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?

<p>It will distort the tissues and dimensions of the sulcus (B)</p> Signup and view all the answers

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

<p>They are deeper and box-shaped (C)</p> Signup and view all the answers

What is one primary objective of impression making?

<p>To capture all denture-bearing surfaces and tissues (C)</p> Signup and view all the answers

How does retention in denture making primarily occur?

<p>Via the peripheral seal (A)</p> Signup and view all the answers

Why is support important when making dentures?

<p>To distribute masticatory forces and prevent trauma (B)</p> Signup and view all the answers

What is a key purpose of preliminary impressions?

<p>To create diagnostic casts for treatment planning (C)</p> Signup and view all the answers

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

<p>In the initial phase for study models (B)</p> Signup and view all the answers

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

<p>They prevent horizontal or rotational movements (C)</p> Signup and view all the answers

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

<p>Ridge shape and undercuts (C)</p> Signup and view all the answers

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

<p>They are adaptable to a patient’s specific oral anatomy (A)</p> Signup and view all the answers

What is a disadvantage of stock trays?

<p>They may distort jaw tissues. (C)</p> Signup and view all the answers

What function do retention perforations serve in impression trays?

<p>Facilitate better adhesion of impression material. (A)</p> Signup and view all the answers

Why are custom trays preferred over stock trays?

<p>They offer a better fit and accuracy. (A)</p> Signup and view all the answers

Which material is NOT commonly used for preliminary impressions?

<p>Gypsum (D)</p> Signup and view all the answers

What characteristic of alginate makes it suitable for preliminary impressions?

<p>It is cost-effective and easy to manipulate. (A)</p> Signup and view all the answers

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

<p>They are time-consuming to fabricate. (B)</p> Signup and view all the answers

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

<p>It enhances the accuracy of impressions. (A)</p> Signup and view all the answers

How do custom trays aid in the impression process?

<p>By allowing uniform distribution of the impression material. (B)</p> Signup and view all the answers

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

<p>Mucostatic (D)</p> Signup and view all the answers

What characterizes the mucocompressive impression technique?

<p>Records tissues under functional pressure (C)</p> Signup and view all the answers

Which statement about selective pressure technique is correct?

<p>It enhances retention and comfort by balancing compression and relief. (C)</p> Signup and view all the answers

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

<p>Allows for mucostatic recording (B)</p> Signup and view all the answers

What is one common cause of under-extended impressions?

<p>Tray not covering the entire denture-bearing area (B)</p> Signup and view all the answers

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

<p>Increasing material viscosity (A)</p> Signup and view all the answers

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

<p>Mucostatic (B)</p> Signup and view all the answers

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

<p>Type of impression tray used (A)</p> Signup and view all the answers

What is a major disadvantage of impression compounds?

<p>It must be poured shortly after use to maintain dimensional stability. (D)</p> Signup and view all the answers

Which characteristic distinguishes polyvinyl siloxane putty consistency from impression compounds?

<p>It has good dimensional stability. (D)</p> Signup and view all the answers

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

<p>The impression should be as thin as possible to reduce material costs. (D)</p> Signup and view all the answers

What is a disadvantage of impression compounds related to technique?

<p>They require careful technique and adaptation if deformed. (B)</p> Signup and view all the answers

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

<p>It can lead to an inaccurate impression. (D)</p> Signup and view all the answers

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

<p>It is highly elastic and flexible. (A)</p> Signup and view all the answers

Which statement about polyvinyl siloxane putty is accurate?

<p>It supports itself and is elastic. (B)</p> Signup and view all the answers

What is essential for configuring a proper impression tray?

<p>A guiding mechanism should assist in correct positioning. (C)</p> Signup and view all the answers

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

<p>Insufficient material flow into the vestibules (D)</p> Signup and view all the answers

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

<p>Increase the amount of impression material used (A), Ensure the tray seats properly before capturing (C)</p> Signup and view all the answers

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

<p>Firmly hold the tray until the material starts to set (B), The tray should always be centered on the upper arch (D)</p> Signup and view all the answers

What is a common cause of a distorted impression?

<p>Flexing or moving the tray during the setting process (A)</p> Signup and view all the answers

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

<p>Apply the material slowly and steadily (A)</p> Signup and view all the answers

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

<p>Add wax or compound to improve coverage (A)</p> Signup and view all the answers

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

<p>Wait for at least one minute before removal (C)</p> Signup and view all the answers

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

<p>The tray must allow 3-5 mm space for material without excess (B)</p> Signup and view all the answers

Flashcards

Impression Tray

A device used to hold and control impression material during the process of taking a dental impression.

Stock Trays

Prefabs, or ready-made impression trays available in a variety of sizes and shapes, providing a generic fit.

Labial Notch

A small bump on the tray that aligns it with the frenum, aiding in proper placement.

Flange

The area on the tray that extends past the teeth and covers the soft tissues. It ensures accuracy by capturing the entire denture-bearing area.

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Tray Selection Criteria

Choosing the right tray size is crucial for a good impression. Select a tray that fits closely with 3-5mm of clearance. This will help with proper material flow and prevent tissue distortion.

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Impression Making in Prosthodontics

The process of capturing the shape and contours of the edentulous (toothless) arch using impression materials to create a replica of the oral tissues.

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Purpose of Preliminary Impressions

A preliminary (initial) impression provides a general overview of the edentulous arch and helps create study models. These models are essential for planning the denture treatment and creating customized trays.

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Stability in Denture Design

When a denture doesn't move excessively when the patient is eating or talking, it is considered stable. Proper impressions help ensure stability by capturing the shape of the edentulous ridge, leading to a better-fitting denture base.

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Support in Denture Design

The supporting tissues underlying the denture need to be able to bear the pressure of chewing. Accurate impressions help distribute forces evenly, preventing pressure points and tissue damage, thus providing good support.

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Retention in Denture Design

The retention of a denture refers to its ability to stay in place. A precise impression ensures a tight seal between the denture and the oral tissues, enhancing retention by creating a suction effect.

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What are custom trays used for?

Custom trays are specifically designed and fabricated for individual patients based on the initial impression. They ensure a more precise impression of the edentulous arch for the final denture.

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What is a peripheral seal?

The peripheral seal of the denture is a crucial factor in retention. It refers to the tight, continuous seal between the outer edges of the denture and the gum tissue.

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Importance of study models

Creating study models from preliminary impressions allows for the visualization of anatomical landmarks and helps plan the next steps of denture treatment. This includes determining the size, shape, and position of the denture base.

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Stock Trays: Advantages/Disadvantages

Stock trays are readily available, inexpensive, and basic, but they may not fit perfectly and require modifications.

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Why Use Custom Trays?

Custom trays are individually made for each patient, ensuring a precise fit, reducing material waste, and better capturing details.

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Custom Tray Purpose

Custom trays are crafted to match the unique contours of a patient's mouth for more accurate impressions.

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Custom Tray Fabrication Components

Spacer: Prevents the tray from directly touching the teeth. Extensions: Extend beyond the teeth for capturing the gum margins. Perforations: Small holes for material retention. Adaptation: Blocking out undercuts to avoid distortions. Material: Usually acrylic for strength. Handle: For comfortable grip.

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Custom Tray Benefits

A custom tray is made by a dental professional specifically for the patient for a precise fit. This results in a better impression, less material used, and a more accurate final result.

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Custom Tray Drawbacks

Custom trays are made by a dental professional and require expertise, time, and materials, making them more expensive than stock trays.

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Impression Material Retention

Retention perforations in the tray help hold the impression material in place during setting by creating a mechanical grip. Adhesive can enhance this grip and rim lock creates a physical seal.

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Alginate: Impression Material

Alginate is a common, easy-to-use material for preliminary impressions. It is hydrophilic, meaning it absorbs moisture well, which is helpful in capturing details of the mouth.

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Impression Compound

A thermoplastic material that can be softened with heat and molded in the patient's mouth. Supplied in cake or stick form. It can be used for preliminary impressions or border molding.

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Polyvinyl siloxane Putty Consistency

A high viscosity silicone that is dimensionally stable. Supplied as base and catalyst and hand mixed. It's known for its good stability, easy handling, and elastic properties.

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Taking the Impression

Recording the tissues of the mouth during impression taking to create a mold.

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Impression Philosophies

Maintaining consistency in how the tissues are recorded during impression making, regardless of the technique used.

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Dimensional Stability

The ability of a material to retain its size and shape.

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Proper Space for Impression Material

The amount of space needed between the impression tray and the teeth for the material to flow and capture a detailed impression.

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Guiding Mechanism for Tray Positioning

Making sure the tray is positioned correctly in the mouth. This is important to capture accurate details.

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Compression of Oral Tissues During Impression Taking

The tissues of the mouth, especially those supporting the denture, can be compressed during impression taking. Recording these tissues under compression can cause the denture to compress the tissues when it's placed in the mouth, leading to instability.

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Mucostatic Impressions

Impression techniques that capture tissues in their natural, undisturbed state, minimizing pressure and displacement.

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Mucocompressive Impressions

Impression techniques that apply pressure to the tissues, simulating the forces experienced during chewing.

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Selective Pressure Impression Technique

A hybrid approach that combines mucostatic and mucocompressive elements. Applies pressure selectively to key areas, minimizing stress on sensitive tissues.

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Viscous Impression Material

A material that is thick and resists flow, aiding in displacing the tissues and creating a mucocompressive impression.

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Vent Holes

Areas on the impression tray designed to reduce pressure by allowing air to escape, minimizing tissue displacement.

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Open Tray (Window)

A larger opening on the impression tray that serves the same purpose as vent holes, but with a greater effect on reducing pressure.

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Under-Extended Impression

A common error in impression taking where the tray does not extend far enough to encompass the entire denture-bearing area.

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Voids in an Impression

Gaps or spaces within the impression that are caused by inadequate material or improper placement.

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Air Bubbles in the Impression

A thin layer of air trapped within the impression material, often appearing as a small bubble. It can affect the accuracy of the impression and the final denture.

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Improper Impression Centering

The tray is not properly positioned within the mouth, causing the impression to be misaligned or distorted. This can affect the fit of the denture.

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Distorted Impression

The impression material has been distorted, leading to an inaccurate representation of the jaw. This is often caused by premature removal of the tray or movement during the setting process.

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Common Causes of Air Bubbles

Rapid seating of the tray traps air, leading to bubbles in the impression. Insufficient material flow into the vestibules (soft tissues surrounding the teeth) creates voids.

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Troubleshooting Under-Extended Impressions

Adding wax or compound to the tray's edge solves gaps in coverage.

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Troubleshooting Improper Impression Centering

Align the tray handle with the patient's nose to center the impression.

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Common Causes of Distorted Impression

Distorted impressions can happen when the tray is removed too early or if there is movement during the process.

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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.

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