Thanks for asking your query,
Listen to what your dentist
advised you,and go ahead with Root canal treatment
.They are couple of things you should know why your dentist recommended for RCT.
1.First since the filling was metallic.amalgam filling material is called metallic, it can conduct hot and cold
from the mouth environment to the pulp quite easily, enhancing the feeling of sensitivity. With tooth-colored composite fillings that provide better insulation of the tooth, sensitivity symptoms are rare.
2.Secondly dentist would have checked the vitality status of the nerve
- sometimes when you have a large cavity or filling, the nerve in the tooth may die over time and you will have a lot of discomfort when you chew - if this is the case, you need a root canal.(or) suppose when a filling is very deep, it irritates the nerve of the tooth and if this does not go away over weeks to a month it is probably time for a root canal.
Visit your dentist as soon as possible,