Dental Stone vs. Plaster of Paris
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Questions and Answers

What is the primary advantage of dental stone over Plaster of Paris?

  • It is easier to acquire
  • It is less expensive
  • It is stronger and more durable (correct)
  • It is easier to mix

What is the purpose of using a mold in the casting process?

  • To identify the casting material
  • To create a detailed impression of the teeth
  • To mix the dental stone with water
  • To prevent the casting material from spreading over a wide area (correct)

What is the ideal consistency of the dental stone mixture?

  • Thin and runny
  • Very thick and dry
  • Thin pancake batter or thick cream (correct)
  • Thick and watery

What is the recommended ratio of dental stone to water?

<p>2lbs of dental stone to 8 oz of water (B)</p> Signup and view all the answers

What is the purpose of pouring the mixture behind the leading edge?

<p>To push the mixture into the impression (D)</p> Signup and view all the answers

How long should the casting be left to harden before removing it from the ground?

<p>15-20 minutes (C)</p> Signup and view all the answers

What is the recommended time to wait before removing any soil or debris from the casting?

<p>24-48 hours (B)</p> Signup and view all the answers

What is the purpose of labeling the casting with identifiers, date, location, and initials?

<p>To document the evidence (D)</p> Signup and view all the answers

What is the primary reason for using a ruler alongside the impression during photography?

<p>To link the impression to the identifier number (D)</p> Signup and view all the answers

Why is casting more valuable than photography in certain cases?

<p>It captures a positive representation of the shoe (D)</p> Signup and view all the answers

What is a limitation of photography when enlarged to natural size?

<p>Loss of sharpness and resolution (D)</p> Signup and view all the answers

What was the casting material of choice prior to 1970?

<p>Plaster of Paris (C)</p> Signup and view all the answers

Why is it important to position the camera directly 90° above the impression?

<p>To ensure the sensor is parallel to the impression (D)</p> Signup and view all the answers

What is an advantage of casting over photography for deep impressions?

<p>It captures more details of the side of the shoe (A)</p> Signup and view all the answers

What is the purpose of using Live View Mode or viewfinder during photography?

<p>To assure the impression and ruler fill the image frame (C)</p> Signup and view all the answers

What is a disadvantage of using Plaster of Paris as a casting material?

<p>It is a soft form of gypsum that can be destroyed by water and soft brush (B)</p> Signup and view all the answers

What is the purpose of sifting a small amount of material over the impression to cover the bottom of the impression?

<p>To prepare the surface for the remainder of the casting material (A)</p> Signup and view all the answers

Which casting material is less flammable than sulfur?

<p>Sulfur Cement (A)</p> Signup and view all the answers

What is the advantage of highlighting impressions in snow?

<p>It enables better contrast for photography (A)</p> Signup and view all the answers

What is the recommended approach for working with moist snow?

<p>Using Dry Casting with Dental Stone (D)</p> Signup and view all the answers

What is the primary purpose of photographing impressions in snow?

<p>To create a permanent record of the impression (C)</p> Signup and view all the answers

What is the characteristic of impressions in snow that varies considerably?

<p>The amount of detail (C)</p> Signup and view all the answers

Which casting material is known for producing excellent detail of snow impressions?

<p>Yellow Sulfur (A)</p> Signup and view all the answers

What is the recommended approach for casting larger impressions in snow?

<p>Using Sulfur Cement (D)</p> Signup and view all the answers

Flashcards

Dental Stone

A strong, durable plaster made from calcium sulfate dehydrate.

Plaster of Paris

A weaker plaster than dental stone.

Calcium Sulfate Dehydrate

The raw ingredient for dental stone.

Calcium Sulfate Hemihydrate

Hardened dental stone.

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Mixing Ratio (Dental Stone)

Approximately 2lbs of dental stone to 8oz of water.

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Mold Preparation

Creating a form for the casting material.

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Mixing Time

3 minutes of mixing for consistent pour and strength.

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Pouring Technique

Directing the mix into the mold starting outside, filling the mold completely.

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Casting Footwear

Creating a cast of a shoe to capture details.

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Snow Print Wax

Aerosol spray to create a wax shell for casting snow impressions.

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Dry Casting

Layering dry dental stone to create casts of snow.

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Yellow Sulfur

Material to cast snow impressions, but requiring more time and prep.

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Casting Snow Impressions

Capturing the form of an impression in snow for future use.

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Sulfur Cement

Less flammable alternative to sulfur.

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Casting Importance

Provides tangible 3-D evidence and confirms photographic evidence.

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Snow Impression Photography

Capturing images of snow prints for record-keeping.

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Impression Detail Variation

Differences in amount of detail recovered from snow impressions.

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High Contrast Impressions

Highlighting to enable better snow print photography.

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Casting in Dentistry

Making an exact copy of something in dentistry.

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3-D Representation

A detailed visual representation.

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Study Notes

Dental Stone vs. Plaster of Paris

  • Dental stone is stronger and more durable than Plaster of Paris.
  • Dental stone is easy to use and acquire.
  • It is a form of plaster, made from calcium sulfate dehydrate, a natural material mined from the earth.
  • Calcium sulfate dehydrate is calcinated (heated) to become calcium sulfate hemihydrate, the hardened version.

Using Dental Stone

  • Dental stone is mixed with a pre-determined amount of water to achieve a consistency similar to thin pancake batter or thick cream.
  • The mixture can be mixed in a container or a Ziplock bag.
  • A metal form, cardboard, or built-up surrounding soil can be used as a mold to prevent the casting material from spreading.
  • The mold should be slightly larger than the impression, and approximately 2lbs of dental stone to 8oz of water is used.
  • The mixture is mixed for 3 minutes before pouring to ensure an even pour and a stronger cast.

The Pouring Process

  • Start pouring the mixture just outside of the impression, directing the flow into the impression.
  • Move along the impression while pouring to ensure the mixture fills the entire impression.
  • Pour behind the leading edge to push the mixture into the impression.
  • Once poured, the casting should be left to harden, and a label can be placed into the casting with identifiers, date, location, and initials.

Casting Footwear

  • Casting footwear impressions is recommended whenever there is a 3-D impression.
  • Casting captures the positive representation of the shoe, including uneven surfaces and microscopic characteristics.
  • Casting provides tangible 3-dimensional evidence and confirms photographic evidence.

Casting Impressions in Snow

  • Snow Print Wax, developed in 1982, is an aerosol spray that produces a wax shell when applied to the impression, allowing for casting with dental stone.
  • Dry casting with dental stone involves layering the impression with dry dental stone and then preparing a regular mix of dental stone.
  • Yellow Sulfur can be used to cast impressions in snow, but it is more time-consuming and requires melting and continuous stirring.
  • Sulfur Cement, introduced in 2007, is less flammable than sulfur and requires the same method as sulfur.

Key Points

  • The amount of detail varies considerably in different types and conditions of snow.
  • Impressions in snow should always be photographed first.
  • Highlighting impressions can enable better contrast recovered through photography.
  • Casts of snow impressions provide additional detail to supplement photography of snow impressions alone.

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Description

Compare and contrast dental stone and plaster of Paris, including their properties, uses, and advantages. Learn about their applications in dentistry.

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