Getting ‘long in the tooth’ is when the gum (usually) on the outside face of the teeth shrinks, leaving the tooth looking longer. (This is not gum disease, which usually affects the gums tight between the teeth).
Apart from the appearance of the teeth due to receded gums, the main problem is usually that of sensitive dentine, which has been exposed by the gum shrinkage.
Our dentine is made up of millions of tubes which go from the surface to the nerve and can be extremely sensitive. Toothpastes like Sensodyne and Colgate Pro Relief Sensitive block these tubes and make the teeth less sensitive. Your dentist can also treat the surface with different materials.
Dentists can apply special varnish to make teeth less sensitive in the short term.
It is now understood that a combination of hard brushing and also heavy grinding forces on particular teeth seem to cause gum recession to be worse.