Dental bridges: can 4 abutment teeth be enough for 7 Pontic teeth?

This length of bridge might work for a while, but at some point it will start to break down the abutment teeth. No one can say for sure how long it will last, but if you want bridges the best option is implant supported bridges (assuming you have enough bone for implants).

Probably not.  The general rule of thumb is that you need to have as much root surface in bone available to support the bridge as there would have been for the teeth being replaced.  Seven teeth, including the canines, is a lot of root surface.  This long a bridge would not be stable with forces on the front area eventually rocking the back teeth right out of the jaw. 

A better solution for you would be 3 or four implants to support the seven tooth span.  Your dentist and oral surgeon can help you determine if you are a candidate for implants and what the procedure would entail.  Another option would be a removable partial denture.  Good luck.

 If you're a candidate your best option  is to do single crowns and place implants in the areas that have no teeth. You should consult with a Dentist that specializes in implants.  The treating specialist may need a ct scan  to fully evaluate you and also to check your sinus cavity. If the sinus Cavity is to low another procedure would be needed in order to place implants. Though nothing is guaranteed you want to make sure you visit your dentist & hygienist regularly to maintain & keep everything healthy.