Teeth that are least affected by periodontal disease are:

 # Teeth that are least affected by periodontal disease are: 

A. Lower first molars and upper anteriors 

B. Lower premolars and upper canines 

C. Lower first molars and upper incisors and premolars 

D. Lower centrals, laterals and upper molars 

The correct answer is B. Lower premolars and upper canines.

Teeth least affected by periodontitis are upper canine and lower second premolar. Most affected are lower molars. The teeth that are moderately affected by periodontal disease are all the upper molars; the upper centrals. laterals, and premolars; and the lower canines. 

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The malleting force is directed:

 # The malleting force is directed:

A. Perpendicular to the walls

B. Parallel to the long axis of crown

C. 45 degrees to the wall

D. 30 degrees to the wall

The correct answer is C. 45 degrees to the wall.

To ensure dense masses in corners and at the junction between two walls, the line of force must be directed to bisect line angles and trisect point angles.

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Which of the following is not a function of flux?

 # Which of the following is not a function of flux?

A. To remove any oxide coating on parent metal

B. To restrict the flow of solder over the parent metal

C. To protect metal surface from oxidation during soldering procedures

D. To permit the flow of solder over parent metal

The correct answer is B. To restrict the flow of solder over the parent metal, this is the function of antiflux, not flux.

The Latin word ‘flux’ means flow. For a solder to wet and flow properly, the parent metal must be free of oxides. This is accomplished with the help of a flux.

FUNCTION OF FLUX

1. To remove any oxide coating on the parent metal.

2. To protect the metal surface from oxidation during soldering.

TYPES

Fluxes may be divided into three activity types.

- Protective: This type covers the metal surface and prevents access to oxygen so no oxide can form.

- Reducing: This reduces any oxide present to free metal and oxygen.

- Solvent: This type dissolves any oxide present and carries it away. Most fluxes are usually

combination of two or more of the above.

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The temperature difference between gelation and liquefaction temperature of hydrocolloid is:

 # The temperature difference between gelation and liquefaction temperature of hydrocolloid is: 

A. Syneresis

B. Imbibition

C. Hysteresis

D. Chelation

The correct answer is C. Hysteresis.

Most materials melt as well as resolidify at the same temperature. However in agar this does not coincide. Gelation (solidification) occurs at 37°C approximately, whereas liquefaction (melting) occurs at a higher temperature, i.e., 60 to 70°C higher than the gelation temperature. This temperature lag between liquefaction and gelation is known as hysteresis.

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