What is hygroscopic expansion?
expansion of their peripheral boundaries that is known as “normal setting expansion.” When additional water is brought into contact withthe setting material, an increased. expansion is observed. This latter expansion has been termed “hygroscopic expansion.”
How is setting expansion controlled?
However, the most effective method by which to control setting expansion is through the addition of chemicals by the manufacturer. ). Consequently, the observed setting expansion that occurs when the gypsum product sets under water is greater than that which occurs during setting in air.
Why is the coefficient of thermal expansion significant in dental materials?
Restorative dental materials are subjected to temperature changes in the mouth. These changes result in dimensional changes in the materials and to the neighboring tooth structure. To make a comparison between materials easier, the linear thermal expansion is expressed as a coefficient of thermal expansion.
What are the other terms for type IV stone?
The properties of Type IV stone, (also referred to as Densite or Improved stone), are improvements over the earlier Type III stone, (hydrocal).
What are the factors that affect the setting time of dental plaster?
A. Water, powder ratio: the more water used for mixing (thin mix), the fewer nuclei will be per unit volume; consequently, the setting time will be prolonged. B. Mixing time and rate: the longer and the more rapidly the gypsum is mixed, the shorter is the setting time.
How many types of setting expansion are there?
Intro – Setting expansion Mechanism Types (Linear and Hygroscopic) Controlling the expansion. 4.
What are the factors that affect how dental materials are manufactured for the oral cavity?
Dental materials are influenced in the oral cavity environment by: Chemical reactions – corrosion (hydrolysis, oxidation), polymer chain degradation/ scission with decrease in the polymer chain length), Mechanical failire – abrasion, attrition, fracture, fatigue, creep.
What is gypsum used for?
Gypsum is a mineral found in many items we use every day, like toothpaste and shampoo. It is also used to make Portland cement and drywall, create molds for dinnerware and dental impressions, and to build roads and highways.
What are the factors affecting the setting time of gypsum?
How does hygroscopicity affect the growth of aerosol particles?
those of standard particles of known hygroscopicity. Hygroscopic properties are key properties of aerosol particles, affecting particle growth by water vapor, scattering efficiency of particles, and potential for the formation of cloud condensation nuclei. Also, an accurate measurement of hygroscopic properties of
When does hygroscopic material need to be predried?
Hygroscopic materials need to be predried prior to injection molding. The market contains a number of options for drying that also include built-in delivery systems to feed the material to the hopper as required.
What happens when hygroscopic material is pneumatically conveyed?
If a hygroscopic material is pneumatically conveyed, it may absorb moisture from the air that is used to convey the material and become very cohesive, and have poor flowability as a result.
What causes hygroscopic materials to pick up moisture?
Air leaks in the materials handling system will allow hygroscopic materials to pick up moisture after drying and will either create processing defects or require drying to a much lower level to get the correct moisture content at the machine (which is what counts anyway).