A real simple exercise that may help them is to get a wooden dowel, about 4 inches long, 1/4 inch diameter, tape the ends with surgical tape. They then insert it as far back, between the teeth as possible. (like a bit in a horses mouth, except it doesn't stick out the sides.) Bite down on it, gently, 15 times, 3 sets. This helps open the joint, realign it and strengthen it also.