Unconscious clenching of the teeth (bruxism), whether at night or during the day, can be triggered by many factors. Sometimes patients tell us they were already clenching before treatment started; sometimes we find signs of clenching and grinding in someone who has no idea they have this problem. Usually, the discomfort teeth feel with braces makes people stop any clenching or grinding they did before. However, placing cement on the teeth together with the braces acts as a trigger and causes clenching, even in patients who have never clenched before. Aligners also cause clenching in the first few months of treatment, because the material between the teeth raises the bite. Generally speaking, any material placed between the back teeth can trigger bruxism. The clenching stops once the material is removed or once you get used to it.
This answer is for general information. Your own case needs an examination by an orthodontist.