What do I do for decreased saliva after masseter Botox?

Your parotid salivary glands, the largest ones, live just behind your masseters, and BTX does decrease salivary production. This will be completely temporary. Your saliva production will start to increase soon, and will be completely normal. Hope this helps. Dr Joseph

Your injector most likely inadvertently injected the parotid glands (which lie on top of the masseter muscles just in front of your ears) and/or the submandibular glands (located along the lower jawline). These glands makes saliva and Botox injected here will stop saliva production for a few months. This will fully resolve in a few months

Xerostomia (dry mouth) is rare after Botox injections The symptoms wear off in time (1-2 months) and you should consider the following remedies for Xerostomia:
Chew sugar-free gum or suck on sugar-free hard candies to stimulate the flow of saliva. For some people, xylitol, which is often found in sugar-free gum or sugar-free candies, may cause diarrhea or cramps if consumed in large amounts.
Limit your caffeine intake because caffeine can make your mouth drier.
Don't use mouthwashes that contain alcohol because they can be drying.
Stop all tobacco use if you smoke or chew tobacco.
Sip water regularly.
Try over-the-counter saliva substitutes — look for products containing xylitol, such as Mouth Kote or Oasis Moisturizing Mouth Spray, or ones containing carboxymethylcellulose, or hydroxyethyl cellulose, such as Biotene Oral Balance.
Try a mouthwash designed for dry mouth — especially one that contains xylitol, such as Biotene Dry Mouth Oral Rinse or ACT Total Care Dry Mouth Mouthwash, which also offer protection against tooth decay.
Avoid using over-the-counter antihistamines and decongestants because they can make your symptoms worse.
Breathe through your nose, not your mouth.
Add moisture to the air at night with a room humidifier.
Best wishes,
Dr. Taranow