This chapter discusses the cumulative effect of oral parafunctions (OPFs) on the health of a patient's natural dentition, dental restorations, oral soft structures, and temporomandibular joints (TMJs). Nail biting and other OPFs are common in young children. Consequently, unmanaged parafunctional habits may contribute to the etiology of trauma in the stomatognathic systems of adolescents and adults. Prevention, early detection, and intervention are important clinical activities to diminish the influences of chronic OPFs on the teeth, muscles, and temporomandibular joints. The dentist can assist in detecting OPFs, protecting vulnerable oral and TMJ structures, and making appropriate referrals. Although occlusal splints can protect the oral structures from wear, they have little effect on parafunctional habits. Growing evidence suggests that psychological interventions to address factors contributing to the maintenance of these adverse habits can assist patients in overcoming them.