The first thing to do is to pull the crown out and stop the watch. If glass gets in the way and stops the hands, or tiny fragments of glass are pushed into the opening around the pinion (center post) as the hands turn, the watch movement (mechanism) can be damaged. Next, get the crystal replaced a soon as possible since dust and moisture from the environment can also damage the watch movement.
If the crystal is scratched, it is a mineral glass crystal. Synthetic sapphire crystals do not scratch, although they do fracture or shatter.
Most likely yes. Many Seiko Kinetics come standard with sapphire crystals and so it is not difficult to find a replacement sapphire crystal that will precisely fit the Seiko watch case.
Most likely, no. Relatively few Citizen watches come standard with sapphire crystals. Because a genuine Citizen part will not be available, we would have to locate a generic part. The generic part will not fit with the friction gasket that currently holds the existing crystal in. This gasket creates an air and water tight seal around the crystal. It would have to be removed and the generic sapphire glued in. With a glued in generic crystal, we cannot guarantee the water resistance of the watch. Ill-fitting sapphire crystals are also more prone to break.
Since we only use the genuine Seiko or Citizen replacement crystals, the new crystal will fit as precisely as the one we replace. Many Citizen and Seiko watches have a friction gasket that creates a watertight seal between the case and the crystal. We make sure the crystal is properly installed with the friction gasket to recreate this seal.