Dental Impressions and Special Trays Quiz

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Questions and Answers

What is the correct thickness of base-plate wax to trim short for the ZnO eugenol impression material?

2 mm

3 mm

4 mm

0.5-1 mm (correct)

Where should tissue stops be positioned on the special tray?

Evenly spaced along the entire tray border

On the canine eminences and the posterior of the ridge (correct)

At the tips of the incisors and the posterior ridge

Only at the center of the tray

What could happen if the powder to liquid ratio is not maintained in the Finger Adapted Dough Method?

The mixture will remain in a liquid state

It will result in excessive shrinkage and porosities (correct)

It will speed up the curing process

It will improve the strength of the material

What is the primary purpose of using spacers on a special tray?

To allow variability in impression material thickness Signup and view all the answers

What materials are commonly used for the construction of special trays?

Auto polymerizing acrylic resin and visible light cure resin Signup and view all the answers

What is the primary purpose of an impression in dental prosthetics?

To create a negative reproduction for a cast of the oral tissues Signup and view all the answers

Which of the following best describes the function of an impression tray?

To carry and support the impression material during hardening Signup and view all the answers

What distinguishes a preliminary impression from a final impression?

Final impressions require more precise detail Signup and view all the answers

What is a cast in the context of dental prosthetics?

A positive reproduction of the oral tissues Signup and view all the answers

Which of the following is NOT a function of an impression tray?

Confined space for measuring oral dimensions Signup and view all the answers

Which step occurs first in the complete denture construction process?

Primary impression (preliminary) Signup and view all the answers

What is typically done after pouring the master cast?

Recording jaw relation Signup and view all the answers

What is the primary purpose of a study (diagnostic) cast?

To construct a custom tray or for diagnostic purposes. Signup and view all the answers

Which type of impression is made using a custom tray?

Final Impression Signup and view all the answers

What objective of impression focuses on the quality of prosthesis to resist dislodging forces?

Support Signup and view all the answers

What is the main concern when creating an impression to avoid tissue damage?

Employing proper pressure control during the impression technique. Signup and view all the answers

How should the border thickness be varied during the impression process?

Based on the extent of residual ridge loss. Signup and view all the answers

What does stability in denture support mean?

Resistance to horizontal or rotational movements. Signup and view all the answers

Which part of the impression tray does NOT interfere with the lip?

Handle Signup and view all the answers

Which aspect of the impression process focuses on restoring facial contour?

Esthetics Signup and view all the answers

What is the purpose of the master cast?

To fabricate the denture. Signup and view all the answers

What is a key requirement for stock impression trays?

They should retain their shape during the impression procedure. Signup and view all the answers

Which type of impression tray is typically used for making preliminary impressions?

Stock impression trays Signup and view all the answers

What should the angulation of the handle be designed for?

To aid in manipulation without distorting lip contour. Signup and view all the answers

Which of the following factors does NOT affect tray selection?

Cost of the trays Signup and view all the answers

What type of tray is used for compound impression material?

Non-perforated trays Signup and view all the answers

What size of arches corresponds to size 2 in stock trays?

Medium Signup and view all the answers

What is the minimum clearance required between the ridge and stock trays?

3-4 mm Signup and view all the answers

Which material is NOT typically used for stock impression trays?

Glass Signup and view all the answers

What is one method of modifying a stock impression tray?

Bending Signup and view all the answers

What is the purpose of the border extension in stock trays?

To ensure it does not interfere with muscle or frenal attachments. Signup and view all the answers

What is one advantage of using custom trays over stock trays?

They are less bulky and more comfortable for the patient. Signup and view all the answers

Which requirement is essential for a custom tray to ensure correct fit?

It must simulate the finished denture in size and shape. Signup and view all the answers

What is the function of incorporating a custom tray in the impression process?

To ensure final impressions are more accurate and well-fitted. Signup and view all the answers

Which step is NOT part of the construction of a custom tray?

Extending the tray beyond the vestibular depth. Signup and view all the answers

What could happen if mistakes are made during the impression using a custom tray?

The final denture may have inaccuracies that affect fit and retention. Signup and view all the answers

What thickness is recommended for the palatal area of a custom tray?

At least 2 mm. Signup and view all the answers

Why should a custom tray have a contrasting color?

To make the margins visible when placed in the patient's mouth. Signup and view all the answers

What characteristic should a custom tray have in relation to impression material?

It should not react with the impression material. Signup and view all the answers

Which part of the sulcus should the custom tray be extended to the full depth?

Lingual sulcus of the mandibular arch. Signup and view all the answers

Study Notes

Impression Trays

Impression trays are devices used to hold impression materials during procedures to create a cast of the mouth.
Different types of impression trays exist, classified by arch (upper, lower) and type (stock, custom).
Stock trays are pre-fabricated, while custom trays are made for a specific patient.

Impression

An impression is a negative reproduction of an object, which is then used to create a positive likeness (cast) of the object.
In dental prosthetics, an impression is a negative registration of the entire denture-bearing area.
Impressions are taken to create a positive form of the oral tissues (cast).

Cast

A cast is a positive reproduction of the form of the upper or lower arch tissues.
It serves as a model for creating denture bases or other dental restorations.

Impression Tray Parts

Handle: The handle of the tray does not interfere with the lip.
Body: Consisting of a floor and flanges.

Types of Impression Trays

Arch Related:
- Upper tray: Features a palatal part and a vault.
- Lower tray: Includes a lingual flange.
Impression Type:
- Stock trays: Pre-fabricated trays used for preliminary impressions.
- Custom trays: Individually made for the patient, allowing for a more detailed and accurate impression and preventing errors.

Objectives of Impression

1. Preservation of Remaining Tissues:
- Pressure is directly reflected in the denture base, potentially damaging soft tissues and causing bone resorption. Proper techniques minimize this impact.
2. Support:
- Support is a crucial quality, opposing forces that dislodge the denture. Comprehensive coverage is important for stable support and distributing applied forces across a wide area.
3. Retention:
- Resistance is needed to dislodge the denture, effectively keeping it firmly in place. Forces working against insertion (away from tissue) must be resisted.
4. Stability:
- Resistance to movements (horizontal and rotational) trying to dislodge the denture.
5. Aesthetics:
- Border thickness is adjusted according to residual ridge loss to maintain a natural facial contour.

Preliminary Impression

An impression taken in a stock tray to make a study cast that is subsequently used to create a custom tray.

Study (Diagnostic) Cast

Formed from a primary impression, serving for diagnosis and fitting.

Final Impression

An impression produced by a custom tray, for detailed reproduction of the tissues enabling accurate construction of the master cast, which in turn serves as a basis for the denture construction.

Master Cast (Definitive)

A cast created from a final impression to fabricate the prosthesis.

Factors Affecting Stock Tray Selection

Presence or absence of natural teeth
Impression material type
Size of arch
Material of tray fabrication (metal, plastic)

Stock Tray Requirements

Rigid but not overly thick, to maintain shape.
Adequate space between the ridge and the tray for comfortable insertion.
Flanges that are sufficiently angulated to aid handling without distorting the lip contour.
Short of vestibular extension, avoiding contact or interference with the vestibule.
Rounded, smooth borders, preventing injury to the surrounding tissues.
Suitable for modifications, if needed.

Stock Tray Modifications

Bending: Metal trays can be bent with specialized tools.
Cutting: Metal trays can be trimmed to properly fit a patient.

Addition of Moldable Material

Moldable materials (wax, green compound) accommodate irregularities by filling areas for more accurate support.
This process can create under-extension flanges in high palatal areas, increase tray support, and define better seal areas to prevent excess material from flowing back into the throat.

Advantages of Custom (Special) Trays

Economical due to reduced material for impression.
Comfortable, for patient and minimizes tissue displacement.
Allows for accurate adaptation to the vestibules, increasing denture retention.
More accurate impressions.

Requirements of Custom Trays

Perfectly adapted to the primary cast and patient's mouth.
Needs rigidity and stability.
Easily removable from the cast.
Does not react with impression material.
Simulates the final denture's shape and size.
Border molding, extends 2mm short of the sulcus, adds rigidity, is a suitable colour for the patient's mouth, fits all anatomical landmarks.

Steps of Custom Tray Construction

Determining the sulcus and creating the periphery.
Creating the tray outline short of the vestibular depth.
The tray should be outlined in such a way as to accommodate the anatomical landmarks, for example, the maxillary posterior border is determined from the hamular notches, passing posterior to the fovea palatine. The entire retromolar pad should be included within the outline.
Adapting the proper base-plate wax thickness and trimming.

Materials used for Custom Tray Construction

Auto polymerizing (chemical cured) acrylic resin: Two techniques include finger adapted dough method and sprinkle-on acrylic method.
Visible light-cure resin (VLC): Supplied in lightproof packages; molded to desired shape then exposed to high-intensity light.
Vacuum-form vinyl polysiloxane sheets: A common method to construct custom trays.
Pre-existing dentures (if applicable):

Zinc Oxide Eugenol Impression

Used for taking impressions of the oral structures.

Digital Impression

Taking an optical impression using digital capture units (intra-oral scanners). Images are captured and converted into a 3D model on a computer. The digital impression is a valid alternative to traditional impression trays.

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Description

Test your knowledge on dental impressions and special trays with this informative quiz. Covering topics like the thickness of base-plate wax, the positioning of tissue stops, and the purposes of various materials, this quiz is essential for dental students and professionals. Explore key concepts that are critical in the field of dental prosthetics.