This gap can be due to caries in adjacent teeth or loss of bone in between tooth region(interdental bone) or may be some issues related to cap.
Next Steps
Get an xray done to find the exact cause.
If there is caries in adjacent teeth, you need to get the teeth filled, as that caries progression and food lodgement can increase the periodontal problems as well.
If there are problems related to cap, get it replaced asap.
Health Tips
Get resolved this problem asap.
Keep proper hygiene to avoid food lodgement by using interdental brush.
Hope this was helpful.
Keep smiling.