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Dental materials > dental cements > Flashcards

dental cements Flashcards

1
Q

What are dental cements?

A
  • hard, brittle materials that are formed by mixing a power with a liquid
  • when mixed to a thin consistency, they are used to hold restorations such as gold crowns on prepared teeth
  • when mixed to a thicker consistency, cements are used as temporary filling materials or to provide thermal insulation to teeth restored with amalgam
  • some other cements are used for special purposes such as in endodontics, periodontics, oral surgery, and orthodontics
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2
Q

What are the requirements of dental cements?

A
  • non toxic or irritant to pulp
  • insoluble in saliva and oral fluids
  • when used as insulating base: they should be strong so that the filling material can be condensed on it, should provide electrical, thermal and chemical insulation to pulp, should have an obtundent i.e. reduce pain and should be bacteriostatic if placed in a cavity with residual caries
  • when used for cementation they should have a low film thickness
  • should adhere to enamel and dentine
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3
Q

What are the types of zinc oxide based cements?

A
  • zinc oxide powder + eugenol (zinc oxide eugenol)
  • zinc oxide powder + phosphoric acid (zinc phosphate)
  • zinc oxide powder + polycarboxylic acid (zinc carboxylate)
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4
Q

What are the types of alumino silicate glass based cements?

A
  • alumino silicate glass + phosphoric acid (silicate cement which is very old and not used today)
  • alumino silicate glass + polycarboxylic acid (glass ionomer cement which is very recent and widely used today)
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5
Q

What does the powder of unmodified zinc oxide and eugenol cement contain?

A
  • zinc oxide
  • magnesium oxide (to maintain the white color of the cement)
  • zinc acetate (accelerator)
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6
Q

What does the liquid of unmodified zinc oxide and eugenol cement contain?

A
  • eugenol and 15% olive oil
  • acetic acid (accelerator)
  • water (essential for setting reaction)
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7
Q

What is the main disadvantage of unmodified ZnO/E cement and how is it improved?

A
  • main disadvantage is its very low strength
  • additives cn be used to improve its strentgh
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8
Q

What is the composition of resin bonded ZnO/E cement?

A
  • the same powder (ZnO) + 20% PMMA
  • the same liquid (eugenol) + 10% polystyrene dissolved in the eugenol
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9
Q

What is the composition of ethoxy-benzoic acid cement?

A
  • the same powder (ZnO) + 30% alumina
  • the same liquid (37.5% eugenol) + 62.5% EBA
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10
Q

What is the setting reaction of ZnO/E?

A

zinc oxide + eugenol –(in presence of water and it is called chelation reaction)–> amorphous zinc eugenolate matrix holding unreacted ZnO particles + free eugenol

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11
Q

What is the property of ZnO/E regarding effect of pulp?

A

pH of set cement is 7 (neutral), moreover it has an obtundant or sedative (pain killer) effect on the pulp and hence can be used in deep cavities. Moreover they can protect pulp thermally, electrically and chemically

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12
Q

What is the solubility of ZnO/E?

A

highest soluble dental cement (main disadvantage)

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13
Q

What is the strength of ZnO/E cements?

A
  • compressive strength is about 5, 38, and 90 MPa for the unmodified type
  • the resin bonded type and the EBA cements respectively
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14
Q

What is the opacity of ZnO/E cement?

A

opaque due to the presence of unreacted ZnO particles

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15
Q

What is the adhesion of ZnO/E?

A
  • no chemical bonding with enamel and dentin
  • bonding by mechanical interlocking only
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16
Q

Why s ZnO/E cement contraindicated under cmposite fillings?

A

they cause discoloration and inhibit polymerization

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17
Q

What is the manipulation to ZnO/E?

A
  • mixing is done using a glass slab and a stainless steel spatula
  • powder is added to the liquid in small increments until a thin or thick consistency is obtained according to its application
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18
Q

What is the powder of zinc phosphate cement?

A
  • zinc oxide
  • magnesium oxide (to maintain the white color of the cement)
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19
Q

What is the liquid of zinc phosphate cement?

A
  • 40% phosphoric acid
  • 40% water (to control the acid ionization and thus the reaction rate)
  • 20% zinc and aluminum phosphate buffers to stabilize the pH of the acid
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20
Q

What is the setting reaction of zinc phosphate?

A

zinc oxide + phosphoric acid –> zinc phosphate matrix hold unreacted ZnO particles + heat

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21
Q

What is the effect of zinc phosphate cement on the pulp?

A
  • pH = 1.5 to 3.5  highly acidic and highly irritant to pulp
  • a sub-base should be placed under it
22
Q

What is the solubility of zinc phsophate cement?

A

least soluble dental cement

23
Q

What is the strength of zinc phosphate cement?

A
  • high compressive strength
  • low tensile strength
24
Q

What is the film thickness of zinc phosphate?

A

as low as 15 micron. i.e. the least film thickness

25
Q

Is zinc phosphate cement opaque?

A

yes

26
Q

What is the adhesion of zinc phosphate cement?

A
  • do not form chemical bond with enamel or dentine
  • the retention of cemented restorations depends on the mechanical interlocking of the set material with surface roughness of both the tooth and the restoration
27
Q

What is the manipulation of zinc phosphate cement?

A
  • mixing is done using a thick, cool, and dry glass slab with a stainless steel spatula
  • the powder liquid ratio depends on the purpose for use i.e. the P/L ratio is 2.5:1 for luting purposes and 3.5/1 for cavity lining
  • the powder is divided into 4-6 parts then mixed with the dispensed liquid to obtain the desired consistency
  • mixing is done over a large area on the glass slab
  • when mixed for luting (cementation) purposes, the cement should string 1 inch, while for a base consistency, the cement should roll into a ball
28
Q

What is the powder of zinc polycarboxylate cement?

A
  • zinc oxide
  • magnesium oxide
29
Q

What is the liquid of zinc polycarboxylate cement?

A
  • 40% aqueous polycarboxylic acid
    (too viscous liquid)
  • Na-OH to adjust the pH and viscosity
30
Q

What is the setting reaction of zinc polycarboxylate cement?

A

zinc oxide + polycarboxylic acid –> zinc phosphate matrix hold unreacted zinc oxide powder

31
Q

Why do polycarboxylate cements have little irritant effect on pulp?

A
  • polycarboxylic acid is a weak acid
  • polycarboxylic acid has large molecular size so cannot penetrate dentinal tubules
  • the rapid raise of pH of mixed cement on setting (it reach neutrality within 24 hours)
32
Q

What is the solubility of zinc polycarboxylate?

A

more soluble than zinc phosphate cement in acids

33
Q

What is the strength of zinc polycaboxylate?

A
  • high compressive strength
  • low tensile strength
34
Q
A
34
Q

What is the film thickness of zinc polycarboxylate?

A

25-40 microns

35
Q

What is the opacity of zinc polycarboxylate?

A

more opaque due to the presence of unreacted ZnO particles

36
Q

What is the adhesion of zinc polycarboxylate?

A

bonds chemically to both enamel and dentine (main advantage)

37
Q

What is the bond strength of zinc polycarboxylate cement?

A
  • bond strength to enamel = 8 MN/m2 and 4 MN/m2 to dentin
  • adhesion to enamel is stronger than to dentin due to greater calcium content in enamel (96%) than in dentine (70%)
  • for optimum adhesion, enamel and dentine surfaces should be clean, smooth and dry
38
Q

What is the manipulation of zinc polycarboxylate cement?

A
  • the P/L ratio of 1:1 (as a luting agent) or 2:1 (as a base) are mixed on a special waxed paper pad or glass slab using a plastic spatula
  • mix over a small area of the slab to avoid destruction of the gel
  • properly mixed cement is glossy and appears viscous
  • it should be used before losing its glossy surface
  • viscosity decreases when force placed on mix and as spatulation increases
39
Q

What are the types of glass ionomer cements?

A
  • type 1: as a luting (cement) agent
  • type 2: as a restorative filling material
  • type 3: as a base
  • type 4: as pit and fissure sealants
40
Q

What is the composition and reaction of glass ionomer cements?

A
  • cement powder is a finely ground aluminosilicate glass and the viscous liquid is a polycarboxylate copolymer in water
  • the components of glass ionomer cements react to form a gel matrix surrounding the partially reacted glass powder particles
  • chelation reaction between the polycarboxylate molecules and calcium on the surface of the tooth results in a chemical (adhesive) bond
41
Q

What is the compressive strength of glass ionomer cements?

A
  • the 24-hour compressive strength of glass ionomer cements ranges from 150-250 MPa
  • the strength of the glass ionomer cements improves more rapidly when the cement is protected from moisture during the first 24 hours after filling
42
Q

Is glass ionomer cement brittle?

A

yes

43
Q

What is the bond strength of glass ionomer cements?

A
  • bond chemically to tooth structure by the reaction of carboxylic group (COOH) of polyacrylic acid with the calcium of tooth structure
  • the bond strength of glass ionomer cement to tooth structure is lower than that of the polycarboxylate cements because of the sensitivity of the glass ionomer cements to moisture during setting
  • to obtain a good bond to dentin, the surface must be treated with a conditioner to remove any smear layer which interferes with bonding
44
Q

What are the optical properties of glass ionomer cement?

A

translucent, therefore, can be used as anterior restoration but in low stress-bearing areas

45
Q

What is the manipulation of glass ionomer cements?

A
  • powder liquid form is mixed on a special paper pad using a plastic spatula
  • pre-proportioned capsules are mixed using a mechanical mixer then placed into the prepared cavity using an applicator
  • a typical mix of glass-ionomer cement, notice the shiny surface and stringiness of the mix
  • paint the surface of recently placed glass-ionomer to protect it from premature moisture contamination
46
Q

What is the composition of cavity varnishers?

A
  • consist of a resin dissolved in a volatile solvent such as acetone, chloroform, or ether
  • when the varnish is applied to the cavity preparation, the solvent evaporates and leaves a thin resinous film on the surface
47
Q

What are the uses of cavity varnishers?

A
  • to seal the exposed dentinal tubules and hence protect the pulp from the irritation of chemicals in the filling materials
  • to reduce marginal leakage around most filling materials, especially amalgam
  • to cover glass ionomer restorations immediately after insertion protecting it from dehydration or disintegration during the initial 24 hours
48
Q

What is the composition of calcium hydroxide?

A

simplest form is one or two pastes contain only aqueous suspension of calcium hydroxide

49
Q

What are the properties of calcium hydroxide?

A
  • alkaline (PH = 12) which is harmful to microorganisms found in carious dentin
  • if it contacts the pulp, it stimulates formation of secondary dentin
  • it is very weak therefore should be used as a sub-base under a strong base for better protection against condensation force of amalgam and against masticatory forces
50
Q

What are the uses of calcium hydroxide?

A
  • as a sub-base under zinc phosphate in deep cavities
  • it is the material of choice for pulp capping in case of microscopic pulp exposure

Dental materials (9 decks)

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