Dental Cements Question And Answers

Dental Cement

Question  1. Classify dental cement. Write composition, manipulation, and uses of zinc phosphate cement.
Or
Classify cement. Write composition, manipulation, and uses of zinc phosphate cement.
Answer:

Cement: Dental cement are materials of comparatively low strength substance that harden to act as a base, liner, filling material, or adhesive to bind devices and prostheses to tooth structure or to each other.

Read And Learn More: Dental Materials Question And Answers

Classifiation of Cement:

• Philips, Craig’s, and Coombe’s classifications are described as follows:

Craig’s Classification:

EC Coombe Classification:

• Acid-base reaction cement.
• Polymerizing materials:
  • Cyanoacrylates
  • Dimethacrylate polymers
  • Polymer ceramic composites.
• Other materials:
  • Calcium hydroxide
  • Gutt-percha
  • Varnishes.

Zinc Phosphate Cement:

Zinc phosphate is the oldest of the luting cements, the terms “crown and bridge” and “zinc oxyphosphate” have also been used for this cement.

Composition of Zinc Phosphate Cement:

Powder:

Liquid:

Manipulation of Zinc Phosphate Cement:

• Spatula used – Stainless steel
• Mixing time – 1 min 15 sec
• Dispense the cement – 1.4 gm / 0.5 ml

The steps involved in the manipulation of zinc phosphate cement are as follows:

• A cool glass slab is used in order to delay the settling and allow more powder to be incorporated before the matrix formation occurs.
• The liquid should be dispensed just before mixing.
• The powder is added in small increments.
• A large area is covered during mixing in order to dissipate the exothermic heat.
• Maximum amount of powder should be incorporated in the liquid to ensure minimum solubility and maximum strength.
• An appropriate consistency is attained by the addition of more powder to the liquid and not by allowing a thin mix to thicken.

Procedure of Zinc Phosphate Cement:

The powder is added in small increments (to adjust the consistency) mixing is done with stainless steel spatula using a brisk circular motion. Each increment is mixed for 15 to 20 seconds. A large area is covered during mixing in order to dissipate the exothermic heat. Maximum amount of powder should be incorporated in the liquid to ensure minimum solubility and
maximum strength.

Question  2.  Describe The uses, advantages, and disadvantages of phosphate cement.
Or
Describe the Zinc Phosphate Cement
Answer:

Uses of Zinc Phosphate Cement:

• Luting of restorations (cementations)
• High strength bases
• Temporary restorations
• Luting of orthodontic bands and brackets.

Advantages of Zinc Phosphate Cement:

• Zinc phosphate cement is stronger (103.5 MPa) than zinc oxide-eugenol.
• The strength is sufficient when used as a base or luting agent.
• Its modulus of elasticity is high. This makes it stiff and resistant to elastic deformation.
• This is necessary when it is employed as a luting agent for restorations that are subjected to high masticatory stresses.
• Zinc phosphate cement is a good thermal insulator and may be effective in reducing galvanic effects.

Disadvantages of Phosphate Cement:

• When phosphate cement is exposed to the oral environment,
• For example, Temporary restorations, its bitterness and low strength cause it to fracture and disintegrate.
• Tensile strength is weaker, thus making it brittle.
• In the mouth, they show greater disintegration over a period of time.
• Pulp response is moderate. The acidity is high at the time of insertion due to phosphoric acid.
• It has no anti-cariogenic properties.
• It shows poor aesthetics.
• It does not show chemical adhesion.

Question  3. Compare and contrast zinc oxide eugenol cement with
zinc phosphate cement in all its properties.
Answer:

Comparison between Zinc Oxide Eugenol and Phosphate Cement

Properties of Phosphate Cement:

• Compressive strength:
  • Zinc oxide eugenol cement: They are relatively weak cement. The compressive strength, therefore, ranges from a low of 3–MPa up to 50–55 MPa.
  • Zinc phosphate cement: Zinc phosphate cement is stronger (103.5 MPa) than zinc oxide eugenol cement. The strength of zinc phosphate cement is sufficient when used as a base or luting agent. However, when it is exposed to the oral environment, For example, Temporary restorations, it’s brittleness and low strength cause it to fracture and disintegrate.

• Tensile strength:
  • Zinc oxide eugenol: Ranges from 0.32–5.3 MP
  • Zinc phosphate cement: The cement is weaker in tension (5.5 MPa) thus making it brittle.

• Modulus of elasticity: Zinc oxide eugenol cement—low 0.22–5.4 GP
  • Zinc phosphate cement: It is comparatively high (13.5 GPa) which makes it stiff and resistant to elastic deformation. This is necessary when it is employed as a luting agent for restorations that are subjected to high masticatory forces.

• Solubility and disintegration:
  • Zinc oxide eugenol cement: The solubility of set cement is highest among the cement (0.4% wt.) This breakdown is due to the hydrolysis of the zinc eugenolate.
  • Zinc phosphate cement: In the mouth, they show greater disintegration over a period of time. When tested according to ADA specifications it shows low solubility (0.06% wt.)

• Thermal properties:
  • Zinc oxide eugenol cement: Their thermal insulating properties are excellent and are approximately the same as for human dentin.
  • Zinc phosphate cement: Z inc phosphate cement are good thermal insulators and may be effective in reducing galvanic shock.

• Adhesion:
  • Zinc oxide eugenol cement: They do not adhere well to enamel or dentin.
  • Zinc phosphate cement: The retention of a cemented restoration is by mechanical interlocking of the set cement with a surface roughness of the cavity and restorations.

• Biological properties:
  • Zinc oxide eugenol cement (pH: 6.6–8): They are the least irritating of all cement pulpal response is mild.
    •  They inhibit the growth of bacteria and have a soothing effect on the pulp in deep cavities, reducing pain.
  • Zinc phosphate cement: Pulp response—Moderate. The acidity is high at the time of insertion due to phosphoric acid. The pH is 3.5 and it is neutralized in 24 to 48 hours. If dentin is not protected against the infiltration of this acid, a pulpal injury may occur.

Question  4. Explain cavity varnishes, liners, and cement bases. State their various uses. Give composition properties, manipulation, and uses of zinc polycarboxylate cement.
Or
Write a short note on zinc polycarboxylate cement.

Zinc Polycarboxylate Cement:

• Polycarboxylate cement: Polycarboxylate cement was the first system developed with the potential for adhesion to the tooth structure.

Composition of Zinc Polycarboxylate Cement:

Powder:

Liquid:

• Aqueous solution of 32 to 42% of polyacrylic acid.
• The copolymer of acrylic acid with other unsaturated carboxylic acids, i.e. iticonic acid, maleic acid, or tricarballylic acid.

 Manipulation of Zinc Polycarboxylate Cement:

• Conditioning: The tooth structure should be clean for proper bonding, for conditioning 10% polyacrylic acid solution followed by rinsing water or 1 to 3% hydrogen peroxide may be used. Then dry and isolate the tooth.
• Proportioning: 1.5 parts of powder to 1 part of liquid by wt.
• Procedure: The powder and liquid are taken on a cooled glass The powder is incorporated into the liquid in bulk (90%) with a stiff cement spatula and the remaining powder is added to adjust the consistency. The mix appears
  quite thick, but this cement will flow readily into a thin film when seated under pressure.

Properties of Zinc Polycarboxylate Cement:

Mechanical properties:

• Compressive strength: 55 MP inferior to zinc phosphate cement.
• Tensile strength— 6.2 MP It is slightly higher than zinc phosphate cement.
• Solubility and disintegration: It tends to absorb water and is slightly more soluble (0.6% wt) than zinc phosphate cement.
• Biocompatibility: Pulmonary response is mild. The pH of this cement rises more rapidly than phosphate cement.
• Adhesion: This cement bonds chemically with the tooth structure. The carboxyl group in polymer molecules chelates with calcium in the tooth structure. Bond strength to enamel is 3.4 to 13.1 MPa and to dentine is 2.07 MP
• Optical properties: They are very opaque due to large quantities of unreacted zinc oxide.
• Thermal properties: They are good thermal insulators.

Uses of Polycarboxylate Cement:

• Primarily for luting permanent restorations.
• As bases and liners.
• Used in orthodontics for the cementation of bands.
• Also used as root canal filings in endodontics

Question  5. Describe GIC in detail (Glass Inomer Cement).
Or
Write a short note on glass ionomer cement.
Or
Write a brief on glass ionomer cement.
Or
Write a short note on GIC cement.
Or
Write a note on glass ionomer cement.
Or
Write in detail about glass ionomer cement. 
Or
Write in detail about glass ionomer cement.
Or
Classify GI Write the composition, uses, advantages, and disadvantages of GI 
Or
Write composition, properties, advantages, disadvantages, and uses of GI
Or
Write types, composition, properties, and uses of glass ionomer cement.
Or
Write the classification, composition, and uses of glass ionomer cement.
Or
Write a short note on glass ionomer cement classification and uses. 
Or
Describe in detail the composition, properties, and uses of glass ionomer cement.
Answer:

Glass Ionomer Cement:

• Glass ionomer cement was first reported by Wilson and Kent in 1972.
• These are adhesive tooth-colored anti-cariogenic restorative
  materials.
• These cements have the combined properties of silicate cement and polycarboxylate cement.
• It was named glass ionomer because the powder is glass and the settling reaction and adhesive bonding to the tooth structure is due to the ionic bond.

Classifiation/Types of GIC:

1. Traditional Classification (Based on application):

• Type I: Luting cement
• Type II: Restorative cement
• Type II.1: Restorative aesthetic
• Type II.2: Reinforced materials (Fuji IX, Fuji II LC)
• Type III: Liner or Base.

2. Newer Classification:

• Type I: Luting cement
• Type II: Restorative esthetic or reinforced cement
• Type III: Liner or base.

3. Classification (Based on use):

• Type I: Luting cement
• Type II: Restorative cement restorative aesthetic

4. Reinforced materials (Fuji IX, Fuji II LC):

• Type III: Lining cement
• Type IV: Fissure sealant
• Type V: Orthodontic cement
• Type VI: Core Build-up cement.

Application / Uses Glass Ionomer Cement:

• As anterior, aesthetic restorative material for class III cavityFor eroded areas and class V cavities
• As a luting agent for restoration and orthodontic brackets
• As liners and bases
• For core build-up
• To a limited extent as pit and fissure sealants.
• Intermediate restorative material.

Composition of Glass Ionomer Cement:

Powder:

The powder is an acid-soluble calcium floroalumino-silicate glass.

Liquid:

Setting Reaction of Glass Ionomer Cement: 

• Leaching: When the powder and liquid are mixed together, the acid attacks the glass particles. Thus calcium, aluminum, sodium, and fluoride ions leach out into the aqueous medium.
• Calcium cross-links: The initial set occurs when the calcium ions cross-link the polyacrylic acid.
• Aluminum cross-links: In the next phase, the aluminum also begins to cross-link with polyacrylic acid chains.
• Sodium and fluoride ions: These ions do not take part in the cross-linking. Some of the sodium ions may replace the hydrogen ions in the carboxylic groups. The rest combine with fluoride to form sodium fluoride which is uniformly distributed within the cement.
• Hydration: Water plays a very important role in the cement. Initially, it serves as the medium. Later it slowly hydrates the matrix, adding to the strength of the cement.
• Silica gel sheath: The unreacted glass particle is sheathed by a silica gel. It is formed by the leaching of ions (Ca²⁺, Al³⁺, Na⁺, F^–) from the outer portion of glass particles.

Structure of Set Cement: The set cement structure is composed of an agglomeration of unreacted powder particles surrounded by a silica gel sheath and embedded in a matrix of hydrated calcium and aluminum cross-linked polyacrylic gel.

Properties of GIC:

• Mechanical Properties:
  • Compressive strength: Compressive strength of restorative
  • GIC is 150MP Compressive strength of luting GIC is 85 MP
  • Tensile strength: For luting GIC it is 6.2 MPa and for restorative GIC it is 6.6 MP
  • Hardness: It is less hard than silicate and composite. It is 49 KHN.
  • Fracture toughness: Type II GICs are inferior in fracture toughness.
  • Modulus of elasticity: It is 7.3 GPa
  • Wear resistance: GICs are most susceptible to toothbrush abrasion and occlusal wear.

• Solubility and Disintegration: Initial solubility due to the leaching of intermediate products is high. The complete setting reaction occurs in 24 hours, so it is recommended that cement should be protected by saliva in the mouth. For the luting type of cement solubility in water is 1.25% wt, while for the restoration type of cement, solubility is 0.4% wt.
• Adhesion: GIC adheres well to enamel and dentin. The shear bond strength of GIC is 3 to 5 MPa
• Esthetics: In esthetics, GICs are inferior to silicate cement and composites. GICs lack translucency and have rough surface textures. GICs can stain with time.
• Biocompatibility: Pulmonary response to GIC is mild. Type II glass ionomer cement are biocompatible. Luting type GIC is more acidic
• Anticariogenic Properties: GIC releases fluoride in amounts. Since GIC is adhesive in nature it has the potential for reducing infiltration of oral fluids at the cement tooth interface and prevent secondary caries.

Advantages of  Glass Ionomer Cement:

• Mechanical properties are good.
• Adhesion: It adheres well to the enamel and dentine. GIC bonds chemically to the tooth structure.
• Esthetics: They are tooth-colored restorative materials so can use as an anterior restorative material.
• Biocompatibility: Pulmonary response is mild.
• Anti-cariogenic properties: It releases fluoride and continues to do so over an extended period of time.
• Thereby preventing secondary caries.
• GIC is the best restorative material for children due to its good marginal integrity.

Disadvantages of  Glass Ionomer Cement:

• Its hardness or wear resistance is less than composite.
• Fracture toughness is inferior to composite.
• Solubility: The initial solubility is high due to the leaching of intermediate products.
• GIC is extremely sensitive to air and water during setting, so requires protection during setting.

Manipulation of Glass Ionomer Cement:

The steps involved in the manipulation of glass ionomer cement are:

• Preparation of tooth surface
• Manipulation
• Protection of cement during setting
• Finishing

Preparation of Tooth Surface:

• The tooth should be clean for effective adhesion of cement.
• The smear layer present after cavity preparation which tends to block of the tooth surface should be removed to achieve adhesive bonding.
• This is achieved by pumice wash and polyacrylic acid.
• For conditioning apply 10% polyacrylic acid for l0 to l5 seconds and then rinse with water for 30 seconds.
• Very deep areas of the preparation should be protected by a dab of calcium hydroxide.
• After conditioning and rinsing, the surface is dried but not desiccated. It should be kept free of contamination with saliva or blood, as these will interfere with bonding

Manipulation: Proportioning and Mixing:

• Powder: Liquid ratio should be 3: l by weight. A low P/L ratio reduces mechanical properties and increases the chances of cement degradation.
• Manual mixing: The powder and liquid are dispensed just before mixing.
  • A cool and dry glass slab is used as it allows all the powder to be incorporated into the mix and yet maintain its plasticity.
  • Here the spatula used for mixing is agate or plastic.
• Divide the powder into two equal increments.
  • The first increment is incorporated into the liquid rapidly with the stiff-bladed spatula to produce a homogenous milky consistency.
  • The remainder of the powder is then added. The mixing is done in a folding method in order to preserve the gel structure.
  • Mixing time should be of 45 seconds. The mix is immediately packed into
    the cavity with a plastic instrument.
• Mechanical mixing: GIC supplied in capsule form containing preproportioned powder and liquid is mixed in an amalgamator which is operated at a very high speed. The capsule has a nozzle, so the mix can be injected directly into the cavity.

Protection of Cement During Setting:

Glass ionomer cement is extremely sensitive to air and water during settling. So, immediately after placement into the cavity, a preshaped matrix is applied to:

• To protect the cement from the environment during the initial set.
• To provide maximum contour so that minimal finishing is required.
• The matrix is removed after 5 minutes. Immediately after removal, the cement surface is again protected with:
• A special varnish supplied by the manufacturer or
• An unfiled light-cured resin bonding agent or Cocoa butter.

Finishing of Cement During Setting:

• Trim the excess material and the cement from the margins.
• To avoid ditching hand instruments are preferred to rotary tools.
• If required further fishing is done after 24 hours.

Question  6. Write a short note on calcium hydroxide.
Or
Write briefly on calcium hydroxide.
Or
Write a short note on the uses of calcium hydroxide.
Or 
Describe the Calcium Hydroxide Cement
Answer:

Calcium hydroxide is a relatively weak cement. Due to its alkaline nature, it also serves as a protective barrier against irritants from certain restorations.

Applications / Uses of  Calcium hydroxide:

• For direct and indirect pulp capping.
• As low-strength bases-beneath silicate and composite restorations for pulp protection.
• Apexification procedure in young permanent teeth where root formation is incomplete.
• Used as a liner.

Composition of Calcium hydroxide:

Base Paste:

• Glycol salicylate—40%
• Calcium sulfate
• Titanium dioxide—inert fillers, pigments
• Calcium tungstate or barium sulfate—provides radioopacity

Catalyst Paste of  Calcium hydroxide:

Setting Reaction of Calcium Hydroxide:

Calcium hydroxide reacts with l-methyl trimethylene salicylate ester to form a chelate viz. amorphous calcium salicylate. Zinc oxide also takes part in this reaction.

Ca(OH)₂+ l-methyl trimethylene salicylate → calcium salicylate

Properties Calcium hydroxide:  Calcium hydroxide cements have poor mechanical properties.

• Mechanical Properties:
  • Compressive strength: 10-27 MPa after 24 hours.
  • Tensile strength: 1 MPa is low.
  • Modulus of elasticity: 0.37 GP
• Thermal Properties: If used in sufficient thick layers they provide some thermal insulation.
• Solubility and Disintegration: The solubility in water is high 0.4 to 7.8%.
• Biological Properties:
  • Effect on pulp: The cement is alkaline in nature. The high pH is due to the presence of free Ca (OH)₂ in the set cement. The pH ranges from 9.2 to 11.7.
  • Formation of secondary dentine: The high alkalinity and its consequent antibacterial and protein lysing effect help in the formation of reparative dentine.

Question  7. Write a short note on adhesive cement.
Answer:

• Generally, there are two adhesive types of cement in dentistry that undergo strong bond formation with enamel.
• The adhesive cement is glass ionomer cement and zinc polycarboxylate cement.

Glass Ionomer Cement:

Glass ionomer cement chemically bonds to enamel and dentin, though the precise mechanism of bonding is unclear,

There are two probable theories of adhesion:

• The first theory suggests that polyacid molecules chelate with calcium on the tooth interface. This is supported by the formation of the interfacial calcium polyalkeonate salt.
• According to another theory the acid present in the fresh mix when contacts the tooth structure acts as a self-etching agent leading to the dissolution of hydroxyapatite crystals which results in the release of calcium and phosphate ions.  Hydrogen ions are rapidly buffered by the phosphate ions from hydroxyapatite crystals and pH begins to rise.

To maintain an electrolytic balance, phosphate ions take with them a calcium ion

• These calcium ions are then taken up by the carboxylic groups adjacent to the tooth to form.
• An ion-enriched layer composed of calcium phosphatepolyalkeonate complexes which are firmly bound to both enamel and dentin.
• So, the polyacid chains are bound to a reprecipitated layer on the tooth surface.

In conclusion, the adhesive mechanism of glass ionomer cement primarily involves the chelation of carboxyl groups of the polyacids with the calcium in the hydroxyapatite of the enamel and dentin. Because of the greater homogeneity and inorganic content of enamel, glass ionomer cement bonds better to enamel than to dentin.

It is always preferred to condition the tooth surface before bonding for improving the bonding of GIC with tooth structure. Conditioning causes the removal of the smear layer without removing the smear layer plugs from the dentin tubule orifices or calcium ions. A commonly used conditioner for glass ionomer cement is polyacrylic acid (10 to 25%) applied for 10 to 15 seconds.

After using conditioner, the use of the dilute solution of ferric chloride on the tooth has been shown to improve the bonding by deposition of Fe³⁺ ions which further increases the ionic interaction between the cement and dentin. It chemically bonds to dentin/enamel.

Zinc Polycarboxylate Cement:

This cement bonds chemically with tooth structure. The Carboxyl group in the polymer molecule gets chelate with calcium in the tooth structure and makes a bond. Bond strength to enamel is from 3.4 to 13 MPa and for dentin it is 2.1 MP

Factors Affecting Adhesiveness of the Cement:

• Clean and dry tooth surface enhances bonding.
• If the inside surface of the metal crown is not clean, cement does not bond with the metal. For doing so the internal surface of the metal should be abraded.
• Adhesion is better to smooth surfaces.

Question 8. Write classification, composition, the chemistry of setting, manipulation, properties, and uses of zinc oxide eugenol cement.
Or
Write a short note on zinc oxide eugenol cement.
Or
Write in brief on the classification and uses of zinc oxide eugenol cement. 
Answer:

Zinc Oxide Eugenol Cement:

Classification of Zinc Oxide Eugenol Cement:

ISO 3107:2004:

• Type I ZOE — For temporary cementation
  • Class I – Settng cement
  • Class II – Non-setting cement
• Type II ZOE — For permanent cementation
• Type III ZOE — Temporary filing and thermal base
• Type IV ZOE — Cavity liners

The above classification of ISO 3107:2004 recently has been replaced by ISO 3107: 2011 in which only two classes are described.

ISO 3107: 2011:

• Type I: For temporary cementation
• Type II: For bases and temporary restorations

Type I ZOE cements: 

They are meant for short-term luting. They are used to cement provisional restoration for the period it takes to make a definitive restoration. Permanent restorations are also sometimes for a short period for the patient to try it. They have low strength which allows easy removal of restoration without damage to the restoration or tooth.

Type II ZOE cement:

They are used for interim periods when a tooth is undergoing treatment or until it is ready for permanent restoration. They can also be used as bases under non-resin-based permanent restorations.

Composition of  Zinc Oxide Eugenol Cement:

Powder:

Liquid:

Chemistry of Setting Zinc Oxide Eugenol Cement:

The setting reaction and microstructure are the same as that of the zinc oxide eugenol impression paste. In the first reaction, hydrolysis of zinc oxide to its hydroxide take place. Water is essential for the reaction.

ZnO + H₂O  →  Zn (OH)₂
The reaction proceeds as a typical acid-base reaction.

Zn (OH)₂      +       2HE   →   ZnE₂  +  2H₂O
Base             Acid          Salt
(Zinc hydroxide)   (Eugenol)  (Zinc eugenolate)

The chelate formed is an amorphous gel that tends to crystallize imparting strength to the set mass.

Manipulation of  Zinc Oxide Eugenol Cement:

Powder/liquid ratio 4: 1 to 6: 1 weight. Bottes are shaken gently. A measured quantity of powder and liquid is dispensed into a cool glass slave bulk of the powder is incorporated into the liquid and spatulated thoroughly in a circular motion with a stiff-bladed stainless steel spatula Smaller increments are then added until the mix is complete.

Properties  of  Zinc Oxide Eugenol Cement:

• Mechanical Properties:
  • The compressive strength of the cement ranges from 5 to 55 MPa.
    1. For Type I—6 to 28 MPa
    2. For Type II—45 to 55 MPa
  • Tensile strength ranges from 0.32 to 5.3 MPa
  • The modulus of elasticity is 0.22 to 5.4 GP

• Thermal Properties:
  • Thermal conductivity: Its thermal insulating properties are excellent. Thermal conductivity is in the range of insulators such as cork and asbestos.
  • Its coefficient of thermal expansion is 35 × 10–6/°C

• Solubility: Its solubility is highest among the cement. These cements disintegrate in oral fluids.
• Film Thickness: The film thickness of zinc oxide eugenol cement is 25 µm which is higher than other cement.
• Adhesion: It does not adhere to enamel or dentin.
• Biological Properties:
  • Effect on pulp: Its pH is 6.6 to 8.0. It is the least irritating to all the cement. Its effect on pulp is mild.
  • Bacteriostatic and obtundent properties: It stops the growth of bacteria and provides a soothing effect to the pulp.
  • Eugenol is irritating to the skin and eyes and can cause allergic dermatitis.
• Optical Property: Set cement is opaque.

Uses  of  Zinc Oxide Eugenol Cement: 

• For temporary cementation
• For temporary restoration
• Cavity liners and base
• Pulp capping agent
• Secondary use:
• Root canal restorations
• A periodontic bandage or surgical pack.

Question  9. What are tooth-colored restorative materials? 
Answer:

Tooth-colored restorative materials give the appearance of a natural tooth.

Tooth-colored materials are:

• Composite resin
• Porcelain
• Glass ionomer cement
• Acrylic resin.

Question 10. Write in detail about Recent advancements in glass ionomer cement.
Answer:

Recent Advancements:

1. Metal Modifid GIC:

The metal-modified GIC was introduced to improve the strength, fracture toughness, and resistance to wear and yet maintain the potential for adhesion and anti-cariogenic properties.

Types of  Metal Modified GIC:

• Silver alloy admixed: Spherical amalgam alloy powder is mixed with type II GIC powder (miracle mix).
• Cermet: Silver particles are bonded to glass particles. This is done by sintering of a mixture of the powders at a high temperature.

Uses of Metal Modified GIC:

In the restoration of small class I cavities as an alternative to amalgam or composite resins. They are particularly useful in young patients who are prone to caries. For the core build-up of grossly destructed teeth”

Properties of Metal Modified GIC:

• Mechanical properties:
  • As compared to that of conventional cement the strength of either type of metal-modified cement (150 MPa) is not greatly improved.
  • Fracture toughness of GIC whether modified or not is extremely low.
  • It is far more resistant to wear than type II GI
• Anticarcinogenic property:
  • Both metal-modified ionomers have anti-cariogenic capability due to the leaching of fluoride.
• Esthetics:
  • As they are gray in color because of their metallic phases within them, they are unsuitable for use in anterior teeth.

2. Resin-Modified GIC:

The two drawbacks of conventional GIC, i.e. moisture sensitivity- ity and low early strength which occur due to slow acid base setting reaction are overcome by adding some polymerizable functional group for the additional curing process.

Other names–Are light-cure GIC, dual-cure, Tricure, resin ionomer, compomer, and hybrid ionomer.

Classification of  Resin-Modified GIC:

Depending on the predominant component in them. These materials have been classified by McClean et al, as:

• Resin-modified glass ionomer cement (RMGI), for example. Fuji II LC, Vitremer, Photac-Fil, etc.
• Polyacid-modified composites (PMC), for example. Dyract,
  Variglass VL

Uses of  Resin-Modified GIC:

• Restoration of class I, III, or V cavities
• As bases and liners
• As adhesives for orthodontic brackets
• In the cementation of crowns and bridges
• For repair of damaged amalgam cores or cusps
• As retrograde root filling.

Supplied As  Resin-Modified GIC:

They are supplied as follows:

• Chemically cured
• Light-cured
• Dual-cured (combined chemical and light-cured)

All of them are usually supplied as powder and liquid. The light-cured type is supplied in dark-shaded bottoms for light protection.

Properties of Resin-Modified GICs:

• Strength: When resin-modified GICs are compared to conventional GICs their compressive strength is slightly lower (105 MPa) whereas the diametric tensile strength is greater (20 MPa) due to the plastic nature of the resin component.
• Hardness: Hardness (40 KHN) is comparable to that of conventional GICs.
• Adhesion: The bonding mechanism to tooth structure is the same to that of conventional GICs.
• Microleakage: These materials have a greater amount of microleakage when compared to conventional GICs.
• This may be partly due to the polymerization shrinkage and partly due to the reduced wetting of the tooth by the cement.
• Anticariogenicity: They have a significant anti-cariogenic effect due to the fluoride release.
• Esthetics: They are less translucent due to the significant differences in the refractive index between the resin matrix and powder particles.

3. High Viscous or Packable Glass Ionomers:

Fuji VIII for anterior teeth and Fuji IX for posterior teeth To simplify the insertion of the material, the GIC has to be pressed into the cavity.

To achieve this, the particle size of the powder and the P/L ratio is increased to obtain a highly viscous mix that can be easily packed. This modified, highly viscous GIC has high strength and better physical properties. Fifty percent of the particles have an average particle size of about 8 µm while about 90% of the particles have a particle size of less than

9.6 µm. This resulted in a mix with a thicker consistency that could be easily inserted with minimal hand instruments and pressed into place. These cements are widely used in atraumatic restorative techniques.

4. Compomers:

This class of restorative material combines some of the chemical and mechanical properties of composite resin and ion-leachable glass particles of GICs as filers. By adding aluminosilicate, it was thought that a better composite resin with fluoride-releasing properties was achieved.

Compomers Applications

• As restorative material in pedodontics
• As restorative material in non-stress bearing areas.
• In Class V lesions
• As bases
• In permanent luting

5.  Amino Acid-Modified Glass Ionomer Cement:

The fracture toughness of GIC can be improved by modifying acrylic acid and copolymers with N-acryloyl-glutamic or Nmethacryloylamino acids.

6. Nano-ionomers:

They are the hybrids of resin-modified GIC and nano-filed dental composites. They are designed for quick and easy mix, for example, Ketac nano light curing GIC. These cement have greater wear resistance.

7. Ceramic Reinforced Posterior Glass Ionomer Cement:

They are designed to match the strength and durability of amalgam. It is present in white and universal tooth shades. This is dispensed in powder and liquid form, water settable form is also present.

Question  11. Write a short note on polyalkeonate cement.
Answer:

Polyalkeonate cement is also known as glass ionomer cement alumina silicate polyacrylic acid or dentin substitute or man-made dentin. Polyalkeonate cement is the combination of the powder of silicate cement with the liquids of polycarboxylates, so the term polyalkeonate cement is given.

Question  12. Enumerate permanent luting agents. 
Answer:

Enumeration of Permanent Luting Agents:

• Zinc phosphate cement
• Polycarboxylate cement
• Silicophosphate
• Glass ionomer cement
• Resin.

Question  13. Describe the uses of advantages and disadvantages of Zinc oxide eugenol cement.
Answer:

Advantages of Zinc Oxide Eugenol Cement:

• It has higher biocompatibility than other cement.
• It is a good insulator.
• It is a good sealer of the pulp dentin organ.
• It has an antiseptic effect.
• It has a sedative and anti-inflammatory action on the pulp dentin organ.

Disadvantages of Zinc Oxide Eugenol Cement:

• The strength is not sufficient enough to resist the forces of mastication.
• It lacks resistance.
• It has a high solubility in the oral cavity.

Question  14. Describe the Zinc Oxide Eugenol Cement.
Answer:

These cements are of low strength, are the least irritating of all dental cement, and have an obtundent effect on dentin.

Composition of  Zinc oxide eugenol cement.

Powder:

Liquid:

Setting Reaction of Zinc oxide eugenol cement:

The setting reaction and microstructure are the same as that of ZOE impression paste.

In the first reaction hydrolysis of zinc oxide to its hydroxide takes place. Water is essential for reaction.

ZnO   +   H₂O   →   2O  Zn (OH)₂

The reaction proceeds as a typical acid-base reaction

Zn (OH)₂  +   2HE    →    ZnE₂  +  2H₂O
Base      Acid            Salt
(Zinc     (Eugenol)    (Zinc eugenolate)
hydroxide)

The chelate formed is an amorphous gel that tends to crystallize imparting strength to the set mass.

Manipulation of Zinc oxide eugenol cement:

The powder/liquid ratio is 4: 1 to 6: 1 by weight.

• The bottoms are shaken gently.
• A measured quantity of powder on liquid is dispensed onto a cool glass slab.
• The bulk of the powder is incorporated into liquid and is spatulated thoroughly in a circular motion with stiff bladed stainless steel spatula
• Small increments are then added until the mix is complete.

Question  15. Write a short note on compomers.
Answer:

Compomers are composites modified with polyacid groups and are used for restoration in low-stress-bearing areas.

• They are a combination of composites and glass ionomers.
• This class of restorative material combines some of the chemical and mechanical properties of composite resin and ion-leachable glass particles of GICs as filers.
• By adding aluminosilicate, it was thought that a better composite resin with fluoride-releasing properties is achieved.

Applications of Compomers:

• As restorative material in pedodontics
• As restorative material in non-stress bearing areas.
• In Class V lesions
• As bases
• In permanent luting.

Composition of Compomers:

These materials have two main constituents: Dimethacrylate monomer with two carboxylic groups present in their structure and a filer that is similar to the ion-leachable glass present in

GICs. The ratio of carboxylic groups to backbone carbon atoms is approximately 1:8. There is no water in the composition of these materials and the ion-leachable glass is partially silanized to ensure some bonding with the matrix.

Single component system—silicate glass, sodium fluoride, and polyacid modified monomer, photoinitiator.

• Double component system
• Powder—glass filers, accelerators, initiators, TiO2
• Liquid—acrylic monomers, photoinitiator, water, carboxylic acid methacrylate.

Supplied As Compomers:

• These materials are sensitive to moisture and they are usually supplied as:
• Light-cured single paste in moisture-proof packets (direct, compoglass)
• Powder/liquid (principle)
• Two-paste static mixing system (permanent)

Manipulation of Compomers:

• For the single-component system, the tooth is etched and a bonding agent is applied. The material is injected into the cavity and cured by light.
• For the powder/liquid system, the powder and liquid is dispensed and mixed according to the manufacturer’s instructions for 30 seconds.
• For the static mixing system, the material comes out mixed when it is extruded through spirals in the mixing tips.

Properties of Compomers:

• Tensile strength, flexural strength, and wear resistance are superior to GIC but inferior to resin composite.
• Fluoride release: Though these materials release fluoride, they have significantly lower levels of fluoride release as compared to GICs.
• Although low, the level of fluoride release has been reported to last at least 300 days.
• Adhesion: Unlike glass ionomers, they do not have the ability to bond to hard tooth tissues. Like composite; acid etching and the use of bond agents are necessary.
• Biocompatibility: With the exception of concern about the release of HEMA from these materials, no other biocompatibility issues are present.

Advantages of Compomers:

• Low heat release during curing
• Less shrinkage on curing
• Higher flexural strength
• Better wear resistance
• Excellent tissue biocompatibility.

Disadvantages of Compomers:

• Harder, more Britte
• Expensive.

Question  16. Write a short note on cermet. 
Or
Write a short note on cermet cement.
Answer:

Cermet was first introduced by McLean and Gasser in 1985.

The meaning of cermet is ceramic metal:

• By fusing GIC powder along with silver particles by sintering at high temperatures the product is known as cermet.
• Microfie silver alloy particles of 40% weight and less than 3.5 µm in diameter are mixed with glass powder particles and then sintered together at 800°C under pressure.
• Unreacted silver particles are washed out. Up to 5% of titanium dioxide is added to modify the color.
• The pellet that is formed is ground into fine particles which are cermet

Mechanical Properties of cermet is ceramic metal:

• Greater strength and wear resistance
• Mechanical strength is 150 MPa
• Tensile strength is 6.7 MPa
• Fracture toughness is similar to conventional GIC
• Produces anti-cariogenic property
• Highly radiopaque because of its gray color.

Uses of cermet are ceramic metal:

• As core build-up for cast crowns.
• As a class I restoration in young patients with a high incidence of caries.

Question  17. Discuss polycarboxylate cement in setting reaction, and its advantages.
Answer:

Setting Reaction of Polycarboxylate Cement:

When powder and liquid are mixed, the surface of powder particles is attacked by the acid and releases zinc, magnesium, and tin ions. These ions bind to the polymer chain via carboxyl groups. They also react with carboxyl groups of adjacent polyacid chains to form cross-linked salts.

Advantages of Polycarboxylate Cement:

• It is less irritating to the pulp.
• It bonds chemically with the tooth structure.

Question  18.  Write in detail about the physical properties and uses of zinc phosphate cement. 
Or
Write a short answer on zinc phosphate cement.
Answer:

Physical Properties of Zinc Phosphate Cement.:

• Compressive strength: Zinc phosphate cement is stronger (103.5 MPa) than zinc oxide eugenol cement. The strength of zinc phosphate cement is sufficient when used as a base or luting agent. However, when it is exposed to the oral environment, for example, Temporary restorations, its brittleness and low strength cause it to fracture and disintegrate.
• Tensile Strength: The cement is weaker in tension (5.5 MPa) thus making it brittle.
• Modulus of elasticity: It is comparatively high (13.5 GPa) which makes it stiff and resistant to elastic deformation. This is necessary when it is employed as a luting agent for restorations that are subjected to high masticatory forces.
• Solubility and disintegration: In the mouth, they show greater disintegration over a period of time. When tested according to ADA specifications it shows low solubility (0.06% wt).
• Thermal properties: Zinc phosphate cement are good thermal insulator and may be effective in reducing galvanic shock
• Adhesion: The retention of a cemented restoration is by mechanical interlocking of the set cement with a surface roughness of the cavity and restorations.

Question  19.  Describe its biological and chemical bonding properties. Add a note on its modifications. Mechanism of bonding with tooth structure.

Answer:

Biological Properties:

• Pulpal response to glass ionomer cement is mild.
• Type I GIC is more acidic than Type II GIC because of the lower powder-to-liquid ratio. Sensitive patients show painful responses to GIC luting cement.
• Deeper areas are protected by calcium hydroxide cement before giving GIC restoration.

Chemical Bonding Properties:

Glass ionomer cement chemically bonds to enamel and dentin, though the precise mechanism of bonding is unclear, there are two probable theories of adhesion:

1. The first theory suggests that polyacid molecules chelate with calcium on the tooth interface. This is supported by the formation of the interfacial calcium polyalkeonate salt.

2. According to another theory the acid present in the fresh mix when contacts the tooth structure acts as a self-etching agent leading to the dissolution of hydroxyapatite crystals which results in the release of calcium and phosphate ions. Hydrogen ions are rapidly buffered by the phosphate ions from hydroxyapatite crystals and pH begins to rise.

To maintain an electrolytic balance, phosphate ions take with them a calcium ion; these calcium ions are then taken up by the carboxylic groups adjacent to the tooth to form an ion-enriched layer composed of calcium-phosphatepolyalkeonate complexes which are firmly bound to both enamel and dentin.

• So, the polyacid chains are bound to a reprecipitated layer on the tooth surface. In conclusion, the adhesive mechanism of glass ionomer cement primarily involves the chelation of carboxyl groups of the polyacids with the calcium in the hydroxyapatite of the enamel and dentin.
• Because of the greater homogeneity and inorganic content of enamel, glass ionomer cement bonds better to enamel than to dentin. It is always preferred to condition the tooth surface before bonding for improving the bonding of GIC with tooth structure.
• Conditioning causes removal of the smear layer without removing smear layer plugs from the dentin tubule orifices or calcium ions. A commonly used conditioner for glass ionomer cement is polyacrylic acid (10 to 25%) applied for 10 to 15 seconds.
• After using conditioner, use of the dilute solution of ferric chloride on the tooth has been shown to improve the bonding by deposition of Fe3 + ions which further increases the ionic interaction between the cement and dentin. It chemically bonds to dentin/enamel.

Question  20. Write a brief on the miracle mix. 
Answer:

Miracle mix is metal-modified glass ionomer cement.

• By adding spherical silver alloy particles in the proportion of 8 parts cement powder to one part alloy by volume, i.e. 8:1 ratio mixed to a suitable consistency with polyacrylic acid at a ratio of 3:2 by weight this is silver alloy admix.
• Since the product was introduced in 1980 when mercury controversy was evident this material consisting of only silver alloy particles without mercury was named Miracle Mix.
• In miracle mix, spherical amalgam alloy powder is mixed with restorative type GIC powder.

Uses of Miracle Mix:

• Restoration in small Class I cavities as an alternative to amalgam or composite resins.
• For the core build-up of grossly destructed teeth.

Properties of Miracle Mix:

• Mechanical Properties: Strength, diametral tensile strength, fracture toughness, and wear rate of miracle mix is the same as conventional GI
• Anticarcinogenic Property: Since leaching of fluoride occurs from it, it has anti-cariogenic properties.

Esthetics of Miracle Mix: It is gray in color so it is unsuitable for use in anterior teeth

Question  21. Define dental cement. Enumerate ideal requirements
for dental cement.
Answer:

Dental cement: Dental cement are hard, brittle material formed by mixing powder and liquid together. They are either resin cement or acid-base cement.

Ideal Requirements of Dental Cements:

• It should be non-toxic and non-irritant to the pulp and oral tissues.
• It should be biocompatible.
• It should be capable to adhere with tooth structures.
• It should not be soluble in oral fluids.
• It should have sufficient strength to withstand the masticatory load.
• It should be a thermal insulator, or electrical insulator to prevent galvanic current conducting through the tooth and oral tissues.
• It should protect the pulp from chemical insults.
• It should have anti-cariogenic properties.
• It should not react with the materials placed over them.
• It should be radiopaque.
• It should be hard enough to resist abrasion.