Dental insurance

Anyone work in dental insurance? Is it common for dental plans not to offer orthodontic care after the age of 19? Because apparently you don’t need orthodontic work as an adult? I have to get a night shield or my teeth will fall out (from clinching/grinding) and since I’m over the age of 19, I have to pay for it 100% out of pocket. Is this normal or Do I have bad dental insurance?