Objective: Traditionally, swallowing rehabilitation has involved the use of muscle strengthening exercises, such as the head-lift manoeuvre (Shaker et al., 1997), to strengthen the floor of mouth muscles. Clinical reasoning suggests that this particular exercise may be problematic for patients with cervical spine injuries or increased frailty. Recently, Bauer and Huckabee (2010) attempted to determine the efficacy of an alternative exercise for the floor of mouth muscles in healthy adults. The present study aims to expand on this work in a larger population of healthy adults. Study design: Controlled trial; participants matched for age and sex. Participants: 23 healthy adults with no history of neurological or muscular impairment. Method: Participants were assigned into one of two groups: jaw opening exercise (JOE; n = 12) and sham exercise (SE; n = 11). Groups were matched for age and gender. Participants performed their respective exercises three times per day, five days per week, over a six week period. At three times during this period, measures of submental 2-D cross-sectional area and anterior hyoid movement were taken via ultrasound. Additionally, measures of submental muscle myoelectrical activity were taken via surface electromyography. Pre- and post-treatment comparisons, as well as inter-group comparisons, were undertaken. Results: No significant differences were observed between groups on measures of muscle size, anterior hyoid movement, or myoelectrical activity over time. However, this study has contributed to the future development of an alternative exercise to target the submental muscle group.

The focus of this thesis was to study an action that humans perform regularly, namely, to hold a morsel between the teeth and split it into smaller pieces. Three different issues related to this biting behavior were addressed:  (1) the effect of redu­c­ed perio­dontal tissues on food holding and splitting behavior; (2) the behavioral conse­quences of performing different bite tasks with different functional requirements, i.e., to split a peanut half resting on a piece of chocolate or to split both the peanut and the chocolate; and (3) the reflex modulations resul­ting from such a change in the intended bite action. The main conclusions from the experi­mental studies were the following: First, perio­dontitis, an inflam­matory disease that destroys the peri­o­dontal ligaments and the embedded perio­dontal mechanoreceptors, causes significant impairments in the masticatory abili­ty: the manipulative bite forces when holding a morsel are elevated compared to a matched control population and the bite force development prior to food split is altered. These changes are likely due to a combination of reduced sensory informa­tion from the damaged ligaments and to changes in the bite stra­tegy secon­d­ary to the unstable oral situation. Second, people exploit the anatomy of jaw-closing muscles to regulate the amount of bite force that dissipates following a sudden unloading of the jaw. Such control is necessary because without mechanisms that quickly halt jaw-closing movements after sudden unloading, the impact forces when the teeth collide could otherwise damage both the teeth and related soft tissues. Splitting a piece of chocolate, for instance, regularly requires >100N of bite force and the jaws collide within 5 ms of a split. On the other hand, when biting through heterogeneous food, the bite force needs to be kept high until the whole morsel is split. The required regulation is achieved by differen­tial­ly engaging parts of the masseter muscles along the anteroposterior axis of the jaw to exploit differences between muscle portions in their bite force generating capa­ci­ty and muscle shortening velocity. Finally, the reflex evoked by suddenly unloading the jaw—apparent only after the initial bite force dissipation—is modulated according to the bite intention. That is, when the intention is to bite through food items with multiple layers, the reflex response in the jaw opening muscles following a split is small, thus minimizing the bite force reduction. In contrast, when the intention is to rapidly decrease the bite force once a split has occurred, the reflex response is high. This pattern of reflex modulation is functionally beneficial when biting through heterogeneous food in a smooth manner. The presented studies show the significance of integrating cogni­tive, physiological and anatomical aspects when attempting to understand human masticatory control.