Pain Control by Proprioceptive and Exteroceptive Stimulation at the Trigeminal Level

Figures

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  FIGURE 1. (A) Picture of the device used for mandibular extension in the trigeminal stimulation tests (proprioceptive type). The device consists of a 10 or 5-mm thickness to be placed in the mouth at the level of the incisors, having a width ranging from canine to canine. (B) Neurophysiological Stimulation Device (NSD) (Ficacci, 2014): an endoral neurophysiological stimulation having a half-moon shape, with a 10 or 5-mm thickness (trigeminal self-stimulation element for proprioceptive mandibular extension) similar to that described in (A) to be positioned in the anterior portion of the oral cavity, from canine to canine, between the upper and lower dental arches. The oblique fin of about 2–3 cm has the function to stimulate the palatine area. (C,D) Frequency distributions of PPT and PTL values. The experimental data were fitted with normal distributions (solid lines), with mean and standard deviation of 28.2 ± 5.0 and 38.8 ± 5.7, respectively. (E) Plot showing the strong linear correlation between the two parameters, with a Pearson coefficient of 0.97. The line is obtained from the fitting of the experimental data.

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  FIGURE 2. (A) Scheme of the experimental protocol used in this experiment. The participants were subject to a first test for the evaluation of the pain perception threshold (PPT) and pain tolerance level (PTL), 2 min after entering the testing room (min 2). After a further minute of rest (min 3) the subjects spent the next 7 min in one of the following conditions: (I) at rest without any auto-stimulation, and closed mouth (CTRL); (II) proprioceptive stimulation (PROP) with the device shown in Figure 1A, using a mandibular extension of 1 cm. Subsequently, at 0 (T2) and 5 min (T3) from the end of the stimulation, the PPT and PTL were recalculated. (B) Plot of the PPTs measured in CTRL subjects (circles) and in subjects undergoing a PROP stimulation (triangles) at the three different times. Also plotted is the mean ± SE of each group of the data (closed circles). (C) Same analysis made in (B) but on PTL values. ∗∗∗, t-test, p < 0.001; n.s., t-test, p > 0.05.

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  FIGURE 3. (A) Scheme showing all the time points were the PPT and PPT were assessed, in the three different experiments performed. (A,B) Time course of the effects of proprioceptive stimulation (PROP, 1 cm extension) on PPT (B) and PTL (C). The circles represent control subjects (CTRL), while the triangles represent treated subjects (PROP). The data are from three separate experiments, as described in Methods. Black symbols refer to data already presented in Figure 2. ∗∗∗, t-test, p < 0.001; n.s., t-test, p > 0.05.

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  FIGURE 4. Time course of the mean effects promoted by proprioceptive stimulation (PROP, white triangles) or proprioceptive plus exteroceptive stimulation (PROP+EXT, black triangles) on the PPT (A) and PTL (B). The circles represent control subjects (CTRL), the data come from six different experiments using a 1 cm high device for proprioceptive stimulation, and carried out as described in Methods.

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  FIGURE 5. (A,B) Plot of the mean PPT (left) and PTL (right) taken after 7 min of stimulation and 5 min from the end of the stimulation, and normalized to their values assessed at the beginning of the experiment. The stimulation was performed with devices having two different heights (0.5 and 1 cm) with (B) or without (A) the palatal stimulation. ∗∗∗, t-test, p < 0.001.