Dental Materials: Hydrocolloid and Alginate Quiz

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Questions and Answers

What is the primary reason elastomeric impression materials are preferred over hydrocolloid materials?

Lower cost

Easier mixing

Greater accuracy (correct)

Wider availability

Which of the following types of elastomeric impression materials is NOT categorized according to ISO classifications?

Heavy-bodied

Extra-low

Flexible (correct)

Putty

What distinguishes the static automixing method from hand mixing?

Base and catalyst are in separate cylinders (correct)

It requires mechanical mixing

It involves using equal lengths of materials

It produces air-bubbles

Which of the following is a disadvantage of using a dynamic mechanical mixer?

Higher cost compared to other mixing methods Signup and view all the answers

What is the primary purpose of the putty-wash technique in impression making?

To combine two different viscosities Signup and view all the answers

Which mixing method ensures a uniform mix with no air-bubbles?

Static automixing Signup and view all the answers

In the context of elastomeric materials, what is the significance of filler content?

It determines material viscosity and handling characteristics Signup and view all the answers

Which technique is described as utilizing a simultaneous application of low and high viscosity materials?

Simultaneous dual-viscosity technique Signup and view all the answers

What is the primary purpose of using low viscosity material in dental impressions?

To fill the critical areas accurately Signup and view all the answers

Which material consistency is used mainly in the tray for dental impressions?

High viscosity Signup and view all the answers

What is a key characteristic of pseudoplastic materials in dental applications?

Decreased viscosity when subjected to high shear rates Signup and view all the answers

What is the initial step in the putty-wash technique for taking dental impressions?

Creating a preliminary impression with putty-consistency material Signup and view all the answers

In addition silicone impression materials, what is the role of the chloroplatinic acid catalyst?

To facilitate the polymerization reaction Signup and view all the answers

What happens if hydroxyl groups are present in addition silicone materials?

They can produce bubbles in gypsum casts Signup and view all the answers

What is the primary reason for dimensional change during the setting of addition silicones and polyether materials?

Cross-linking and bond rearrangement Signup and view all the answers

What is the elastic recovery percentage for epoxy dies?

99.8% Signup and view all the answers

Why is it recommended to wait at least 30 minutes after taking an addition silicone impression before pouring gypsum?

To allow adequate time for dimensional stability Signup and view all the answers

What is the major disadvantage of traditional impression materials compared to addition silicone?

Formation of volatile by-products during setting Signup and view all the answers

Which characteristic is NOT associated with addition silicone impression materials?

Low elastic recovery Signup and view all the answers

How much dimensional change occurs in addition silicones after 24 hours?

-0.1% Signup and view all the answers

What should be done with an impression before pouring an epoxy die?

It should stand overnight Signup and view all the answers

Polyether impression materials have a setting reaction mechanism that involves which type of polymerization?

Cationic addition polymerization Signup and view all the answers

What is the compatibility of addition silicones with gypsum products?

They are hydrophilic with contact angles of about 20° to 40° Signup and view all the answers

Which type of product allows for immediate pouring of impressions?

Addition silicones with hydrogen absorber Signup and view all the answers

In which state must hydrocolloid be inserted in the mouth to accurately catch intraoral details?

Fluid state Signup and view all the answers

What is the process called that occurs when alginate hydrocolloid sets?

Crosslinking Signup and view all the answers

What is an important reason to wear a mask when handling alginate powder?

To prevent inhalation of airborne particles Signup and view all the answers

What type of alginate has had modifications to reduce dust exposure?

Dustless alginate Signup and view all the answers

Which temperature range is recommended for the water used in alginate dispensing?

22° to 23° C Signup and view all the answers

What component of alginate is primarily responsible for its structure?

Alginic acid Signup and view all the answers

What is the suitable method for loading alginate into the impression tray?

Add in layers from posterior to anterior Signup and view all the answers

What should be done to minimize permanent deformation when removing alginate impressions?

Remove with a sharp rapid snap Signup and view all the answers

What is the primary function of the catalyst in polysulfide impression materials?

To cause the mercaptan groups to chemically react. Signup and view all the answers

What effect does shear force have on the viscosity of polyether impression materials?

It causes the triglyceride network to align and lowers viscosity. Signup and view all the answers

What type of polymerization occurs in polysulfide impression materials?

Condensation polymerization with water as a by-product. Signup and view all the answers

Which component in the base paste of condensation silicone impression materials contributes to the formation of a cross-linked structure?

Alkyl silicate. Signup and view all the answers

How much do polysulfide impression materials typically shrink within the first 24 hours?

0.3% to 0.4% Signup and view all the answers

What is the main characteristic of condensation silicone impression materials regarding permanent deformation?

It maintains low values of permanent deformation. Signup and view all the answers

What is the impact of preparing models or dies 30 minutes after removal of polysulfide impression materials?

Increases accuracy significantly. Signup and view all the answers

Which of the following statements about polyether impression materials is NOT true?

They can only be mixed using a static mixer. Signup and view all the answers

Study Notes

Hydrocolloid Impression Materials

Hydrocolloid impression material must be placed in the mouth in a fluid state to capture intraoral detail accurately.
It must be left in the mouth long enough to become elastic to allow for removal without distortion.

Alginate

Alginate is an irreversible hydrocolloid.
Silicosis and pulmonary hypersensitivity can occur if inhaling alginate dust when handling the material.
“Dustless” alginate is available to prevent the release of airborne particles.
The setting reaction of alginate involves crosslinking of alginic acid molecules with calcium ions.
Alginic acid is extracted from brown seaweed.
Alginate is a linear copolymer made up of β-D-mannuronic acid and α-L-guluronic acid.

Dispensing Alginate

Water temperature should be between 22° and 23°C during alginate mixing.
Use a full scoop of powder, avoiding voids.
Remove excess powder with a spatula before mixing completely.
Alginate is the most flexible elastic impression material.
Alginate should be snapped quickly out of the mouth to minimise permanent deformation.

Factors Impacting Alginate Impression Quality

Consistency of the alginate mixture and removal time influence impression tear strength.

Elastomeric Impression Materials

Elastomeric impression materials dominate the market due to their greater accuracy, dimensional stability with time, and ability to record detail compared to hydrocolloid materials.
Common elastomeric materials: addition silicones and polyethers.

Viscosity of Elastomeric Impression Materials

Extra low, low, medium, heavy, and putty are the categories for elastomeric impression materials based on viscosity.
Putty consistency is only available for condensation and addition silicones based on filler content.
ISO classification:
- Type 0: putty
- Type 1: heavy
- Type 2: medium
- Type 3: light

Mixing Techniques for Elastomeric Impression Materials

1. Hand mixing:
- Materials are dispensed in equal lengths onto a mixing pad.
- Catalyst paste is spread over the base paste, mixing until a uniform colour is reached.
2. Static Automixing:
- Materials are stored in separate cylinders of a plastic cartridge.
- Used primarily for heavier materials.
- No mechanical mixing needed.
- Uniform mixing with no air bubbles.
3. Dynamic Mechanical Mixer:
- More expensive than hand and static mixing methods.
- Enables ease of use, speed, and good mix quality.
- Collapsible plastic bags placed in a cartridge.
- Motor driven mixer forces materials through a mixing tip and into a tray or syringe.

Impression Techniques

Three common methods for fixed restorations include:
- 1. Simultaneous, Dual-Viscosity Technique:
  - Low and high viscosity impression material mixes at the same time.
  - Low viscosity is injected onto prepared teeth.
  - High viscosity is placed in the tray.
  - Tray is then placed in the mouth.
- 2. Single-Viscosity or Monophase Technique:
  - Uses a medium-viscosity impression material.
  - Pseudoplastic materials, like addition silicon and polyethers, exhibit decreasing viscosity under high shear rate (shear thinning property).
- 3. Putty-Wash Technique:
  - A two-step impression procedure.
  - A preliminary impression is made with a high- or putty-consistency material before tooth preparation.
  - After preparation, a low-consistency material is syringed into the area and the preliminary impression is reinserted.

Addition Silicone Impression Materials

Also known as vinyl polysiloxanes (VPS).
Supplied as a two-paste or a two-putty system.
One paste contains silicone with vinyl groups, reinforcing filler, and a chloroplatinic acid catalyst.
The other contains silicone with silane hydrogens and reinforcing filler.
Setting occurs through addition polymerization reaction, which does not produce volatile byproducts.
Minimal dimensional change occurs during setting.
If hydroxyl groups are present, hydrogen gas can form.
It is recommended to wait at least 30 minutes before pouring models or dies to allow for complete setting and minimize the risk of bubbles caused by hydrogen gas.
Some products contain hydrogen absorbers, such as palladium, allowing for immediate pouring.
Properties:
- Low dimensional change in 24 hours.
- High elastic recovery (~99.8%).
- High tear strength compared to hydrocolloids.
- Viscoelastic.

Polyether Impression Materials

Similar properties to addition silicones.
The polyether polymer is hydrophilic and exhibits good wetting.
Setting reaction: Cationic addition polymerisation by opening of the reactive terminal rings.
Triglyceride network in polyethers enables shear thinning properties, reducing viscosity under pressure (like syringe use).
Available as:
- Cartridge with a mixing gun.
- Sausage that fits into a dynamic mechanical mixer.

Polysulfide Impression Materials

Supplied as two pastes: one labeled as catalyst or accelerator and the other as base.
Base contains a low-molecular weight organic polymer with mercaptan groups, and reinforcing agents.
Catalyst contains lead dioxide, filler, plasticizer, and oleic or stearic acid to control setting speed.
Three viscosities: light, regular, and heavy.
Setting reaction is condensation polymerization, producing water as a byproduct.
Good elastic recovery (97-98%).
Shrinkage of 0.3% to 0.4% in the first 24 hours.
It is recommended to pour models or dies within 30 minutes of removal to maximize accuracy.
Long delays should be avoided.
Electroplating is possible with polysulfide materials.
Lead-free polysulfide materials are available.
Highest tear strength among impression materials.

Condensation Silicone Impression Materials

Used as an accurate duplicating material in dental laboratory.
Base paste contains a silicone liquid with hydroxyl groups and reinforcing agents (silica).
Accelerator consists of tin organic ester suspension and alkyl silicate.
Setting occurs through condensation polymerization with water as a byproduct.
Hydrophobic.

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Description

Test your knowledge on hydrocolloid impression materials, focusing on alginate's properties, handling precautions, and preparation techniques. This quiz covers essential information for dental students and professionals dealing with impression materials.