Dental Materials and Impression Techniques Quiz

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Questions and Answers

Which material's accuracy is improved with a higher bulk of material, unlike elastomeric materials?

Polyether

Alginate

Agar-agar (correct)

Polysulfide

What is the primary component of irreversible hydrocolloids?

Lead dioxide

Polysulfide

Unsaturated polyether

Soluble salt of alginic acid (correct)

What is a disadvantage of using polysulfide impression material?

Fast setting time

Low cost compared to other elastomeric materials

High tear resistance

Shrinkage due to water byproduct (correct)

What is the primary reason for immediate pouring of alginate impressions?

To prevent distortion (B) Signup and view all the answers

Which of the following materials is known for having 'snap set' property?

Polyether (D) Signup and view all the answers

Which material has a characteristic brown color due to lead dioxide?

Polysulfide (C) Signup and view all the answers

What is the main disadvantage of polyether impression material related to moisture?

It absorbs moisture from the air and swells (B) Signup and view all the answers

For what is alginate mainly used for?

To make study models (B) Signup and view all the answers

Which impression material is primarily associated with removable prosthodontics?

Hydrocolloids (A) Signup and view all the answers

What distinguishes reversible hydrocolloids (agar) from irreversible hydrocolloids (alginate)?

Reversible hydrocolloids can be reused by heating the material, whereas irreversible hydrocolloids cannot. (C) Signup and view all the answers

Which of the following is a key characteristic of addition silicone?

It is a type of synthetic elastomer used for crown and bridge impressions. (D) Signup and view all the answers

What is the primary by-product released during the setting reaction of condensation silicone?

Ethyl alcohol (D) Signup and view all the answers

Which of the following materials is categorized as a non-elastic impression material?

Impression waxes (D) Signup and view all the answers

Which of these was introduced to dentistry first?

Reversible hydrocolloids (C) Signup and view all the answers

Which of the following impression materials has the lowest polymerization shrinkage?

Addition silicone (A) Signup and view all the answers

When using condensation silicone, what is the recommended time frame for pouring the impression with gypsum to avoid dimensional changes?

Within 1 hour (B) Signup and view all the answers

Which of the following is a disadvantage of using reversible hydrocolloids?

They require a bulky cooling apparatus and have a long setting time. (B) Signup and view all the answers

What material is known for causing pitting in stone casts when used in impression making?

Addition silicone (C) Signup and view all the answers

What is the primary reason that immediate pouring is required when using reversible hydrocolloids?

To avoid distortion of the impression. (B) Signup and view all the answers

What effect does cooling have on the working and setting time of addition silicone?

It increases working and setting time by 25% (C) Signup and view all the answers

Which of the following is a type of silicone impression material?

Condensation silicone (D) Signup and view all the answers

Which impression material is considered the material of choice for fixed work impressions?

Addition silicone (A) Signup and view all the answers

Which of these impression material requires a dry field to perform well?

Condensation silicone (A) Signup and view all the answers

What substance found in some gloves can hinder the polymerization of addition silicone?

Latex (B) Signup and view all the answers

Which material is commonly used for custom-made impression trays?

Cold or light-cured acrylic (B) Signup and view all the answers

How are custom-made impression trays adjusted?

With an acrylic bur (B) Signup and view all the answers

In the two-stage impression technique, what is the purpose of the heavy body material (putty)?

To modify the stock tray into a close-fitting tray (A) Signup and view all the answers

What is the next step after selecting the stock tray and verifying it intraorally in the two-stage impression?

Applying the tray adhesive (C) Signup and view all the answers

Why is it important to avoid overfilling the tray with heavy body material?

It could expand the tray walls and cause rebound (B) Signup and view all the answers

Which of these is NOT a step to prepare the heavy body impression after removal from the mouth?

Polishing the impression (D) Signup and view all the answers

What is the purpose of creating venting channels in the heavy body impression?

To allow excess light body material to escape (C) Signup and view all the answers

Which of the following is NOT a common impression technique?

Three-stage technique (triple mix) (B) Signup and view all the answers

What is the primary purpose of using a polyethylene sheet in a two-stage impression technique?

To act as a separator and create space for the light body material, avoiding the need for trimming (D) Signup and view all the answers

In a two-stage impression technique, what should be done to the first impression before applying the light body material?

Dry it thoroughly to ensure optimal adhesion between the two materials (D) Signup and view all the answers

Why is it important to inject light body material into the indentations of all teeth in a two-stage impression?

To ensure the impression accurately captures the morphology of all teeth (D) Signup and view all the answers

What is critical to avoid distortion when removing an impression from the mouth?

Applying pressure on the border of the tray away from the teeth from one side then the other (C) Signup and view all the answers

What is a key advantage of the one-stage impression technique compared to the two-stage technique?

It is less time-consuming because the dentist can take the whole impression in one step (A) Signup and view all the answers

For a one-stage impression technique, when is the retraction cord removed?

Just before taking the impression (as a single shot) (D) Signup and view all the answers

In a monophase impression technique, which type of material is typically used?

Medium body material only (A) Signup and view all the answers

What is a critical step when seating any impression tray intraorally?

Gently seat the tray and hold it stable until it sets (D) Signup and view all the answers

What is the minimum uninterrupted cuff of impression material that should be present beyond the finish line?

1 mm (A) Signup and view all the answers

In a two-stage impression technique, what is a potential consequence of the light body not covering the entire impression and improper seating?

An inaccurate master model which will lead to an inaccurate final prosthesis (D) Signup and view all the answers

What is a common cause of horizontal crease lines in a one-stage impression technique?

Improper blending of the putty and wash, or the wash setting on prepared teeth before tray insertion (C) Signup and view all the answers

What causes shiny mesial margin of preparation on a dental impression?

Poor moisture control (A) Signup and view all the answers

Why is it important to extrude a small amount of light body material outside the tip before injecting it into the preparation?

To remove any air bubbles in the tip, preventing voids in the impression (B) Signup and view all the answers

What is a primary cause of impression tearing?

Removing the tray before the material has fully set, or inadequate retraction (D) Signup and view all the answers

What causes drag marks in impression procedures?

Delay in inserting the tray after loading with impression material (B) Signup and view all the answers

What can cause tray separation during an impression procedure?

Inadequate application of tray adhesive, or excessive force during tray removal (A) Signup and view all the answers

Study Notes

Impression Making Part 2

Impression materials are categorized as non-elastic, elastic, and non-elastic.
Non-elastic materials are primarily used for removable dental prosthetics. Hydrocolloids, like reversible (Agar) and irreversible (Alginate), are examples. Addition silicone is common for crown and bridge impressions.
Elastic materials include hydrocolloids (reversible and irreversible), synthetic elastomers (polysulphides, polyether, silicones), and condensation and addition silicone.
Reversible hydrocolloids, introduced in 1925, are made of agar, borax, and water. The material can be reversed and reused by heating it. initial cost is for the apparatus and water-cooled impression trays needed. Patients may find this type less comfortable due to the bulky cooling apparatus and long setting time. Immediate pouring is necessary to avoid distortion. The material is fluid which allows for fine detail but it is low in tear resistance. Agar-agar is liquid between 50-100°C, turning to gel below 50°C.
Irreversible hydrocolloids were introduced in 1941, made of soluble salt of alginic acid. This produces a calcium alginate gel. Flavors are often added to make them more palatable to patients. They are cheaper than elastomers, but easily distorted and have low tear resistance. They are mainly used to make study models and Cr&Br, only for the opposing arch.

Impression Materials: Elastic Materials

Polysulphides: Introduced in the 1950s, made of polysulfide, sulfur, and lead dioxide. This gives it a brown color. It has an unpleasant odor but is the least expensive type of elastomer. Reactions produce water as a byproduct which causes shrinkage (0.5% - 1.5%). It has a long setting time (around 10 minutes) and should be poured within 1 hour to reduce distortion. The less volume, the more accurate the impression.
Polyether: Introduced in the 1960s. It's made of unsaturated polyether, plasticizer, and filler. Setting time is 3-6 minutes. It's costly but does not produce byproducts. It can absorb moisture from the air and swell. For this reason, it needs to be poured within 1 hour. It features high accuracy and tear resistance, but also has a bitter taste.
Silicones: First silicone impression materials were introduced in the 1950s. Two types exist: condensation and addition silicone. Condensation silicone (lab putty): used for making copies of dentures. It is hydrophobic and needs a dry field. It is more difficult to pour with gypsum stone. The pouring needs to be done within one hour, using a surfactant. Good tear resistance and excellent elastic recovery/detail reproduction. Must be mixed with gloves. Addition Silicone (PVS): introduced in the 1970s, also known as polyvinyl siloxane. It is made from silicone polymer, filler, and cross-linking agent(s), and activator. It's more expensive than condensation silicone but is dimensionally stable. Setting time is 4-6 minutes (variable). Less affected by temperature and humidity. Polymerization shrinkage is 0.3%-0.6%, and additional setting time is possible. It produces Ethyl alcohol.

Impression Making: Tray Selection

Stock trays are low-cost and readily available. They feature larger quantities, potentially rigid or partially rigid materials (e.g., metal, plastic), and generally standard sizes. They are difficult to adapt.
Custom trays take longer to create but are more tailored to individual patients' needs. Fabrication needs laboratory procedures, smaller quantities, and are rigid acrylic materials. They are adjustable with acrylic burs and sizes are tailored to the patient's specific primary cast.

Impression Techniques

Two-stage technique: Putty and wash
One-stage technique: Double mix.
Monophase technique: Single mix.

Two-Stage Technique

The putty is used to modify the stock tray into a close fitting one.
The next step is using a lighter and more flowable wash material. The wash material is placed inside the tray and re-seated in the mouth. This technique is also referred to as putty and wash.
Steps: select and verify the stock tray intraorally, apply tray adhesive to the tray, isolate prepared teeth, and apply retraction cord, mix equal amounts of base and catalyst of the heavy body, mix into a homogenous color, form a cylinder shape, place this cylinder in the tray. Avoid overfilling. Seat intraorally and hold still until fully polymerized. Once set remove from the mouth. Trim excess material with a blade. Create venting channels, use a straight, low-handpiece to remove undercuts, and test the tray intraorally to confirm easy reseating. Variations include using polyethylene as a spacer or taking the first impression prior to tooth preparation.
Steps for two stage technique include checking the stock tray intraorally, and applying tray adhesive, isolating prepared teeth, and applying retraction cord, mixing heavy body material, forming a cylinder shape, placing it in the tray, avoiding overfilling, seating intraorally, holding, removing from mouth, trimming excess material, creating venting channels, using a handpiece to remove undercuts, checking tray reseating. Options are using a spacer and taking an initial impression before tooth prep.

One-Stage Technique

Both heavy and light body impression materials are in the tray.
Retraction cord is removed just prior to taking the impression as a single shot impression.
This technique is faster than the two-stage process and can be used with custom or stock trays.
Steps for one-stage technique include tray selection, applying tray adhesive, mixing heavy and light body materials, injecting light body over prepared teeth while the assistant loads the tray with heavy body, gently seats the tray, holds until set, and inspects for accuracy.

Monophase Technique

One material (medium body) is used for a one-step impression.
Custom made trays are used.
Impression is seated and held until fully set.
Accuracy is checked after removal.

Acceptable Impression Features

Continuous finish line reproduction without gingival interference.
Absence of tears, voids, or bubbles.
At least 1 mm of uninterrupted cuff of material beyond the finish line.
No mixing streaks.
No gap between the impression and the tray.
No exposure of the tray surface.

Errors

Two-Stage Technique: Light body failure to cover the entire impression during seating can result in an imperfect master model, leading to inaccurate occlusal final prosthesis.
One-Stage Technique: Poor blending of putty and wash materials can lead to horizontal crease lines. This is sometimes caused by differences in viscosity between the heavy and light putty, or improper setting time of the wash on the prepared teeth. Failure to seat the impression properly and improper injection technique of the light body can lead to a poor result.
General: Inadequate moisture control resulting in shiny mesial prep margins, improper injection of light body resulting in voids, insufficient retraction cord or premature tray removal before material sets, drag marks in undercut areas, or tray separation from adhesive application or excessive pressure during removal.

Disinfection

Rinse dental impressions under running water to remove debris.
Immerse in the appropriate disinfectant for the manufacturer's recommended time.
Avoid spray disinfectants; they reduce disinfection effectiveness and can cause inhalation hazards.
Rinse impressions before sending to the lab.
Alginate and polyether impressions can be temporarily covered in damp gauze. Elastomeric impressions can be immersed in the disinfectant solution. Many disinfectants are available commercially (e.g., chlorine, chlorhexidine, glutaraldehyde, phenolics).

References

Contemporary Fixed Prosthodontics by Rosentiel, Land, and Fujimoto (chapter 14).

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Description

Test your knowledge on dental materials and their properties with this quiz. Questions cover various impression materials, their applications, and characteristics. Perfect for students in dental hygiene or prosthodontics courses.