plastic spatula over paper pad2. Water-settable powder- Dry powder of PAA copolymer is blended with cement powder in the same bottle. - The material is mixed with regular water3. Capsules- Both cement powder and liquid are contained in the same capsule and separated from each other by a diaphragm4. Two-paste system- Recently introduced as a cement (luting material) material. - Equal lengths to be mixed over a paper pad

Conventional G.I. cementsCompositionPowder:

1. Calcium-fluoro-alumino-silicate glass particlesAll compositional ingredients (CaF2, Al2o3, Sio2, NaF, AlPo4) are fused together at 1100-1500oC ingot then grind into the desired particle size

2. Radio-opaque glass particles in which barium or strontium replaces the calcium

Conventional G.I. cementsCompositionLiquid:

1. Aqueous solution of Poly-alkenoic acidPAA or its copolymer with maleic or itaconic acidSometimes the acid may present in the dry powder form to be blended with cement powder in case of water-settable material

2. Tartaric acid To viscosity of PAA and to the setting time

Conventional G.I. cementsSetting reactionChemical reaction of acid-base type

H+ from the acid attacks the aluminum sites

Decomposition of the surface of glass particles Release of Ca++ and Al+++ ions into the aqueous medium the Ca++ and Al+++ cross-link the poly acrylate chains by forming poly-acid sol (initial setting) the sol transfers into poly-acid gel forming cement matrix (hardness and strength) surface of the un-reacted glass particles is coated with a layer of silica gel

Conventional G.I. cementsSetting reactionThe set material is composed of;

Non-reacted powder coated with silica gel in an amorphous matrix of hydrated poly-acid salts (gel (Calcium and aluminium poly-acid gel)Water is a component of the set material. The loosely bonded water could evaporate out of the material

desiccation and contractionFluoride ions remain free, and released only when the material becomes wet

Conventional G.I. cementsManipulation1. Mixing Mixing is achieved over a paper pad using plastic spatulaStainless steel spatula is contraindicated to avoid the contamination of mix by the abraded metal particlesLarge amount of powder is incorporated into the liquid at onceThin mix cementationThick mix filling or cavity base

2. Tooth should be cleaned or even conditioned by PAA before cement application

Conventional G.I. cementsManipulation (Cont.d)3. Restorative material Should be inserted as one bulk into the cavityThe excess is removed after partial setting using sharp hand instrumentThe material left to set in 24 hrs and then finished

4. Surfaces of fillings or margins of cement should be protected from saliva by applying varnish or resin coating

5. Recoating is strongly recommended after finishing and polishing

Characters of conventional G.I. cements1. Biological properties Freshly-mixed cement may cause mild or moderate pulp irritation, accordingly deep cavities should be lined with calcium hydroxideThe material provides chemical bonding to both tooth structure and restoration surfaces --> the rate of microleakageThe fluoride release --> help in the rate of caries recurrence

2. Interfacial propertiesThe material is chemically-bond to the apatite part of the tooth, base metal alloys and tin-plated gold alloys

3. Chemical properties The set G.I. cement is more resistant to solubility in oral fluids than other cements based on the acid-base reaction However, fresh cement is easily soluble in saliva and the material should be protected either with resin or varnish coating

4. Mechanical propertiesThe cement is stronger on compression than other zinc-oxide based cementsHowever, the set material is brittle having low DTS and fracture toughness

Characters of conventional G.I. cements

5. Esthetic properties The set G.I. cement is translucent and could be used to cement ceramic restorations

6. Thermal propertiesThe cement has low thermal diffusivity and could be used as cavity base under amalgam restorations

7. PracticabilityThe cement is easily mixed on paper pads using only non-metallic spatulas

Characters of conventional G.I. cements

7. Practicability (Cont.d)Cleaning and conditioning of tooth surfaces together with using the freshly-mixed material all improve the bondThe material could be used as a liner under composite restorations (Sandwich technique)Restorative material should be applied as one piece while filling tooth cavities (bulk filling technique) as the increments do not cohere togetherResin or varnish coating is required to protect the setting materialCareful and delayed (after 24 hrs) finishing should followed with resin or varnish coating

Characters of conventional G.I. cements

Metal-Modified Glass-Ionomer CementsInclusion of metal particles within the composition or the structure of cements powder

Cement powder is a simple blend of regular glass and amalgam particlesThe blend is reacted with regular cement liquid (PAA)The mixed material sets via acid-base reaction typically as that of the conventional glass-ionomer

1. Ketac SilverCharacters of the modified material

- Shows a little bit higher strength than that of Conventional G.I.- Shows an increased rate of solubility- Become opaque with gray metallic color- Used to fill the primary molars

A small amount of silver is fused with cements glass particles at the time of manufacturingThe resulted particles react with regular cement liquid (PAA) and the mixture also sets via acid-base reaction typically as that of the conventional glass-ionomer

Characters of the modified material

- Shows higher strength and better resistance to wearing than the conventional G.I.- The material is also opaque having gray metallic color- Used for core build-up and as posterior filling in selected cases2. Cermet

Resin-Modified Glass-Ionomer Cements(RMGI)Inclusion of resin monomer to form (after its polymerization) a protective matrix in which the regular cement setting takes place

The resultant material owns a dual mechanism of setting that includes both polymerization and acid-base reactionsDual-cured Cements:

A. PowderAlumino-silicate glass particlesPolymerization initiatorChemical initiator (Benzoyl peroxide) in case of chemically-activated polymerizationPhoto-initiator (Camphroquinon) in case of light-activated polymerizationBoth in case of triple-cured materilas

A. LiquidAqueous solution of Poly-alkenoic acidPoly-acrylic acid having some carboxylic groups modified with methacrylate or HEMA monomer

Composition of RMGI

The initial and rapid setting of the material is provided through polymerization of resin monomer

Slow acid-base reaction also takes place within the cured resin matrix. This reaction is responsible for maturing process and the final strength

The water content is too little to complicate the polymerizaton, however its presence is essential for the acid-base reaction.

Setting of RMGI

The modification provides material having

Higher strength and fracture toughness than that of conventional G.I.

Lower solubility of the freshly-set material

Possibility for immediate finishing and polishing

No need for resin or varnish coating

Lower rate of fluoride release

Characters of RMGI

Esthetic filling materials in non-stress bearing areas, cervical erosions

Fissure sealant

cavity base and liner

Bonding agent

Core building-up material

Cement for ceramic restoration

Applications of RMGI

Continuum of Esthetic Restoratives

CEMENTS SET BY POLYMERIZATION REACTION

A. Resin composite cementB. Resin compomer cement

Note.Composite = Resin matrix + inorganic fillers + coupling agent + polymerization initiatorCompomer = polyacid-modified composite resin

A. RESIN COMPOSITE CEMENTSFirstly developed in the early 1970s to be used with adhesive/ resin bonded bridges

They are less heavily-filled composites (filler load = 65%)

These materials set via polymerization reaction

Present materials can be classified according to its m