Effects of gender and acute dental pain on thermal pain responses

Ganoderma tsuage promotes pain sensitivity in aging mice

Advances in modern medicine have extended human life expectancy, leading to a world with a gradually aging society. Aging refers to a natural decline in the physiological functions of a species over time, such as reduced pain sensitivity and reaction speed. Healthy-level physiological pain serves as a warning signal to the body, helping to avoid noxious stimuli. Physiological pain sensitivity gradually decreases in the elderly, increasing the risk of injury. Therefore, geriatric health care receives growing attention, potentially improving the health status and life quality of the elderly, further reducing medical burden. Health food is a geriatric healthcare choice for the elderly with Ganoderma tsuage (GT), a Reishi type, as the main product in the market. GT contains polysaccharides, triterpenoids, adenosine, immunoregulatory proteins, and other components, including anticancer, blood sugar regulating, antioxidation, antibacterial, antivirus, and liver and stomach damage protective agents. However, its pain perception-related effects remain elusive. This study thus aimed at addressing whether GT could prevent pain sensitivity reduction in the elderly. We used a galactose-induced animal model for aging to evaluate whether GT could maintain pain sensitivity in aging mice undergoing formalin pain test, hot water test, and tail flexes. Our results demonstrated that GT significantly improved the sensitivity and reaction speed to pain in the hot water, hot plate, and formalin tests compared with the control. Therefore, our animal study positions GT as a promising compound for pain sensitivity maintenance during aging.

Sociodemographic Profile: A Forgotten Factor in Temporomandibular Disorders? A Scoping Review

The literature on Temporomandibular Disorders (TMD) incidence commonly reports sociodemographic factors such as gender and age. However, the role and prevalence of other sociodemographic factors in TMD are not well defined. Therefore, this scoping review aimed to report the prevalence of sociodemographic factors in TMD patients. A systematic search was conducted in the PubMed and Web of Science databases to identify clinical trials in adult populations, using the Research Diagnostic Criteria for TMD (RDC/TMD) or the Diagnostic Criteria for TMD (DC/TMD) and reporting sociodemographic data in TMD patients. Twenty-seven studies meeting the criteria were included in this review. The most commonly reported sociodemographic factors assessed in the included studies were age, race, education, job, income, and marital status. TMD prevalence was observed to be higher among younger and divorced individuals among the included studies. However, conflicting results were found for education level, and employment was not considered a risk factor for TMD. Although this review has methodological limitations, it suggests an association between TMD incidence and certain sociodemographic factors; nevertheless, further studies are needed to establish this relationship more conclusively.

Present status and future directions - Mechanisms and management of local anaesthetic failures

Pain control during root canal treatment is of utmost importance for both the patient and the dental practitioner and many studies have investigated ways of overcoming problems with gaining adequate anaesthesia during treatment. The PubMed and Cochrane databases were searched for evidence-based studies regarding local anaesthesia for root canal treatment. Many variables, including premedication, pain during needle insertion, pain on injection, premedication with various types of drugs, volume of anaesthetic solutions, supplemental anaesthetic techniques, and additives to the anaesthetic solutions, may influence pain perception during root canal treatment. Differences between teeth with healthy pulps versus those with irreversible pulpitis should be considered when the effects of variables are interpreted. There are several concerns regarding the methodologies used in studies that have evaluated anaesthesia success rates. There are some conditions that may help to predict a patient's pain during root canal treatment and these conditions could be overcome either by employing methods such as premedication with a non-steroidal anti-inflammatory drug prior to the treatment visit or by using supplementary anaesthetic techniques before or during the treatment. However, authors need to be more careful when reporting details of their studies to reduce concerns regarding their study bias.

Genetic study in patients operated dentally and anesthetized with articaine-epinephrine

Aims: In this study we wanted to figure out if there was a correlation between OPRM1 N40D, TRPV1 I316M, TRPV1 I585V, NOS3 −786T>C and IL6 −174C>G polymorphisms and the response to locally applied articaine-epinephrine anesthetic.

Methods: In this observational study, 114 oral cell samples of patients anesthetized with articaine-epinephrine (54 from men 60 from women), were collected from dental centers in Madrid (Spain). High molecular weight DNA was obtained from oral mucosa cells. The analysis of OPRM1 N40D (rs1799971), TRPV1 I316M (rs222747), TRPV1 I585V (rs8065080) and IL6 −174C>G polymorphism was performed through real-time PCR allelic discrimination using TaqMan probes. Polymorphism NOS3 −786T> C (rs2070744) was analyzed using RFLP-PCR.

Results: The studied polymorphisms are involved neither in the response to the anesthetic, nor in the intensity of perceived dental pain. However, in a subset of female patients we found that TRPV1 I316M was associated with a delayed onset of anesthesia.

Conclusions: There is no association among these polymorphisms and the time elapsed between the application of the anesthetic and the onset of its effect.

Does past pain influence current pain: biological and psychosocial models of sex differences

Previous studies have generally indicated sizeable sex differences for both laboratory pain reactivity and clinical pain reports. Numerous biological and psychosocial models have been invoked to account for these findings, but the laboratory and clinical findings have generally been examined in isolation. This paper reviews data which show a relationship between past clinical pain experiences and current responses to experimentally induced pain. Individuals with a greater pain history tend to show lower pain tolerance. Since women often have high pain experience levels and lower pain tolerance, one might ask whether the two factors are related. We review several models, based upon concepts of neonatal differences in pain reactivity, hypervigilance following early pain experiences, and concepts of peripheral and central sensitization or plasticity which might help to bridge the gap between clinical and experimental findings.

Blockade of opioid receptors in the medullary reticularis nucleus dorsalis, but not the rostral ventromedial medulla, prevents analgesia produced by diffuse noxious inhibitory control in rats with muscle inflammation

Diffuse Noxious Inhibitory Controls (DNIC) involves application of a noxious stimulus outside the testing site to produce analgesia. In human subjects with a variety of chronic pain conditions, DNIC is less effective; however, in animal studies, DNIC is more effective after tissue injury. While opioids are involved in DNIC analgesia, the pathways involved in this opioid-induced analgesia are not clear. The aim of the present study was to test the effectiveness of DNIC in inflammatory muscle pain, and to study which brainstem sites mediate DNIC- analgesia. Rats were injected with 3% carrageenan into their gastrocnemius muscle and responses to cutaneous and muscle stimuli were assessed before and after inflammation, and before and after DNIC induced by noxious heat applied to the tail (45 °C and 47 °C). Naloxone was administered systemically, into rostral ventromedial medulla (RVM), or bilaterally into the medullary reticularis nucleus dorsalis (MdD) prior to the DNIC-conditioning stimuli. DNIC produced a similar analgesic effect in both acute and the chronic phases of inflammation reducing both cutaneous and muscle sensitivity in a dose-dependent manner. Naloxone systemically or microinjected into the MdD prevented DNIC-analgesia, while naloxone into the RVM had no effect on DNIC analgesia. Thus, DNIC analgesia involves activation of opioid receptors in the MdD.

PERSPECTIVE

The current study shows that DNIC activates opioid receptors in the MdD, but not the RVM, to produce analgesia. These data are important for understanding clinical studies on DNIC as well as for potential treatment of chronic pain patients.

Are there any cross-ethnic differences in menstrual profiles? A pilot comparative study on Australian and Chinese women with primary dysmenorrhea

AIM

To explore and compare the features of menstruation, perception and management of menstrual pain between two cohorts of Australian and Chinese women.

METHODS

A pilot comparison study was carried out using modified valid menstrual questionnaires. The study included 120 Australian women and 122 Chinese women aged from 18 to 45 years with primary dysmenorrhea.

RESULTS

Australian women rated menstrual pain as more intense than Chinese women (8.5 ± 1.5 on a 10-point pain scale vs 7.3 ± 1.8, P < 0.001), duration of pain was 36% longer (3.0 ± 2.5 vs 2.2 ± 0.9 days, P = 0.002) and menarche commenced earlier (12.7 ± 1.5 vs 14.2 ± 1.4 years, P < 0.001). The mean reported menstrual interval was also shorter (29.2 ± 5.3 vs 30.52 ± 3.7, P = 0.020) with heavier overall menstrual flow (P = 0.002) and fewer clots in menstrual blood (83% vs 95.8%, P = 0.001). There was no significant difference in duration of menstruation (5.2 ± 1.3 vs 5.4 ± 1.1 days; P = 0.180). Correlations were found between earlier menarche and increased intensity of menstrual pain (r = -0.16, P = 0.011), and between heavier menstrual flow and increased intensity of menstrual pain (r = 0.19, P = 0.003).

CONCLUSION

Evidence from this pilot study suggested that the clinical menstrual presentations in the cohorts of Australian and Chinese women were different. Although the findings are preliminary, evaluating ethnic differences in menstruation and experimental menstrual pain models may not only provide some information about underlying mechanisms but may also predict or explain group differences.

Psychological intervention in acute dental pain: review

Acute dental pain is an unpleasant experience. This article studies acute dental pain and examines the role of psychological intervention. After identification of the psychological factors associated with dental pain we go on to assess the role of psychological interventions.

Mechanisms underlying development of spatially distributed chronic pain (fibromyalgia)

Chronic fibromyalgia (FM) pain is prevalent (estimated as high as 13%), predominantly affects women, and is associated with a variety of focal pain conditions. Ongoing FM pain is referred to deep tissues and is described as widespread but usually is maximally located within a restricted region such as the shoulders. Palpation of deep tissues reveals an enhanced nociceptive sensitivity that is not restricted to regions of clinical pain. Similarly, psychophysical testing reveals allodynia and hyperalgesia for cutaneous stimulation at locations beyond regions of clinical pain referral. The combination of widely distributed clinical pain and generalized hypersensitivity is highly disabling, but no satisfactory treatment is regularly prescribed. A thorough understanding of mechanisms will likely be required to develop and document adequate therapies. The generalized hypersensitivity associated with FM has focused considerable interest on central (CNS) mechanisms for the disorder. These include central sensitization, central disinhibition and a dysfunctional hypothalamic-pituitary-adrenal (HPA) axis. However, the central effects associated with FM can be produced by a peripheral source of pain. Chronic nociceptive input induces central sensitization, magnifying pain, and it activates the HPA and the sympathetic nervous system. Chronic sympathetic activation indirectly sensitizes peripheral nociceptors and sets up a vicious cycle. Thus, it appears that central mechanisms of FM pain are dependent on abnormal peripheral input(s) for development and maintenance of this condition. A substantial literature defines peripheral-CNS-peripheral interactions that are integral to FM pain. These reciprocal actions and related phenomena of relevance to FM pain are reviewed here, leading to suggestions for testing of therapeutic approaches.

Influence of low doses of naltrexone on morphine antinociception and morphine tolerance in male and female rats of four strains

In a recently proposed bimodal opioid receptor model, the inhibitory actions of opioids on action potential duration in dorsal root ganglion neurons have been proposed to produce antinociception, and the excitatory actions of hyperalgesia. Recent studies indicate that selectively blocking these excitatory actions with low doses of opioid antagonists enhances opioid antinociception and attenuates the development of opioid tolerance. To determine if the excitatory actions of opioids contribute to sex as well as strain differences in opioid sensitivity, the effects of morphine alone and in combination with low doses of naltrexone were examined in male and female rats of four strains. The strains examined differed in their sensitivity to opioid antinociception and magnitude of sex differences in opioid sensitivity. All testing was conducted using a thermal tail-flick procedure with the nociceptive stimulus intensity adjusted so that baseline latencies were comparable across strains/sexes. In chronic studies, the morphine dosing regimen was adjusted in each strain/sex to produce comparable levels of tolerance. In each of the strains tested, morphine produced dose-dependent increases in antinociception, with differences in morphine potency observed across strains and sexes. In male and female Sprague-Dawley and Long-Evans rats, naltrexone enhanced morphine antinociception and attenuated the development of morphine tolerance. These effects were not observed in F344 and Lewis rats, even when tests were conducted across a range of morphine and naltrexone doses. These results suggest that the ability of low doses of naltrexone to enhance opioid antinociception does not contribute to sex or rat strain differences in opioid sensitivity.

Quantitative Somatosensory Testing of Warm and Heat-Pain Thresholds: The Effect of Body Region and Testing Method

OBJECTIVES

To study whether the sensitivity to noxious and innocuous heat varies across the body.

METHODS

Heat-pain threshold and warm sensation threshold were measured in 20 patients, using the Method of Limits (MLI) and the Method of Levels (MLE) in 5 regions: the chest, forearm, mid thigh, and the dorsal surface of the hand and foot.

RESULTS

With the Method of Limits, heat-pain threshold increased gradually from the lowest level in the chest (mean 42 degrees C) to peak level in the foot (44.5 degrees C, P < 0.001). With the Method of Levels, heat-pain threshold did not differ between body regions. Warm sensation thresholds measured with both Method of Limits and the Method of Levels was higher in the chest (36.2 degrees C) and foot (36.8 degrees C) compared to the other regions (mean of 35.3 degrees C, P < 0.01). The correlation between heat-pain threshold and warm sensation threshold was low to moderate, depending on the tested region. Differences in heat-pain threshold and warm sensation threshold between the methods were highest in the legs and smallest in the chest. The correlation between the Method of Limits and Method of Levels was moderate for heat-pain threshold (0.57) and good for warm sensation threshold (0.71).

DISCUSSION

The sensitivity to noxious heat is uniform across the body when measured with a reaction-time-free method (Method of Levels), but is greater in proximal than in distal regions, when measured with a reaction-time-dependent method (Method of Limits). Regardless of measuring method, the sensitivity to innocuous heat is not uniform across the body. It is concluded that the Method of Levels is preferred when heat-pain threshold is to be compared between body regions. For heat-pain threshold, within-patient comparisons can be made between each pair of regions tested. However, for warm sensation threshold, within-patient comparisons should be conducted between contralateral symmetrical regions.

Effects of diffuse noxious inhibitory controls on temporal summation of the RIII reflex in humans

The aim of this study was to investigate the effects of diffuse noxious inhibitory controls (DNICs) on the temporal summation of the nociceptive flexion reflex (RIII reflex) in humans. Recordings were obtained from 36 healthy adults (16 M, 20 F), and the area and temporal summation threshold (TST) of the RIII reflex were measured. The subjective intensity of the painful sensation was rated on an 11-point visual analogue scale (VAS). Neurophysiological and VAS measurements were recorded after activation of DNICs by means of the cold pressor test (CPT), which involved immersing the hand in cold water (2-4 degrees C). A slight significant lower TST was found in the females versus the males. In all the subjects, the CPT induced a significant TST increase and RIII area reduction compared with the control session. The VAS results paralleled those of the RIII reflex area and TST. During the CPT, a significant difference in the percentage TST increase emerged between females and males, being lower in the former. Similarly, we found a significantly lower percentage reduction of the RIII area in women than in men during the CPT. To summarize, activation of DNICs through the CPT significantly increased the TST of the RIII reflex in healthy subjects. This inhibitory effect was gender-specific. Whereas other findings are based on psychophysical evaluations, the results of this experimental study provide an objective neurophysiological demonstration that DNICs attenuate temporal summation in humans and confirm the presence of significant differences in pain modulation mechanisms between men and women.

Sex differences in delayed onset muscle pain

OBJECTIVE

In contrast to the research using typical experimental pain stimuli, there is no consensus that women are more sensitive to delayed onset muscle pain than men. The purpose of this study was to examine sex differences in delayed onset muscle pain with use of a quantified stimulus intensity and multidimensional and valid pain measures.

METHODS

Ninety-five participants (49.5% women) completed eccentric exercise and then returned to the laboratory at 24 and 48 hours postexercise. The same relative intensity of the eccentric exercise was administered to women and men based on their eccentric strength.

RESULTS

The occurrence of muscle pain was confirmed by increases in intensity, F2, 182 = 162.28, P<0.01, eta = 0.64, and unpleasantness, F2, 182 = 204.03, P < 0.01, eta = 0.69, and standardized pain ratings, F2, 180 = 67.44, P < 0.01, eta = 0.43. The affective ratios indicated that the muscle pain was more unpleasant than intense. No sex differences were detected except that men reported higher affective ratios than women, F1, 92 = 4.06, P < 0.05, eta = 0.04.

DISCUSSION

The absence of higher muscle pain ratings in women than men in this investigation resembles a review of the delayed onset muscle soreness and pain literature. However, the findings contradict a few other acute muscle pain investigations, in which actual muscle tissue damage was not induced by eccentric contractions. Additional research is required to identify the parameters that influence the detection of sex differences.

Sex differences in temporal characteristics of descending inhibitory control: an evaluation using repeated bilateral experimental induction of muscle pain

Little is known about sex differences in the temporal pattern of descending inhibitory mechanisms, such as descending noxious inhibitory control (DNIC). Sex differences in temporal characteristics of DNIC were investigated by measuring pressure pain thresholds (PPTs) over time in the trapezius muscles (local pain areas) and the posterolateral neck muscles (referred pain areas) following repeated bilateral injection of hypertonic versus isotonic saline into both trapezius muscles. Ten females and 11 males received two consecutive bilateral injections, with 15 min interval, of either 5.8% hypertonic saline (0.5 ml in each side for each bilateral injection) or isotonic saline as a control in a randomized manner. Following hypertonic saline injection, the maximal pain intensities of the first and second bilateral injections were significantly higher in females than in males. The PPTs in the trapezius muscles were significantly lower in females than in males. Significantly higher PPTs (hypoalgesia) in men than in women were shown 15 min after the first bilateral injection, and 7.5 and 15 min after the second bilateral injection in the referred pain areas. Importantly, the second bilateral injection failed to further increase the PPTs for both sexes. These results showed that there were sex differences in temporal characteristics of descending inhibition with long-lasting hypoalgesia in men than in women. Repeated noxious muscular stimuli may inhibit further build-up of DNIC, which may reflect a mechanism of plasticity of the descending inhibitory systems following recurrent nociceptive barrage for both sexes.

Do ethnicity and gender have an impact on pain thresholds in minor dermatologic procedures? A study on thermal pain perception thresholds in Asian ethnic groups

BACKGROUND AND OBJECTIVES

The perception of pain is a personal experience influenced by many factors, including genetic, ethnic and cultural issues. Understanding these perceptions is especially important in dermatologic patients undergoing minor surgical operations and who often differ in their pain response to surgical treatments. Little is known about how these differences affect the perception of experimental pain. The purpose of this study was to determine experimental pain perception differences in three distinct East Asian ethnic populations.

METHODS

Pain thresholds were examined with a psychophysical computerized quantitative thermal sensory testing device (TSA 2001) in healthy volunteers recruited from three different Asian ethnic groups. Using the methods of limits, experimental pain perception threshold was measured on the forehead and volar aspect of the forearm in 49 healthy subjects. The measurements were then repeated after skin barrier perturbation with adhesive tape stripping of the stratum corneum. All three ethnic groups were analyzed separately with respect to age, gender educational level and skin type.

RESULTS

A total of 20 Chinese, 14 Malay and 15 Indian subjects completed the study. Thermal pain thresholds were similar in all three ethnic groups before and after tape strippings. No significant differences were noted between genders.

CONCLUSIONS

Using quantitative sensory thermal testing, we demonstrated that no significant differences in pain occur between different races and genders.

Psychosocial mediators of sex differences in pain responsivity

The objective of this study was to examine gender role and primary pain appraisal as mediators of the relation between sex and pain responsivity in experimental pain. A sample of 145 introductory psychology students participated in a cold pressor task and completed inventories that assessed pain appraisal and gender role. Results showed that threat appraisals of pain and positive feminine gender role, in combination, mediate the relation between sex and experimental pain responsivity, suggesting that psychosocial variables play an important role in this relation. However, the influences of gender role and threat appraisal were relatively independent, suggesting that psychosocial mediators of the sex/pain relation are complex.

Influence of expectations and actual pain experiences on satisfaction with postoperative pain management

Experience of moderate or even severe postoperative pain has remained a clinical problem despite major progress in pain assessment and management. The aim of the present study was to assess any association between different pre- as well as postoperative factors, actual pain experiences in the postoperative period, and the overall patient satisfaction with the pain management. A random sample of surgical patients (n =191) responded to pre- and postoperative questionnaires detailing presence of preoperative baseline pain, expected and actually experienced postoperative pain levels and perceived adequacy of the pain relief provided. Patient satisfaction was assessed and factors of importance for satisfaction/dissatisfaction were analysed. It was found that 88% of the patients had previously undergone surgical procedures and that 53% of these patients claimed to have experienced moderate or severe pain at that time. Current pain prior to the present surgical procedure was reported by 61% of the patients. Most patients (91%) expected pain of moderate to severe intensity and 76% reported to have experienced such pain levels. In spite of this 81% of the patients claimed to be satisfied with the pain management while only 8% were dissatisfied. Sex, age, pre-operative expectation and actual experience of pain relief, and the overall pain experience were found to be factors associated with the probability of being satisfied/dissatisfied. Main characteristics of the dissatisfied patient were a younger age and female sex. It is concluded that patients commonly expect moderate to severe pain in the postoperative period and that the actual pain experience is mainly in accordance with the pre-operative expectations. Therefore, the validity of patient satisfaction as an optimal outcome variable in quality assurance processes of postoperative pain management may be questioned.

Sex-related differences in human pain and rat afferent discharge evoked by injection of glutamate into the masseter muscle

Animal studies have suggested that tissue injury-related increased levels of glutamate may be involved in peripheral nociceptive mechanisms in deep craniofacial tissues. Indeed, injection of glutamate (0.1-1 M, 10 microl) into the temporomandibular region evokes reflex jaw muscle responses through activation of peripheral excitatory amino acid receptors. It has recently been found that this glutamate-evoked reflex muscle activity is significantly greater in female than male rats. However, it is not known whether peripheral administration of glutamate, in the same concentrations that evoke jaw muscle activity in rats, causes pain in humans or activates deep craniofacial nociceptive afferents. Therefore we examined whether injection of glutamate into the masseter muscle induces pain in male and female volunteers and, since masseter afferent recordings were not feasible in humans, whether glutamate excites putative nociceptive afferents supplying the masseter muscle of male and female rats. Injection of glutamate (0.5 M or 1.0 M, 0.2 ml) into the masseter muscle of both men and women caused significantly higher levels of peak pain, duration of pain, and overall pain than injection of isotonic saline (0.2 ml). In addition, glutamate-evoked peak and overall muscle pain in women was significantly greater than in men. In rats of both sexes, glutamate (10 microl, 0.5 M) evoked activity in a subpopulation of masseter muscle afferents (n = 36) that projected to the subnucleus caudalis, an important relay of noxious input from the craniofacial region. The largest responses to glutamate were recorded in muscle afferents with the slowest conduction velocities (2.5-5 m/s). Further, glutamate-evoked masseter muscle afferent activity was significantly greater in female than in male rats. These results indicate that glutamate injection into the masseter muscle evokes pain responses that are greater in women than men and that one possible mechanism for this difference may be a greater sensitivity to glutamate of masseter muscle afferents in females. These sex-related differences in acute experimental masseter muscle pain are particularly interesting given the higher prevalence of many chronic muscle pain conditions in women.