Viva voice questions in Gypsum Products
A reproduction of the shape and features of. Surface made from an impression of the surface.
what is model?
A positive likeness of an object
What is Dental plaster?
The bet form of calcium sulfate hemihydrate
what is Dental Stone?
The alpha form of calcium sulfate hemihydrate
A reproduction of a prepared tooth made from a gypsum product, epoxy resi , a metal or a refractory material.
what is Alabaster?
Alabaster is a form of gypsum. It is believed that the alabaster is used in the building ofKing Solomon’s temple.
Define Hygroscopic expansion?
The amount of setting expansion that occurs when a gypsum bonded casting investment is immersed in water
what is Normal setting expansion?
The amount of setting expansion that occurs when a gypsum bonded casting investment is allowed to set in air.
Define wet strength or green strength?
wet strength or green strength is the strength obtained when excess waster than that required for hydration of hemihydrate is left in the specimen.
what is the most commonly used accelerator in gypsum products?
Potassium sulfate and Sodium chloride accelerate the setting reaction of gypsum products. But at higher concentration NaCl act as retarder.
powdered gypsum added to hemihydrate also accelerate the setting reaction as these particles act as nuclei of crystallisation.
what are the uses of gypsum products in dentistry?
- for the preparation of study models
- are important auxiliary materials for dental laboratory operations that are involved in the production of dental prostheses
- various types of dental plaster are produced, modified for specific property requirements,and used to form moods and casts on which dental prosthesis and restorations are constructed.
- Impression plaster is used to take impression of oral and Maxill o facial structures
- Dental Stone is used to prepare model, master cast or die.
The alpha hemihydrate is called as
Artificial Stone, die stone or improved stone
what are the differences between alpha hemihydrate and beta hemihydrate?
alpha hemihydrate(dental stone) consists of smaller, regularly shaped crystalline particles in the form of rods or prisms.
beta hemihydrate consists of large, irregularly shaped crystal particles with capillary pores.
what are the factors that cause tease in setting expansion?
- Less water powder ratio
- allowing setting under water
- increased rate of spatulation
- fine or smaller silica particles
- alpha hemihydrate
what are the factors that cause decrease in setting expansion?
- more water powder ratio
- addition of modifiers like potassium sulfate, NaCl, borax
- reduced spatulation
what is the reason for the rough or chalky surface of the cast?
The rough orchalky surface of the cast is due to
- high speed accelerator
- air incorporation in the mox
- not waiting for 20 mins before pouring.