Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concerns.. As per your complain it seems that you are suffering from Angular Cheilitis leading to dry and cracked corners of the mouth and can occur due to a number of common causes Iron deficiency or Anemia, fungal infection,ill fitting dentures, loss of teeth leads to folds of skin at the mouth corners,systemic diseases like Coeliac disease etc.. In your case, as you wear night guard at night and that too is too old seems to be a probable cause for the Angular Chelitis and you should consult your dentist and get evaluated and he can assess the mouthguard and also the cracks over the mouth corners to look for the exact cause.. Treating the underlying problem that is causing the symptoms will help in its resolution.. In case if it is due to mouth guard, then getting anew one fabricated with a proper fit will help.. You can also apply a thick coat of Petroleum jelly over the corners to relieve the dryness and smoothen the area.. Do cool compresses.. A low potency steroid ointment along with antibiotic ointment can also be advised.. Take multivitamin tablet for 15 days.. Drink plenty of water.. Hope this information helps.. Thanks and regards. Dr.Honey Nandwani Arora.