glass ionomer cement

what is glass ionomer cement?

a tooth colored material introduced by Wilson and Kent in 1942, it is a material that is based on the reaction between silicate glass and poly acrylic acid that bonds chemically to the tooth structure and releases fluoride for a relatively long period, having a strong anticariogenic effect

how is glass ionomer cement made?

by mixing two components, usually a powder and when mixed together, they undergo an acid-base reaction and harden.

what does the viscosity of GIC depend on?

the intended use, and it can be adjusted by varying liquid to powder ratio

what is the powder component of glass ionomer cement composed of?

it is an acid-soluble calcium fluoroaluminosilicate glass similar to that of silicate but with higher alumina silicate ratio which makes it more reactive with liquid

what is the composition of the powder in GIC?

1. silica 41.9%

2. alumina 28.6%

3. aluminum fluoride 1.6%

4. calcium fluoride 15.7%

5. sodium fluoride 9.3%

6. aluminum phosphate 3.8%

how is glass ionomer cement components prepared?

the raw materials used to make Glass Ionomer Cement (GIC) are fused by heating them to a temperature of 1100–1500°C to form a uniform glass material and allow all components to combine chemically.

what is the role of fluoride compounds in GIC?

act as a ceramic flux. they lowers the melting temperature of the glass, helps the components fuse more easily, provides fluoride release from the final cement and contributes to anticariogenic properties.

what elements are added to make GIC more visible on X-rays?

• lanthanum

• strontium

• barium

• zinc oxide

after fusion, what is done to the glass?

it is ground into a fine powder in the range of 15–50 µm

the liquid of GIC is mainly what?

aqueous solution of polyacrylic acid (~50% concentration)

what does GIC liquid portion include?

additional acids to improve handling and setting properties, such as itaconic acid, maleic acid, tricarballyic acid and tartaric acid

what is the composition of liquid in GIC?

1. Polyacrylic Acid (Main component)

• Present as an aqueous solution (dissolved in water).

• Usually around 50% concentration.

• It reacts with the glass powder to form the cement matrix.

It is often in the form of a copolymer with:

• Itaconic acid

• Maleic acid

• Tricarballylic acid

what is the role of the copolymer acids?

1. increases the reactivity of the liquid

2. decreases viscosity

3. reduce the tendency for gelation

why is tartaric acid added?

improves the handling characteristics, increases the working time and shortens the setting time

how can be special type of GIC can be made?

freeze-drying the polyacrylic acid copolymer and mixing it with the glass powder. in this case, the liquid is either water or water and tartaric acid. this is known as water settable cement and it usually sets faster

what are three stages of the setting reaction of GIC?

• dissolution

• gelation

• hardening

what is GIC known as?

a water-setting cement because water is essential for the setting reaction.

what is the setting reaction for GIC?

an acid base reaction between the acidic polyelectrolyte and the aluminosilicate glass. the polyacid attacks the glass particles and it is known as leaching and release cations and fluoride ions, forming a salt-gel matrix

what does the set cement consist of?

an agglomeration of unreacted powder particles surrounded by a silica gel in an amorphous matrix of hydrated calcium and aluminum polysalts, which is known as gelation

what occurs even after the cement appears to be clinically set?

post-hardening precipitation continues, more aluminum ions form stronger cross-links and the cement continues to gain strength over time.

what is responsible for the initial hardening of GIC?

Calcium polysalt

what gives GIC its final mechanical strength?

the slower-forming aluminum polysalt becomes the dominant matrix and gives the cement its final mechanical strength.

how does GIC bond to enamel and dentin during the setting process?

chemically via an ionic interaction with calcium and phosphate ions from the surface of enamel or dentin

why is the bond to enamel always higher than that of denint?

because of its greater inorganic content

what makes bonding of GIC more effective?

a clean surface

how can GIC bonding to dentin be improved?

by treatment of it with an acidic conditioner followed by a dilute solution of ferric chloride

what plays a critical role in the setting of GIC?

water, as it serves as the reaction medium initially, and then slowly hydrates the cross-linked agents and results in a stable gel structure that is stronger and less susceptible to moisture contamination

what will happen to freshly mixed GIC if left exposed to air without any protective covering?

the surface will craze and crack as a result of desiccation (it will dry up)

what happens to the GIC if it is contaminated with water before it sets?

dissolution of the matrix, leading to a weakened restoration

how is GIC classified based on its application or uses?

1. type 1 for luting

2. type 2 for restorations

3. type 3 for liners and bases

4. type 4 for pit and fissure sealants

5. type 5 for orthodontic cement

6. type 6 for core build up

how is GIC classified based on chemical classifications?

1. conventional glass ionomer cements

2. hybrid ionomer cements or resin modified glass ionomers or dual cured GIC

3. tri cure glass ionomer cements

4. metal reinforced GICs or cermets

when were convention glass ionomer cements first introduced?

1972 by Wilson and Kent

what are resin modified GICs?

GICs that combine the acid-base reaction of traditional GIC with a self-cure amine peroxide polymerization reaction, and, they use a light cured system, which is done by adding a polymerizable functional methacrylate groups with a photo-initiator to the formulation.

why is it called a dual-cure GIC?

the materials undergo both an acid-base reaction as well as curing by photo-inhibition and self-cure of methacrylate carbon double bonds and their acid-base ionomer reaction are supplemented by a second resin polymerization initiated by a light curing process, which is why they are called dual cured GIC

what are tri-cure glass ionomer cements?

some systems have incorporated a chemical curing tertiary amine peroxide reaction to polymerize the methacrylate double bonds along with the photoinitiation and acid-base ionic reaction

what are metal reinforced GICs or cements?

introduced in 1977, they are also known as metal modified GICs. the modification by the inclusion of filler particles is done to improve the strength, fracture toughness and resistance to wear

what are the two methods of modifications?

1. mixing spherical silver amalgam alloy powder with type II GIC powder known as silver-alloy admix, or miracle mix

2. bonding of silver particles by fusion to the glass powder particles through high temperature sintering of a mixture of the two powders, and it is known as cermat

what is the setting time of GIC like?

it sets within 6-8 minutes from the start of mixing

setting time is less for:

type I than type II cements

how can setting be slowed?

by mixing it on a cold slab

what setting

what setting time of GIC type II?

within 10 minutes

what is the esthetics like of conventional GICs?

tooth colored and available in different shades, so it is better than amalgam

what is the esthetic quality of Resin-modified GICs (RMGICs)?

it improves the translucency but they are still not as aesthetic as composites, as they lack the translucency of enamel and have a rougher surface texture.

what do GIC carry the risk of?

they have potential for discoloration and staining

what is the water sensitivity, solubility and disintegration of GICs like?

the initial solubility is high (0.4%) due to leaching of intermediate products as the complete setting reaction takes place in 24 hours. the cement should be protected from saliva to prevent solubility and disintegration

how is the adhesion and bonding of GIC like?

the bonding between the cement and dental hard tissues is achieved through an ionic exchange at the interface, which occurs due to the reaction occurring between carboxyl group of polyacid and calcium of hydroxyl apatite, which leads to the development of an ion, an enriched layer of cement that is firmly attached to the tooth. bonding with enamel is higher than that of dentin due to greater inorganic content

what is the marginal adaption and leakage of GIC like?

they have a good marginal adaptation as the coefficient of thermal expansion is close to that of enamel and dentin. the marginal seal is less of that compared to that of composites

what is the physical strength of GIC like?

the main limitation of GIC is their relative lack of strength and low resistance to abrasion and wear

conventional GIC have low what?

flexural strength but high modulus of elasticity, therefore very brittle and prone to bulk fracture

what are glass cermet cements stronger than?

conventional cement, but their fracture resistance remains low.

resin modified cements have higher what?

flexure and tensile strengths, hence more fracture resistance

what is the compressive strength of conventional GIC?

150 Mpa or 22,000 Psi (pounds per square inch)

what is the tensile strength of conventional GIC?

6.6 Mpa or 960 Psi

what is the hardness of conventional GIC?

48 KHN

what is the solubility of conventional GIC?

0.4

since the strength properties are inferior compared to composites, GIC are?

should not be placed where it will receive heavy occlusal (biting) forces, unless they are well supported by surrounding tooth structure.

what is the biocompatibility of GICs?

the pulpal response is favorable and causes a mild response due to high buffering capacity of hydroxyl apatite and large molecular weight of the polyacrylic acid which prevents entry into dentinal tubules

how does the anticariogenic effect of GICs work?

by the release of fluoride. it is released at the time of mixing and lies within a matrix and it is released without affecting the physical properties of the cement. it is high initially and declines after 3 months. afterwards, the fluoride release is continues to release small amounts of fluoride for many months or even years.

one of the unique features of GIC is that it can what?

absorb fluoride from external sources, such as fluoride toothpaste and mouthwash, professional topical fluoride gel or varnish. after absorbing fluoride, the cement can release it again later, this is why GIC is called a fluoride reservoir or fluoride-rechargeable material.

how is manipulation and placement of GIC?

clean surfaces are essential for good adhesion (bonding). the smear layer should be removed in order to achieve adhesive bonding to the dentin. powder and liquid ratio is 3:1 by weight and dispensed just prior to mixing. a glass slab is preferable to the paper pad, since the glass is cool and maintains the temperature for a longer period of time. first increment is incorporated rapidly to produce a homogenous milky consistency. mixing is done in folding method that preserves the gel structure. the finished mix should have a glossy surface. the mixed cement is immediately packed, and then the pre-shaped matrix is applied for contouring and finishing is done. matrix also prevents restoration exposure from air and loss of water

how are enamel and dentin cleaned?

first with pumice slurry followed by swabbing with polyacrylic acid 10% for 5 seconds. then, the tooth surface should be isolated and dry

why is the mixed cement immediately packed?

any delay leads to a dull appearance denoting that the setting reaction has progressed

what is placed on cement to protect cement?

special varnish

what should be trimmed by hand instruments?

excess material from the margins

what is used to prevent desiccation during contouring and finishing?

micron finishing diamonds with petroleum lubricants

what is done to get a smooth surface for GIC?

a fine grit aluminum oxide polishing paste applied with prophy cup

before dismissing the patient, what is done to the GIC?

the restoration is again coated with protective agent to prevent chalky or crazed surface

when is final finishing and polishing done?

after 24 hours

what are the 3 cardinal rules for the success of GIC?

1. conditioning of the tooth surface

2. proper manipulation

3. protection of the cement during setting

what are advantages of GICs?

1. inherent adhesion to the tooth structure

2. good marginal seal

3. less shrinkage

4. anticariogenic as it releases fluoride

5. biocompatible

6. very minimal cavity preparation required

what are disadvantages of GICs?

1. brittle

2. soluble

3. water sensitive during setting

4. not inherently radiopaque

5. less esthetic than composite

6. low fracture resistance, so they shouldn’t be restored in stress bearing areas

7. low wear resistance

what are the indications of GIC?

they are generally indicated for the restoration of low stress areas because of their limited strength and wear resistance such as:

1. used as an anterior esthetic restorative material for class III and class V restorations (eroded areas) and notched cervical defects of idiopathic erosion or abrasion origin

2. the restorations of root caries lesions in older patients or those with high caries activity

3. as a luting agent for permanent cementation of crowns, bridges and veneers

4. as liners and bases as they bond to enamel and dentin and release fluoride and help to prevent decay and secondary caries

5. pit and fissure sealants, with the material being mixed to a more fluid consistency to allow flow into the depths of the pits and fissures

6. as orthodontic cements for orthodontic bracket bonding

7. as a core buildup for modified GICs are used, for example, silver alloy admixed or glass cements are used

8. in ART (atraumatic restorative treatment) mainly used in poor countries. the caries are excavated as much as possible by using hand instruments and the remaining cavity is restored by GIC

9. as restoration for deciduous teeth because of high fluoride release and minimal cavity preparation

what is the sandwich technique?

when GICs are used as dentin replacement with composite used to replace enamel, as this takes advantage of the desirable qualities of ionomer system and provides the esthetics of the composite restoration

what are the contraindications of GIC?

• high stress bearing areas

• places where aesthetics is most important

what is cavity preparation like for GIC?

a definite cavity preparation is not required as it has very good adhesive quality

when is a slot like preparation indicated for GIC?

class II or class III for cervical locations not involving the proximal contact or when gingival recession sometimes provides access to the carious lesion from the facial or lingual direction