Anatomy of Mandible

# Which of the following structure is not present on the internal surface of mandible?

a) Lingula
b) Genial tubercle
c) Mylohyoid ridge
d) Mental foramen 

The correct answer is D. Mental foramen.

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Contents of Brainstem

# Which is not a part of brainstem?
a) Midbrain
b) Cerebellum
c) Medulla oblongata
d) Pons 

The correct answer is B. Cerebellum.

WHO Oral Health Assessment Form - Filled Sample

Hardness of Dental Materials

Hardness
–– Hardness is defined as the ability of a material to resist scratching.
–– Can be divided into microhardness and macrohardness.

Tests for Microhardness:
- Knoop Hardness Test
- Vickers Hardness Test

Tests for Macrohardness:
- Brinell hardness
- Rockwell hardness

1. Brinell Hardness Test

• Oldest test employed for determining the hardness of metals
• A hardened steel ball is pressed under a specified load into the polished surface of a material. The load is divided by the area of the projected surface of the indentation, and the quotient is referred to as the Brinell hardness number, usually abbreviated as BHN.
• For a given load, the smaller the indentation, the larger is the number and the harder is the material.
• Used extensively for determining the hardness of metals and metallic materials used in dentistry
• It is related to the proportional limit and ultimate tensile strength of dental gold alloys.

2. Rockwell Hardness Number 

• Is somewhat similar to Brinell test in that a steel ball or a conical diamond point is used
• Instead of measuring the diameter of the impression, the depth of penetration is measured directly by a dial gauge on the instrument
• Neither the Brinell test for the Rockwell test is suitable for brittle materials.

3. Vickers Hardness Test

• Employs the same principle of hardness testing as Brinell test
• Instead of a steel ball, a diamond in the shape of a square based pyramidal is used
• The lengths of the diagonals of the indentation are measured and averaged
• The Vickers test is employed in the ADA specifications for dental casting gold alloys
• Suitable for determining the hardness of brittle materials
• Used for measuring the hardness of tooth structure

4. Knoop Hardness Test

• Employs a diamond indenting tool that is cut in the geometric configuration
• The impression is rhombic in outline, and the length of the largest diagonal is measured
• The hardness value is virtually independent of the ductility of the material tested.

5. Shore and Barcol Test

• Are employed for measuring the hardness of dental materials, particularly rubbers and plastics

MCQs on Radiation Biology and Safety - Part 1

# Among the natural radiation, the one that contributes to more radiation exposure of general population:
A. Cosmic
B. Terrestrial
C. Radon
D. Consumer products

# X rays cause radiation damage primarily by their property of:
A. Penetration
B. Radioactivity
C. Electromagnetic induction
D. Ionisation

Most radiosensitive cells:

# The most radiosensitive cells in the body are:
A. Endothelial cells
B. Epithelial cells
C. Red blood cells
D. White blood cells

The correct answer is D. White blood cells.

Identical twins develop from:

# Identical twins are produced by fertilization of:
A. 1 ovum by 1 sperm
B. 2 ova by 1 sperm
C. 1 ovum by 2 sperms
D. 2 ova by 2 sperms

The correct answer is: A. 1 ovum by 1 sperm

Twins can be either monozygotic ('identical'), meaning that they develop from one zygote, which splits and forms two embryos, or dizygotic ('non-identical' or 'fraternal'), meaning that each twin develops from a separate egg and each egg is fertilized by its own sperm cell.