Dental malocclusion stimulates neuromuscular circuits associated with temporomandibular disorders

Abstract

Unilateral anterior crossbite (UAC) has been demonstrated to cause masseter hyperactivity via the periodontal trigeminal mesencephalic nucleus (Vme)–trigeminal motor nucleus circuit. Here, we studied activation of motor neurons of the facial nucleus (VII), hypoglossal nucleus (XII), nucleus ambiguus (Amb), and spinal nucleus of the accessory nerve (SNA) in rats with UAC via their similar connections with Vme. An anterograde tracer, biotinylated dextran amine (BDA), was injected into the Vme to identify the central axon terminals around the motor neurons of VII, XII, Amb, and SNA. The expression of vesicular glutamate transporter 1 (VGLUT1) in neurons of VII, XII, Amb, and SNA, and the expression of acetylcholinesterase (AChE) were measured in the stapedius, lingualis, palatopharyngeal, and sternocleidomastoid muscles. In BDA‐treated rats, many BDA‐labeled cell bodies in the Vme and terminals in VII, XII, Amb, and SNA were identified. Compared with control rats, rats with UAC showed higher expression of VGLUT1 in these nuclei, and statistically significantly higher expression of AChE in the stapedius, lingualis, and sternocleidomastoid muscles, but not in the palatopharyngeal muscle. These findings suggest that UAC activates orofacial, head, and cervical multimotor behaviors via connections between the Vme and the corresponding motor nuclei.

Malocclusion Generates Anxiety-Like Behavior Through a Putative Lateral Habenula–Mesencephalic Trigeminal Nucleus Pathway

“…As we proposed in our recent publication, UAC elicited hyperactivity of jaw closing muscles, probably through a circuit of periodontal mesencephalic trigeminal afferents (Vme) to trigeminal motor neurons (Vmo; Liu et al, 2017). A similar impact of the Vme on multiple orofacial motor nuclei in the brain stem has also been reported (Liu et al, 2018). Therefore, the UAC model could be used in explorations of Vme-related problems, which are worthy of investigation.…”

Effect of dental malocclusion on cerebellar neuron activation via the dorsomedial part of the principal sensory trigeminal nucleus

“…The dental occlusion contribution to postural control has been proposed to depend on external disturbances [ 39 , 40 ]. Our published data [ 14 , 25 , 35 , 41 ] and the present work bring about supportive evidence. The existence of an ascending pathway mediating proprioception from the periodontal region to the cerebellum provides a possible neuroanatomical basis for the trigeminal mechanism of somatic movement and balance.…”

“…This makes it possible for the projections of neurons in the Vme to target many other neurons in the brainstem. The neurons of Vme innervate spindles in the jaw‐closing muscles and periodontal pressoreceptors [ 25 , 35 , 41 , 43 ]. Axons involved in trigeminal proprioception from periodontal mechanoreceptors and spindles in the jaw‐closing muscles directly bypass the trigeminal ganglion and leave their cell bodies in all the rostro‐caudal levels of the entire mesencephalon [ 44 ].…”

“…Reports have indicated that there are projections from Vme to the trigeminal motor nucleus, facial nerve nucleus, hypoglossal nerve nucleus, nucleus ambiguous, accessory nerve nucleus, and Vpdm [ 21 , 33 , 34 ]. In UAC treated female rats, the VGLUT1 mRNA expression level of Vme was upregulated [ 25 ] and the VGLUT1 protein expression level of trigeminal motor nucleus, facial nerve nucleus, hypoglossal nerve nucleus, nucleus ambiguous, and accessory nerve nucleus was increased [ 35 ]. It is of dental interest to determine whether the Vpdm‐cerebellum circuit of UAC rats is excited.…”

Can Botulinum Toxin-A Contribute to Reconstructing the Physiological Homeostasis of the Masticatory Complex in Short-Faced Patients during Occlusal Therapy? A Prospective Pilot Study

“…In the early stage, dentists only focused on the teeth and occlusal relationship, which was generally static and non-functional [4][5][6]. Until the prevalence of functional occlusion in recent years [7,8], the concept of complete dentistry was put forward [9], with the studies on dynamic occlusion and masticatory function valued by interdisciplinary oral researchers [1-3,10-18], especially in the fields of orthodontics [1-3], occlusal reconstruction [10,11], dental implant [12,13], periodontal disease [14,15], dental caries treatment [16], temporomandibular joint disorders (TMD) [17], bruxism [18], etc. Dentists have begun to realize the integrality of the masticatory system (MS) (i.e., the stomatognathic system (SS)), which is generally composed of teeth and occlusion, the temporomandibular joint (TMJ), neuromuscular factors, jaw, periodontal tissue, etc.…”