Download 1- What are the characteristic of the ideal dental materials

Dental Biomaterials
Date: 21/3/09
Student No.: ………………..….
I.
Student name: …………………
What are the characteristic of the ideal dental materials?
1
II. In the following multiple-choices questions, one or more of the responses may be
correct.
1. Which of the following conditions could lead to corrosion in restorative dentistry?
a.
b.
c.
d.
A composite contaminated with iron during handling in the dental laboratory.
A chemical attack of a metal by components in food or saliva.
Polished amalgams that have become dull and discolored with time.
Adjacent restorations constructed of dissimilar metals.
2. An amalgam has a force of 111N applied over contact area of 0.645 mm2 , which
of the following is the stress applied to the amalgam? Would you expect the amalgam
to fracture? (Note, the ultimate compression strength of amalgam over 300 MPa)
a.
b.
c.
d.
17.2 MPa
1720 MPa
172 MPa No will not fracture
1.72 MPa
3. Which of the following statements are true?
a. The yield strength is always slightly higher than the proportional limit.
b. Above the stress associated with yield strength, a material no longer functions
as an elastic solid.
c. Above the stress associated with the yield strength, a material will be
permanently deformed, even after the applied force is removed.
d. Most restorations are not classified as clinical failures until fracture has
occurred.
4. Which of the following are example of Galvanism in restorative dentistry?
a. A piece of aluminum foil from a backed potato becomes wedged between
two teeth and contact a gold restoration.
b. A temporary plastic crown contacts a gold restoration.
c. A temporary aluminum crown contacts a gold restoration.
d. A metallic taste is a frequent complaint of patients.
2
5. Adhesion of composite restoration with tooth surface by using acid etching and
bonding agent consider as:
a.
b.
c.
d.
Mechanical retention.
Chemical retention.
Micro-mechanical retention
Combination of micro-mechanical and chemical retention.
6.The restoration material used to restore a small portion of an anterior tooth
should have which of the following properties?
a- Esthetic
b- High strength
c- Durability
d- Ease of casting
7. Full denture bases are usually made from which of the following materials?
a- Composite restorative resin
b- Gold alloys
c- Acrylic resin
d- Ceramic
8. Which of the following conditions could lead to microleakage between tooth and
restoration:
a. Difference in Co-efficient of thermal expansion between a restoration and tooth
structure.
b. Difference in surface hardness between restoration and tooth structure.
c. Poor adhesion between restoration and tooth surface.
d. Difference in melting temperature between restoration and tooth structure.
3
9. Which of the following statements are true?
a. The initial setting time characterizes the start of the chemical reaction of model
plaster.
b. The initial setting time of model plaster can be detected clinically by
the phenomenon know as loss of gloss.
c. Common practice allows the plaster cast to harden for 45 to 60 minutes. before
removal of it from impression.
e. The setting time of gypsum can be altered easily by the operator with the use of
accelerator.
10. Increasing the water-powder ratio of high-strength stone would do which of the
following?
a.
b.
c.
d.
Lengthen the initial setting time.
Increase the 1 hour compressive strength.
Increase the setting expansion.
Increase the amount of excess water used to mix the material.
11. A pattern wax might be used to do which of the following:
a.
b.
c.
d.
Make corrective impression.
Form a mold around an impression.
Form a general size and contour of a restoration.
Useful for bite registration.
12. Which of the following is true of residual stress?
a. Is developed in wax when it is cooled under stress.
b. Results in a uniform dimensional change that can be compensated for in the
casting process
c. Can be minimized by the manipulation of wax at a temperature as high as is
practical
d. Can cause warpage that increases at higher storage temperatures and during
longer storage times.
4