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Periodontal-Masseteric Reflexes Decrease with Tooth Pre-load
P.F. Sowman1 and
K.S. Türker1,2,*
1 Research Centre for Human Movement Control, Discipline of Physiology, School of Molecular and Biomedical Science, University of Adelaide, SA 5005, Australia; and
2 Department of Physiology, Faculty of Medicine & Centre for Brain Research, Ege University, Izmir 35100, Turkey
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Figure 1. Left masseteric EMG responses to 10-Hz incisal stimulation from a single person. (A) Rectified averaged EMG (n = 60) in response to decreasing amounts of pre-load. Top trace (red) shows response at the lowest pre-load (0.1 N) when periodontium is anesthetized. Bottom trace (black) is the averaged stimulus force (n = 60) applied at the lowest pre-load (0.4 N superimposed on a 0.1-N pre-load). Pre-load was varied to include the 4 steps tested (0.1, 0.2, 0.5, and 2.0 N). (B) Stimulus to EMG coherence for the data shown in (A). Traces are color-matched to (A). The horizontal dotted line represents the 99% confidence interval for significant coherence. (C) Spike trigger averaged EMGs of the same data shown in (A) and (B). Traces are color-matched. Top trace in each frame is the rectified, averaged EMG (trigger at time = 0); bottom trace is the cumulative sum of that reflex. Vertical dotted color-matched lines in each frame illustrate the onset latency and offset latency for the inhibitory response elicited by the stimulus. In the top left corner, the reflex size (n = 60) is displayed. Reflex latencies and size calculated as per Brinkworth and Türker (2003).
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Figure 2. Significant interactions identified by the repeated-measures ANOVA performed on the coherence Z-scores across all participants (n = 10). (A) Averages (± SEM) for the condition (control or local anesthetic) by pre-load interaction (n = 50). (B) Averages (± SEM) for the condition by frequency interaction (n = 40). Pairwise comparisons performed with Tukey’s HSD.
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Figure 3. Effects of pre-load on the entrainment of left masseteric EMG to 20-Hz stimulation of an incisor. The data displayed in this Fig. come from the six participants who had significant coherence values at all pre-loads when 20-Hz stimulation was applied (n = 6). (A) Average normalized gain response ± SEM (red) and average coherence Z-scores plotted against pre-load. The strength of correlation is expressed alongside the respective plot. Hyperbolic curves were fitted. (B) Coherence data presented in (A). (black) Compared with (i) the tooth movement/force relationship presented in Fig. 3 in Parfitt (1960); and (ii) the periodontal mechanoreceptor steady-state response/force relationship presented in Fig. 1b in Trulsson and Johansson (1994). Datapoints coinciding with the pre-load forces used in the current study were extracted directly from the Figs. presented in Parfitt (1960) and Trulsson and Johansson (1994). Y-axes for the current data have been inverted to illustrate the similarity to the previous data.
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Journal of Dental Research, Vol. 87, No. 2,
175-179 (2008)
DOI: 10.1177/154405910808700213
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