As Chad suggests you really need to consult an attorney before investing time and money in a concept that someone else may own. Only a professional practicing in your jurisdiction area and in intellectual property(IP) can give you sound legal advice.
But before even going that far here is a litmus test of sorts. Some common sense questions to ask yourself.
Was the idea/concept copyrighted, trade marked, patented, otherwise documented?
If the answer to any of these is yes then even if the company has been dissolved there may well still be an 'owner' of the concept. This can be one of the principals, a creditor, or some form of holding company. Untangling the ownership can, and most likely would be, an expensive and time consuming ordeal.
To what level was the concept/idea developed?
Generally speaking broad concepts and ideas are difficult to claim as your IP. Where as the more detailed, thought out and planned concepts/ideas by their nature tend to prove ownership.
To use examples:
While brainstorming at work someone throws out the idea of X during the session.
- The idea is dropped quickly. Maybe even dismissed outright and the business doesn't invest any further time and energy on it.
- Everyone likes the idea and decides to invest additional time in discussing, prototyping, and documenting the concept. The concept is never implemented.
- Great (or even bad) idea and the company runs with it.
Obviously these are the extremes, but they illustrate my point in that the each represent the shades of gray that our legal and moral systems tend to deal with.
In most cases example one would be fair game. Well at least the lightest gray of the three.
Example two is the middle of the road. You're in a gray area here and a court could rule either way.
Example three, well it's pretty black. You'd be hard pressed to prove that the ideas was yours since it would be easy to prove that your previous employer had already implemented it.