BIOLOGICAL EFFECTS OF Radiation IN DENTISTRY. ppt.pdf

Radiation damage to tissue and/or organs depends on the dose of radiation received, or the absorbed dose which is expressed in a unit called the gray (Gy). The potential damage from an absorbed dose depends on the type of radiation and the sensitivity of the different tissues and organs.

1. BIOLOGICAL EFFECTS
OF RADIATION
DR M REDDY

2. INTRODUCTION
Although the amount of x-radiation used in
dental radiography is small, biologic damage
can occur.
The dental radiographer must have a working
knowledge of radiation biology, the study of
effects of ionizing radiation on living tissue in
order to understand the harmful effects of x-
radiation.

3. ACCUMULATION OF
RADIATION
The effect of radiation is cumulative
Effects of the exposure increases every time
the individual is exposed to radiation: “long
term effect”
Exposure to radiation:
Natural (sun, earth, atmosphere)
Artificial (X-rays used for diagnoses, TV,
airline travel, tobacco)

4. LATENT PERIOD
Is the time that elapses between the
exposure to ionizing radiation and the
appearance of clinical symptoms
Time may vary from hours to years
depending on the magnitude of the exposure
and the tissues involved

5. MECHANISMS OF INJURY
In diagnostic radiography, not all x-rays pass through the patient
and reach the dental x-ray film.
Some are absorbed by the patient’s tissues.
Absorption is the total transfer of energy from the x-ray photon to
patient tissues.
When x-ray energy is absorbed by the patients tissues, chemical
changes occur that will result in biologic damage.
There are two forms of radiation injury:-
Ionisation –produced through the photoelectric effect. Chemical
changes occur within the cell that result in biologic damage.
Free Radical formation –results in cell damage.

6. THEORIES OF RADIATION
INJURY
Direct Theory –cell damage results when
ionising radiation directly hits critical areas or
targets within the cell. X-rays may directly
break part of the chromosome and this could
lead to abnormal cell formation or cell death.
Can be passed onto later generations.
Indirect Theory –x-ray photons are absorbed
within the cell and cause the formation of
toxins, which damage the cells.

7. CLASSIFICATION
The biologically damaging effects of ionizing
radiation
are classified into three main categories:-
Somatic deterministic effects (acute or
immediate effects)
Somatic stochastic effects (chronic or long
term effects, latent period, eg. Leukemia)
Genetic stochastic effect

8. SOMATIC DETERMINISTIC
EFFECTS
Results from a specific high dose of radiation.
Damaging effects to the body:
Skin reddening, cataract formation
Severity proportional to dose received
A threshold dose exists below which there will
be no effect.

9. SOMATIC STOCHASTIC
EFFECTS
Effects that maydevelop.
Development is random and depends on the
laws of chance or probability.
Eg. Leukemia, certain tumours

10. GENETIC STOCHASTIC
EFFECTS
Mutations could result from any sudden change to a
gene or chromosome
Changes in genetic cells cannot be detected in the
exposed patient but are passed onto succeeding
generations
Could be caused by radiation or may occur
spontaneously
Radiation maydamage the DNA of the sperm or egg
cell
Mayresult in a congenital abnormality in the
offspring

11. EFFECTS OF RADIATION ON
CELLS
Division of cells:
Somatic –all cells in the
body except reproductive
cells.
Genetic –reproductive
cells
Cell types:
Radiosensitive cells
Radioresistant

12. DENTAL RADIOGRAPHY
Doses used are small and well below the
threshold
Do not irradiate the reproductive organs,
therefore somatic stochastic effects of
radiation are of most concern

13. RADIATION EFFECTS ON
TISSUES AND ORGANS
Critical organs
Skin
Thyroid
Eye lens
Bone marrow

14. TISSUE SENSITIVITY: THE EFFECT OF
RADIATION ON TISSUES AND ORGANS
High Sensitivity Intermediate Sensitivity Low Sensitivity
Bone marrow
Testes
Intestines
Skin
Cornea
Salivary Glands
Lungs
Kidneys
Liver
Optic lens
Muscle cells
Neurons
Fine vasculature
Growing cartilage
Growing bone

15. Dose Whole Body Effect
0.25 Sv Nil
0.25-1.0 Sv Decrease in white blood cell count
1-2 Sv Vomiting in 3 hours, fatigue, loss of appetite, blood changes. Recovery few
weeks
2-6 Sv Vomiting in 2 hours, severe blood changes, loss of hair. Recovery 1 month to 1
year
6-10 Sv Vomiting in 1 hour, intestinal damage, severe blood changes. Death in 2 weeks.
80-100%
> 10 Sv Brain damage, coma, death

16. RADIATION EFFECTS ON
ORAL TISSUE
Oral mucosa
Taste buds
Salivary Glands
Teeth (Radiation caries)
Alveolar bone

17. ORAL MUCOSA
Basal layer is radiosensitive
Redness and inflammation
Mucositis, followed by ulcerations and
pseudomembranous coverings
Secondary infection is common
Long term exposure can lead to atrophy,
avascularity and fibrosis

18. TASTE BUDS
Radiosensitive
Patients lose sensation within two weeks
If posterior aspect of tongue is irradiated,
bitter and acid taste is affected
If anterior two-thirds of the tongue are
irradiated, salt and sweet taste is affected
Decreased salivary flow may also account for
loss in taste sensation

19. SALIVARY GLANDS
Parotid gland more radiosensitive than
submandibular sublingual glands
Gland becomes fibrotic, fatty with loss of vasculature
Saliva becomes more viscous, volume is decreased,
pH is lower and leads to a tender oral cavity
This change in saliva has profound changes on the
oral microflora and on the dentition
The microflora becomes more acidogenic and
together with the reduced buffering capability, leads
to radiation caries

20. RADIATION CARIES
Treatment of head and neck cancer
High doses of radiation affects the salivary glands
Salivary production more viscous, leading to
xerostomia (dry mouth)
Altered quality and quantity of saliva. Patient more
susceptible to rampant caries
Affects the cervical areas of teeth
Fluoride trays, artificial saliva and frequent recall
visits are all part of an accepted means to cope with
this condition

21. TEETH
Adult teeth are relatively radiosensitive
If teeth are irradiated during development,
growth may be retarded and calcification
process altered or hindered
Extraction of carious teeth or periodontally
involved teeth is indicated prior to radiation
therapy

22. BONE
Reduced blood vasculature
Changes leaves bone vulnerable to infection
Osteoradionecrosis can occur

23. SKIN
Erythema (reddening of skin)
250 cSv is needed to produce this effect
Full mouth series (70kvp, D-speed film and round
collimation) produces a skin dose of 8.4.m Sv
60 full mouth series in a 14-day period will be
necessary to produce this effect. (clinically this is not
possible)
Skin erythemas can be seen on patients undergoing
radiation therapy for the head and neck

24. EYES
Required dose to produce this change is
2000-5000mSv
Corneal surface dose for a full mouth series
is 0.6mSv.
Cataract formation

25. THYROID
A dose of approx. 6000mrads is necessary to
produce cancer in the thyroid gland.
Such a large dose is not incurred in dental
radiography. The thyroid exposure for a full
mouth series is about 0.94mSv
Recommendation: use of a thyroid collar

26. BONE MARROW
Potential somatic hazard to patients:
leukemia induction
Numerous studies show no changes in the
complete blood count after dental X-ray
examination

27. GONADS
Very radiosensitive
Sterility from acute exposure from the dental X-ray
beam is an impossibility
400R is needed in the male (radiation absorbed
dose: 1 Gray = 100 Rads)
625R is needed for the female
Dose to gonads is in the form of secondary radiation
Full mouth series without lead apron: dose is
0.5mSv
With lead apron, effect can be reduced by 95%

28. PREGNANCY
Non-differentiated, rapidly growing cells are
extremely radiosensitive
Foetus sensitive to radiation 2-9 weeks after
conception
Radiation to the foetus: through secondary radiation
Congenital abnormalities and death with large doses
of radiation
Mental retardation with low doses
Radiographs should be deferred during pregnancy
as a precautionary measure