L3 Detrimental Effects of Ionising Radiation

Question 1

What proportion of all X-rays taken in the UK each year are dental?

Answer 1

25-30%

Question 2

What does ionising radiation mean?

Answer 2

High photon energy, short wavelength, able to remove electrons from atoms.

Question 3

What are the 2 groups of radiation dangers and what do they mean?

Answer 3

• Tissue reactions: things which definitely happen with high doses of radiation, higher the dose the more severe the consequences
• Stochastic effects: chance effect which may or may not happen, higher the dose the more probable that consequences will exist, e.g. cancer development (if somatic cell is affected), heritable disease (genetic cells)

Question 4

What are the early effects following radiation of different doses?

Answer 4

• 0.25Sv = nil effect
• 0.25-1Sv = slight blood changes
• 1-2Sv = vomiting, fatigue, loss in appetite
• 2-6Sv = vomiting, severe blood changes, alopecia (70% chance of recovery)
• 6-10Sv = 80-100% chance of death
• > 10Sv = brain damage, coma, death

Question 5

What are the 3 types of tissue radiation?

Answer 5

• Inflammatory type: e.g. radiation burn after radiotherapy
• Cell loss type: such as mucositis (high dose of radiation to oral cavity causing inflammation of the oral mucosa)
• Generic type: e.g. osteoradionecrosis (bone loss after radiotherapy)

Question 6

What are the main effects of radiation on the oral cavity (therapeutic doses)?

Answer 6

• Mucositis
• Atrophic mucosa
• Loss of taste (due to salivary glands and taste buds being damaged)
• Dry mouth
• Radiation caries
• Can lead to defects in developing dentition in children

Question 7

Tissue reactions are not possible with dental caries, but there is a chance of stochastic effects, what does this mean?

Answer 7

• Every exposure to ionising radiation carries a posibility of cancer induction
• Size of exposure does not affect the severity of damage induced, only the probability of it occuring

Question 8

Which type of X-ray damage is more likely: direct or indirect?

Answer 8

Indirect damage is much more common (approx. 2/3rds).

Question 9

Explain direct X-ray damage.

Answer 9

DNA or RNA in the chromosome takes a direct hit from the X-ray photon, disrupting the bonds between the nucleic acids, can result in:

• Cell death
• Abnormal replication
• Failure of transference of info

If somatic cells are affected -> radiation induced malignancy

If genetic cells are affected -> congenital abnormality

Question 10

Explain indirect X-ray damage.

Answer 10

Photon hits a water molecule, produces free radicals, free radicals can combine to produce gas (e.g. hydrogen peroxide gas) or combine with other substances to produce hydrogen gas.
These microbubbles of gas are enough to break the DNA links and could lead to cancer development or a congenital abnormality.