Threshold variations of medial pterygoid single motor units during vertical or horizontal force tasks.

OBJECTIVES: To test the hypotheses that (a) the force thresholds at onset of medial pterygoid muscle single motor unit (SMU) activity do not decrease with an increase in the rate of force generation in standardised vertical or horizontal jaw-force tasks, and (b) there is evidence for functional heterogeneity within the medial pterygoid muscle. METHODS: In 14 healthy participants, electromyographic recordings of the right medial pterygoid muscle were performed with intramuscular fine-wire electrodes during four isometric force tasks: vertical, horizontal contralateral, horizontal protrusion and horizontal ipsilateral, performed at two rates of force development (slow ramp, fast ramp). Computer tomography scans confirmed electrode location within the muscle, which was divided into medial and lateral parts. Force thresholds of onset of discriminated SMUs were compared between rates in each task; significance accepted at p < 0.05. RESULTS: Of 45 SMU force thresholds studied in one or more tasks, there was no significant difference between slow and fast ramp within each force task, except slow ramp thresholds from the lateral part during the vertical force task were significantly higher than fast ramp thresholds. Reversals of recruitment order between tasks provided evidence for functional heterogeneity within the muscle. Force thresholds of the vertical tasks (range: 1-292.6 N) were mostly higher than for the horizontal tasks (range: 0.1-12.5 N). CONCLUSION: The data are consistent with the proposal that the medial pterygoid muscle stabilises the jaw in the vertical plane during isometric force generation in the jaw closing, as well as horizontal directions.

Single motor units from the medial pterygoid muscle can be active during isometric horizontal and vertical forces.

OBJECTIVES: To determine (a) whether the medial pterygoid muscle is active in an isometric vertical force task and in isometric horizontal force tasks in the contralateral, protrusion and ipsilateral directions; (b) whether the same single motor units (SMUs) could be active across different directions of isometric force generation; and (c) whether different regions of the medial pterygoid muscle exhibit different patterns of SMU activation during the generation of any one direction of isometric force. METHODS: Intramuscular electromyographic (EMG) recordings were made from the right medial pterygoid muscle in 15 healthy participants during isometric force tasks: vertical and horizontal contralateral, protrusion and ipsilateral. A computed tomography scan divided the EMG recording site into a medial or lateral part in each participant. Single motor units were discriminated in each task. RESULTS: Medial pterygoid SMU activity was recorded in 100% of participants for the vertical biting tasks, 86% of participants for the horizontal contralateral and horizontal protrusion tasks and 57% of the horizontal ipsilateral tasks. Of the 72 SMUs that were discriminated, 36% were active in all tasks; 18% were active only in the vertical tasks and 17% were active in the vertical, horizontal contralateral and horizontal protrusion tasks. The proportion of SMUs that was active in at least 1 horizontal task in the lateral part (33/39) was significantly higher than the proportion (21/33) in the medial part (Chi-Square, P < 0.05). CONCLUSION: The data are consistent with a stabilisation role for the medial pterygoid muscle in isometric jaw forces in the vertical and horizontal planes.

Synergistic effects of cigarette smoke and saliva

Objectives: The aim of this study was to evaluate the cytotoxic effects of Cigarette Smoke on the human peripheral blood lymphocytes in the presence of stimulated or non-stimulated saliva in an in vitro model. Methods and Materials: Ten healthy volunteers in the age range of 21 to 29 were selected and samples of peripheral blood lymphocytes and saliva (whole and stimulated saliva) collected. Peripheral blood lymphocytes suspensions (PBS) were taken and exposed to 6 different media. Samples were collected from all media at both 20 and 80 min- ute time points. The survival rates of PBL were then determined at both 20 and 80 minute time points. Results: The cell survival rates following exposure to cigarette smoke (CS) in the presence of PBS supplemented with whole or stimulated saliva were significantly lower at 80 minutes when compared with the 20 minute rates (P<0.05). Conclusion: Tobacco effects were significantly increased in the presence of saliva especially stimulated saliva (AU)

Synergistic effects of cigarette smoke and saliva.

OBJECTIVES: The aim of this study was to evaluate the cytotoxic effects of Cigarette Smoke on the human peripheral blood lymphocytes in the presence of stimulated or non-stimulated saliva in an in vitro model. METHODS AND MATERIALS: Ten healthy volunteers in the age range of 21 to 29 were selected and samples of peripheral blood lymphocytes and saliva (whole and stimulated saliva) collected . Peripheral blood lymphocytes suspensions (PBS) were taken and exposed to 6 different media. Samples were collected from all media at both 20 and 80 minute time points. The survival rates of PBL were then determined at both 20 and 80 minute time points. RESULTS: The cell survival rates following exposure to cigarette smoke (CS) in the presence of PBS supplemented with whole or stimulated saliva were significantly lower at 80 minutes when compared with the 20 minute rates (P<0.05). CONCLUSION: Tobacco effects were significantly increased in the presence of saliva especially stimulated saliva.