38 Questions
What is the purpose of using non-eugenol containing paste?
To reduce irritation
What is the function of potassium sulfate in impression materials?
To accelerate the setting reaction
Which impression material is commonly used for making primary casts?
Impression plaster
Why is it necessary to pour the impressions immediately?
To prevent distortion of the impression
What type of impression material is used for border molding?
Impression compound
What is the characteristic of zinc oxide pastes?
Low thermal conductivity
What is the main advantage of using β CaSO₄.½ H₂O over ᾁ-hemihydrate in impression plaster?
It requires a lower water-to-powder ratio, reducing the exothermic heat.
What is the purpose of using Zincoxide and Eugenol (ZnO/E) in impression materials?
To make the material more rigid and non-elastic.
What is the composition of impression plaster?
β CaSO₄.½ H₂O
What is the primary use of impression plaster in dentistry?
To make secondary impressions for edentulous patients without bony undercuts.
What is the setting time of impression plaster?
5 minutes
Why is a separating medium required when using impression plaster?
To prevent the material from sticking to the cast.
What is the dimensional stability of impression plaster?
0.06% change on setting
What type of tray is recommended for use with impression plaster?
Acrylic tray
What is the main reason for the dry mouth sensation during impression taking?
The impression compound absorbs water
What is the characteristic of Type I Impression Compound?
It is a low-fusing impression compound
What is the purpose of adding a plasticizer to the impression compound?
To decrease brittleness
What is the primary role of inert oil in the Zinc Oxide Eugenol impression material?
To increase the fluidity of the paste
What is the essential component for the hydrolysis of Zinc Oxide to its hydroxide?
Moisture
What happens to the impression compound when it is heated to 45-55°C?
It softens
What is the result of the reaction between Zinc Oxide and Eugenol?
Zinc Eugenolate
What is the purpose of kneading the impression compound outside the water bath?
To avoid leaching out of constituents
Why is it necessary to allow time for cooling during impression taking?
To reduce plastic flow and distortion on removal
What is the effect of adding a drop of water to the Zinc Oxide Eugenol mixture?
Speeds up the setting reaction
What is the characteristic of Type II Impression Compound?
It is a high-fusing impression compound
What is a disadvantage of impression compound?
It has poor thermal conductivity
Why is Type II Impression Compound used as a tray material?
It is sufficiently rigid and has less flow
What is the characteristic of the Zinc Oxide Eugenol impression material that makes it suitable for edentulous patients?
Rigidity
What is the purpose of applying Vaseline paste to the skin around the lips before taking an impression?
To prevent the material from adhering to the skin
What is the characteristic of the Zinc Oxide Eugenol impression material that allows it to accurately register surface details?
Sufficient flow
What is the advantage of using a cool glass slab for mixing the Zinc Oxide Eugenol pastes?
Slower setting reaction
Why should impression compound be poured within one hour?
To minimize distortion
What is a use of zinc oxide eugenol impression material?
Making secondary impressions for edentulous patients
What is a component of zinc oxide eugenol impression material?
Oil of gloves
What is a component of the base paste in zinc oxide eugenol impression material?
Zinc oxide powder
What is a use of sheets of impression compound?
For making special trays
What is a characteristic of impression compound?
High shrinkage on removal from the oral cavity
What is the purpose of the catalyst reactor paste in zinc oxide eugenol impression material?
To act as an accelerator
Study Notes
Zinc Oxide Pastes
- Used for making impressions for edentulous patients
- Can be used as a surgical pack in periodontal treatments, temporary filling material, surgical pack in dental surgeries, insulating base in deep cavities, temporary relining of dentures, and root-canal filling material
- Can be used for occlusal bite registration
- Require a non-eugenol containing paste in case of eugenol sensitivity
- Where ZnO reacts with carboxylic acid instead of eugenol oil
Properties of Zinc Oxide Pastes
- Rigid material, cannot record undercut areas
- Adheres to acrylic tray material, no need for adhesive
- Adheres to skin around lips, requires Vaseline paste protection
- No separating medium required before pouring the cast material
- Sufficient flow, accurate registration of surface details
- Most dimensionally stable rigid impression material (less than 0.1% shrinkage on hardening)
Manipulation and Setting Reaction of Zinc Oxide Pastes
- Equal lengths of each paste mixed on a glass slab or oil-resistant paper pad
- Mixing time: 1 minute
- Factors controlling setting time: drop of water, high temperature and humidity, smaller particle size of Zinc-oxide powder, prolonged mixing of both pastes, drop of oil, and cool glass slab for mixing
- Setting reaction: chelation reaction
Impression Plaster
- Used to make secondary impressions for edentulous patients without bony undercut
- Powder mixed with water in a rubber bowl, low viscosity and high flow
- Hydrophilic, good adaptation to soft tissues, perfect recording of fine details
- Setting time: 5 minutes, rigid after setting, cannot record undercut areas
- Very good dimensional stability (0.06% change on setting)
- Should be used in acrylic special tray (1.5 spacer)
- Requires separating medium
Impression Compound
- Definition: rigid impression material that sets by a physical reaction, reversible, and thermoplastic
- Composition: natural resin and waxes, plasticizer, filler, and coloring agent
- Types: Type I (Low-fusing Impression Compound) and Type II (Tray Compound)
- Manipulation: sheets inserted in hot water bath, kneaded outside water bath to avoid leaching out of constituents
- Setting mechanism: physical process, reversible, changes its physical state by temperature change
- Properties: rigid impression material, muco-compressive, high viscosity and low flow, poor thermal conductivity, and poor dimensional stability
- Advantages: can be reused several times to correct mistakes and inaccuracies during impression taking
This quiz tests your knowledge of dental materials, their properties, and various uses in dentistry. Identify the correct uses of different materials in dental treatments.
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