Have you ever noticed small h airline cracks in your front teeth? This is enamel crazing. They rarely cause pain or sensitivity. These cracks are only in the enamel and don't extend into the dentin. The potential for decay in these cracks is small but they can develop some stain especially if you drink coffee, tea, or concord grape juice. Enamel crazing is caused by wide variations in temperature; like hot pizza followed by cold soda, again and again. These cracks rarely show up on an x-ray and require no treatment.
Unfortunately, there are other kinds of cracks in the front teeth. These are caused by physical trauma. The forces come from clenching or biting end to end on the front teeth. Because the front teeth are thin, they can't take these hard forces and they can break. The fractures are different from enamel crazing. The crack goes through the tooth into the dentin and through the enamel on the other side. These cracks show up on an x-ray. They are serious. I have seen this kind of broken tooth three times in the last year. They need to have crowns because the break goes all the way through and the tooth is very weak.
The good thing is these breaks are rare. Most cracks are just enamel crazing and you can go your whole life without problems.