Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concern... As per your complain CPAP mask is one of the most common cause of dry mouth and the other symptoms that you are experiencing like cotton mouth and soreness of inner lip are all due to dry mouth.. It is more common in case of patients who have sleep apnea along with mouth breathing habit.. You can continue using biotene mouthwash as it is a good for dry mouth problems.. Along with it if you have mouth breathing habit you can apply a vertical strip of micropore tape [doctor s tape] over your closed lips so that you can induce a habit of breathing from nose.. A chin strap can also be uses along with the CPAP mask for keeping mouth closed.. Other thing that you can do is to get your mask checked for any leakages.. For maintaining lubrication in mouth you can use Xylitol containing mucosal patches that are placed over the mucosa at night time just before sleeping and it maintains a coating in the mouth and prevents dry mouth as well as xylitol helps in improving saliva flow.. Drink water every time you wake up at night.. During the day time if yu experience dry mouth chew sugarfree chewing gums as they stimulate saliva flow.. Biotene ora rinse can be used 3 to 4 times a day.. Drink plenty of water.. For soreness of the inner lip suck on ice pops and do cold water rinses as it is happening due to inflammation caused by dry mouth.. Hope this information helps.. Thanks and regards.. Dr.Honey Nandwani Arora..