Chapter 15 Impression Materials

Chapter 15  Impression Materials

Complete Chapter Questions And Answers
 

Sample Questions

MULTIPLE CHOICE

1. The completed impression forms a _____ reproduction of the teeth and tissues, and the replica or model forms a _____ replica of the teeth and tissues.
a.
positive; positive
b.
positive; negative
c.
negative; positive
d.
negative; negative

ANS: C
The completed impression forms a negative reproduction of the teeth and tissues, and the replica or model forms a positive replica of the teeth and tissues. The replica is called a cast or model. In the initial diagnosis and treatment planning phase, the dentist may request that the dental assistant or hygienist make impressions of the teeth and surrounding structures so that diagnostic casts, commonly called study models, can be made for further study when the patient is no longer present.

REF: p. 244 TOP: Overview of Impressions

2. Which statement is true about impression trays?
a.
The triple tray is a custom full-arch tray used for bite registration.
b.
Stock trays are made of plastic rather than metal and can be solid or perforated.
c.
Plastic trays are inexpensive and disposable, whereas metal trays are more expensive and must be cleaned and sterilized between uses.
d.
Custom trays are constructed in the patient’s mouth with chemically cured, light-cured, or thermoplastic resins on casts of the teeth.

ANS: C
Plastic trays are inexpensive and disposable, whereas metal trays are more expensive and must be cleaned and sterilized between uses. Stock trays can be metal or plastic, and each of these can be solid or perforated. Custom trays are usually constructed in the laboratory with chemically cured, light-cured, or thermoplastic resins on casts of the teeth. The triple tray is a stock sectional tray that is used to make an impression of the teeth being treated and the opposing teeth at the same time and, if used properly, will capture the correct centric occlusion of the patient.

REF: p. 247 TOP: Impression Trays (Stock Trays)

3. Which of the following is true for hydrocolloids in dentistry?
a.
Agar hydrocolloid is a reversible hydrocolloid.
b.
Agar hydrocolloid requires the use of custom impression trays.
c.
The main clinical use of reversible hydrocolloid is for impressions for diagnostic casts.
d.
When agar powder is mixed with water, it forms a gluelike suspension that entraps the water, making a colloidal suspension called a gel.

ANS: A
Agar hydrocolloid is a reversible hydrocolloid. When agar powder is mixed with water, it forms a gluelike suspension that entraps the water, making a colloidal suspension called a sol. When the agar sol is chilled, it will gel, becoming a semisolid or jelly-like. The main clinical use of reversible hydrocolloid is for impressions of operative and crown and bridge procedures. The use of agar hydrocolloid requires stock metal trays with tubing running through them that connects to a water line by rubber hoses to circulate tap water through the tray.

REF: p. 247 TOP: Hydrocolloids

4. The temperature at which the hydrocolloid liquefies is not the same temperature at which it solidifies. What is this property called?
a.
Hysteresis
b.
Hydrophilic
c.
Hydrophobic
d.
Agglutination

ANS: B
The temperature at which the hydrocolloid liquefies is not the same temperature at which it solidifies, a property called hysteresis. When the hydrocolloid gels are heated to 71° C to 100° C, they become liquid. When the hydrocolloid is cooled to 30° C to 45° C, it returns to a solid.

REF: p. 247 TOP: Hydrocolloids