Questions and Answers
What is the primary use of a 2-master cast?
What material is a refractory cast made from?
What is the function of the handle in an impression tray?
Which part of the impression tray aids in covering the palatal area?
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How is an optical/digital impression created?
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What is the main purpose of the die in dental procedures?
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What modification involves bending the tray to create adequate space for impression material?
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Which shape is recommended for the buccal frenum due to its unrestricted movement?
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What should be added to a tray if the flange is found to be short?
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What is the purpose of a custom 'special' tray?
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How should the border of a tray be altered if it is overextended?
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What is the recommended gap between the tray and tissues when shaping for impression material?
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What are the characteristics of the lingual flanges of the lower tray in relation to tongue movement?
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When selecting a stock tray for an edentulous patient, which feature is specific to its design?
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For a partially edentulous patient, what shape is the floor of the tray typically?
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Which type of tray is used primarily for secondary impressions?
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What is an essential characteristic for selecting an impression material when using perforated trays?
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Which of the following is a characteristic of metallic trays?
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What does the tray choice depend on when selecting a stock tray?
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When using agar-agar for impressions, what feature must the tray include?
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What is the required thickness of a special tray to maintain rigidity?
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Which of the following is NOT an advantage of using a special tray?
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Which characteristic is essential for a special tray when applying pressure?
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Which of the following materials is commonly used for constructing a self-cure acrylic resin special tray?
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What is a disadvantage of using shellac base plates for special trays?
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During the construction of a special tray using the finger-adapted dough method, which tool is used to mark the cast?
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How should the borders of a shellac base plate be modified to enhance strength?
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What is the primary use of a primary impression taken by modeling compound in the special tray process?
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What is a disadvantage of using heat cure acrylic?
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Which method allows for rapid polymerization reaction?
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What is the purpose of using spacers in impression techniques?
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What is a primary aim of boxing in impression pouring?
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Which of the following materials requires a special machine for construction?
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What distinguishes the mucocompressive technique from the mucostatic technique?
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What is a disadvantage of using metal trays for impressions?
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How does the plastic sheet technique benefit from its construction method?
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In the boxing method using wax, what is the width for beading wax required?
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Study Notes
Master Casts and Impressions
- 2-Master Cast: Replica of prepared teeth and residual ridge made from final impression using dental stone; essential for constructing record blocks and processing dentures.
- Refractory Cast: Made from investment material by duplicating the master cast; exclusively used for constructing metallic denture frameworks.
- Optical/Digital: Utilizes camera imaging of the oral cavity to design prosthetics on a computer.
- Die: A positive replica of a single tooth, specifically where a crown is fabricated.
Impression Tray
- Definition: Device for carrying, confining, and controlling impression material during impression making.
Parts of the Tray
- Handle: Facilitates insertion and removal; not for support during impression setting.
- Body: Comprises floor and flange; includes vault for palatal coverage or flanges for tongue movement in lower trays.
Tray Shapes by Patient Type
- Dentulous: Flat floor and long flange; handle in line with tray floor.
- Edentulous: Round floor and short flange; handle at a right angle to the floor.
- Partially Edentulous: Anterior flat floor, posterior round; anterior long flange, posterior short.
Types of Trays
- Stock Tray: Ready-made trays for primary impressions, different available sizes (No. 1, 2, 3).
- Custom Tray: Specially made for secondary impressions from preliminary casts.
Stock Tray Features
- Selection: Based on patient's condition (dentulous, edentulous, partially edentulous), arch size, shape (U, V, ovoid), and impression material (e.g., alginate, agar).
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Types:
- Metallic (stainless steel, aluminum, low fusing alloy)
- Plastic (autoclavable, non-autoclavable).
- Modification: Involves bending, trimming, or building additional material for proper fit.
Custom Tray Requirements
- Must fit accurately on supporting tissues, be dimensionally stable, free of voids, and 2-3mm thick for rigidity; should have a handle.
Advantages of Custom Trays
- Better adaptation, uniform thickness, fine detail capture, and increased patient comfort.
Materials for Special Trays
- Thermoplastic Material: Shellac base plates are inexpensive but prone to breakage and warpage.
- Acrylic Resin: Commonly used; methods include self-cure, heat-cure, and light-cure with distinct advantages and disadvantages.
- Plastic Sheets: More fitted but require special machines; not widely used due to need for finishing.
- Metal Trays: Rarely used due to difficult construction and time consumption.
Spacers and Stoppers
- Function: Create uniform thickness for impressions.
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Technique Types:
- Mucostatic (uniform spacer thickness).
- Mucocompressive (no spacer).
- Selective pressure (variable thickness based on stress-bearing areas).
Pouring Impressions
- Conventional Method: Involves soft plaster or stone application and vibration for even distribution.
- Boxing: Building vertical walls around impression for base production, preserving anatomical landmarks, and controlling pouring.
Methods of Boxing
- Wax Boxing: Utilizes beading and boxing wax for molding plaster impressions.
- Plaster and Pumice: Applies vertical walls around rubber impressions; includes separating medium.
- Children's Clay: Used for irreversible hydrocolloids; no separating medium required.
- Magnetic Strips: Simple, efficient method without the need for adhesion between strips.
Additional Tips
- To enhance cast hardness, K-sulphate can be employed to resist scrapping.
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Description
Test your knowledge on dental impressions, including the use of master casts, refractory casts, and optical imaging techniques. This quiz covers the processes involved in creating accurate dental frameworks and prosthetics. Understand the essential materials and methods used in the field of dentistry.
