“Why do teeth suddenly become sensitive?”

So many things! Change in type of toothpaste, diet/hormonal changes, grinding, hard brushing are some of those reasons.

A sudden change in sensitivity alerts me to suspect nerve involvement or trauma to the tooth. The degree of sensitivity would need to be investigated and an X-ray would be needed to determine the cause.

One of the most common causes of sensitive teeth is grinding or clenching. I have found this to be a lot more common of a problem during the pandemic to the extra stress it has caused. I still advise you to see your dentist as there may be other reasons for your sensitivity,

Hello,

Perhaps you are brushing too hard or using a medium to hard toothbrush which creates gum recession and thermal sensitivity. Perhaps you are eating sweets frequently and have a cavity. Perhaps you are chewing ice or grinding your teeth due to stress. It’s hard to say exactly without seeing your dentist and getting X-rays.
Thank you.

Hi,

Teeth are made up by 3 distinct layers, enamel, dentin, and the pulp. The pulp houses the nerves which traverses into the dentin. Enamel is the layer without nerves and also the hardest layer, so teeth’s protective layer. The enamel, however, is only present on the crown portion of the tooth in variable thickness. Teeth are innervated by nerves and when the free ends are exposed, sensitivity ensues. Nerves are usually exposed when enamel is lost or gums and bone recede. So, factors which can lead to this (in otherwise healthy - no decay - teeth) is acid wear, grinding, clenching, and periodontal (gum) disease. At least, these are the usual suspects.
Hope this helps.

Bruised teeth, damaged enamel, cracked teeth, or decay usually. All reasons to see a dentist.