There are also very many people who grind their teeth and who do not develop TMD. Bruxism and other parafunctional activities may play a role in perpetuating symptoms in some cases.Other parafunctional habits such as pen chewing, lip and cheek biting (which may manifest as morsicatio buccarum or linea alba), are also suggested to contribute to the development of TMD. Other parafunctional activities might include jaw thrusting, excessive gum chewing, nail biting and eating very hard foods. Trauma
Trauma, both micro and macrotrauma, is sometimes identified as a possible cause of TMD; however, the evidence for this is not strong. Prolonged mouth opening (hyper-extension) is also suggested as a possible cause. It is thought that this leads to microtrauma and subsequent muscular hyperactivity. This may occur during dental treatment, with oral intubation whilst under a general anesthetic, during singing or wind instrument practice (really these can be thought of as parafunctional activities). Damage may be incurred during violent yawning, laughing, road traffic accidents,  sports injuries, interpersonal violence, or during dental treatment, (such as tooth extraction).It has been proposed that a link exists between whiplash injuries (sudden neck hyper-extension usually occurring in road traffic accidents), and the development of TMD. This has been termed "post-traumatic TMD", to separate it from "idiopathic TMD". Despite multiple studies having been performed over the years, the cumulative evidence has been described as conflicting, with moderate evidence that TMD can occasionally follow whiplash injury.
It is the gold standard method for assessing disc position and is sensitive for intra-articular degenerative alterations.Indications for MRI are pre-auricular pain, detection of joint clicking and crepitus, frequent incidents of subluxation and jaw dislocation, limited mouth opening with terminal stiffness, suspicion of neoplastic growth, and osteoarthritic symptoms. It is also useful for assessing the integrity of neural tissues, which may produce orofacial pain when compressed.MRI provides evaluation of pathology such as necrosis and oedema all without any exposure to ionizing radiation. However, there is a high cost associated with this method of imaging, due to the need for sophisticated facilities. Caution should be taken in patient selection, as MRI is contraindicated in those with claustrophobic tendencies, pacemakers and metallic heart valves, ferromagnetic foreign bodies and pregnant women. Ultrasound
Where internal TMJ disorders are concerned, ultrasound (US) imaging can be a useful alternative in assessing the position of the disc While having significant diagnostic sensitivity, US has inadequate specificity when identifying osteoarthrosis. Moreover, it is not accurate enough for the diagnosis of cortical and articular disc morphology based on the findings done related to morphological alterations. However, with US, identification of effusion in individuals with inflammatory conditions associated with pain is possible and confirmed by MRIUS can be a useful alternative in initial investigation of internal TMJ dysfunctions especially in MRI contraindicated individuals despite its limitations.