Radicular cysts are only formed at devital teeth which have an inflammation at the root tip. An accurate diagnosis of a cyst is only possible with a histological examination, as the soft tissue of parodontitis apicalis looks similar to a cyst on an X-ray. The formation of a cyst is always preceded by pulpal necrosis. Bacteria colonise the root canal and trigger an infection at the root tip, i.e., a parodontitis apicalis. A mostly painless cyst is formed from this apical inflammation, whereby the cavity created around the root tip is filled with a cloudy liquid.