Can dental sealants stick to dental fillings?

Sometimes. The materials used for dental sealants stick to tooth surface but won't stick to metal fillings. Some times dentists place dental sealants next to fillings to fill in any small gaps between the filling and the tooth's surface.
Not really. Dental sealants are ideally designed to seal grooves in teeth that have NO decay, the idea being to prevent bacteria from invading the grooves and causing decay. As they are dependent on bonding technology, sealants won't bond to silver or gold fillings and if there is already any filling, probably the old filling should be removed, the tooth checked for decay /removed if needed and re-filled.
Yes. Yes, sealants will stick to white fillings but there really should not be any need for a sealant on top of a filling.
Depends. A dental sealant is typically placed into a tooth that does not contain prior filling material but this material is compatible with composites (tooth colored filling material) but if a tooth already has a composite present in the pits and fissures use of a sealant would not be indicated but it can be repaired depending on the defect at the composite with additional composite.
Dental Sealants. Most patient have a misconception about the use of dental sealants. They are really meant to seal small pits and fissures that are prone to decay due to a break in the integrity of the enamel surface or the inability for the bristles of the brush to adequately remove food debris. Anything more than that requires a restoration such as a composite or amalgam filling.
Impossible. To stick dental filling to a sealants would involve composite bonding procedures the same one that used in dental filling placement. However, because sealants can prevent more than 80% of dental decay in children, they reduce the need for fillings and other future expensive treatment. Take care.
No. Usually once a tooth has a filling it is useless to apply a sealant. Most fillings occupy the same area on a tooth that the sealant would go in.