Dental Occlusal Changes Induce Motor Cortex Neuroplasticity

Abstract

Modification to the dental occlusion may alter oral sensorimotor functions. Restorative treatments aim to restore sensorimotor functions; however, it is unclear why some patients fail to adapt to the restoration and remain with sensorimotor complaints. The face primary motor cortex (face-M1) is involved in the generation and control of orofacial movements. Altered sensory inputs or motor function can induce face-M1 neuroplasticity. We took advantage of the continuous eruption of the incisors in Sprague-Dawley rats and used intracortical microstimulation (ICMS) to map the jaw and tongue motor representations in face-M1. Specifically, we tested the hypothesis that multiple trimming of the right mandibular incisor, to keep it out of occlusal contacts for 7 d, and subsequent incisor eruption and restoration of occlusal contacts, can alter the ICMS-defined features of jaw and tongue motor representations (i.e., neuroplasticity). On days 1, 3, 5, and 7, the trim and trim-recovered groups had 1 to 2 mm of incisal trimming of the incisor; a sham trim group had buccal surface trimming with no occlusal changes; and a naive group had no treatment. Systematic mapping was performed on day 8 in the naive, trim, and sham trim groups and on day 14 in the trim-recovered group. In the trim group, the tongue onset latency was shorter in the left face-M1 than in the right face-M1 (P < .001). In the trim-recovered group, the number of tongue sites and jaw/tongue overlapping sites was greater in the left face-M1 than in the right face-M1 (P = 0.0032, 0.0016, respectively), and the center of gravity was deeper in the left than in the right face-M1 (P = 0.026). Therefore, incisor trimming and subsequent restoration of occlusal contacts induced face-M1 neuroplasticity, reflected in significant disparities between the left and right face-M1 in some ICMS-defined features of the tongue motor representations. Such neuroplasticity may reflect or contribute to subjects' ability to adapt their oral sensorimotor functions to an altered dental occlusion.

Bite or brain: Implication of sensorimotor regulation and neuroplasticity in oral rehabilitation procedures

“…The cortical neuroplastic changes have also been associated with the altered stomatognathic system for, for example, tooth loss, intraoral pain or nerve injury. Previous studies in rodents have suggested that the reorganisation of the MI may occur after peripheral nerve injuries . Further, experimental studies in humans have shown that manipulation of peripheral sensory inputs from oro‐facial structures alters the cortical excitability of the oro‐facial muscles …”

Dental deafferentation and brain damage: A review and a hypothesis

“…Should one or more “musicians” (teeth) change their function or become absent, the orchestra's overall harmony will be affected, creating temporary or long‐term dissonances and increasing mental and physical stress [36]. To adapt to alterations, cope with stress, and maintain the effectiveness of the eating‐mastication function when facing such changes, it is necessary have related sensory cortical and motor reorganization [1–4]. This “symphony” can also be orchestrated by different organ systems such as mastication‐related muscles, different sensory organs, the temporal‐mandibular joint (TMJ), and the autonomic nervous system.…”

“…Unlike most other types of peripheral deafferentations, DDs may develop as a frequently recurring event of significant quantity, such as multiple teeth loss at different periods of time, in various locations, and in different dental arches. After persistent occurrences of DDs, the masticatory apparatus (including TMJs, all related masticatory musculatures, as well as associated musculatures such as supra‐ and infra‐hyoid groups of muscles) may also be affected peripherally and centrally [2–4].…”

“…However, a recent study showed that in different age groups, losing anterior teeth or having had root canal therapy could also result in taste deficits [8]. It is indicated that peripheral DDs can cause central neuroplastic changes and reorganizations of sensory and motor cortices [1–4] as well as influence cross modal sensibility [10,11].…”

“…Examples of DD include: Tooth loss, local and/or generalized periodontal detachment, improper operative or prosthetic restorations, and orthodontic managements and the unavoidable consequence of impaired mastication. These DDs may cause sensory and motor cortical reorganization [1–4], affect cerebral functional streams toward multisensory hubs [5,6], impair gustatory, auditory and olfactory perceptions [7–11], and result in memory and cognition impairment [12–30].…”