Is daytime, continual teeth grinding always a sign of stress?

My s/o has dental implants. He grinds his teeth all day long. I can hear it in an adjacent room. He broke something on his teeth and they fixed it but he’s still doing it. I know that all his growing up years the rule in the house was don’t upset your mother. The doctor said she must be humored or she could have another breakdown. Just go along with her remarks. She ended up terribly spoiled, irritable and coddled. He does not seem stressed out at all. But is this proof that he is?