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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The principal ingredient of modeling plastic is:

 # The principal ingredient of modeling plastic is:

A. Waxes

B. Zinc oxide

C. Aluminium oxide

D. Silicon oxide

The correct answer is A. Waxes.

In general, impression compounds (modelling plastic) are composed of a mixture of waxes, thermoplastic resins, filler, and a coloring agent. Shellac, stearic acid, and gutta-percha are added to improve plasticity and workability. The waxes or resins in the impression compound are the principal ingredients of the matrix. Filler is added to increase the viscosity at temperatures above that of the mouth and to increase the rigidity of the compound at room temperature.

Reference: PHILLIPS’ SCIENCE OF DENTAL MATERIALS, Anusavice, Shen, Rawls, 12th Edition, Page No: 178

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Chemically gypsum is:

# Chemically gypsum is:

A. Calcium sulphate dihydrate

B. Calcium aluminofluorosilicate

C. Calcium carbonate

D. Magnesium carbonate

The correct answer is A. Calcium sulphate dihydrate.

Gypsum (CaSO4•2H2O; calcium sulfate dihydrate) is a mineral mined in various parts of the world, but it is also produced as a by-product of flue gas desulfurization in some coal-fired electric power plants. Various crystalline forms of gypsum, such as selenite and alabaster, exist in nature. Gypsum products are supplied as fine hemihydrate powders that are produced by heating ground gypsum particles. After mixing with water, the mixture reverts back to gypsum. This unique property of gypsum products has led to numerous applications through history.

Reference: PHILLIPS’ SCIENCE OF DENTAL MATERIALS, Anusavice, Shen, Rawls, 12th Edition

Page no: 182

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Serial extraction is indicated primarily in:

 # Serial extraction is indicated primarily in:

A. Class I malocclusion

B. Class II malocclusion

C. Class III malocclusion

D. Lower anterior crowding only

The correct answer is D. Lower anterior crowding only.

Serial extraction is directed toward severe dental crowding. For this reason, it is best used when no skeletal problem exists and the space discrepancy is large-greater than l0mm per arch. If the crowding is severe, little space will remain after the teeth are aligned, which means there will be little tipping and uncontrolled movement of the adjacent teeth into the extraction sites. If the initial discrepancy is smaller, more residual space must be anticipated. It is unwise to start serial extraction in a child who has a skeletal problem, because the closure of extraction spaces would be affected by how the skeletal problem was being addressed.

Serial extraction treatment begins in the early mixed dentition with extraction of primary incisors if necessary, followed by extraction of the primary canines to allow eruption and alignment of the permanent incisors. 

Ref: Comtemporary Orthodontics, 4th Edition, Proffit, Page 490

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