Without a personal consultation it is impossible to know the exact cause of your chin dimpling and mouth asymmetry. Many patients without a history of maxillary surgery have chin dimpling. BOTOX can be very helpful in temporarily improving the muscular activity of the mentalis muscle that covers the chin. It is possible that this approach could improve your chin dimpling.
The inability to purse the lips could represent a motor nerve injury. Did this loss of function occur following your surgery? If so, it is possible that the nerves were injured during the procedures. Motor nerves that are partially injured may recover. However, these are often permanent injuries. If it has been more than 6 months since your surgery and there is still dysfunction, this has a much lower probability of ever recovering.