Background: The study was aiming to optimize excessive gum chewing as an experimental model to induce jaw muscle pain and fatigue similar to those in painful TMDs with durations that would allow immediate investigations of jaw-motor function. Further, if any sex differences would be detected in the expression of pain. Methods: This randomized, double blinded study included 31 healthy participants of both sexes. A standardized chewing protocol of either 40-or 60-min of chewing was used with a wash-out period of 1 week. Subjective fatigue, pain characteristics and functional measures were assessed. For statistical analyses, Wilcoxon Signed Rank test, Mann-Whitney Rank Sum test and Friedman's ANOVA with Tukey post-hoc test were used. Results: High subjective fatigue scores that lasted up to 20 min after the end of the trial were significantly induced both in the 40-and 60-min chewing trials (P < 0.001*). Significant but mild pain was induced only in the 60-min trial (P = 0.004*) and only in men (P = 0.04*). Also, the induced pain area was significantly bigger in the 60-min trial (P = 0.009*). However, this increase in pain and pain area did not last to the first 10-min follow-up. There were no significant differences neither between the 40-and 60-min chewing trials, except regarding the pain area (P = 0.008*), nor between the sexes. Conclusion: Taken together, excessive chewing in its current form does not seem to be a proper pain experimental model. The model needs further adjustments in order to mimic TMD-pain especially in women and to prolong the pain duration.

Abstract Background: The study was aiming to optimize excessive gum chewing as an experimental model to induce jaw muscle pain and fatigue similar to those in painful TMDs with durations that would allow immediate investigations of jaw-motor function. Further, if any sex differences would be detected in the expression of pain. Methods: This randomized, double blinded study included 31 healthy participants of both sexes. A standardized chewing protocol of either 40- or 60-minutes of chewing was used with a wash-out period of one week. Subjective fatigue, pain characteristics and functional measures were assessed. For statistical analyses, Wilcoxon Signed Rank test, Mann–Whitney Rank Sum test and Friedman’s ANOVA with Tukey post-hoc test were used. Results: High subjective fatigue scores that lasted up to 20 minutes after the end of the trial were significantly induced both in the 40- and 60-minute chewing trials (P<0.001*). Significant but mild pain was induced only in the 60-minute trial (P=0.004*) and only in men (P=0.04*). Also, the induced pain area was significantly bigger in the 60-minute trial (P=0.009*). However, this increase in pain and pain area did not last to the first 10-minute follow-up. There were no significant differences neither between the 40- and 60-minute chewing trials, except regarding the pain area (P=0.008*), nor between the sexes. Conclusion: Taken together, excessive chewing in its current form does not seem to be a proper pain experimental model. The model needs further adjustments in order to mimic TMD-pain especially in women and to prolong the pain duration.

Abstract Background The study was aiming to optimize excessive gum chewing and investigate if it could be an experimental model to induce jaw muscle pain and subjective fatigue similar to those in painful TMDs. Secondarily, to investigate if the induced pain and fatigue had a duration that would allow immediate investigations of jaw-motor function. Finally, if any sex differences would be detected in the expression of pain. Methods This randomized, double blinded study included 31 healthy participants of both sexes. A standardized chewing protocol of either 40- or 60-minutes of chewing was used with a wash-out period of one week. Subjective fatigue, pain characteristics and functional measures were assessed. For statistical analyses, Wilcoxon Signed Rank test, Mann–Whitney Rank Sum test and Friedman’s ANOVA with Tukey post-hoc test were used. Results High subjective fatigue scores that lasted up to 20 minutes after the end of the trial were significantly induced both in the 40- and 60-minute chewing trials. Significant but mild pain was induced only in the 60-minute trial and only in men. Also the induced pain area was significantly bigger in the 60-minute trial. However, this increase in pain and pain area did not last to the first 10-minute follow-up. Although there were significant differences detected regarding fatigue within both of the trials and pain within the 60-minute trial, there were no significant differences neither between the trials, other than regarding the pain area, nor between sexes. Conclusion Taken together, excessive chewing in its current form does not seem to be a proper pain experimental model. The model needs further adjustments in order to mimic TMD-pain especially in women and to prolong the pain duration.