There could be a constant push exerted by your lower front teeth that may be causing this. Or some lesion under your upper front teeth. I'll suggest that you should visit your trusted dentist and have them check it out clinically as well as with the suitable x-rays so that a correct treatment approach may be taken.
Next Steps
Consult your dentist.
Health Tips
Take any previous dental records with you for your consultation with the dentist, it may be of some useful information.