Short-term, don't worry about teeth or hooves. Focus on keeping fresh water in his pen at all times (full-grown horses can drink 20+ gallons per day in the summer) and good hay (not straw, and no mold or weeds) several times a day. Pick up some fly spray from the feed store and spray him down daily so he's not miserable. He also needs a large, safe enclosure. No barbed wire, no plain wire unless it's electrified and clearly marked, and no protruding t-posts or dangerous objects in his pasture. If there's really lush grass available, buy him a grazing muzzle so he doesn't founder.
It's imperative that you continue to search for his owner. Put up flyers in the feed store, on telephone posts (no picture, they need to be able to identify him themselves to weed out liers), on local FaceBook groups, etc. Post his picture on NetPosse and check it regularly for new missing horses. Contact the police station and give them a picture and information. Call local farriers and vets in your area.