Unfortunately, dental x-rays sometimes don’t show up the cracked tooth. This is because the x-ray beam must be parallel to the crack before it can penetrate it.
However, sometimes other signs of a crack may show up. With a vertical root fracture, if the crack has been there long enough, vertical bone loss near to the root can be seen. Your dentist may use a bright light or a magnifying glass to find the crack. They may also use a special dye to follow the course of the crack.