The influence of orofacial pain on sleep pattern: A review of theory, animal models and future directions

Causal associations between sleep traits and temporomandibular disorders: a bidirectional mendelian randomization analysis

Objectives

This study aims to investigate the relationship between five sleep traits (insomnia, sleep duration, getting up in morning, snoring, and daytime nap) and temporomandibular disorders (TMD) using bi-directional Mendelian randomization.

Methods

The bi-directional Mendelian randomization study was conducted in two stages. Initially, sleep traits were examined as exposures while TMD was evaluated as an outcome, whereas the second step was reversed. The inverse variance weighted (IVW) method and other Mendelian randomization methods were used for analysis. Furthermore, we performed the MR-Egger intercept, MR-PRESSO, Cochran's Q test, and "Leave-one-out" to assess the levels of pleiotropy and heterogeneity.

Results

The IVW method indicates that getting up in the morning reduces the risk of developing TMD (OR = 0.50, 95% CI 0.30-0.81, p = 0.005), while insomnia may increase the risk of TMD (OR = 2.05, 95% CI 1.10-3.85, p = 0.025). However, other sleep traits are not associated with the risk of TMD, and having TMD does not alter an individual's sleep traits. After removing outliers, the results remained robust, with no pleiotropy detected.

Conclusion

Genetically determined difficulty in getting up in the morning and insomnia can increase the risk of TMD. By optimizing sleep, the risk of developing TMD can be reduced. This underscores the importance of sleep in preventing TMD.

Association Between Pharmacotherapy and Sleep Quality in Patients with Chronic Orofacial and Chronic Body Pain: A Cross-Sectional Study

Purpose

Sleep impairment is associated with many chronic pain disorders. While there is an association between chronic pain and sleep disturbances, little is known about the influence of pharmacotherapy for chronic pain conditions, particularly chronic opioid therapy, on sleep. This study aimed to 1) compare the sleep quality (SQ) in patients with two different pain conditions-chronic body pain and chronic orofacial pain; 2) assess the correlation of SQ and pain intensity; and 3) evaluate the association between pharmacotherapy and SQ.

Patients and Methods

The Pittsburgh Sleep Quality Index (PSQI) was used to measure the SQ in subjects with 1) chronic body pain (n = 100) and 2) chronic orofacial pain (n = 100). The visual analogue scale was applied for pain intensity rating. All subjects were adults recruited at Massachusetts General Hospital, United States. The subjects' demographic data, pain intensity, diagnosis and concurrent use of medications were extracted from their electronic medical records (EMR). Statistical analyses were performed using T-test and Pearson correlation coefficient.

Results

Among 200 subjects (mean age 51.01 ± 15.52 years), 141 (70.5%) were females. PSQI and pain intensity were statistically significantly different between the two groups (p < 0.05 and p < 0.0001, respectively) and higher in subjects with chronic body pain. There was a positive correlation between PSQI and pain intensity (chronic orofacial pain r = 0.3535, p = 0.0004; chronic body pain: r = 0.2247, p < 0.026). PSQI was higher in chronic orofacial pain subjects utilizing opioids and benzodiazepines (PSQI = 15.25).

Conclusion

Chronic pain impairs SQ, which is noticeably worse in subjects with body pain conditions. In addition, pain intensity was correlated with poorer SQ, which in turn was linked to the concomitant use of opioid and benzodiazepine therapy in chronic orofacial pain.

Associations between obstructive sleep apnea and painful temporomandibular disorder: a systematic review

The relationship between obstructive sleep apnea (OSA) and diverse types of pain conditions have been proposed. However, no consensus on the relationship between OSA and painful temporomandibular disorders (TMDs) has been established. Therefore, this systematic review has been conducted to review the existing literatures and provide comprehensive synthesis of such literatures about OSA and painful TMDs using the evidence-based methodology. A literature search was conducted using two electronic databases, Scopus, and PubMed. Risk of bias was assessed using the risk-ofbias assessment tool for non-randomized study version 2.0. A total of 158 articles were screened from the initial search and eventually, 5 articles were included in this systematic review. One study adopted both the longitudinal prospective cohort and case-control designs and other 4 articles adopted the cross-sectional design. Two studies employed polysomnography (PSG) for the diagnosis of OSA and mentioned the results from the PSG. All crosssectional studies demonstrated higher OSA prevalence among patients with TMD, and one cohort study suggested OSA as a risk factor for TMD. OSA appears to have potential influences on the development of TMD; however, the role of TMD in the development of OSA remains to be unknown owing to the lack of high-quality evidences.

Interacting Influences of Sleep, Pain, and Analgesic Medications on Sleep Studies in Rodents

This overview provides a brief summary of the complex interactions that link sleep, pain, and analgesic medications. Sleep scientists and clinicians are well aware of these relationships and understand that maintaining healthy pain-free subjects in a stable environment is essential to generating interpretable data and valid conclusions. However, these concepts and the data that support bidirectional interactions between sleep and pain may be less known to those who are not sleep scientists yet need such information to protect and advance both animal wellbeing and research validity (for example, veterinarians, IACUC members). Abundant human evidence supports the disruptive effect of pain and the modulatory effects of analgesic drugs on sleep; however, analgesic drugs can alter both sleep and the electroencephalogram, which is the primary objective measure for identifying sleep and evaluating sleep properties in both humans and animals. Consideration of the modulatory and interactive relationships of sleep, pain, and analgesic medications is essential to designing and conducting valid and reproducible sleep research using animal subjects.

A preliminary study: The effect of ergonomic latex pillow on pain and disability in patients with cervical spondylosis

Background: Cervical pillows are considered to be part of the therapeutic strategy in cervical spondylosis, but there is little or no convincing scientific evidence on the effectiveness of these pillows in relieving pain and disability in these patients. Hence, this study investigated the effects of ergonomic latex pillow in conjunction with routine physiotherapy versus routine physiotherapy alone on disability and pain intensity in patients with cervical spondylosis.

Methods: 22 patients with cervical spondylosis in a single-blinded pilot study with a pre/post-test design were randomly assigned to experimental and control groups. Both groups received 12 sessions of physiotherapy for four weeks. In the experimental group, participants were given an ergonomic latex pillow to sleep it for four weeks. Participants in the control group slept on their own usual pillow. All the participants filled out the Neck Disability Index questionnaire, and scored their neck pain intensity on the Numerical Pain Rating Scale before and after the intervention. Changes of variables (pain and disability) within and between groups were compared by Paired T-test and the Independent Sample T-test, respectively via SPSS v.20 (p<0.05).

Results: Numerical Pain Rating Scale and Neck Disability Index scores were decreased statistically significant within groups. In the experimental group, neck disability scores were significantly lower than those in the control group (p=0.038). However, pain intensity scores were not significantly different between groups.

Conclusion: Ergonomic latex pillows can significantly decrease disability related to neck pain in patients with cervical spondylosis after four weeks.

The IMPROVE Guidelines (Ischaemia Models: Procedural Refinements Of in Vivo Experiments)

Most in vivo models of ischaemic stroke target the middle cerebral artery and a spectrum of stroke severities, from mild to substantial, can be achieved. This review describes opportunities to improve the in vivo modelling of ischaemic stroke and animal welfare. It provides a number of recommendations to minimise the level of severity in the most common rodent models of middle cerebral artery occlusion, while sustaining or improving the scientific outcomes. The recommendations cover basic requirements pre-surgery, selecting the most appropriate anaesthetic and analgesic regimen, as well as intraoperative and post-operative care. The aim is to provide support for researchers and animal care staff to refine their procedures and practices, and implement small incremental changes to improve the welfare of the animals used and to answer the scientific question under investigation. All recommendations are recapitulated in a summary poster (see supplementary information).

Ergonomic approach for pillow concept design

Sleep quality is an essential factor to human beings for health. The current paper conducted four studies to provide a suitable pillow for promoting sleep quality. Study 1 investigated the natural positions of 40 subjects during sleep to derive key-points for a pillow design. The results suggested that the supine and lateral positions were alternatively 24 times a night, and the current pillows were too high for the supine position and too low for lateral positions. Study 2 measured body dimensions related to pillow design of 40 subjects to determine pillow sizes. The results suggested that the pillow height were quite different in supine position and lateral position and needed to take into consideration for a pillow design. Study 3 created a pillow design based on the results of above studies. The pillow was a U-form in the front of view in which the pillow height in the middle area was lower for the supine position, and both sides were higher for the lateral positions. Study 4 assessed sleep quality of 6 subjects by using the proposed pillows and the current pillows. The results showed that the newly designed pillow led to significantly higher sleep quality, and the new design received an innovation patent.

Blockade of spinal glutamate recycling produces paradoxical antinociception in rats with orofacial inflammatory pain

In our current study, we investigated the role of spinal glutamate recycling in the development of orofacial inflammatory pain. DL-threo-β-benzyloxyaspartate (TBOA) or methionine sulfoximine (MSO) was administered intracisternally to block spinal glutamate transporter and glutamine synthetase activity in astroglia. Intracisternal administration of high dose TBOA (10 μg) produced thermal hyperalgesia in naïve rats but significantly attenuated the thermal hyperalgesia in rats that had been pretreated with interleukin (IL)-1β or Complete Freund's Adjuvant (CFA). In contrast, intracisternal injection of MSO produced anti-hyperalgesic effects against thermal stimuli in CFA-treated rats only. To confirm the paradoxical antinociceptive effects of TBOA and MSO, we examined changes in c-Fos expression in the medullary dorsal horn produced by thermal stimulation in naïve, IL-1β-, or CFA-treated rats, after intracisternal injections of TBOA and MSO. Intracisternal administration of TBOA significantly increased c-Fos immunoreactivity in naïve rats. In contrast, intracisternal administration of TBOA significantly decreased the up-regulation of c-Fos immunoreactivity in the medullary dorsal horn of IL-1β- and CFA-treated rats. However, intracisternal injection of MSO blocked the up-regulation of c-Fos immunoreactivity in CFA-treated rats only. We also investigated the effects of botulinum toxin type A (BoNT-A) on TBOA-induced paradoxical antinociception in CFA-treated rats, as BoNT-A inhibits the release of neurotransmitters, including glutamate. BoNT-A treatment reversed behavioral responses produced by intracisternal administration of TBOA in CFA-treated rats. These results suggest that the paradoxical responses produced by blocking glutamate transporters under inflammatory pain conditions are mediated by the modulation of glutamate release from presynaptic terminals. Moreover, blockade of glutamate reuptake could represent a new therapeutic target for the treatment of chronic inflammatory pain conditions.

Improving the quality of sleep with an optimal pillow: a randomized, comparative study

Because sleep comprises one-third of a person's life, using an optimal pillow for appropriate neck support to maintain cervical curve may contribute to improve quality of sleep. Design of orthopedic pillow conforms to orthopedic guidelines to ensure the right support of the cervical curve. The aim of this study was to investigate effect of different pillow shape and content on cervical curve, pillow temperature, and pillow comfort. A feather pillow is regarded as a standard pillow, and a memory foam pillow is one of the most popular pillows among pillow users. We, therefore, compared these two pillows with an orthopedic pillow. Twenty healthy subjects (10 men and 10 women; age range, 21-30 years) participated in the study. Each subject was asked to assume the supine position with 3 different pillows for 30 minute in each trial and then cervical curve, pillow temperature, and pillow comfort were measured. When comparing the cervical curve of the 3 different pillows, that of the orthopedic pillow was significantly higher than that of the other 2 pillows (p < 0.001). The degree of temperature increase was significantly lower for the orthopedic pillow than for the memory foam and feather pillows (p < 0.001). The visual analog scale (VAS) score of pillow comfort was significantly higher in orthopedic pillow than the other 2 pillows. This study shows that pillow shape and content plays a crucial role in cervical curve, pillow temperature, and pillow comfort and orthopedic pillow may be an optimal pillow for sleep quality.

Facial pain associated with fibromyalgia can be marked by abnormal neuromuscular control: a cross-sectional study

BACKGROUND

Temporomandibular disorder (TMD) development in fibromyalgia syndrome (FMS) is not yet fully understood, but altered neuromuscular control in FMS may play a role in triggering TMD.

OBJECTIVE

The purpose of this study was to verify the association between neuromuscular control and chronic facial pain in groups of patients with FMS and TMD.

DESIGN

A cross-sectional study was conducted.

METHODS

This study involved an analysis of facial pain and electromyographic activity of the masticatory muscles in patients with FMS (n=27) and TMD (n=28). All participants were evaluated according to Research Diagnostic Criteria for Temporomandibular Disorders and surface electromyography (SEMG). Myoelectric signal calculations were performed using the root mean square and median frequency of signals.

RESULTS

The data revealed premature interruption of masticatory muscle contraction in both patient groups, but a significant correlation also was found between higher median frequency values and increased facial pain. This correlation probably was related to FMS because it was not found in patients with TMD only. Facial pain and increased SEMG activity during mandibular rest also were positively correlated.

LIMITATIONS

Temporal conclusions cannot be drawn from the study. Also, the study lacked a comparison group of patients with FMS without TMD as well as a control group of individuals who were healthy.

CONCLUSIONS

Altered neuromuscular control in masticatory muscles may be correlated with perceived facial pain in patients with FMS.

Differences in suprathreshold heat pain responses and self-reported sleep quality between patients with temporomandibular joint disorder and healthy controls

The purpose of this study was to examine differences in heat pain threshold (HPTh) and heat pain tolerance (HPTo) between temporomandibular joint disorder (TMJD) patients and healthy controls. Using suprathreshold heat pain, this study also examined between-group (i.e. TMJD vs. healthy controls) differences in hyperalgesia and temporal summation (TS) of heat pain. Lastly, whether between-group differences in these heat pain outcomes were mediated by self-reported sleep quality was also tested. A total of 119 participants (41% TMJD) completed the current study. HPTh and HPTo responses were assessed at the ventral forearm with an ascending method of limits, while hyperalgesia and TS responses were assessed at the dorsal forearm at temperatures of 46, 48 and 50 °C. Prior to completion of heat pain procedures, participants completed the Pittsburgh Sleep Quality Index. Significant between-group differences in HPTh and HPTo were not observed. TMJD patients demonstrated significantly greater hyperalgesia than healthy controls at 46 °C only, but there were no differences for TS. Furthermore, TMJD patients reported significantly poorer sleep quality compared with healthy controls. Data analysis revealed a significant simple mediation effect whereby the presence of TMJD was strongly associated with poorer self-reported sleep quality, which, in turn, was related to enhanced hyperalgesia at 46 °C. These findings support the hypothesis that the thermal hyperalgesia demonstrated by TMJD patients may be related to poor quality of their self-reported sleep. The ability of interventions that improve sleep quality to also affect pain sensitivity is currently the topic of ongoing investigation.

Persistent orofacial muscle pain

The pathophysiology of persistent orofacial myalgia has been the centre of much controversy. In this article we suggest a novel descriptive term; 'persistent orofacial muscle pain' (POMP) and review current evidence that supports the hypothesis that the induction of POMP involves the interplay between a peripheral nociceptive source in muscle, a faulty central nervous system component and decreased coping ability. In this context it is widely accepted that a complex interaction of variable intrinsic and extrinsic factors act to induce POMP and dysfunction.

Distinct gender-related sleep pattern in an acute model of TMJ pain

Since it is recognized that acute inflammation of the temporomandibular joint results in sleep disturbances in male rats, and that the orofacial region may display a site-specific effect of ovarian hormones on nociception, we hypothesized that distinct genders would respond differently when subjected to this inflammatory acute orofacial pain. Sleep was monitored after injection of saline/Freund's adjuvant into the temporomandibular joint in male and female (proestrus and diestrus phases) rats. Progesterone and stress-related hormones were also assessed. In males, Freund's adjuvant induced a significant nociceptive response and sleep disturbances. Behavior and sleep architecture in the females remained unaffected. Our results suggest that females and males present distinct responses to an acute model of orofacial pain.