Can too many teeth x-rays be dangerous?

Depends... If you are having x-rays of your mouth ever day, maybe. However, the x-ray exposure from normal routine dental care is not dangerous.
Need to have lots! With today's technology you would need a whole bunch of x-rays to cause problems. The new x-ray machine emit minimal radiation with a very tight scatter pattern. High speed films and digital radiography also reduce what a pt gets in radiation exposure. A huge majority of problems you've heard about are in older adults who were exposed using the older equipment.