Oral Implant-Prostheses: New Teeth for a Brighter Brain

Abstract

Several studies have demonstrated that chewing can be regarded as a preventive measure for cognitive impairment, whereas masticatory deficiency, associated with soft-diet feeding, is a risk factor for the development of dementia. At present the link between orofacial sensorimotor activity and cognitive functions is unknown. In subjects with unilateral molar loss we have shown asymmetries in both pupil size and masticatory muscles electromyographic (EMG) activity during clenching: the molar less side was characterized by a lower EMG activity and a smaller pupil. Since implant-prostheses, greatly reduced both the asymmetry in EMG activity and in pupil’s size, trigeminal unbalance, leading to unbalance in the activity of the Locus Coeruleus (LC), may be responsible for the pupil’s asymmetry. According to the findings obtained in animal models, we propose that the different activity of the right and left LC may induce an asymmetry in brain activity, thus leading to cognitive impairment. According to this hypothesis, prostheses improved the performance in a complex sensorimotor task and increased the mydriasis associated with haptic tasks. In conclusion, the present study indicates that the implant-prosthesis therapy, which reduces the unbalance of trigeminal proprioceptive afferents and the asymmetry in pupil’s size, may improve arousal, boosting performance in a complex sensorimotor task.

Short-Term Effects of Chewing on Task Performance and Task-Induced Mydriasis: Trigeminal Influence on the Arousal Systems

“…Fibers from trigeminal nuclei could affect the distal dendrites of the pericoerulear region ( Aston-Jones et al, 1986 , 1991 ), as well as, via the paragigantocellularis and the prepositus hypoglossi nuclei ( Lovick, 1986 ; Buisseret-Delmas et al, 1999 ), the LC cell bodies ( Aston-Jones et al, 1986 ). So, an increase in LC activity could occur during the trigeminal-induced enhancements in task-related mydriasis and in cognitive performance (see De Cicco et al, 2014 , 2016 ), which would benefit of the release of noradrenaline at cerebral cortical level ( Gabay et al, 2011 ).…”

“…Pupillographic measurements have been previously used to indirectly track the activity of LC neurons ( Silvetti et al, 2013 ; Hoffing and Seitz, 2015 ; Kihara et al, 2015 ; Hayes and Petrov, 2016 ; see also Laeng et al, 2013 ; De Cicco et al, 2014 , 2016 ).…”

Trigeminal, Visceral and Vestibular Inputs May Improve Cognitive Functions by Acting through the Locus Coeruleus and the Ascending Reticular Activating System: A New Hypothesis

“…Recent experiments have shown that the presence of a sensorimotor trigeminal imbalance (related to occlusal problems)—consisting in an asymmetric activation of masseter muscles during clenching—is strongly correlated to an asymmetry in pupils size, either in the normal jaw resting position, with the arches few millimetres apart, or with the teeth in contact (De Cicco et al, 2014 , 2016 ). Since pupil size is considered as a reliable indicator of LC activity and its asymmetry is strongly reduced following removal of the trigeminal imbalance by occlusal correction, these data suggest that the trigeminal imbalance makes the LC discharge asymmetric.…”

Central Sensitization-Based Classification for Temporomandibular Disorders: A Pathogenetic Hypothesis

“…An alteration of this balance due to central or peripheral phenomena, such as an alteration in the occlusion [ 106 – 108 ], may induce a state of CS at this level, in part justifying the hyperarousal state in CSSs. LC has been also linked to a category of disorders characterized by imbalance of the arousal systems and alteration of tonic-phasic function of the LC, including disorders of affective-emotional sphere [ 109 ], chronic pain disorders [ 110 , 111 ], and migraine [ 112 , 113 ].…”