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24 Apr 2016

Associations between Community Orofacial Pain and Experimental Orofacial Pain with Physical, Social and/or Psychological Variables

Tantry  Maulina, July 2013
University of Sydney

Abstract
As a chronic pain condition, chronic orofacial pain can influence the quality of life of the sufferer. Based on previous studies, there are several aspects of life that can be affected by orofacial pain, from physical functioning, work functioning, to social functioning. One of the physical functions that is altered the most by chronic orofacial pain is mastication and the Vicious Cycle Theory and the Pain Adaptation Model have been two models that have attempted to explain these motor effects of pain. There is conflicting evidence for both of these models in the literature. Social functioning might also be altered as a result of the chronic orofacial pain, as the chronic pain sufferer might also be affected psychologically, e.g. may become depressed and may became socially isolated. A chronic pain sufferer may also experience interference in their work activity. The management of chronic orofacial pain needs to address the biopsychosocial elements.

Despite the well-known impact of orofacial pain, the distribution of orofacial pain may differ between communities. Therefore, prior to the planning of the management of chronic orofacial pain, an investigation of the prevalence of orofacial pain as well as the types of orofacial pain experienced in a community is needed. Guidance on management would also benefit from information as to how orofacial pain affects muscle activity and thereby provide insights into how clinical orofacial pain has its effects on physical and social functioning in the community. Therefore, a study of experimental orofacial pain was performed. Therefore, we designed an epidemiological study to reveal the prevalence of orofacial pain in an Indonesian community followed by an experimental muscle pain study carried out in Sydney.

The general aims of the present study were: (1) To determine the association between the prevalence of orofacial pain and Socieconomic Status (SES) indicators in the Indonesian population, (2) To use epidemiological information to infer the level of interference from orofacial pain on physical and social functioning, (3) To determine whether any of the interferences in physical functioning observed in the epidemiological study can be explained by the effects observed on jaw muscle activity of jaw muscle pain in an experimental pain model, (4) To determine the physical functioning of the jaw during jaw muscle pain and the significance of the findings in relation to some previous models of pain-motor interactions, namely the Pain Adaptation Model and the Vicious Cycle Theory, (5) To study possible associations between chronic pain and psychological factors through an experimental pain model.

The hypotheses were: (i) There will be a significant association between the prevalence of orofacial pain in an Indonesian population sample and the Socioeconomic Status (SES) indicators, (ii) There will be a high level of interference of orofacial pain on physical and social functioning in an Indonesian population sample, (iii) The interference level in physical functioning observed in the epidemiological study can be partly explained by the effects observed on jaw muscle activity of jaw muscle pain in an experimental pain model, (iv) Experimental jaw muscle pain will result in an effect on the physical functioning of the jaw that is not consistent with the proposals of the Pain Adaptation Model or Vicious Cycle Theory, (v) Orofacial pain and associated motor effects will be significantly associated with some psychosocial measures used in this study.

The specific aims: (1) To determine the prevalence of orofacial pain in Indonesian population sample. For this specific aim, we conducted a two year survey in 20 Indonesian Community Health Centres. From the survey, the prevalence as well as the type of orofacial pain symptoms that were experienced were obtained; (2) To determine associations between the prevalence of orofacial pain with educational attainment and residential area. For this specific aim, we used the Crosstabs analysis to see whether there is a correlation between the prevelence of orofacial pain and educational attainment and residential area; (3) To determine the interference level of chronic orofacial pain in work activity, daily task activity, as well as social/recreational activity in people suffering from chronic orofacial pain. (4) To determine whether any of the interferences in physical and social functioning observed in the epidemiological study can be explained by the effects observed on jaw muscle activity of jaw muscle pain in an experimental pain model. Experimental muscle pain was induced by injection of 5% hypertonic saline through an infusion into the right anterior temporalis muscle of 14 human volunteers. Another infusion of 0.9% isotonic saline was also performed in order to compare the two conditions and reveal the net effect of pain. Under both conditions, jaw movement was recorded and the EMG activity of the right anterior temporalis muscle (RAT), left anterior temporalis muscle (LAT), right masseter muscle (RMAS), left masseter muscle (LMAS), and right digastric muscle (RDIG) was also recorded whilst the participant performing a standardized vertical jaw movement task, and non-standardized (i.e. free) chewing, and chewing standardized for the rate of chewing; (5) To determine whether the experimental muscle pain induced by 5% hypertonic saline infusion into the anterior temporalis muscle and whether any pain-induced EMG effects correlate with some psychological variables recorded will affect the EMG activity of the jaw muscles during the jaw tasks. Participants rated their pain on Visual Analogue Scales. The EMG activity from the five muscles was recorded and then transformed to logRMS. A linear mixed model analysis was then performed in order to determine whether there were differences in EMG activity between hypertonic and isotonic saline infusion; Participants completed the DASS (Depression, Anxiety, Stress, Scale) 21, PCS (Pain Catastrophizing Scale), FPQ (Fear of Pain Questionnaire)-III, and the PSEQ (Pain Self-Efficacy Questionnaire), which results were then correlated by using Pearson Correlation analysis.

The results for the first part of the study demonstrated that the prevalence of orofacial pain in an Indonesian patient sample was as high as 55.9% and that the high prevalence was correlated to two Socioeconomic Status indicators used in the current study, the educational attainment level and the residency area. Statistical analysis revealed a significant correlation between several types of orofacial pain symptoms (jaw stiffness when waking up in the morning, pain in the jaw or jaw joints, pain in or around the eyes, prolonged burning sensation in the tongue or other parts of the mouth, clicking or popping in the jaw when the participant closed their mouth or while chewing, grating or grinding noise while opening or chewing, jaw pain shortly after eating, difficulty during jaw-opening and educational attainment as well as residency area.

A high level of interference of orofacial pain was concluded given that, of the 391 participants who experienced orofacial pain in the last six months, 254 (65%) participants complained of interference in performing daily activities, 251 (64.2%) complained of social interference in their daily life, and 251 (64.2%) complained of work interference. There were 12 types of physical activities interference investigated in this study. From 391 participants who experienced orofacial pain in the last six months, 293 (74.9%) participants complained of chewing interference, 254 (65.0%) participants complained of not being able to chew hard food, and 243 (62.2%) complained of interference during night time sleep.

In the second experimental pain study, the mean (SD) VAS score was 47.1 (6.6) mm for the hypertonic saline induced experimental muscle pain. There were some significant differences identified for the musles investigated (RAT, LAT, RMAS, LMAS, and RDIG) when comparing the control isotonic saline condition to the test hypertonic saline condition during the standardized vertical jaw-movements (closing phase), standardized chewing (closing phase), and non-standardized chewing (opening and closing phase).

During the opening phase of standardized vertical jaw-movement task, there were no significant effects of pain on EMG activity, that is there was no significant difference in EMG activity between hypertonic and isotonic saline infusion, which is not consistent with Pain Adaptation Model or Vicious Cycle Theory. During the closing phase, there were changes in EMG activity that were consistent with the Pain Adaptation Model for 2 of the muscles (RMAS, an agonist in closing) and an increase in RDIG (antagonist during closing). During the opening phase of the standardized chewing, there was no significant difference in EMG activity between hypertonic and isotonic saline infusion. Therefore, these findings are consistent with neither the the Vicious Cycle Theory nor the Pain Adaptation Model. During the closing phase, there were no significant pain effects (in comparison with control isotonic saline) in RAT and RDIG, and this is consistent with neither the Vicious Cycle Theory nor the Pain Adaptation Model. The significant increases in EMG activity in the LAT, RMAS, and LMAS are supportive of the Vicious Cycle Theory. During the opening phase of the non-standardized chewing,there were significant effects for the LAT muscle and LMAS muscle that was consistent with the Pain Adaptation Model. During the closing phase, there were no significant pain effects on EMG activity, which is contradictory to the Pain Adaptation Model.

During the opening phase of standardized chewing with experimental muscle pain, we found significant correlations between LMAS muscle EMG activity during hypertonic saline infusion and the PCS questionnaire, RDIG muscle and FPQ-III subscale medical pain, and RDIG muscle and PSEQ. We also found a significant correlation between the LAT muscle and FPQ-III subscale minor pain during the closing phase of this task. During the opening phase of non-standardized chewing with experimental muscle pain, we found several significant correlations between the EMG activity of the RDIG and the RMAS muscle during hypertonic saline infusion with the FPQ-III questionnaire subscale severe pain. There were no significant correlations found during the opening phase.

Based on the findings of the current study, we concluded that there is a high prevalence of orofacial pain symptoms in Indonesian patient sample as well as a significant correlation between these symptoms and educational attainment and residential area. This high prevalence of orofacial pain symptoms was associated with an interference with daily activities, social/recreational activities as well as work activities. Physical activity that was interfered the most by orofacial pain was chewing, with 294 participants (out of 391 who complained about orofacial pain) complaining about the interference. An experimental muscle pain study that was performed during several jaw tasks indicated some changes in the EMG activity of the masticatory muscles that was significantly related to the pain experienced by participants. These EMG changes were also significantly related to some of the psychological factors investigated in this study. Despite the presence of some data consistent with the Vicious Cycle Theory and Pain Adaptation Model, much of the data were not consistent with these models. Further, the associations demonstrated between some psychological variables and some EMG activity changes cannot be explained by these earlier models.

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