Radiation is energy and mankind has been sustained to it from time out of mind. In fact, it has contributed to mankind's high development among the mammals. This radiation comes from different sources and the medical diagnostic source is of minor magnitude (see my report 9901). The dental radiation source is included in the medical and is only about some percent of the medical. The largest single radiation source is radon from our houses and foundations.

There are two types of radiation. Particulate and electromagnetic. The first one consists of atomic nuclei or smaller atomic units, which move with a high velocity, while the last one is a combination of electric and magnetic field energy waves. Radiation can also be divided into ionizing or non ionizing radiation. Examples of non- ionizing radiation are microwaves and visible light, magnetic fields, laser, radiation from screens and radiation in a solarium. Examples of ionizing radiation are electromagnetic waves as nuclear radiation and x-rays.

Ionizing radiation has enough energy to remove tightly bound electrons in an atom while non ionizing radiation does not.

It is the ionizing effect of radiation, which later on may cause damages in our tissues (free radicals are created within the human body).

At low doses, such as what we receive every day from background radiation, a cell can repair the damage, but with higher doses a cell is often not capable to repair the damage, and the cell may either be changed permanently or die. Cells that die, can be replaced by the body and cells that are changed permanently may go on to produce abnormal cells. Since these cells may become cancerous, this is an origin of an increased risk in cancer due to radiation exposure.

This injury to cells is caused by mechanisms that, in many cases, are similar for radiation and chemicals. However the effects from radiation have been more studied than such exposures to chemicals. This is a surprising fact, the chemical agents are seldom causing such big headline as radiography in Newspapers. But a large number of chemicals, that are human carcinogens, are known. Only tobacco smoke contains a couple of thousand such identified chemicals!

Different organs have a different sensitivity radiation. The primary risk from dental radiography is radiation induced cancer in thyroidea since this is the most sensitive organ, nearby where we deliver our dose (in the jaw and neck area). If then the risk is calculated for fatal cancer per million full mouth intraoral examinations, using different organs, the following values have then been found (according to White SC. Assessment of radiation risk from Dental Radiography. Dentomaxillofac Radiol 21:118-126 1992).

Organs Cancers

Gonads 0

Bone marrow 0.7

Colon 0

Lung 0.1

Stomach 0

Bladder 0

Breast 0.1

Liver 0

Esophagus 0.1

Thyroid 0.8

Skin 0

Bone surface 0.5

Remainder 0.3

2.5

This risk can be compared with the risk for a lot of daily activities: There is a relative risk of 1 in a million chances of dying for the following activities

• Eating 40 tablespoons of peanut butter
• Smoking 1.4 cigarettes (lung cancer)
• Spending 2 days in New York City (air pollution)
• Driving 40 miles in a car (accident)
• Flying 2500 miles in a jet (accident)
• Canoeing for 6 minutes

(Adapted from DOE Radiation Worker Training, based on work by B.L Cohen, Sc.D. "Catalogue of Risks Extended and Updates", Health Physics, Vol. 61, September 1991.)

Leif Kullman