Last time I had a professional cleaning with the hygienist my teeth were very sensitive for a couple of days and I was worried they had been damaged by the process?

The ultrasonic instruments and hand scalers used by the Hygienists are very safe and when used correctly cannot damage the tooth surface. The reason there is sensitivity for a few days after a cleaning is that the build up of plaque over the months,  turns hard and forms calculus (dental stone) and it is this calculus that coats the root surface of the tooth along the gum line.

​Removal of this stone during the cleaning process results in the exposure of the root surface to the oral environment and this exposed surface will be hypersensitive to cold air and water for a few days until the flouride in the toothpaste or the ingredients of a paste like Sensodyne or Tooth Mousse seals off the tubules, leaving the teeth in a normally responsive state.