Can a filling cause a root canal? told i had small cavity no pain before during filling i said it felt wrong came back in week with pain xray looked fine at 6 month cleaning tooth still hurting a new xray still say fine nerve test say need root canal?

Multiple posts of the same issue. If the vitality test indicates that the tooth is non-vital, it needs root canal therapy. All other symptoms or prior history is irrelevant.

Caries is a disease caused by bacteria. When a tooth has caries the destruction it causes on the tooth can vary, depending on many factors, from little damage to extensive. When the bacteria that cause caries get to the pulp of the tooth a root canal treatment is necessary to prevent further infection. In your case, when the filling was placed you probably had bacteria in the the tooth´s pulp.