Prof. Janet Gruber, RDH, MS
Two Effects of Ionizing
Excitation – x-ray photon interacts with an
atom’s electron causing it to vibrate and
possibly break apart, but it returns to a
Ionization – orbital electron removed from a
shell causing it to be ionized.
Two Types of Biological
Direct hit effect – x-ray collides with cell
causing no damage or breaking them apart
causing critical damage. Cell repairs or
Indirect hit – Based on the poison H20
theory. H2O is poison for the cells and
potential exists for a cell to turn malignant.
Classification of Damage
Somatic damage – damage to tissues not
inherited from one generation to the next.
75% of somatic cells repair within 24 hours
Genetic damage – damage to reproductive
cells. They never repair themselves.
Time b/w irradiation and clinical
appearance of symptoms. Latent period can
be from a few hours to days. ie. sunburn
Acute effects from excessive radiation:
Nausea, hemorrhage, diarrhea, erythema,
malaise, fever and death 400-500 RADS.
Chronic effects – long term:
Cancers, cataracts (not caused by dental
radiation) genetic defects, nail splitting,
alopecia, shortened life span.
Determinants of Biological
3. Area or volume exposed
4. Patient’s age
5. Individual sensitivity
6. Cell nutrition
7. Rate of cell division
8. Oxygen concentration
9. Cell sensitivity
Hierarchy of Tissue Sensitivity
Lens of the eye
Small blood vessels
Non-Threshold & Threshold
Small exposures produce no observable
changes. When threshold is reached we see
observable changes. ie. sunburn
Non Threshold Dose:
No threshold needed – small dose causes
changes. Genetic tissues fall into this
Stochastic vs. Nonstochastic
Similar to non-threshold – occurrence
increases with absorbed dose. Genetic
mutations and cancer are examples.
Somatic effects that have a threshold.
Below that dose, no damage noted.
Critical Organs in Dentistry
Lens of eye
Radiation Measurement and
Limits set by NCRP based on info gathered…
Maximum Permissible Dose (MPD)
It is the MAXIMUM dose a person may receive
in a stated period of time.
Upper threshold of a permissible dose.
Anything less is not harmful anything more
could result in biological injury if repeated
MPD for radiation workers:
5 REMS = .05Sv (50mSv) / calendar year
MPD for 13 week period for radiation workers:
3 REMS = .03 Sv / 13 weeks
MPD for general public and pregnant workers:
.1REMS = .001Sv (1mSv) / calendar year
20 film FMS = .002REMS…10 sets = .02
REMS and 100 sets = .2 REMS
Lethal Dose = ~4.5 Grays or 450 RADS
GI Series = .01Sv or 1 REM
FMS = ~3 days in the sun
4BWX = ~8 hours in the sun
Radiation Measurement Terms
Exposure is the measurement of ionization in the
air. It is measured in units called
Roentgen/Coulomb per kilogram.
Absorbed Dose is the unit for measuring the
energy absorbed by the tissues from all types of
Dose Equivalent is a unit used to measure the
biological effect of radiation…REMS/SIEVERTS.
100 RADS = 1Gy
100 REMS = 1 Sievert
.001RADS = 1 mRAD
.001 REMS = 1mREM
Effects of Oral Radiation in
Cancer TX Patients
1. Healed and repaired tissue has fewer and smaller
blood vessels = reduced repair potential.
2. Osteoradionucrosis – bone loses blood supply
and susceptible to infection.
3. Xerostomia – dry mouth & increase in caries
4. Rampant caries – decease saliva = plaque =
Overexposure to Certain Organs
Skin = cancer
Lens of the eye = cataract
Blood forming organs = leukemia
Thyroid gland = cancer
Reproductive organs = genetic mutations
Fetus = birth defects
Breast (female) = cancer
Radiation Control for Health and Safety Act
1968, regulation of x-ray machines.
Consumer Patient Radiation Health and
Safety Act 1981, Developed min. standards
for operators of dental equipment.
NY Sanitary code requirements…
Home made film badge
METHOD OF EXPOSURE
AND DOSE REDUCTION
Conduct of the examination
Choice of equipment
Operation of equipment
Establishment of radiation safety procedures
(90-135 angle from primary beam)
CHOICE OF EQUIPMENT
Collimators (rectangular reduces dose 2/3)
Lead aprons and collars
Receptor selection (fast film E / F or digital)
Focal spot to film distance (long PID)