People with implant-supported bridges show an impaired adaptation of the muscle activity to food hardness during mastication. We suggest that a lack of sensory signals from periodontal mechanoreceptors accounts for the impairment.

Tooth loss, decreased mass and strength of the masticatory muscles leading to difficulty in chewing have been suggested as important determinants of eating and nutrition in the elderly. To compensate for the loss of teeth, in particular, a majority of the elderly rely on dental prosthesis for chewing. Chewing function is indeed an important aspect of oral health, and therefore, oral rehabilitation procedures should aim to restore or maintain adequate function. However, even if the possibilities to anatomically restore lost teeth and occlusion have never been better; conventional rehabilitation procedures may still fail to optimally restore oral functions. Perhaps this is due to the lack of focus on the importance of the brain in the rehabilitation procedures. Therefore, the aim of this narrative review was to discuss the importance of maintaining or restoring optimum chewing function in the superageing population and to summarise the emerging studies on oral motor task performance and measures of cortical neuroplasticity induced by systematic training paradigms in healthy participants. Further, brain imaging studies in patients undergoing or undergone oral rehabilitation procedures will be discussed. Overall, this information is believed to enhance the understanding and develop better rehabilitative strategies to exploit training-induced cortical neuroplasticity in individuals affected by impaired oral motor coordination and function. Training or relearning of oral motor tasks could be important to optimise masticatory performance in dental prosthesis users and may represent a much-needed paradigm shift in the approach to oral rehabilitation procedures.

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Jaw actions adapt to the changing properties of food that occur during a masticatory sequence. In the present study, we investigated how the time-varying activation profile of the masseter muscle changes during natural chewing in humans and how food hardness affects the profile. We recorded surface electromyography (EMG) of the masseter muscle together with the movement of the lower jaw in 14 healthy young adults (mean age 22) when chewing gelatin-based model food of two different hardness. The muscle activity and the jaw kinematics were analysed for different phases of the chewing cycles. The increase in the excitatory drive of the masseter muscle was biphasic during the jaw-closing phase showing early and late components. The transition between these components occurred approximately at the time of tooth-food contact. During the masticatory sequence, when the food was particularised, the size of the early component as well as the peak amplitude of the EMG significantly decreased along with a reduction in the duration of the jaw-closing phase. Except for amplitude scaling, food hardness did not appreciably affect the muscle's activation profile. In conclusion, when chewing food during natural conditions, masseter muscle activation adapted throughout the masticatory sequence, principally during the jaw-closing phase and influenced both early and late muscle activation components. Furthermore, the adaptation of jaw actions to food hardness was affected by amplitude scaling of the magnitude of the muscle activity throughout the masticatory sequence.

Previously we have reported a biphasic increase in excitatory drive of the masseter muscle during natural chewing in young adults. We now hypothesize that sensory inputs from the periodontal mechanoreceptors (PMRs) are responsible for the late increase in excitatory drive during this biphasic movement. 13 participants with implant-supported bridges in both jaws, and thus lacking PMRs, and 13 participants with natural dentition chewed and swallowed model food of different hardness. Electromyographic (EMG) activity of the masseter muscle was recorded, along with the position of the mandible, and the muscle activity and jaw kinematics during the different phases of the chewing cycle were analyzed. Throughout the entire masticatory sequence, the excitatory drive of the masseter muscle during the jaw closing increased in a biphasic manner for the dentate participants; whereas biphasic elevation was observed only during the middle and last segments in the implant participants. Dentate participants exhibited significantly greater boosting of the EMG activity during late jaw closing than the implant participants, irrespective of food hardness and segment of the masticatory sequence. Sensory information from PMRs are required for boosting the enhancement of masseter muscle activity during the late jaw closing, during tooth-food contact.