Dry mouth is not a function so much of old age. Most cases are related to the side effects of medications that many senior patients take. Other common causes are mouth breathing and CPAP relieved sleep apnea.
Reduced saliva flow reduces many benefits that we never knew existed. Saliva helps to wash food off our teeth and gums. Without it, all foods tend to be more sticky and the its lingering promotes plaque which increases tooth decay and gum disease. Plaque does its damage by making the pH in our mouths more acidic. Saliva helps to neutralize this. The other detriments of dryness is difficulty swallowing, speaking and the development of sores around removable dental appliances.
Treatment of xerostomia, or dry mouth, can take many forms. Simply drinking more water can help as can chewing sugarless gum or sucking on sugarless lozenges. There are many saliva substitutes available that can be great for people who wear removable appliances. Ask your dentist or hygienist for samples to see which brand suits you. If you have your natural teeth or extensive bridgework, the dentist may recommend wearing a fluoride holding tray at night. The fluoride can help prevent decay around bridgework which can become prevalent and its repair costly.