Canine to canine bridge or double abutment?
This image helps explain why we do a 6 unit bridge canine to canine but do not connect the premolar to get extra support. The premolar ends up getting decay around the margin and rotting out. The physics is explained pretty well by the photo. Bite into something on the front and the canine is the fulcrum and the bridge lifts off the premolar.
|Image from DT thread and more specifically Lane|