If you get cramps in your jaw, it's because there's the erosion of tooth enamel. Your teeth are in contact with more than necessary sugar or acidic foods, making the enamel wear away. It could also happen if you already suffer from gastroesophageal reflux disease (GERD). It can result in cavities and pain after brushing or flossing, and there's a risk for tooth decay. Consult with your dentist for further dental treatment.