Ease with which impression can be poured without bubble formation is related to:

# Ease with which impression can be poured without bubble formation is related to:

A. Hardness of impression material

B. Resiliency of impression material

C. Contact angle of the die material with the impression material

D. Surface contamination

The correct answer is C. Contact angle of the die material with the impression material.

When gypsum products are mixed with water to pour dental models in various types of impressions, wetting must occur between gypsum and the impression to ensure good surface quality of the gypsum model. The basic ingredient of the most popular silicone-based elastomeric impression material today is considered to be hydrophobic, because a contact angle of greater than 90° is observed when an aqueous medium is poured into this elastomeric mold. To improve the wettability of the set impression material by a gypsum-water mixture, the operator usually sprays a surfactant (also called debubblizer). The most direct approach by the manufacturer is to incorporate a wetting agent (also known as a surfactant)

in the impression material during the manufacturing process. 

Reference: PHILLIPS’ SCIENCE OF DENTAL MATERIALS, Anusavice, Shen, Rawls, 12th Edition, Page No: 27

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Which portion of the flame is used while soldering:

# Which portion of the flame is used while soldering?

A. Cold mixing zone

B. Partial combustion zone

C. Tip of the reducing zone

D. Oxidizing zone

The correct answer is C. Tip of reducing zone.

The next zone, dimly blue and located just beyond the tip of the green combustion zone, is the reducing zone. This is the hottest part of the flame, and it should be kept constantly on the alloy during melting. The outer cone (oxidizing zone) is the area in which combustion occurs with the oxygen in the air. Under no circumstances should this portion of the flame be used to melt the alloy. Not only is its temperature lower than that of the reducing zone but it also oxidizes the alloy.

Reference: PHILLIPS’ SCIENCE OF DENTAL MATERIALS, Anusavice, Shen, Rawls, 12th Edition, Page No: 221

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PGCEE MDS 2022: When porcelain is baked, is backed against metal, it should possess a:

 # When porcelain is baked, is backed against metal, it should possess a:

A. High fusion expansion

B. Linear coefficient of thermal expansion less than, but close to that of the metal

C. Linear coefficient of thermal expansion greater than, but close to that of the metal

D. Linear coefficient of thermal expansion greater than that of the metal

The correct answer is B.: Linear coefficient of thermal expansion less than, but close to that of the metal

The metal and porcelain should be selected with a slight mismatch in their coefficient of thermal contraction (the metal CTC being slightly higher) so that the metal contracts slightly more than the porcelain on cooling from the firing temperature to room temperature. This mismatch leaves the porcelain adjacent to the metal in a state of residual compression, which effectively protects the metal-ceramic restoration against fracture of the veneering ceramic.

Reference: PHILLIPS’ SCIENCE OF DENTAL MATERIALS, Anusavice, Shen, Rawls, 12th Edition, Page No: 441

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Smoothening the surface and margin of amalgam restoration:

 # The act of smoothening the surface and margin of amalgam restoration is known as:

A. Condensation

B. Burnishing

C. Trituration

D. Amalgamation

The correct answer is B. Burnishing.

After carving is completed, the surface of the restoration should be smoothed. This may be accomplished by judiciously burnishing the surface and margins of the restoration. Burnishing of the occlusal anatomy can be accomplished with a ball burnisher.

Reference: PHILLIPS’ SCIENCE OF DENTAL MATERIALS, Anusavice, Shen, Rawls, 12th Edition, Page No: 350

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