L6: Luting cements for fixed prosthodontics Flashcards
(40 cards)
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.
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
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)
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.
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.
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.
7
Q
What can bonding mechanism be divided in?
A
- Non-adhesive luting
- Micromechanical bonding
- Molecular Adhesion
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.
9
Q
What kind of reaction occurs in zinc-phosphate cement?
A
Acid-base reaction.
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).
11
Q
Which is the compressive strength of zinc-phosphate?
A
Compressive strength to (80 -100 MPa).
12
Q
Which is the tensile strength of zinc phosphate cement?
A
Tensile strengths (5 to 7 MPa)
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.
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.
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).
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.
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
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).
26
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.
27
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.
28
Which are the characteristics of resin luting cements?
* Different shade and opacity availability.
* Very good bonding to tooth structures.
29
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).
30
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).
31
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._**
32
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.
33
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.
34
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.
35
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.
36
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.
37
Resin modified glass ionomer cement:
Disadvantages:
Water absorption causes expansion and cracking of overlying ceramic.
38
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.
39
Which cement is used for temporary cementation?
Zinc Oxide – Eugenol
40
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.
