Multifactorial. Teeth grinding is a protective mechanism, where a body unconsciously try to remove an interference between upper and lower arch. It is also a response to muscle spasm due to stress, where continuous clenching and grinding leads to excessive occlusal wear and/or tooth hypersensitivity. Malocclusion also cause grindings. Bite guard to alleviate symptom, correct occlusion to eliminate the cause.
Stress, less stress. Stress is by far the major cause of clenching and grinding teeth (bruxism). Stop or reduced the stress and the tooth grinding will probably stop. Anything that you can do to relieve stress will help- exercise, deep breathing, yoga, sports, a good book, meditation, etc. Also consult with your dentist to see if a night guard would be beneficial to limit tooth wear and tear.