Crowns falling out from dental implants, posts in place. Any suggestions?

Call an experienced dentist with dental implants in your area (check online and ask for references with some patients) or a prosthodontist who specializes in crown and bridge. They should be able to get your bridge back in quickly with solid cement. Also, ask if the bridge fits well on the posts and whether the bite is done correctly. Oftentimes, bridges fall off due to poor cement. Implants break because of a bite that is off or overloading the implants. All the best. 

Loosening of crowns over dental implants can be due to several factors: occlusion (bite scheme), retention over the abutments, type of retention (screw or cement); If screw retained, use of proper torque; if cement retained, use of proper cement.  It is best to see your dentist and have him or her evaluate to see which may be contributing.

Based on what you say, you have strong bite, you already destroy the previous teeth, your own teeth, then you placed implants and even implants keep failing , either the implant or the crown, i think you should get 1 implant per tooth you all ready lost, and also there are some techniques to maximize the good life time work of those restorations, remember that implants work amazing but you need to have the proper technique.