Initial dissolution of Tooth Substance by Acid

# In the carious process, the initial dissolution of the tooth substance by acid takes place in which of the following place?
A. Below the dentin Surface
B. Below the enamel surface
C. On the enamel surface
D. Towards the dentin

The correct answer is B. Below the Enamel Surface.

The top portion of the tooth remains intact and it's the subsurface which looses the minerals. This is the stage where it's called as incipient lesion. Once the top protion breaks, it's called a cavitated lesion.

Digestive System and Nutrition - MBBS BDS Entrance Examination

The correct answers are highlighted in green.

# Micelles are the bodies related to:
 A. Secretion of hormones
 B. Secretion of enzymes
 C. Absorption of minerals
 D. Absorption of fat

# Movements of circular muscles in the stomach is called
 A. Digestion
 B. Absorption
 C. Excretion
 D. Peristalsis

Sites of Various Metabolic Pathways

Sites	Metabolic Pathways
Mitochondria	Citric acid cycle Oxidative phosphorylation Fatty acid oxidation Electron transfer Synthesis of ketone bodies
Ribosomes	Protein Synthesis
Golgi Complex	Glycoprotein synthesis
Nucleolus	RNA Synthesis
Cytoplasm	Cholesterol synthesis Glycolysis Fatty acid synthesis Glycogenesis Glycogenolysis HMP shunt Gluconeogenesis
In both mitochondria and cytosol	Urea Cycle Gluconeogenesis

# Clotting factor common to extrinsic and intrinsic pathway is:

# Clotting factor common to extrinsic and intrinsic pathway is:
A. Factor II
B. Factor III
C. Factor V
D. Factor VII

The correct answer is C. Factor V.

Prothrombin activator that is formed in intrinsic and extrinsic pathways converts prothrombin

into thrombin in the presence of calcium (factor IV). 

Once formed thrombin initiates the formation of more thrombin molecules. The initially formed thrombin activates Factor V. Factor V in turn accelerates formation of both extrinsic and intrinsic prothrombin activator, which converts prothrombin into thrombin. This effect of thrombin is called positive feedback effect. 

# Acid etching is done to:

# Acid etching is done to:
A. Decrease microleakage
B. Decrease polymerization shrinkage
C. Decrease Coefficient of thermal expansion
D. Decrease porosity in restorative material

The correct answer is A. Decrease microleakage.

Acid-etching transforms the smooth enamel into an irregular surface  and increases its surface free energy. When a fluid resin-based material is applied to the irregular etched surface, the resin penetrates into the surface, aided by capillary action. Monomers in the material polymerize, and the material becomes interlocked with the enamel surface.The formation of resin microtags within the enamel surface is the fundamental mechanism of resin-enamel adhesion.

As measured in the laboratory, shear bond strengths of composite to phosphoric acid-etched enamel usually exceed 20 megapascals (MPa) and can range up to over 50 MPa, depending on the test method used. Such bond strengths provide adequate retention for a broad variety of procedures and prevent leakage around enamel margins of restorations.

# Iron content in 3M Nickel based steel crowns is:

# Iron content in 3M Nickel based steel crowns is: (MAN -01)
a) 20%
b) 40%
c) 60%
d) 10%

The correct answer is D. 10 %.

Composition of stainless steel crowns:
Stainless steel (18-8) austentic type of alloy is used. Eg.: Rocky mountain and unitek.
Iron -                 87%
Chromium - 17%
Nickel -         12%
Carbon -          0.08 - 1.15%

Nickel base crowns. Eg.: Iconel 600 and 3M crowns
Iron                     -  10%
Chromium -    16%
Nickel - 72%
others - 2%

# A gingival wall is difficult to obtain in primary molar when it extends too far gingivally in class II cavities because: (MAN-97)

# A gingival wall is difficult to obtain in primary molar when it extends too far gingivally in class II cavities because: (MAN-97)
a) Facial pulp horn may be exposed
b) Inclination of cervical enamel rods occlusally
c) Of marked cervical constriction
d) Prime contact is broad and flat

The correct answer is C. of marked cervical constriction.

Gingivally the enamel rods have an occlusal direction in primary teeth so bevel is not required as there will be no unsupported enamel rods. It is difficult to obtain gingival wall when lesion extends too far gingivally in primary molar due to the presence of marked cervical constriction.