ugikghiljo;
Maxillary expansion with a palatal expander is a bit of a hit/miss. Because the expander is attached to the teeth, the expansion has to be done with just the right amount of force in order not to merely tip the teeth while attempting to split the suture. The window between teeth tipping & sutural separation is narrow, and for some it possibly does not exist at all. MSE on the other hand is screwed directly onto the palate, and thus guarantees sutural separation because you are free to increase the amount of pressure until the suture yields.
uiguhlo