Modifica di PaginaEntry (sezione)

==Discussion==
The consideration of the masticatory system as a complex system is further validated in light of recent developments in neurophysiology applied to dental occlusion. Studies conducted on animal models, particularly Sprague-Dawley rats, have shown that even minimal occlusal modifications (e.g., trimming of the mandibular incisor) can induce significant changes in the primary motor cortex of the face (face-M1), with evident manifestations of functional and structural neuroplasticity{{Tooltip|<sup>[22]</sup>|<ref>Avivi-Arber L, Lee JC, Sessle BJ. Motor cortex neuroplasticity associated with dental occlusion. J Dent Res. 2015;94(12):1751–9. doi:10.1177/0022034515596345</ref>|<small>. 🧠 The modification of dental occlusion can influence oral sensorimotor functions, and not all patients can adapt to restorative treatments. By studying Sprague-Dawley rats, neuroplasticity of the facial primary motor cortex (face-M1) was observed in response to repeated trimming of the mandibular incisors, followed by the restoration of occlusal contacts. The changes, mapped with intracortical microstimulation (ICMS), showed significant differences between cerebral hemispheres in the latency and distribution of motor areas of the tongue and mandible. These results suggest that face-M1 neuroplasticity could be an adaptive mechanism to respond to alterations in dental occlusion.</small>}}

These cortical modifications include, for example, the variation in tongue activation latency between cerebral hemispheres, the variation in the number of cortical activation sites for the tongue and mandible, and the modification of the depth of the center of gravity of the involved cortical areas. These results suggest that the loss and subsequent restoration of occlusal contacts can alter orofacial motor representations, paving the way for new interpretative models of masticatory function based on adaptive neuroplasticity.

Similarly, it emerges that both the primary somatosensory cortex (face-SI) and the motor cortex (face-MI) play a central role in orofacial sensorimotor integration, participating not only in the initiation and control of voluntary movements (e.g., mandibular opening) but also in semi-automatic movements such as chewing and swallowing {{Tooltip|<sup>[23]</sup>|<ref>Avivi-Arber L, Martin R, Lee JC, Sessle BJ. The Face Sensorimotor Cortex and its Neuroplasticity in Health and Disease. J Dent Res. 2019;98(11):1184–94. doi:10.1177/0022034519865385</ref>|<small>🧠 The facial somatosensory and motor cortex regulates automatic and voluntary orofacial movements. Their neuroplasticity allows adaptation or lack thereof to oral changes (such as occlusal alterations or prostheses), influencing the recovery of sensorimotor functions and quality of life, especially in patients with neurological disorders or orofacial pain.</small>}}

These two cortical areas, although distinct in function, are deeply interconnected: face-MI continuously receives input from face-SI, and together they form the so-called “face sensorimotor cortex”{{Tooltip|<sup>[24]</sup>|<ref>Iwata K, Sessle BJ. Neural Basis of Orofacial Functions in Health and Disease. J Dent Res. 2019;98(11):1185–1195. doi:10.1177/0022034519865372</ref>|<small>🧠 This article provides an overview of the neural mechanisms involved in the somatosensory and motor functions of the face and mouth and, to a lesser extent, the pharynx and larynx. The focus is particularly on the neural basis of touch, temperature, and orofacial pain, with special emphasis on pain, as it is common in the skin, teeth, muscles, joints, and other tissues of the orofacial region and can cause long-term suffering through various painful states or syndromes. Particular attention is also given to the neural processes that regulate the numerous reflexes and other motor functions of the orofacial area, particularly those related to chewing, swallowing, and associated neuromuscular functions. Only a few details are dedicated to other important functions of the face and mouth, such as smell, taste, and speech.</small>}} Their integrated activity is mediated by complex central circuits, which include corticobulbar projections directed to the motor nuclei of the cranial nerves (primarily the trigeminal nucleus), responsible for mandibular muscle activation.

The ability of these areas to undergo plastic reorganization (neuroplasticity) represents a fundamental mechanism by which the nervous system adapts to peripheral changes—such as tooth loss, trauma, or the introduction of prostheses—as well as to sensory stimulations and the learning of new motor skills {{Tooltip|<sup>[25]</sup>|<ref>Review Prog Brain Res. 2011:188:71-82. doi: 10.1016/B978-0-444-53825-3.00010-3. Chapter 5--face sensorimotor cortex: its role and neuroplasticity in the control of orofacial movements. Barry J Sessle , PMID: 21333803 DOI: 10.1016/B978-0-444-53825-3.00010-3</ref>.|<Small>The range and complexity of orofacial movements require sophisticated neural circuitries that provide for the coordination and control of these movements and their integration with other motor patterns such as those associated with breathing and walking. This chapter is dedicated to Jim Lund whose many research studies have made major contributions to our knowledge of the role of brainstem and cerebral cortex in orofacial motor control. Our own investigations using intracortical microstimulation (ICMS), cortical cold block, and single neuron recordings have documented that the face primary motor area (MI) and primary somatosensory area (SI) are involved in the control not only of elemental and learned orofacial movements but also of the so-called semiautomatic movements such as mastication and swallowing, the control of which have been largely attributed in the past to brainstem mechanisms. Recent studies have also documented that neuroplasticity of the face sensorimotor cortex is a feature of humans and animals trained in a novel oral motor behavior, and that it reflects dynamic and adaptive events that can be modeled by behaviorally significant experiences, including pain and other alterations to the oral environment. Furthermore, our findings of the disruptive effects of the face sensorimotor cortex cold block indicate that the face MI and SI are also critical in the successful performance of an orofacial motor skill once it is learned. Future studies aimed at the further demonstration of such changes and at their underlying mechanisms and their sequence of appearance in the face sensorimotor cortex and associated cortical areas represent crucial steps for understanding the intracortical processes underlying neuroplasticity related to oral motor learning and adaptation. In view of the role that cortical neuronal ensembles play in motor execution, learning, and adaptation (Nicolelis and Lebedev, 2009), these studies should include the properties and plasticity of neuronal ensembles in several related cortical areas in addition to a specific focus on single neurones or efferent microzones within the face MI or SI. As recently noted (Martin, 2009; Sessle et al., 2007, 2009), such research approaches are also important for developing improved rehabilitative strategies to exploit these mechanisms in humans suffering from chronic orofacial pain or sensorimotor disorders.</Small>}}<blockquote>In light of these data, it is evident that alterations in craniofacial and occlusal morphology—traditionally interpreted through static biomechanical models—must instead be understood from a dynamic functional perspective. The clinical evaluation of the patient cannot therefore disregard an integration of morphology, function, and neurophysiological response. Not every "malocclusion" requires treatment, just as not every "ideal occlusion" guarantees functional well-being.</blockquote>In summary, trigeminal neuroplasticity emerges as the key to understanding adaptation (or lack thereof) to occlusal modifications. It must guide both diagnosis and therapeutic strategies, inspiring truly personalized rehabilitation protocols. OrthoNeuroGnathodontic treatments and beyond, being based on this systemic vision, represent the most advanced and coherent clinical model to address the challenges of modern dentistry.