How are X-rays used to find dental cavities?

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Diagram of the electromagnetic spectrum showing different types of waves arranged by wavelength and frequency, from gamma rays and X-rays to ultraviolet, visible light, infrared, microwave, TV/FM radio, shortwave radio, AM radio, and longwave radio. — X-ray The relationship of X-rays to other electromagnetic radiation within the electromagnetic spectrum.

X-rays are a vital diagnostic tool in modern medicine, enabling the nonintrusive detection of dental cavities through their ability to penetrate optically opaque materials.1

The utility of X-ray imaging for identifying cavities relies on the principle of differential absorption. Because materials vary in density, composition, and homogeneity, they absorb X-ray radiation at different rates. When an X-ray beam passes through a tooth, the denser structures, such as healthy enamel and bone, absorb more radiation, while areas affected by decay—which are less dense—allow more radiation to pass through. This difference in absorption creates an image that allows dentists to visualize internal structures and identify diseased conditions that are not visible to the naked eye.1

While X-rays are indispensable for such medical diagnostics, it is important to note that they are a form of ionizing radiation and can cause biochemical changes in living cells. Therefore, their use must always be balanced against the necessity of the diagnostic information required for patient care.1