Hygiene Atlas

Atlas · Plate IX · Dental Radiography · 02

Radiation biology

Most damage is indirect: ionized water forms free radicals that injure DNA. Fast-dividing, immature cells such as lymphocytes are the most sensitive. Stochastic effects like cancer have no threshold, while deterministic effects appear only above a threshold dose. Absorbed dose is measured in gray and effective dose in sievert.

High-yield facts · 11

  1. Most biologic damage is indirect: x-rays ionize water (radiolysis) and form free radicals that damage DNA.T7
  2. Law of Bergonie and Tribondeau: cells that divide quickly, are immature and less specialized are most radiosensitive.T7
  3. Most sensitive: lymphocytes, bone marrow, reproductive cells, intestinal epithelium. Least sensitive: mature bone, muscle and nerve cells.T7
  4. Stochastic effects (cancer, genetic mutations) have no threshold; probability rises with dose.T7S20
  5. Deterministic effects (tissue reactions such as erythema, cataract, xerostomia from therapy) have a threshold, and severity rises with dose.T7
  6. Sequence after exposure: latent period, period of injury, recovery period, cumulative effects.T7
  7. Critical organs in dental imaging: thyroid, active bone marrow, salivary glands, lens of the eye, skin, brain.T7
  8. Units: gray (Gy) for absorbed dose (1 Gy = 100 rad); sievert (Sv) for equivalent and effective dose (1 Sv = 100 rem).T7S22
  9. Average US resident receives about 6.2 mSv (620 mrem) per year, about half from natural background.S22
  10. Typical effective doses (approximate): 4 bitewings about 5 microSv; panoramic about 14-24 microSv; FMX about 35 microSv with rectangular collimation vs about 170 with round. (verify; ranges vary by unit)T7S20
  11. CBCT dose ranges widely (roughly 20 to over 1,000 microSv) depending on field of view.S20T7

Facts are written in our own words; each tag links to its source. Values marked "sources vary" differ between references, so check the one your program uses.