Why are my teeth sensitive?

“Why are my teeth sensitive?” is a common concern I get from patients.  The answer is complicated.  First, we must consider that sensitivity is a safety mechanism built into our bodies.  The teeth, gums, and bone have nerves in them that detect temperature, propioception (positional detection), and pressure.  An extreme in temperature, position, or pressure results in pain.  How can this be a good thing?

If you are biting on something too hard, the nerves will send a signal to the brain that there’s too much pressure and automatically release the muscles, preserving the tooth and bone from damage.
Second, there may be underlying problems such as cavities or gum disease that cause the nerves to become inflamed and painful.
But the answer you want to hear is why the sensitivity is uncomfortable and what can we do about it?
An x-ray will show a lot.  But if you want to do a home diagnosis before coming in for an x-ray, check in the mirror at the tooth or teeth that seem to be bothering you.  Is there plaque or calculus around the neck of the tooth, at the gumline?  Are the gums red, puffy, and prone to bleeding?  Those are signs of gum disease which needs professional care.
If the gums seem to be healthy, are there any chips in the teeth?  Dislodged fillings render the tooth vulnerable to temperatures as there is less insulation over the nerve endings.  Additionally, night-time grinding can wear away the protective enamel and cause chips at the gumline.  If the teeth appear intact, the bone that supports the tooth may be inflamed from an injury, like biting down the wrong way on a nut or from stressful clenching.
For persistent sensitivity, I recommend coming in for an x-ray and evaluation.  We can go from that point.