Quiz 8 Flashcards
What could occur if excess residue remains in the investment mold after the wax pattern is melted out?
This may result in inaccuracies in the object being produced.
It is important that all of the wax is removed from the object onto which it is melted.
What will happen to the monomer if the temperature becomes too great during the polymerization process?
The monomer will vaporize and produce porosity.
Porosity weakens the material, causes it to discolor as stains are absorbed into the pores, and can lead to retention and growth of oral microorganisms.
What is the correct sequence for creation of a casting using the lost wax technique?
3, 2, 1, 4.
A wax pattern of the restoration is carved on the die, a wax or plastic sprue is attached to the pattern, the pattern and sprue are encased in an investment ring, and the enclosed pattern and sprue are heated in a burnout oven at high temperatures.
What is true of the double-pour method for fabricating and trimming diagnostic/working casts?
This technique involves two separate mixes.
The anatomic portion of one or both arches is poured and left in the upright position. Approximately 10 minutes after the loss of gloss, a second mix is produced for the art portion.
What reaction does the free radical initiate in an addition polymerization reaction?
Opening the bond between the two carbon atoms of the monomer.
The broken bond causes the monomer molecule to bond to another monomer, leaving a free radical available for further reaction.
Which dental gypsum product requires the least water for mixing and has the highest final density?
Dental stone, high strength (Type IV).
High-strength dental stone is produced under pressure and at a higher temperature, resulting in an even denser stone.
What is true concerning the chemical properties of gypsum materials?
The amount of water required to mix the calcium sulfate hemihydrate is greater than the amount required for the chemical reaction.
Chemically, the mineral gypsum is a dihydrate of calcium sulfate and is mined as a solid mass.
Which of the following does not apply to porcelain denture teeth?
They are easily repaired.
Porcelain teeth are brittle and prone to fracture if the denture is dropped or overstressed.
What is true regarding trimming of models with a model trimmer?
The casts should be trimmed so that proportionately the base makes up one third and the anatomic portion two thirds of the total depth.
Bases made from dental stones should be soaked in water for 5 to 10 minutes before trimming.
What is the water-to-powder ratio of model plaster?
Approximately 0.45 (mL/g).
This produces a durable but relatively weak cast when compared with the stone categories.
What is true of inlay waxes?
Inlay waxes may be used directly in the mouth and placed onto the prepared tooth in the direct waxing technique.
Most dentists prefer to use the indirect waxing technique.
When should wax patterns be invested after carving?
Within minutes.
If waxes are allowed to stand, dimensional changes occur from the release of residual stress.
What is the result of an increase in the recommended water-to-powder ratio?
A weaker, less accurate model.
An increase in water results in a thin mix that takes longer to set and is considerably weaker.
What is the result of the loss of monomer or inadequate pressure during processing?
Porosities in the material.
Porosity is a result of loss of monomer or inadequate pressure.
What is true of plastic (acrylic) and porcelain denture teeth?
Plastic denture teeth do not wear the opposing natural or artificial teeth or restorations.
Plastic teeth are used more often than porcelain teeth because they are somewhat resilient.
What is the difference between chemical-cured and heat-cured materials when mixed?
Chemical-cured materials have a tertiary amine in the liquid as an activator, whereas heat-cured materials do not.
The acrylic powder is composed mostly of PMMA and benzoyl peroxide.
What is an example of a pattern wax?
Inlay wax.
Pattern waxes are used in the construction of metal castings and bases for dentures.
What is true regarding dimensional accuracy of gypsum products?
High-strength stones have the least amount of setting expansion.
Setting expansion occurs with all gypsum products and is critical for accurate models.
What happens with an increase in spatulation time and rate?
It will shorten the setting time and increase the rate of setting expansion.
Spatulation should continue until a smooth, homogenous mix with a glossy surface is produced.
What happens to the viscosity of the wax as the temperature increases?
The viscosity of the wax decreases until the wax becomes a liquid.
