Can sensitivity toothpaste work if you have had a filling?

No: Desensitizing toothpastes are not intended for this purpose. Let me clarify that, if you were recommended a desensitizing tooth paste for sensitive teeth in general, have gum recession and root sensitivity, they may help for that purpose and whether or not you had one or more fillings will not change that. They do not work to reduce sensitivity for a newly placed filling. Hope this helps.

Yes: Sensitivity toothpaste help with gum recession and root exposure area of your teeth.

It depends: That all depends if the sensitivity started after getting the filling or was it due to recession if sensitivity is due to recession, sensitivity tooth paste will help if sensitivity due to filling, then no with large filling if toyr dentist uses comspoite, some patient develop sensitivity as the filling gets bigger, composite, shrink, that causes sensitivity, alternate treatment might be needed.

Possibly yes: For root / dentinal sensitivity only.

Not what it's for: Desensitizing toothpastes were designed for people with gum recession to reduce sensitivity of root cementum nd underlying dentin to oral bacteria. It's not for post surgical (a filling is a surgical procedure) healing. See your Dentist. Filling may be slightly high, tooth nerve may be involved, etc.