Diagnostic radiation including dental X-rays are safe, specifically if you use a lead cover. Diagnostic radiation has far less X-ray dosage than therapeutic radiation which is used to treat cancer and which exposes you to much higher radiation.
Dental X-rays are taken with the machine focused right on the area where the X-rays need to go, so there is virtually no exposure to anything other than the teeth. When assessing the effects of X-ray on pregnancy we look at the amount of radiation that gets to the ovaries and the uterus. The amount of radiation involved in dental X-rays is too low to reach the ovaries. In addition, the amount of radiation usually disappears within inches from the target, and dental X-rays are far away from the ovaries.