While a single area becoming hot/cold sensitive usually indicates decay or a cracked tooth/filling, generalized temperature sensitivity is more likely to be the result of exposing your teeth to acid. Ever suck on a lime or lemon, then notice your front teeth are sensitive for a few days? (By the way, this is really bad for your teeth, so please don’t do it as an experiment.) That’s from the citric acid in the lemon. Other foods that are acidic include tomatoes, citrus fruits in general, soft drinks, and vinegar-based salad dressing. If you’re eating a lot of acidic foods and notice sensitivity, that’s a probably what’s going on. And the solution is NOT to brush immediately after the acid exposure–the teeth are soft at that point, and will be eroded by the brush. If you’re neurotic, rinse with sodium bicarbonate, but defer brushing for at least an hour or so, and let the teeth reharden.
Stomach acid is another source of sensitive teeth. Many people have asymptomatic stomach acid reflux (Gastro Esophageal Reflux Disorder, or GERD) and bathe their teeth in acid at night. This often results in sensitive teeth on just the side you sleep on, and results in notching of the teeth at the gumline, further accentuating the sensitivity. GERD is a risk factor for Barrett’s Esophagus, which predisposes to esophageal cancer. If you suspect this is going on, ask us at your next visit. And once again, brushing right after you get up–when the teeth are acid-softened–is not a good thing; wait at least an hour or more.