2. From page 325-330
Page 329:
6-Which of the following materials are LEAST
suitable for impressions for cast gold
restorations?
A. Polysulfides.
B. Polyvinyl siloxanes.
C. Polyethers.
D. Irreversible hydrocolloids
Non aqueous
elastomeric material
aqueous elastomeric
material
3. Answer:
Therefore, alginate is an acceptable
impression material for study models, but it
is an unacceptable impression material for
the fabrication of bridges, crowns, and inlays.
Nearly all impression materials are acceptable
for full-denture impressions.
Clinical aspect of dental material chapter 8 page 117
4. The disadvantage of the material being predominantly water is that
water evaporates
from the surface of the impression if it is left
exposed to air. When the water evaporates,
the impression shrinks and is no longer
accurate
5. Hydrocolloid materials contract slightly
after setting and exude water. This process
is called syneresis. Syneresis occurs very
slowly, but it is a second reason to pour
hydrocolloid impressions as soon as possible
6. When disinfecting a hydrocolloid impression,
however, it is important to limit the
time that the impression is exposed to an
aqueous disinfecting solution. The hydrocolloid
will absorb water, swell, and distort.
This is called imbibition.
7. 7-In metal-ceramic crowns, the bond between the
materials is
A. mainly mechanical.
B. mainly chemical.
C. decreased by oxides on the metal surface.
D. decreased when the metal has a high yield point.
9. 8-Nickel-chromium alloys designed for porcelain
bonded to metal crowns should be used with
caution because
A. nickel is an allergen.
B. the modulus of elasticity is low.
C. these alloys cannot be soldered.
D. None of the above.
11. 9-For application of porcelain to a ceramo-metal
alloy, the correct viscosity is achieved by
mixing the porcelain powder with
A. a porcelain modifier.
B. pure methyl alcohol.
C. a mild detergent.
D. distilled water
13. Page 330
1-A model prepared from a vacuum mixed stone
has higher strength because
A. less water is required for vacuum mixing.
B. there is less porosity.
C. some of the water is removed by the vacuum.
D. the nuclei for crystallization are more numerous.
14. Stone is made from gypsum by carefully controlled
calcination under steam pressure in a closed
container. This method of calcination slowly releases
the water of crystallization from the crystal so that the
resultant powder particle (Fig. 9.4B)is more
regular, more uniform in shape, and less porous
compared to that of plaster.
15. Stone is stronger and more expensive than plaster. It is
used mainly in making casts for diagnostic purposes
and casts for complete and partial denture
construction, which require greater strength and
surface hardness than that of plaster
16. The dense particles of stone require less gauging
water to float them, and their regular shape allows
them to roll over one another more easily.
17. This difference in the amount of measured water that
is required to make a workable mix results in different
consistencies for the products when first mixed at the
proper water/powder ratio. Plaster is usually thin in
consistency, like a ‘smoothie,’ whereas improved
stone is like thick cake batter. Dental stone has an
intermediate consistency. The water/powder ratio has
a direct effect on the properties of each gypsum
product and must be controlled for optimum
18. The strength depends on the porosity of the set
material, and the porosity relates to the water/powder
ratio necessary to make a workable mix. Plaster,which
requires the most gauging water to make a fluid mix, is
the weakest in strength, with improved stone being
the strongest and stone being intermediate between
the two.
19. Table 9.1 One-Hour Compressive Strengths and
Water/Powder Ratios of Gypsum Products
Minimum 1-Hour Compressive
Gypsum Strength (lb/in2 [Mpa])a Water/Powder
Ratiob
Plaster (Type II) 1,300 (9) 45–50 ml/100 g (0.45–0.50)
Dental stone (Type III) 3,000 (21) 28–30 ml/100 g (0.28–
0.30)
Dental stone, high-strength (Type IV) 5,000 (34) 19–24
ml/100 g (0.19–0.24)
Clinical aspect of dental material chapter 9 page 132
20. 2-Impression trays should be
A. rigid.
B. flexible enough to permit easy insertion.
C. carefully polished on the interior.
D. held in place by the patient.
21. With any system, tray rigidity is important, because
even slight flexing of the tray will lead to a distorted
impression. This is particularly frustrating because the
errors are usually undetectable until the practitioner
attempts to seat the restoration.
For this reason, thin, disposable plastic trays are
unacceptable . Resin thicknesses of 2 to 3 mm are
needed for adequate rigidity. Clearance between
the tray and the teeth should also be 2 to 3 mm;
however, greater clearance is necessary for the more
rigid polyether Materials.
Contempory fixed prosthesis section II page 365
22. 3-A ceramometal posterior fixed partial denture
pontic should ???
A. A. be constructed to have an occlusal surface one
quarter the width of the tooth it replaces.
B. be constructed to have an occlusal surface wider
than the width of the tooth it replaces.
C. cover as much mucosa as possible.
D. provide adequate embrasure spaces.
