Why saliva matters more than people think
Saliva is the mouth's defence system. It rinses away food, buffers the acid that bacteria produce after every meal, and carries calcium and phosphate that repair early enamel damage before it becomes a hole.
Someone who spends every night with a dry mouth has removed that defence for roughly a third of their life. It shows up as decay at the gum line, decay in places that usually stay clean, sore gums, and bad breath that brushing does not fix.
The common causes
Breathing through your mouth at night. Usually because your nose is blocked, sometimes because the airway is disturbed during sleep. See snoring and sleep apnea.
Medication. A long list of ordinary medicines reduce saliva as a side effect.
Dehydration, alcohol in the evening, and smoking.
Medical conditions affecting the salivary glands, which need diagnosing properly rather than assuming.
What we do about it
First, find the cause, because treating dryness without addressing why it is happening achieves very little. That means a conversation about your sleep, your nose, your medication and your general health, and an examination of the mouth.
Then protect the teeth while the cause is dealt with: high fluoride toothpaste, more frequent check ups because problems develop faster, advice on saliva substitutes, and dealing with any early decay before it grows.
And where the cause points to the airway, investigate that properly rather than treating the symptom.
Children
Habitual mouth breathing in a child is worth taking seriously, and it is not something we manage here. The common causes are enlarged tonsils or adenoids and persistent nasal obstruction, all of which belong with a paediatrician or an ear, nose and throat specialist. We will say so and help you get to the right person.