Just about everyone has at one time or another suffered from a sensitive tooth. Cold or hot fluids sends you through the roof and the darned toothache just came out of nowhere.
Well, sort of. The most common cause of tooth sensitivity is periodontal disease caused by receding gums.
What this means in English is that gums normally cover the sensitive part of the tooth or dentin. The dentin lies just below the enamel or outer covering of the tooth and is normally protected by the gums. If the gums recede or pull downward, then the dentin is exposed, which in turn causes the pain.
Certain habits and foods can make gum recession worse. While it is always a good idea to brush your teeth twice a day for at least two minutes, more is not better. In other words, brushing more often, for longer times and especially more aggressively will irritate the gums and then the gums might recede. Electronic toothbrushes with soft brushes are great for avoiding overdoing it on the gums. Also, when flossing be gentle.
Acidic foods such as wine and citrus (think oranges and grapefruits) can over time damage the gums. Rather than avoiding citrus, which it turns out is really good for you, it is better to wait a few minutes after eating citrus before brushing to let your saliva neutralize the acid. Alternatively, if your tooth is really sensitive hold off for a few days until it feels better.
Fluoride will help strengthen the tooth. You should always brush with fluoride toothpaste.
If all else fails see a dentist who can refer you to a specialist if needed.