There are many reason why your teeth can become sensitive.  If you find you have sensitive teeth you should see your dentist.  Having sensitive teeth could be a warning sign to other more serious dental issues. Here are a few reason for tooth sensitivity

* Brushing your teeth too hard. This can wear away the enamel layer.
* Poor oral hygiene. This may allow tartar to build up at the gum line.
* Long-term tooth wear
* Untreated cavities
* An old filling with a crack or leak
* Receding gums that expose the tooth’s roots. Receding gums often are caused by periodontal diseases or by brushing too hard.
* Gum surgery that exposes a tooth’s roots
* Tooth whitening in people who have tooth roots that already are exposed
* Frequently eating acidic foods or drinking acidic liquids