You can attach a door-on-door, built-in fridge to the front panel door by using flat hinges. This lets your fridge door seamlessly fit onto the front panel, and allows the fridge door to open much further than a fridge with a sliding door. In case you're currently using a sliding door system, it's possible to switch to a built-in fridge that utilizes a door-on-door system. This requires that you remove the hinges and door guides from your front panel. You can't switch from a door-on-door system to a sliding door system.