Topical review: modulation of trigeminal sensory input in humans: mechanisms and clinical implications.

In this review, the modulatory effects of tooth and implant loading, orofacial pain, and psychological factors on somatosensory and jaw-motor function in humans are assessed. Experimental studies on the control of jaw actions have revealed that patients with prostheses supported by osseointegrated implants show an impairment of fine motor control of the mandible. One possibility is that this may be related to the loss of afferent information from periodontal ligament mechanoreceptors, which results in considerably higher and more variable forces to hold and manipulate food between the teeth. However, psychophysical investigations have shown that patients still perceive mechanical stimuli exerted on osseointegrated implants in the jawbone. The use of somatosensory evoked potentials may revealed what specific receptor groups are responsible for this so-called osseoperception phenomenon. Orofacial pain is another modulator of trigeminal system functioning. Experimental jaw muscle pain has several effects on the somatosensory and motor function of the masticatory system, all of them serving to warn the individual about the ongoing damaging of tissues. Finally, the influence of mental state on the sensory and motor functions of the trigeminal system will be addressed. While some animal studies suggest that psychological stress can reduce acute pain, less speculative are the findings in human subjects that the anticipation of receiving a painful stimulus or undertaking difficult mental tasks can modulate jaw reflexes, including those evoked by mechanical stimuli applied to the teeth. Since such stimuli occur regularly during normal oral activities, the study of the resulting motor effects may yield clinically meaningful results in the context of other variables that modulate mandibular function.