What causes my teeth to be sensitive to cold air?

There are many reasons why teeth are sensitive. 

Grinding or clenching can bruise your teeth.
Remedy: Evaluate the way your teeth fit together with a computerized scan (T-Scan) or wear a bite guard while sleeping.

A diet with too many acidic foods and beverages.
Remedy: Reduce the number of acidic foods and beverages. More importantly drink them over a short period of time. Avoid swishing soft drinks and wine.

Brushing with excessively abrasive toothpaste especially after acidic foods and beverages.
Remedy: Use toothpastes with a lower RDA (Relative Dentin Abrasiveness) and avoid brushing after acidic foods and beverages. Instead rinse with plain water, water mixed with a little baking soda or a fluoride rinse.

Poor hygiene, which allows acidic plaque to sit on the teeth.
Remedy: While brushing your teeth, focus on gentle circular motions with a soft toothbrush along the gumline. The bristles should be directed toward the gumline at a 45-degree angle

Acid in the mouth due to GERD (acid reflux) or bulimia.
Remedy: Avoid brushing your teeth. Instead, rinse with plain water, water mixed with a little baking soda or a fluoride rinse.