Certain dental procedures, like an extraction, a root canal treatment or a dental implantation requires a dental x-ray to be taken. The reason for this is that these procedures involve the portion of the mouth that is not visible, the parts below the gum line. Even the best trained dentist cannot work with something he does not see. The periodontal tissue houses bones, tooth roots and nerves, and if any of these become damaged, that can lead to serious problems, including tooth ache, tooth loss and even numbness or partial paralysis.
To avoid these awful and potentially serious symptoms from occurring, a dental x-ray is necessary, that way your dentist will be able to see exactly how your periodontal structure looks like, and he will be able to give you the precise dental treatment that is right for you, and will not incur any sort of damage. As for the cancerous effects of dental x-rays, it is true that x-rays are carcinogenic, but if you get one every six months, you should be fine, and should not develop any sort of tumors whatsoever.