Is it possible to convert an All-on-4 to a snap on? Can you get a new bridge made for the existing implants ?

A less known option to convert an All on Four restoration is the Deutsch Removable Bridge.  The existing implants are used for the new restoration, and it has all the benefits of the All on Four (no covering of the roof of the mouth, chews/functions like it was screwed in place), yet is easily removed to clean and maintain.

Yes, your overcase can be converted to attachments which would be fixed-removable..Cost of surgery would not be involved and thus less expensive than your first outlay..however cost can be somewhat substantial for changing our attachments and new over case..Good luck.

Yes, it is possible to do a snap in overdenture on the same implants.  Advantages include better cleansibility.You can make a new all on four prosthesis as well to give better lip support.I generally prefer snap in overdentures to all on four but both can give excellent esthetic results.Ira L Shapira DDS, D,ABDSM, D,AAPM, FICCMOPast Chair, Alliance of TMD OrganizationsDiplomat,  Academy of Integrative Pain ManagementDiplomat, American Board of Dental Sleep MedicineRegent & Fellow, International College of CranioMandibular OrthopedicsBoard Eligible, American Academy of CranioFacial PainDental Section Editor, Sleep & Health Journal
Member, American Equilibration SocietyMember, Academy of Applied Myofunctional SciencesMember, Academy of Cosmetic Dentistry