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Fixed Prosthodontics I > L6: Luting cements for fixed prosthodontics > Flashcards

L6: Luting cements for fixed prosthodontics Flashcards

1
Q

Which are the three primary factors influencing potential dislodgment?

A
  • Design of the tooth preparation.
  • Fit of the casting
  • The nature of the cement.
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2
Q

What is defined as cement?

A
  • a binding agent used to firmly unite two approximating objects;
  • a material that, on hardening, will fill a space or bind adjacent objects; comp, LUTING AGENT, ADHESIVE RESIN
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3
Q

What is defined as cementation?

A
  • the process of attaching parts by means of cement;
  • attaching a restoration to natural teeth by means of a cement (GPT-4)
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4
Q

What does retention prevent?

A

Retention prevents removal of the restoration along the path of insertion or the long axis of the tooth preparation.

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5
Q

What does resistance prevent?

A

Resistance prevents dislodgment of the restoration by forces directed in an apical direction and prevents any movement of the restoration under occlusal forces.

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6
Q

What must a dental cement be used to act as?

A

A dental cement must be used to act as a barrier against microbial leakage, sealing the interface between the tooth and restoration and holding them together through some form of mechanism.

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7
Q

What can bonding mechanism be divided in?

A
  • Non-adhesive luting
  • Micromechanical bonding
  • Molecular Adhesion
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8
Q

Which are the ideal properties of luting cements for fixed prosthodontics?

A
  • Durable bond between dissimilar materials.
  • Favorable compressive and tensile strengths.
  • Sufficient fracture toughness to prevent dislodgment.
  • Wet the tooth and the restoration.
  • Exhibit adequate film thickness and viscosity to ensure complete seating.
  • Resistant to disintegration.
  • Tissue compatible.
  • Adequate working and setting times.
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9
Q

What kind of reaction occurs in zinc-phosphate cement?

A

Acid-base reaction.

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10
Q

What is the reaction of zinc-phosphate cement initiated by?

A

Initiated by mixing a powder (90% ZnO and 10% MgO) with a liquid (67% phosphoric acid buffered with aluminum and zinc and 33% of water).

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11
Q

Which is the compressive strength of zinc-phosphate?

A

Compressive strength to (80 -100 MPa).

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12
Q

Which is the tensile strength of zinc phosphate cement?

A

Tensile strengths (5 to 7 MPa)

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13
Q

Which are the advantages of zinc phosphate cements?

A
  • Longest track record. Strength results from clinical cases for up to 42 years.
  • High compressive strength and low film thickness.
  • Reasonable working time.
  • Resistant to water dissolution.
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14
Q

Which are the disadvantages of zinc phosphate cements?

A
  • Low tensile strength (preparation geometry very important).
  • Luck of adhesion to tooth or crown material.
  • Not resistant to acid dissolution.
  • Powder/Liquid ratio and mixing technique very important for its material
  • properties.
  • Viscosity of cement increases rapidly with time.
  • Irritating effect on the pulp.
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15
Q

Which are the indications for zinc phosphate cements?

A
  • Single metal or porcelain fused to metal crowns.
  • Metal or porcelain fused to metal (PFM) fixed partial dentures (FPDs).
  • Cementation of post (cast and prefabricated).
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16
Q

Polycarboxylate cement: Reaction

A
  • Fast acid-base reaction that occurs when zinc oxide and magnesium oxide powders are rapidly mixed into a solution of polyacrylic acid.
  • Initiated by mixing a powder (ZnO and MgO) with a viscous solution of high molecular weight polyacrylic acid.
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17
Q

Polycarboxylate cement:

Compressive strength:

Tensile strengths:

A
  • Compressive strength to (55-85 MPa)
  • Tensile strengths (8-12 MPa)
18
Q

Polycarboxylate cement

Advantages:

A
  • Better adhesion to dentin than Zinc Phosphate.
  • High tensile strength.
  • Reasonable working time.
  • Low irritation to the pulp.
19
Q

Polycarboxylate cement

Disadvantages:

A
  • Low compressive strength.
  • Luck of adhesion to gold material.
  • Difficult to mix.
  • Powder/Liquid ratio and mixing technique very important for its material properties.
20
Q

Polycarboxylate cements:

Indications:

A
  • Single metal or porcelain fused to metal crowns in low stress areas.
  • When minimum pulp irritation is desired.
21
Q

Glass ionomer cement:

Reaction:

A
  • Acid-base reaction.
  • Initiated by mixing a powder (mainly calcium fluoroaluminosilicate glass) with a liquid solution (copolymers of polyacrylic acid with itaconic, maleic and tartaric acid)
22
Q

Glass ionomer cement:

Compressive strength:

Tensile strength:

A
  • Compressive strength to (127 MPa).
  • Tensile strength (8 MPa).
23
Q

GIC:

Advantages:

A
  • Adhesion to tooth structures is comparable to Polycarboxylate.
  • Biocompatible.
  • Fluoride release (anticariogenic effect).
  • Low film thickness.
  • High compressive strength.
24
Q

GIC:

Disadvantages:

A
  • Sensitive to early moisture contamination (protection of margins).
  • Low tensile strength.
  • Some concern for post cementation sensitivity (low pH).
  • No molecular adhesion to crown material.
25
Q

GIC:

Indications:

A
  • Single metal or porcelain fused to metal crowns.
  • Metal or porcelain fused to metal fixed partial dentures.
  • Cementation of post (cast and prefabricated).
26
Q

Resin luting cements:

What are resin luting cements?

A

They are composites, composed of a resin matrix (bis-GMA or diurethane methacrylate) and inorganic filler particles.

  • Most commonly used cements
  • Lower filler content and lower viscosity than restorative composites.
27
Q

Resin luting cements:

Which are the categories of resin luting cements based on the polymerization?

A

Category based on polymerization:

  • Chemically (self-cured).
  • Photopolymerization (light cured).
  • Combination of both (dual cured).

Different shade and opacity availability.

Very good bonding to tooth structures.

28
Q

Which are the characteristics of resin luting cements?

A
  • Different shade and opacity availability.
  • Very good bonding to tooth structures.
29
Q

Enamel etching/bonding:

Explain the mechanism.

A
  • The acid (phosphoric) demineralizes the enamel to etch (roughen) the surface.
  • The adhesive (bonding agent) can then penetrate the porosities of the roughen surface and form a micromechanical interlocking for a high bond strength (resin - adhesive - enamel).
30
Q

Dentin etching/bonding:

Explain the mechanism.

A
  • The acid (phosphoric) removes the smear layer, opening the dentin tubules, and demineralizes the intertubular dentin.
  • The adhesive can then penetrate the open dentin tubules and form resin tags which can result to high bond strength (resin - adhesive - dentin).
31
Q

What is smear layer?

A
  • A thin layer with small crystalline characteristics composed mainly of saliva and bacteria.
  • It appears on the surface of teeth that have undergone dental instrumentation procedures such as tooth preparations using dental burs.
  • Requires acid etching to be removed.
32
Q

Resin luting cements:

Advantages:

A
  • High compressive strength and resistance to tensile fatigue.
  • Resistant to water dissolution.
  • Resistant to acid dissolution.
  • Molecular adhesion to tooth and crown material (enhance strength of ceramic restorations that contain silica, ex. Lithium disilicate e.max).
  • Good bond strength to sandblasted base metal alloys as a result of
  • micromechanical retention.
  • Good shade matching for esthetic restorations.
33
Q

Resin luting cements:

Disadvantages:

A
  • Proper use requires multiple steps that are technique sensitive.
  • Variable film thickness.
  • Variable difficulty removing proximal and subgingival excess material.
  • Marginal leakage due to polymerization shrinkage.
  • Postoperative sensitivity varies with materials and technique.
34
Q

Resin luting cements:

Indications:

A
  • Porcelain veneers.
  • Ceramic, Zirconia and composite onlays and inlays.
  • Ceramic, Zirconia crowns or fixed-partial dentures.
  • Resin-bonded metal bridges (Maryland).
  • Metal, Porcelain Fused to Metal crowns and FPD’s.
  • Restorations for non-ideal axial wall preparations.
35
Q

Resin modified glass ionomer cement:

Mechanism.

A
  • Both strength and insolubility of resin cement with fluoride release of glass ionomer.
  • They harden by an acid-base reaction between fluoroaluminosilicate glass powder and a solution of polyalkenoic acids modified with pendant methacrylate groups, and by photo-initiated or chemically initiated free radical polymerization of methacrylate units.
36
Q

Resin modified glass ionomer cement:

Advantages:

A
  • High compressive and tensile strength.
  • Reasonable working time and easy to mix.
  • Low film thickness.
  • Fluoride release.
  • Molecular adhesion to tooth.
  • Resistant to water dissolution.
37
Q

Resin modified glass ionomer cement:

Disadvantages:

A

Water absorption causes expansion and cracking of overlying ceramic.

38
Q

RMGI:

Indications:

A
  • Single metal or porcelain fused to metal crowns and fixed partial dentures, when preparation geometry is borderline.
  • NOT recommended for all ceramic crowns, onlays or veneers.
  • Questionable for post cementation.
39
Q

Which cement is used for temporary cementation?

A

Zinc Oxide – Eugenol

40
Q

Which are the characteristics of Zinc Oxide – Eugenol?

A
  • No pulp irritation.
  • Long use as temporary cements.
  • Attempts were made to improve for long term use but do not perfume well clinically.

Fixed Prosthodontics I (12 decks)

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