If you don't have a fence, then I wonder if you ever let your dogs out without supervision. It seems like it would be a normal thing to do. Those are the dogs I see heading down the road when their owners haven't a clue it has happened. I'm not saying your dogs in particular are a problem, only that I have witnessed it many, many times.
Now on to which breeds are dangerous-they all can be. I have had personal protection dogs, one of my past jobs was working at a security company that trained ppd for Nevada Police Departments. Those dogs were under control, but IF one had ever gotten out of its yard IT could have been dangerous, because part of making a ppd is teaching THEM to be alpha over everyone except the handler.
As a Vet Tech, working in an emergency only hospital, I can tell you all dogs can bite, most will not, and the ones you don't worry about are the ones that will nail you. Breed does not matter. Having a 25lb Sheltie dangling from my hand was not a pleasant experience. But treating lions from the shows, was kind of cool, dangerous, but cool.
Yesterday, two of my WELL TRAINED dogs got through a gate on my property, and with that pack mentality attacked one of my bucks. This all happened while I was in town, and when I returned we called them off, and the goat will be fine. My point is mentioning this, is this is my first dog attack, these dogs have been around the goats under supervision and were always well mannered, no hint of a problem until yesterday. ALL dogs can go off, pack mentality is in their genetic makeup, we control it MOST of the time.