1. Radiobiology is the study of the effects of ionizing radiation on biological tissues. DNA is the most sensitive structure affected, as it regulates cellular activity and contains genetic information. 2. Radiation can directly damage DNA molecules and other cellular components like RNA, enzymes, and proteins. However, most damage occurs indirectly when radiation interacts with water molecules within cells, producing ions and free radicals that then damage DNA. 3. The effects of radiation exposure depend on factors like radiation dose and the type of exposed cells. Somatic effects impact the exposed individual's health while genetic effects can impact future generations if reproductive cells are affected.

1. Dr. Umar Tauqir

2. 
What is Radiobiology?
•The study of effect of ionizing radiation
on biological tissues
What is cell theory?
•Cell are basic functional unit of all plants
and animals

3. 
What is cell
theory?
Cells are the basic
functional units in
all plants and
animals.

4. 
What do
macro
molecules
consist of?

5. 

6. 
 DNA is the most sensitive structure to be affected by
radiations
 It regulates cellular activity and contain genetic
information needed for cell replication.
 Permanent changes alter the cell function and result
in cell death.

7. 
 which cell effect by which type of radiations.

8. 
Direct
effect
Indirect
effect
Effect of Radiations

9. 
 In an X-RAY or some other type of radiation interact
with DNA molecules. Particular radiation because of
its mass cause more damage to DNA molecule.
 Other particles like RNA enzymes and proteins can
also be affected by direct effect of radiations
DIRECT EFFECT OF
RADIATIONS

10. 

11. 
 Most of the damage to DNA molecules take place
through indirect effect. When X-rays enter a cell,
they most likely hit a water molecule because there
are large number of water molecules inside a cell.
The x-ray ionizes a water molecules. Ions, free
radicals are produced which in turn bond with DNA
molecule changing its structure. Since the x-ray
interacted with water molecule before the DNA Was
involved, this is called indirect effect
INDIRECT EFFECT

12. 
 A free radical is any atom or molecule that has a
single unpaired electron in an outer shell. While a
few free radicals such as melanin are not chemically
reactive, most biologically-relevant free radicals are
highly reactive. It is the primary mediatory of
indirect effect of radiation
FREE RADICAL

13. 
Change or loss of base
Disruption of hydrogen
bonds between DNA strands
Breakage of one or both
DNA strands
What effects happen on
DNA due to radiations

14. 
Ionization alters the structure of
cell but has no negative effect
Cells are damaged by ionization
but damage is repaired
Mutation can be occurred as well
cell damage is so extensive that
it can damage the cell
CELLULAR EFFECTS

15. 
 Greatest dose of radiation which is not expected to
cause detectable bodily injury to people at anytime
during their life
 The amount of ionizing radiation a person may
exposed to supposedly without being harmed
 The limits of ionizing radiation set for general public
by international commison on radiological
protection. For radiological workers this limit is
50msv
MAXIMUM
PERMISSIBLE DOSE

16. 
The amount of ionizing radiation
that will kill 50% of population in a
specified time
MEDIAN LETHAL
DOSE

17. 
 Stochastic effects occur by chance and can be
compared to deterministic effects which result in a
direct effect.
 The damaging effects may be induced when body is
exposed to any dose of radiations. Experimentally it
is not possible to establish a safe dose. It is therefore
assumed that there is no thresh-hold dose so that
every exposure does carry a stochastic effect
Stochastic effects

18. 
 Non-stochastic (deterministic effects) are somatic
effects that have a threshold that increase in severity
with the absorbed dose
 Examples of non-stochastic effect include erythema,
loss of hair, cataract formation and decreased fertility
 Compared to stochastic effects, deterministic effects
required a large dose to cause serious impairment of
health
DETERMINISTIC
EFFECTS

19. 
 Following the latent period, effects that are seen
within minutes, days, or weeks are termed short-
term effects. Short-term effects are associated with
large amounts of radiation absorbed in a short time
(e.g., exposure to a nuclear accident or the atomic
bomb).
 Acute radiation syndrome (ARS) is a short-term
effect and includes nausea, vomiting, diarrhea, hair
loss, and hemorrhage.
 Short-term effects are not applicable to dentistry
Short term effects

20. 
 Effects that appear after years, decades, or
generations are termed long-term effects.
 Long-term effects are associated with small amounts
of radiation absorbed repeatedly over a long period.
Repeated low levels of radiation exposure are linked
to the induction of cancer, birth abnormalities, and
genetic defects
Long term effects

21. 
 All the cells in the body can be classified as either
somatic or genetic.
 Somatic cells are all the cells in the body except the
reproductive cells.
 The reproductive cells (e.g., ova, sperm) are termed
genetic cells.
 Depending on the type of cell injured by radiation,
the biologic effects of radiation can be classified as
somatic or genetic.
SOMATIC AND
GENETIC EFFECTS

22. 
 Somatic effects are seen in the person who has been
irradiated. Radiation injuries that produce changes
in somatic cells produce poor health in the irradiated
individual.
 Major somatic effects of radiation exposure include
the induction of cancer, leukemia, and cataracts.
 These changes, however, are not transmitted to
future generations
SOMATIC EFFECTS

23. 
 The developing fetus is particularly sensitive to the effects of
radiation, especially during the period of organogenesis (2–9
weeks after conception).
 Exposures in the range of 2 to 3 Gy during the first few days
after conception are thought to cause undetectable death of the
embryo.
 The period of maximal sensitivity of the brain is 8 to 15 weeks
after conception.
 The major problems are:
1.Congenital abnormalities or death associated with large doses
of radiation
2.Mental retardation associated with low doses of radiation.
 As a result, the maximum permissible dose to the abdomen of a
woman who is pregnant is regulated by law.
EFFECT ON THE
UNBORN CHILD

24. 

25. 

26. 
 1. Skin: The reaction of the skin to radiation may be categorized as:
i. Early or acute signs:
• Increased susceptibility to chapping.
• Intolerance to surgical scrub.
• Blunting and leveling of finger ridges.
• Brittleness and ridging of finger nails.
ii. Late or chronic signs:
• Loosening of hair and epilation.
• Dryness and atrophy of skin, due to destruction of the sweat glands.
• Progressive pigmentation, telangiectasis and keratosis.
• Indolent type of ulcerations.
• Possibility of malignant changes in tissue.
RADIATION EFFECTS
ON CRITICAL ORGANS

27. 
 All these changes in the skin are due to radiation
trauma to:
1-The blood vessels.
2- Connective tissue.
3- Epithelium.
 Early erythema may appear from a single dose of
about 450 rads.
 With lower doses no erythema occurs

28. 
 13 mR for full mouth intraoral periapical radiographs.
 A maximum dose of 200 R is required for any damage to
the marrow or blood forming organs.
 Hence, the risk of bone marrow damage from dental X-
rays is small.
 The primary somatic risk from dental radiography is
leukemia induction,especially in young individuals.
 This is because at birth all bones contain only red bone
marrow. younger individuals are at a greater risk of
developing leukemia.
BONE MARROW

29. 
 THYROID
40 mR for full mouth intraoral periapical radiographs.
A dose of 10 R will produce thyroid cancer.
 Gonadal – a single intraoral radiograph gives 100 to 900
mR to the face.
From this;
Male gonads receive 0.3 mR.
Female gonads receive 0.03 to 0.001 mR,
 Eye – a series of full mouth intraoral periapical
radiographs, will give only a few mR.
Cataract of the lens is produced after 500 R of exposure

30. 