Questions and Answers
What are the 4 steps of preparing a master cast?
What are the goals of preparing a master cast?
Making accurate, dense, strong master cast; preserve peripheral border contour of edentulous master impression; facilitate subsequent clinic & lab procedures in CD fabrication.
Type ___________ stone provides master cast with sufficient strength to resist alteration or damage during subsequent steps.
III dental stone
What type of casts are used to fabricate record bases and occlusion rims?
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What type of casts are used to reproduce maxillomandibular relationships on an articulator?
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What type of casts are used to contour trial dentures?
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List all steps of CD fabrication that require the use of Master cast.
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What is the ideal vertical height of the base of the master cast?
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If the base of the master cast is too thick (>15mm), what problems does this cause?
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If the land area of the master cast is completely removed, what anatomic features are compromised?
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What is the ideal dimension of the land area of the master cast?
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If the land area of the master cast is too THIN, what problems does this cause?
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If the land area of the master cast is too SHORT, what problems does this cause?
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What step is necessary to preserve the peripheral border contours of the master impression?
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What is 'Indexing' a master cast?
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________________ is the portion of the cast that extends beyond the impression area laterally.
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Master cast can be largely divided into 2 areas. What are they?
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______________ is the portion of the cast that reproduces the surface of oral tissues recorded in master impression.
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Before trimming the master cast to the right dimension, we should soak it in _________________. For how long?
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What are the dimensions & criteria for the trimmed master cast?
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What is the purpose of indexing the master cast?
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Indexing comes before trimming the master cast.
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Indexing the base of the master cast provides 3D fit between the cast and ______________, allowing easy ______________ & ______________ of the cast.
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What are the dimensions & criteria of the indexing base of cast?
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What's the name of the wheel that's used for indexing base of the cast?
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What can you use to shape & refine index grooves afterwards?
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Study Notes
Preparing Master Cast
- Four steps: trim the master cast, index the master cast, identify anatomic landmarks, and place a postpalatal seal.
Goals of Preparing Master Cast
- Create an accurate, dense, and strong master cast.
- Preserve the peripheral border contour of the edentulous master impression.
- Aid in clinical and laboratory procedures for complete denture (CD) fabrication.
Type of Dental Stone
- Type III dental stone (Microstone) offers adequate strength for the master cast while being easy to remove from dentures.
Master Cast Functions
- Used for fabricating record bases and occlusion rims.
- Essential for reproducing maxillomandibular relationships on an articulator.
- Necessary for contouring trial dentures.
Ideal Vertical Height
- The ideal base height of the master cast ranges from 13 to 15 mm.
Consequences of Base Thickness
- If the base exceeds 15 mm, it may not fit into the articulator or denture flask.
Land Area Importance
- Removal of the land area compromises the pterygomaxillary notches and retromolar pads.
Ideal Land Area Dimensions
- Should be 3 mm wide and 2 mm high.
Consequences of Land Area Thickness
- If too thin, the cast may break and border contours are lost.
- If too thick, it hampers denture flask fitting.
Consequences of Land Area Height
- A short land area leads to lost cast border contours.
- A tall land area can hinder record base polymerization and removal from the cast.
Boxing Purpose
- Boxing is necessary to preserve peripheral border contours of the master impression.
Indexing Definition
- Indexing involves placing grooves or notches in the base of the cast.
Master Cast Division
- The master cast consists of a land area and an impression area.
Impression Area Definition
- The impression area reproduces the surface of oral tissues documented in the master impression.
Pre-Trimming Treatment
- Before trimming, soak the master cast in clear slurry water for 5-10 minutes.
Trimmed Master Cast Criteria
- Thickness should be 13-15 mm in the thinnest area.
- The base must be parallel with the residual ridge, with sides smooth, flat, and perpendicular.
Indexing Purpose
- Facilitates removal and accurate replacement of master casts on the articulator.
- Essential for reproducing maxillomandibular relationships, evaluating trial dentures, and correcting occlusal errors.
Timing of Indexing
- Indexing is performed after trimming the master cast.
3D Fit and Function of Indexing
- Provides a 3D fit between the cast and the mounting stone, enabling separation and replacement without damage.
Indexing Dimension and Criteria
- Should be 2 mm deep by 3 mm wide with two perpendicular V-shaped grooves and no undercuts or voids.
Tools for Indexing
- Use a #461 blue abrasive wheel for indexing, with a #7 green handle knife for shaping and refining index grooves.
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Description
Test your knowledge on the steps and goals involved in preparing a master cast. This quiz covers the essential processes such as trimming, indexing, and identifying landmarks. Perfect for dental students aiming to improve their understanding of cast fabrication.