Had terrible toothache in upper left tooth. pain went away after three days. x-rays-no root canal needed. gums sore and cheek puffy. root canal needed?

RCT needed?: The presence or absence of pain does not necessarily indicate the need for RCT. One can require RCT on a tooth even though an x-ray does not substantiate the need. The bottom line: The need for RCT may require a number of tests, observations and history of symptoms and cannot be determined over the internet. See your own dentist or an Endodontist to determine whether or not it is indicated.

Probably: Radiographs are not a crystal ball... they don't disclose everything. Did your dentist check to see if the tooth was vital (alive)? Swelling may be from a periodontal issue, so yes, in that case root canal may not be needed. More info necessary to make a proper diagnosis. Have your dentist re-examine you or refer you to an endodontist if s/he can't determine the cause of your swelling.