Back tooth feels tight why?

Teeth shifts: Did you have a new crown or filling on any bicuspid or molar? Please see your dentist if you haven't seen one yet and he/she will take a panoramic x-ray to detect, e.g., possible third molar that may have moved.

Many possibilities-: Recent dental work, bruxism, food impaction, inflammation are just some of the possibilities. See your own dentist to have this evaluated.

Exam: No idea what you mean by "tight," but any unusual sensations should be investigated. Please call your Dentist for an examination.