Impression Tray Functions and Characteristics

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Questions and Answers

What is the primary function of an impression tray?

To maintain occlusal contacts during the procedure

To carry, confine, and control the impression material (correct)

To facilitate the dentist's practice techniques

To provide an aesthetic shape to the dental arch

Which characteristic is true about stock trays?

They can only be made from plastic material

They are available in standardized sizes and shapes (correct)

They provide a precise fit for every patient

They are always customizable for individual patient needs

What is the minimum recommended clearance between the impression tray and patient's tissues?

1-2 mm

Above 10 mm

3-5 mm (correct)

5-10 mm

What will likely happen if the impression tray is too large?

It will distort the tissues and dimensions of the sulcus Signup and view all the answers

What is a distinguishing feature of dentate trays compared to other types of trays?

They are deeper and box-shaped Signup and view all the answers

What is one primary objective of impression making?

To capture all denture-bearing surfaces and tissues Signup and view all the answers

How does retention in denture making primarily occur?

Via the peripheral seal Signup and view all the answers

Why is support important when making dentures?

To distribute masticatory forces and prevent trauma Signup and view all the answers

What is a key purpose of preliminary impressions?

To create diagnostic casts for treatment planning Signup and view all the answers

In what phase of denture treatment are preliminary impressions typically used?

In the initial phase for study models Signup and view all the answers

What do accurate impressions ensure regarding the denture's stability?

They prevent horizontal or rotational movements Signup and view all the answers

What aspect of a patient's oral anatomy can preliminary impressions provide information about?

Ridge shape and undercuts Signup and view all the answers

What is the significance of creating custom trays in denture treatment?

They are adaptable to a patient’s specific oral anatomy Signup and view all the answers

What is a disadvantage of stock trays?

They may distort jaw tissues. Signup and view all the answers

What function do retention perforations serve in impression trays?

Facilitate better adhesion of impression material. Signup and view all the answers

Why are custom trays preferred over stock trays?

They offer a better fit and accuracy. Signup and view all the answers

Which material is NOT commonly used for preliminary impressions?

Gypsum Signup and view all the answers

What characteristic of alginate makes it suitable for preliminary impressions?

It is cost-effective and easy to manipulate. Signup and view all the answers

What is a disadvantage associated with the use of custom trays?

They are time-consuming to fabricate. Signup and view all the answers

What is one benefit of using light cured acrylic in custom trays?

It enhances the accuracy of impressions. Signup and view all the answers

How do custom trays aid in the impression process?

By allowing uniform distribution of the impression material. Signup and view all the answers

Which impression technique is specifically designed to record tissues in their non-displaced, resting position?

Mucostatic Signup and view all the answers

What characterizes the mucocompressive impression technique?

Records tissues under functional pressure Signup and view all the answers

Which statement about selective pressure technique is correct?

It enhances retention and comfort by balancing compression and relief. Signup and view all the answers

How does increasing the space between the tray and the tissues affect pressure during an impression?

Allows for mucostatic recording Signup and view all the answers

What is one common cause of under-extended impressions?

Tray not covering the entire denture-bearing area Signup and view all the answers

Which method could NOT be used to reduce pressure during an impression?

Increasing material viscosity Signup and view all the answers

What impression philosophy would be most beneficial for patients with fibrous tissues?

Mucostatic Signup and view all the answers

Which factor contributes least to the creation of a mucocompressive impression?

Type of impression tray used Signup and view all the answers

What is a major disadvantage of impression compounds?

It must be poured shortly after use to maintain dimensional stability. Signup and view all the answers

Which characteristic distinguishes polyvinyl siloxane putty consistency from impression compounds?

It has good dimensional stability. Signup and view all the answers

To take an ideal impression, which concept is NOT recommended?

The impression should be as thin as possible to reduce material costs. Signup and view all the answers

What is a disadvantage of impression compounds related to technique?

They require careful technique and adaptation if deformed. Signup and view all the answers

What effect can compression of the oral mucosa during the impression taking process have?

It can lead to an inaccurate impression. Signup and view all the answers

Which of the following is NOT a characteristic of impression compound?

It is highly elastic and flexible. Signup and view all the answers

Which statement about polyvinyl siloxane putty is accurate?

It supports itself and is elastic. Signup and view all the answers

What is essential for configuring a proper impression tray?

A guiding mechanism should assist in correct positioning. Signup and view all the answers

What is a common cause of voids or air bubbles in an impression?

Insufficient material flow into the vestibules Signup and view all the answers

What action can be taken to troubleshoot under-extended impressions?

Increase the amount of impression material used Signup and view all the answers

Which statement is true regarding proper tray alignment during an impression?

Firmly hold the tray until the material starts to set Signup and view all the answers

What is a common cause of a distorted impression?

Flexing or moving the tray during the setting process Signup and view all the answers

To prevent air bubbles during the seating of the tray, one should:

Apply the material slowly and steadily Signup and view all the answers

What is an appropriate intervention for a tray that does not cover the entire denture-bearing area?

Add wax or compound to improve coverage Signup and view all the answers

What is the recommended course of action after the impression material begins to harden?

Wait for at least one minute before removal Signup and view all the answers

Which of the following indicates correct knowledge of tray selection for impressions?

The tray must allow 3-5 mm space for material without excess Signup and view all the answers

Study Notes

Preliminary Impressions in Prosthodontics

Course: Prosthodontics/Preclinical-1 1603340
Semester: First Semester 2024
Date: 27-30/10/2024
Lecturer: Dr. Ibrahim Khatib DDS, MClinDent, Mpros
Course Objective: Creating preliminary impressions to capture denture-supporting surfaces and tissues for accurate support, retention, and stability of a denture under function.

Lecture Outline

Introduction
Diagnostic/Preliminary Impressions
- Purpose and Indications
- Trays
- Materials
- Impression Philosophies (Mucostatic, Mucocompressive, Selective Pressure)

Importance of Accurate Impressions

Retention: Proper impressions accurately capture the edentulous ridge contours, ensuring good suction or adhesion between the denture and oral tissues.
Support: Dentures need support from underlying tissues to handle masticatory forces. Accurate impressions ensure the denture base fully contacts supporting structures, distributing pressure evenly and preventing trauma.
Stability: Accurate impressions capturing the oral tissues' functional form ensure denture stability during chewing or speaking, preventing unwanted movements.

Impression Trays

Definition: A device for controlling and carrying impression material into and out of the patient's mouth during the impression-taking process.
Types:
- Stock Trays: Prefabricated, available in standard sizes and shapes. Can be for dentate or edentulous patients, made of plastic or metal (flexible or rigid). Also, perforated or non-perforated (for retention).
- Custom Trays: Individually fabricated to fit the patient's specific oral anatomy. Provides better control over the extension and border molding process for more accurate impressions. More time-consuming and costly.

Stock Trays - Selection Criteria

Selection depends on both the impression material and function of the tray.
Appropriately sized for the patient's arch with at least 3-5 mm clearance.
Maxillary and mandibular trays must properly extend into vestibules.

Stock Trays - Modifications

Under-extended: Using wax or acrylic to increase extensions.
Over-extended: Adjusting the tray using acrylic burs.

Impression Material Types

Rigid/Inelastic: Impression plaster, Impression compound, Zinc Oxide Eugenol
Elastic: Reversible hydrocolloid (agar), Irreversible hydrocolloid (alginate), Elastomeric impression materials (polysulfides, Condensation silicones, Polyvinyl siloxanes, Polyether)
Properties of Materials: Alginate: hydrophilic and cost-effective; Impression compound: thermoplastic; Polyvinyl siloxane: dimensionally stable and elastic.

Rim Lock

Definition: A method/tool to ensure retention of the impression materials.
Description: A type of impression tray that has a locking mechanism to enhance material retention.

Impression Philosophies

Mucostatic: Impressions recording tissues with minimum displacement. Suitable for patients with minimal ridge or for non-functional loading.
Mucocompressive: Recording tissues under functional pressure.
Selective Pressure: Applies pressure selectively to support areas to facilitate retention and comfort.

Taking the Impression

Important Steps: Healthy oral tissues, proper tray alignment, proper material space, and the necessary mechanisms for positioning.
Distortion Prevention: Sufficient material for the tray volume and avoiding early removal of the tray before the material sets.

Common Errors and Troubleshooting

Under-Extended Impressions: Tray doesn't cover the entire denture bearing area. Solution: Add wax/acrylic.
Voids or Air Bubbles: Air is trapped in the impression or improper material distribution. Solution: Adequate material.
Improper Impression Centering: Tray not correctly positioned. Solution: Alignment with patient's midline.
Distorted Impressions: Removing the tray too soon or flexing during the setting process. Solution: Wait for full set, minimize movement.

Q& A; Thank You

Reference: Prosthodontic Treatment for Edentulous Patients, Treating the Complete Denture Patient, Lab Brief 02

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Description

Test your knowledge on impression trays in dentistry with this quiz. Explore their functions, characteristics, and the importance of accurate impressions in denture making. Understand the distinctions between stock and custom trays, as well as the implications for dental treatment.