J Manipulative Physiol Ther 2003 (Jul); 26 (6): E16 ~ FULL TEXT
Gary A. Knutson, DC
840 W 17th, Suite 5,
Bloomington, IN 47404, USA;
OBJECTIVE: To discuss the management of chronic sleep bruxism in a 6-year old girl.
CLINICAL FEATURES: The patient had morning headaches and cervical spine pain. Due to abnormal tooth wear, bruxism had been previously diagnosed and was verified by observation during sleep. She also had abnormal postural and palpatory findings, indicating upper cervical joint dysfunction.
INTERVENTION AND OUTCOME: Bilateral rotary cervical stretching/mobilization and a vectored high-velocity, low-amplitude adjustment were performed in the upper cervical spine, using the atlas transverse process as the contact point. There was complete relief of the chronic subjective symptoms concomitant with remission of the objective signs of joint dysfunction.
CONCLUSION: Cervical, particularly upper cervical, spine muscle-joint dysfunction should be considered as a potential etiology in chronic childhood sleep bruxism.
From the Full-Text Article:
This case study appears to show a relationship between putative upper cervical muscle-joint dysfunction and chronic sleep bruxism in a young child. Given the temporal association between the manipulative treatment and cessation of the chronic symptoms, spontaneous remission is less likely. A positive symptomatic reaction to the clinical encounter and not the treatment is also possible. However, such a positive psychosomatic reaction was not obtained with the prior dental or chiropractic therapeutic approaches.
Molina et al  note that severe bruxers may present with increased nociception input to the trigeminal system. The trigeminal system has been found to connect with the gray matter in the upper cervical cord (C1 and C2), and appears to be widespread in terms of both sensory and motor reflex activity.  Bogduk  calls this continuation of the gray matter of the spinal tract of the trigeminal nerve and the dorsal horns of the upper 3 cervical spinal cord segments the trigeminocervical nucleus. He writes, As such, the trigeminocervical nucleus is the essential nociceptive nucleus of the upper neck, head and throat. Whatever the actual innervation of structures in this region, noxious stimuli from them will be mediated by the trigeminocervical nucleus. 
Recent hypotheses to explain myofascial and joint dysfunction theorize afferent activity of muscle chemonociceptors driving the gamma motor system in a positive feedback loop causing muscle hypertonicity and increased spindle signal. [8, 9] There is some evidence for this pathophysiological process in the cervical spine. [10, 11] If such chemonociceptive input from muscle-joint dysfunction was located in the upper cervical spine, it may provide the nociceptive input necessary to the trigeminal system to cause sleep bruxism.
Input from the small intrinsic muscles of the upper cervical spine are thought to be responsible for activation of the tonic neck reflexes,  which have been shown to cause global postural distortion and leg-length alignment asymmetry. [13, 14] Further, it has been theorized that afferent input from upper cervical muscle-joint dysfunction causes pathologic activation of the tonic neck reflexes.  In addition, there appears to be a closely organized relationship between tonic neck reflex activity and trigeminal reflex activity.  Tonic neck reflexes have been shown to have a significant influence on the temporalis muscle,  an elevator of the jaw.
While admittedly speculative, upper cervical muscle-joint dysfunction (subluxation) causing pathologic nociceptive afferent activity could affect the trigeminocervical tract and, in turn, the masseter and temporalis muscles causing sleep bruxism, as well as the tonic neck reflexes, causing the pelvic torsion and supine leg-length alignment asymmetry which were noted concomitantly in this case.
This case study demonstrated a rapid and complete recovery of chronic sleep bruxism, headache, and cervical spine pain in a child after upper cervical vectored manipulation. The possibility of upper cervical muscle-joint dysfunction as a cause of sleep bruxism should be explored.