In response to campbellking, an ENT consultant would find such a referral inappropriate given that the craniofacial skeleton and dentary bones are not part of the ENT remit. However referal to a maxillofacial consultant may be appropriate (as I think this dentist has suggested as an option).
I'm concerned that the dentist has suggested that 'you need a bridge' since no one actually needs a bridge. However this option among others would be one for replacement of a missing tooth or teeth.
It sounds as though you have either a persistant apical granuloma or an odontogenic cyst, leading to bone resorption/loss probably at a slow rate. One option would be to remove the tooth and therefore the problem along with the cyst or granuloma, after which spontaneous healing is likely to occur. Another as you've mentioned would be to repeat the apicectomy which may work but its unlikely to after 25 years.
I'm unsure as to why you think antibiotics would be in any way useful as a 'first line' treatment. Unless there is pain there is no reason to suggest infection of the apical lesion by bacteria so obviously antibiotics would be ineffective. A GP may prescribe you them but only because there isn't any other treatment they could offer you (doesn't mean antibiotics are appropriate) they will then simply suggest seeing a dentist or referring you to an oral surgery department wasting both their time and yours. My advice would be to seek a second oppinion from another dentist if you are not happy or ask for referral to an oral and maxillofacial surgery department.
If you have any other questions or concerns please ask,
Hope this helps, take care bearpooch