Dental Luting cements Flashcards
(43 cards)
What are the uses of dental cements?
Luting agent (short and long term cements)
Pulp protection or cavity sealing (Cavity varnish, liner, and base)
Filling (temporary or permanent)
Others (Root canal sealer, calcium hydroxide cement, and bite registration material)
What are the general requirements for luting cements?
Biocompatibility
Retention
High tensile strength, fracture toughness, fatigue strength
Good marginal seal
Low film thickness
Ease of use
Radiopacity
Aesthetics
What are the types of conventional cements?
Zinc phsophate cement
Zinc oxide-eugenol cement
Polycarboxylate cement
Glass Ionomer cement
What are the types of resin-base cements?
Resin cement
Resin modified glass ionomer cement
What is film thickness?
Thickness of film between 2 flat surfaces
What is the maximum allowable thickness?
25 µm
Low film thickness is preferred
What is zinc phosphate cement made up of?
Typically a powder/liquid system
Liquid is an acid (phosphoric acid), water, and aluminum phosphate
Powder is a base that is insoluble in oral fluid made up of zinc oxide and magnesium oxide
Acid-base reaction and micromechanical retention does the job.
What is the setting reaction for zinc phosphate cement?
Zinc aluminophosphate gel matrix is formed with unreacted zinc oxide dispersed in the matrix.
Reaction is exothermic adding water to it can accelerate it and losing water can lengthen time for setting.
How long is the working and setting time for zinc phosphate cement?
Working time is 3 - 6 minutes
Setting time is 5 - 9 minutes
This depends on manufacturer instruction.
How can setting time of zinc phosphate be made longer?
Reducing the powder/liquid ratio
Mixing on the cool glass slab
Mixing over a large area
Mixing cements in increments
How is zinc phosphate cement mixed?
3 steps:
First: Add small amount of powder into the liquid to achieve slow neutralization of the liquid and to control the reaction.
Second: Larger amount of powder is added to the liquid for further saturation of liquid to newly form zinc phsophate.
Finally: Small amount of powder is added again to control the optimum consistency
What are the ADA specifications for zinc phosphate cement?
Setting time at 37 degrees: 5 - 9 minutes
Minimum compressive strength: 75 MPa
Maximum film thickness: 25 µm (for luting prostheses)
Maximum solubility: 0.2% by weight
How are the following variables affected by Decreased powder/liquid ratio:
Compressive strength
Film thickness
Solubility
Initial acidity
Setting time
Compressive strength: Decreases
Film thickness: decrease
Solubility: Increases
Initial acidity: Increases
Setting time: Increases
How are the following variables affected by increased rate of powder incorporation:
Compressive strength
Film thickness
Solubility
Initial acidity
Setting time
Compressive strength: Decreases
Film thickness: increase
Solubility: Increases
Initial acidity: Increases
Setting time: decreases
How are the following variables affected by increased mixing temperature:
Compressive strength
Film thickness
Solubility
Initial acidity
Setting time
Compressive strength: Decreases
Film thickness: increase
Solubility: Increases
Initial acidity: Increases
Setting time: decreases
How are the following variables affected by water contamination:
Compressive strength
Film thickness
Solubility
Initial acidity
Setting time
Compressive strength: Decreases
Film thickness: increase
Solubility: Increases
Initial acidity: Increases
Setting time: decreases
What is the biocompatibility of zinc phosphate luting cement like?
Acid can penetrate into the dentinal tubule and irritate the pulp.
(pH of liquid is 2 and 3 minutes after mixing 4.2, 1 hour 6, 48 hours 7)
How can zinc phosphate be modified?
Stannous fluoride can be added but this leads to higher solubility and lower strength
Zinc silicophosphate is created from addign silicate. this leads to higher strength and lower solubility and fluoride can be released and this can create better translucency.
What are zinc oxide-eugenol cements used for?
It has a lower strength than zinc phosphate cement.
Usually used as a temporary filling.
What are the types of ZnO Eugenol cements?
Simple ZOE
Reinforced ZOE
EBA cement
What is the composition of simple ZOE?
Powder:
ZnO
Rosin: Reduces the brittleness of the set cement
Zinc stearate: Plasticizer
Zinc acetate Improve strength
Liquid:
Eugenol and olive oil
What is the setting reaction for zinc eugenol cement?
First reaction: ZnO + Eugenol -> Zn(OH)2
Second reaction: Zn(OH)2 + 2HE -> ZnE2 + H2O
What does water do to the setting reaction of zinc eugenol?
It accelerates the reaction
Zinc eugenolate is easily hydrolized by moisture
How is zinc oxide eugenol manipulated?
Paste/paste: Mix 2 equal pastes together until it obtains the homogenous colour
Powder/liquid: Usually 4/1 for maximum strength. Mix the large increment first. (Cool slab not required)
