Grinding or clenching your teeth is called bruxism. It often happens as we sleep but can also be observed during the daytime. It may be caused not just by stress and anxiety but by sleep disorders, an abnormal bite or teeth that are missing or crooked.
A mouth guard or occlusal splint can be made to protect your teeth during sleep or even during the day. This could help in relieving jaw / joint pains and help to protect your teeth. Continued grinding can cause your teeth to wear down and cause severe discomfort and may require extensive treatment.
If stress is the cause you need to find a way to relax! Physical therapy, muscle relaxants, counseling and even exercise may help reduce tension. Don't make your teeth the brunt of your stress.