People who clench or grind their teeth regularly suffer from a condition called bruxism. Here a bit of information about bruxism to help you better understand it. Why Does Bruxism Occur? A primary cause of bruxism is stress. As a person experiences stress or anxiety, they may clench and grind their teeth, even as they sleep. Another cause of dental grinding is undiagnosed sleep apnea. The grinding may occur during the periodic episodes of breathing cessation.