There is an online published article "Dental X-rays and risk of Meningioma" in 2012, which worried a lot of patients. 

Actually, ADA and serveal Radiologists have reviewed this article and reached a conclusion that this study was quite flawed because it uses anecdotal evidence.

Dental X-rays, especially digital dental x-rays, are quite safe.  Below are some of the facts and numbers.

Maxium safe occupational whole body radiation exposure is 5000 mREM per year by Federal, Washington state and other US states.

4 Bitwings intraoral digital x-rays only give expose of  1.3 mREM

Full-mouth series (19 taken digitally)  produce   6 mREM

Digital panoramic only exposes 0.63 to 1 mREM

On the other hand, average person in US is exposed  about 360 mREM per year from background. For example, flying cross country exposes 3-5 mREM over than walking outdoors for the same length of time.