Is this a radiolucent base or lack of material?

[Catirf]

Hello!
I’m struggling to tell which one is it.
The restoration had recently been done when this X-ray was taken. A temporary glass ionomer restoration was made before the permanent resin one.
It’s very radiolucent and defined.
Thank you in advance!

 

[Dr M]

It might be a space or it might be caries left over. Difficult to say exactly. I would make sure the cavity is clean, perhaps by using a caries indicating dye, before the permanent resin filling is placed

 

[MattKW]

It would be easier to assess if that was a bitewing (perpendicular) Xray rather than the periapical (PA) that you are showing. Looking for possible caries using PAs can be misleading.