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.

Children oral cavity wounds causes

# The leading cause of childhood gingivostomatitis in children aged 1 to 3 is:
A. Herpes Simplex
B. Chicken pox
C. Influenza
D. Rubella

The correct answer is A. Herpes simplex

The primary infection (primary herpetic gingivostomatitis) usually occurs in a chlld under ten years of age who has had no contact with the Type I herpes simplex virus and who therefore has no neutralizing antibodies. It may also affect young adults (15-25). Nearly all primary infections are of the subclinical type (they may only have flu- like symptoms) and one or two mild sores in the mouth which go unnoticed by the parents.

In other children, the primary infection may be manifested by acute symptoms (acute herpetic gingivostomatitis). These include fever; irritability; cervical lymphadenopathy; fiery red gingival tissues; and small, yellowish vesicles that rupture and result in painful ulcers on the free and attached mucosa. The most serious potential problem in a child with this infection is dehydration due to the child not wanting to eat or drink because of the pain.

Treatment is supportive and aimed toward the relief of the acute symptoms so that fluid and nutritional intake can be maintained. Primary herpetic gingivostomatitis usually runs a course of 14-20 days and the ulcers heal without scarring.

Remember: Of all of the herpes viruses, herpes simplex viruses 1 and 2 cause manifestations of recurrent infection in otherwise healthy people.

BPKIHS First Year BDS past Question- UNIT 1 - March 2014

21st MAR 2014

B.P. Koirala Institute of Health Sciences, Dharan, Nepal

1st year BDS

Internal Assessment Examination, March 2014

Paper - II A

(GENETICS, GROWTH AND DEVELOPMENT, IMMUNOLOGY & BLOOD)

Time - 2 Hours

 Total Marks: 125

SHORT ANSWER QUESTIONS

SECTION - 'A'

ANATOMY 

1. Classify chromosomal disorders with examples of each.                        5
2. Draw a labeled histological diagram of lymph node.                              5
3. Write the criteria and examples of X-linked recessive disorder.             5


                                                                    SECTION - 'B'
PHYSIOLOGY

4. State Landsteiner's law. Explain Rh and ABO blood group on the basis of this law.      2+2=4

5. With the help of flow diagram, explain the extrinsic pathway in blood coagulation.      4
6. Explain the role of erythropoietin in red blood cells production.       4
7. Draw the general, somatic and neural growth curves and briefly compare their patterns.     4
8. Explain the role of cytotoxic T cell in cellular immunity.              4

SECTION 'C'

BIOCHEMISTRY

9. Define the terms isotypes, idiotypes and allotypes.  Draw a labeled diagram of immunoglobulin.      3+2=5
10. Write similarities and differences between the processes of DNA and RNA synthesis.      5
11. Enumerate different post-translational modifications of polypeptide chain. Explain the function of chaperones.              3+2=5
12. Describe the mechanism of gene regulation with the help of lac operon model.          5
13. Explain how polymerase chain reaction (PCR) helps to amplify a target sequence of DNA.     5
14. Explain with a diagram mechanism of  iron absorption in the intestine.         5

SECTION 'D'

PATHOLOGY

15. Enumerate the types of Hypersensitivity reactions. Give at least two examples for each. Write briefly about type II hypersensitivity reaction.          2+1+2=5

16. Enumerate the types of blood components. What are the immediate and delayed blood transfusion reactions.         2+4 =6

17. Describe the peripheral smear and bone marrow findings of Megaloblastic anemia.     5+3=8

18. Enumerate six differences between AML and ALL.                                                     6

19. Classify Hemolytic Anaemia.                                                                                        5

SECTION 'E' 

MICROBIOLOGY

20. Draw a labeled diagram of HIV.                           5

21. Write short note on innate immunity.                   5

22. List the fungi causing opportunistic infection. Add a note on approach to lab diagnosis of any one of them.       2+3=5 

SECTION 'F'

PHARMACOLOGY

23. Explain warfarin effect in pregnancy.                 5

24. Explain Cyclophosphamide effect in urinary bladder.        5

25. Explain Cyclosporine effect in kidney.                               5

***

MCQs in Oral Pathology - Diseases of Microbial Origin

# Endotoxin is released from:
A. Candida albicans
B. Streptococcus sanguis
C. Gram negative bacteria
D. Actinomyces viscosus

# All of the following oral conditions can give rise to bacteremias, EXCEPT:
A. Extraction of tooth
B. Periodontitis
C. Endodontic therapy
D. Dentinal caries

# The most common extraoral cause of halitosis is:
A. Indigestion
B. Alcohol intake
C. Chronic sinusitis
D. Diabetes mellitus

# The typical triad of maxillary sinusitis are:
A. Nasal congestion, pathological secretion, Headache
B. Nasal congestion, trismus, epiphora
C. Nasal congestion, maxillary tooth pain, bloody discharge from the sinus
D. Nasal obstruction, headache, ear ache