L6: Luting cements for fixed prosthodontics Flashcards
Which are the three primary factors influencing potential dislodgment?
- Design of the tooth preparation.
- Fit of the casting
- The nature of the cement.
What is defined as cement?
- 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
What is defined as cementation?
- the process of attaching parts by means of cement;
- attaching a restoration to natural teeth by means of a cement (GPT-4)
What does retention prevent?
Retention prevents removal of the restoration along the path of insertion or the long axis of the tooth preparation.
What does resistance prevent?
Resistance prevents dislodgment of the restoration by forces directed in an apical direction and prevents any movement of the restoration under occlusal forces.
What must a dental cement be used to act as?
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.
What can bonding mechanism be divided in?
- Non-adhesive luting
- Micromechanical bonding
- Molecular Adhesion
Which are the ideal properties of luting cements for fixed prosthodontics?
- 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.
What kind of reaction occurs in zinc-phosphate cement?
Acid-base reaction.
What is the reaction of zinc-phosphate cement initiated by?
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).
Which is the compressive strength of zinc-phosphate?
Compressive strength to (80 -100 MPa).
Which is the tensile strength of zinc phosphate cement?
Tensile strengths (5 to 7 MPa)
Which are the advantages of zinc phosphate cements?
- 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.
Which are the disadvantages of zinc phosphate cements?
- 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.
Which are the indications for zinc phosphate cements?
- 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).
Polycarboxylate cement: Reaction
- 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.
Polycarboxylate cement:
Compressive strength:
Tensile strengths:
- Compressive strength to (55-85 MPa)
- Tensile strengths (8-12 MPa)
Polycarboxylate cement
Advantages:
- Better adhesion to dentin than Zinc Phosphate.
- High tensile strength.
- Reasonable working time.
- Low irritation to the pulp.
Polycarboxylate cement
Disadvantages:
- Low compressive strength.
- Luck of adhesion to gold material.
- Difficult to mix.
- Powder/Liquid ratio and mixing technique very important for its material properties.
Polycarboxylate cements:
Indications:
- Single metal or porcelain fused to metal crowns in low stress areas.
- When minimum pulp irritation is desired.
Glass ionomer cement:
Reaction:
- 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)
Glass ionomer cement:
Compressive strength:
Tensile strength:
- Compressive strength to (127 MPa).
- Tensile strength (8 MPa).
GIC:
Advantages:
- Adhesion to tooth structures is comparable to Polycarboxylate.
- Biocompatible.
- Fluoride release (anticariogenic effect).
- Low film thickness.
- High compressive strength.
GIC:
Disadvantages:
- 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.
GIC:
Indications:
- Single metal or porcelain fused to metal crowns.
- Metal or porcelain fused to metal fixed partial dentures.
- Cementation of post (cast and prefabricated).
Resin luting cements:
What are resin luting cements?
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.
Resin luting cements:
Which are the categories of resin luting cements based on the polymerization?
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.
Which are the characteristics of resin luting cements?
- Different shade and opacity availability.
- Very good bonding to tooth structures.
Enamel etching/bonding:
Explain the mechanism.
- 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).
Dentin etching/bonding:
Explain the mechanism.
- 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).
What is smear layer?
- 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.
Resin luting cements:
Advantages:
- 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.
Resin luting cements:
Disadvantages:
- 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.
Resin luting cements:
Indications:
- 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.
Resin modified glass ionomer cement:
Mechanism.
- 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.
Resin modified glass ionomer cement:
Advantages:
- 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.
Resin modified glass ionomer cement:
Disadvantages:
Water absorption causes expansion and cracking of overlying ceramic.
RMGI:
Indications:
- 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.
Which cement is used for temporary cementation?
Zinc Oxide – Eugenol
Which are the characteristics of Zinc Oxide – Eugenol?
- No pulp irritation.
- Long use as temporary cements.
- Attempts were made to improve for long term use but do not perfume well clinically.
