Tactile and pain thresholds in the intra- and extra-oral regions of symptom-free subjects

The Feel of Speech: Multisystem and Polymodal Somatosensation in Speech Production

PURPOSE

The oral structures such as the tongue and lips have remarkable somatosensory capacities, but understanding the roles of somatosensation in speech production requires a more comprehensive knowledge of somatosensation in the speech production system in its entirety, including the respiratory, laryngeal, and supralaryngeal subsystems. This review was conducted to summarize the system-wide somatosensory information available for speech production.

METHOD

The search was conducted with PubMed/Medline and Google Scholar for articles published until November 2023. Numerous search terms were used in conducting the review, which covered the topics of psychophysics, basic and clinical behavioral research, neuroanatomy, and neuroscience.

RESULTS AND CONCLUSIONS

The current understanding of speech somatosensation rests primarily on the two pillars of psychophysics and neuroscience. The confluence of polymodal afferent streams supports the development, maintenance, and refinement of speech production. Receptors are both canonical and noncanonical, with the latter occurring especially in the muscles innervated by the facial nerve. Somatosensory representation in the cortex is disproportionately large and provides for sensory interactions. Speech somatosensory function is robust over the lifespan, with possible declines in advanced aging. The understanding of somatosensation in speech disorders is largely disconnected from research and theory on speech production. A speech somatoscape is proposed as the generalized, system-wide sensation of speech production, with implications for speech development, speech motor control, and speech disorders.

Personal influencing factors for pressure pain threshold in healthy people: A systematic review and meta-analysis

All studies that investigated personal factors influencing pressure pain threshold (PPT) in healthy people were synthesized. Data was summarized, and risk of bias (RoB) and level of evidence were determined. Results were pooled per influencing factor, grouped by body region and included in meta-analyses. Fifty-four studies were eligible. Five had low, nine moderate, and 40 high RoB. Following meta-analyses, a strong conclusion was found for the influence of scapular position, a moderate for the influence of gender, and a weak for the influence of age (shoulder/arm region) and blood pressure on PPT. In addition, body mass index, gender (leg region), alcohol consumption and pain vigilance may not influence PPT. Based on qualitative summary, depression and menopause may not influence PPT. For other variables there was only preliminary or conflicting evidence. However, caution is advised, since the majority of included studies showed a high RoB and several were not eligible to include in meta-analyses. Heterogeneity was high in the performed meta-analyses, and most conclusions were weak. More standardized research is necessary.

The impact of gender of the examiner on orofacial pain perception and pain reporting among healthy volunteers

Objectives

Pain on palpation of jaw muscles is a commonly used diagnostic criterion when examining patients with orofacial pain. It is not known, however, if pain reports are affected by the gender of the examiner. Our aim was to investigate if pressure pain threshold (PPT), pressure pain tolerance (PTol), and pain intensity assessed over the masseter muscles in healthy individuals are affected by the gender of the examiner.

Materials and methods

Healthy, pain-free individuals were recruited on a voluntary basis. PPT and PTol were assessed using pressure algometry. At the PTol level, participants also rated pain intensity on a 0–10 numeric rating scale. Assessments of PPT and PTol were conducted with six repeated measurements performed twice, separately by one female and one male examiner, on each participant.

Results

In total, 84 participants (43 women; median age 24, IQR 6) were included. With a female examiner, women reported higher pain intensity than men (Mann Whitney U, p = 0.005). In the multivariable analysis, significantly higher PTol was predicted by male examiner. Also, a higher ratio between PTol and reported pain intensity was predicted by male examiner.

Conclusions

The gender of the examiner influences pain reporting and perception in an experimental setting. This effect on pain perception related to gender of the examiner is probably related to normative gender behaviors rather than to biological alterations within the examined individual.

Clinical relevance

In clinical and experimental settings, gender of the examiner may affect not only pain perception but also pain reporting, with potential implications for diagnostics in patients with pain.

Motor cortex transcranial direct current stimulation effects on knee osteoarthritis pain in elderly subjects with dysfunctional descending pain inhibitory system: A randomized controlled trial

BACKGROUND

Although evidence has indicated a positive effect of transcranial direct current stimulation (tDCS) on reducing pain, few studies have focused on the elderly population with knee osteoarthritis (KOA).

OBJECTIVE

To evaluate whether tDCS reduces KOA pain in elderly individuals with a dysfunctional descending pain inhibitory system (DPIS).

METHODS

In a double-blind trial, individuals ≥ 60 years with KOA pain and a dysfunctional DPIS, we randomly assigned patients to receive 15 daily sessions of 2 mA tDCS over the primary motor cortex (anode) and contralateral supraorbital area (cathode) (M1-SO) for 20 min or sham tDCS. Change in pain perception indexed by the Brief Pain Inventory (BPI) at the end of intervention was the primary outcome. Secondary outcomes included: disability, quantitative sensory testing, pain pressure threshold and conditioned pain modulation (CPM). Subjects were followed-up for 2 months.

RESULTS

Of the 104 enrolled subjects, with mean (SD) age of 73.9 (8.01) years and 88 (84.6%) female, 102 finished the trial. In the intention-to-treat analysis, the active tDCS group had a significantly greater reduction in BPI compared to the sham group (difference, 1.59; 95% CI, 0.95 to 2.23; P < 0.001; Cohen's d, 0.58); and, also a significantly greater improvement in CPM-pressure in the knee (P = 0.01) and CPM-pain in the hand (P = 0.01). These effects were not sustained at follow-up. The intervention was well tolerated, with no severe adverse effects.

CONCLUSION

M1-SO tDCS is associated with a moderate effect size in reducing pain in elderly patients with KOA after 15 daily sessions of stimulation. This intervention has also shown to modulate the DPIS.

Age-related changes in oral tactile and thermal sensation throughout adulthood

Although the life expectancy of women is over 80 years in many countries, oral sensation has scarcely been compared between adults ≥ 80 years and younger age groups. The purpose of this study was to clarify age-related changes in oral sensation throughout adulthood. After exclusion of individuals with factors that might have confounded somatosensory performance, 123 female participants were divided into four age groups: 20-39 years, 40-59 years, 60-79 years, and 80-96 years. Perceptions of tactile and thermal sensations were examined at points on the anterior and posterior palate, anterior and posterior tongue, lower labial-attached gingiva, lower lip, and buccal mucosa; two-point discrimination was examined only on the tongue. The tactile and two-point discrimination thresholds for the anterior and posterior tongue were significantly higher in the 80-96-year-old group than in any other age group (p < 0.05). The tactile threshold for the buccal mucosa was significantly higher in the 80-96-year-old group than in the 60-79-year-old group (p < 0.05). The percentage of participants able to perceive a warm stimulus (50 °C) in the buccal mucosa was significantly lower in the 80-96-year-old group than in the 20-39-year-old group (p < 0.05). Only the topography of the warm sensation perception changed with age. This cross-sectional study suggests that oral tactile and thermal sensation for warm stimuli deteriorates with age in a site-specific manner, especially after the age of 80 years, but the same does not occur with cool stimuli.

Unilateral, Alloplastic Temporomandibular Joint Reconstruction, Biomechanically What Happens to the Contralateral Temporomandibular Joint?-A Prospective Cohort Study

PURPOSE

Unilateral alloplastic total temporomandibular joint reconstruction (TMJR) might influence the contralateral side joint function. This study's purpose was to estimate the risk for contralateral TMJR and the jaw function of the contralateral untreated temporomandibular joint (TMJ).

PATIENTS AND METHODS

A prospective cohort study design was used for patients who underwent unilateral alloplastic TMJR. The primary predictor was time after TMJR, and the secondary predictors were pre-TMJR mandibular angle resection, prior ipsilateral TMJ surgeries, and TMJR design (custom, stock). The primary outcome variable was the need for contralateral TMJR. The secondary outcome variables were the results of jaw function-jaw tracking, maximum voluntary clenching, surface electromyography, and pressure pain thresholds (PPT) and patient's quality-of-life (oral health-related quality-of-life [OHrQoL]). Data were collected preoperatively (T0), and 1 year (T1), 2-3 years (T2), and ≥ 4 years postoperatively (T4). Analysis of variance with post hoc Tukey -HSD test and multiple linear regression analysis were used for statistical analysis. P < .05 was considered significant.

RESULTS

Thirty-nine patients were enrolled, 15 males and 24 females, with an average age of 48.9 ± 16.2 years. Two patients (5.1%) required a contralateral TMJR. Contralateral condylar motion, incisal laterotrusion, and protrusion slightly decreased, while incisal opening (P = .003), rotation angle (P = .013), opening deflection, surface electromyography activity, maximum voluntary clenching (P = .01), PPTs, and OHrQoL all increased. Pre-TMJR mandibular angle resection had an impact on PPTs and subjective outcomes and prior ipsilateral TMJ surgeries on the opening rotation angle.

CONCLUSIONS

Based on this study, bilateral TMJR does not appear necessary when the contralateral TMJ is healthy. Unilateral alloplastic TMJR is associated with improved contralateral jaw function and OHrQoL.

A crossover clinical study to evaluate pain intensity from microneedle insertion in different parts of the oral cavity

The objective of the present study was to evaluate discomfort and safety of microneedle (MN) insertion in several intraoral regions. A device was developed to standardize MN insertions. MNs were inserted in the following regions of the oral cavity: gingiva, palatine alveolar process, buccal mucosa, dorsum of the tongue and inner portion of the lower lip. Perforations from MNs post insertion were confirmed with topical gentian violet stain. Pain was evaluated in a randomized, double-blinded, crossover study in 30 volunteers. Each volunteer received a MN patch, a 30G hypodermic needle (positive control) and an identical MN patch with its needles laying flat in the plane of the patch (negative control). Adverse events were visually evaluated immediately after (0 h) and 24 h post MN application. The application device developed a consistent application force (10 N) and promoted perforation of all individual MNs on a patch. At all sites, insertion of the hypodermic needle promoted more pain when compared to the negative control (p < 0.001). Application of the MNs promoted less pain than the hypodermic needle (p < 0.05), but slightly more pain as compared to the negative control (p < 0.05) at all sites except the tongue, where the MN did not differ from the negative control (p > 0.05). Hypodermic needle caused bleeding at all insertion sites. In contrast, MNs did not cause bleeding at most sites except in some cases of insertion into the hard gingiva and the palatine alveolar process where tiny blood spots appeared immediately after MN application for few of the MNs on the patch. There were no cases of bleeding at 24 h post MN application. In conclusion, MNs can perforate different sites of the oral cavity in a safe and significantly less painful manner as compared to the 30G hypodermic needle. Thus, analogous to the skin, MN-based approaches could be an attractive approach for drug delivery in the oral cavity.

Age and Gender as Factors of Pressure Sensitivity of Pain-Free Persons: Are They Meaningful?

Purpose

Prior findings suggest that women and elderly persons are more sensitive to pressure than men and younger persons; however, the magnitudes of these differences are substantially inconsistent. We answered the question whether the higher sensitivity of women and elderly persons is quantitatively meaningful. Specifically, we investigated if it is large enough to hamper the diagnosis, classification and follow-up of pain conditions by clinicians.

Materials and Methods

From each age stratum (18–20, 21–30, 31–40, 41–50, 51–60, 61–70, 71–80, and >80 years), 40 pain-free women and 40 pain-free men were recruited. They rated the intensity of pressure of ten Newtons over ten seconds on an analogue zero to ten rating scale. The pressure was applied on their middle fingers and ear lobes with a threshold algometer. Centile curves visualized the sex- and age-dependent fluctuation of pressure sensitivity.

Results

Over the entire age range from 20 to 80 years, the median curves fluctuated within the interval of less than two points. The distance between the median curves of men and women was also less than two points. On the average, the median difference was half a point on the finger (p = 0.249) and the ear lobe (p = 0.083).

Conclusion

Less than two points is below the minimal clinically important difference for a zero to ten analogue pain rating scale; differences smaller than one point are even below the resolution of the scale. Sex differences and age fluctuations of pressure sensitivity are negligible.

Quantitative sensory testing of periauricular skin in healthy adults

The aim of this study was to investigate the test-retest reliability of quantitative sensory testing (QST) and mechanical sensitivity mapping of the periauricular skin. Twenty volunteers (10 men, 10 women) participated in two sessions at intervals of one week. Cold and warm detection threshold (CDT&WDT), cold and heat pain threshold (CPT&HPT), mechanical detection and pain threshold (MDT&MPT), pressure pain threshold (PPT) and two-point discrimination (2PD) were measured at five sites: bilateral subauricular and postauricular sites (LA, RA, LB, RB) and the dorsum of left hand (control). Pressure stimulation was applied at each of the four periauricular test sites. The test-retest reliability of the QST data implied fair to excellent agreement as evaluated by the intra-class correlation coefficients (ICC; all >0.4) for different days. There was no difference between each side in the QST parameters and mechanical sensitivity mapping (P ≥ 0.057). Significant differences between subauricular and postauricular sites were shown for WDT and PPT (P ≤ 0.028). NRS scores of mechanical sensitivity mapping showed significant effects of gender, site and point (P ≤ 0.040). QST and mechanical sensitivity mapping can be considered to be a reliable technique to assess somatosensory function of the periauricular skin.

Sex differences in pain and opioid mediated antinociception: Modulatory role of gonadal hormones

Sex-related differences in pain and opioids has been the focus of many researches. It is demonstrated that women experience greater clinical pain, lower pain threshold and tolerance, more sensitivity and distress to experimentally induced pain compared to men. Sex differences in response to opioid treatment revealed inconsistent results. However, the etiology of these disparities is not fully elucidated. It is, therefore, conceivable now that this literature merits to be revisited comprehensively. Possible multifaceted factors seem to be associated. These include neuroanatomical, hormonal, neuroimmunological, psychological, social and cultural aspects and comorbidities. This review aims at providing an overview of the substantial literature documenting the sex differences in pain and analgesic response to opioids from animal and human studies within the context of the modulatory effects of the aforementioned factors. A detailed and critical discussion of the cellular and molecular signaling pathways underlying the modulatory actions of gonadal hormones in the sexual dimorphism in pain processing and opioid analgesia is extensively presented. It is indicated that sexual dimorphic activation of certain brain regions contributes to differential pain sensitivity between females and males. Plausible crosstalk between sex hormones and neuroimmunological signaling pertinent to toll-like and purinergic receptors is uncovered as causal cues underlying sexually dimorphic pain and opioid analgesia. Conceivably, a thorough understanding of these factors may aid in sex-related advancement in pain therapeutic management.

Current status of the anterior middle superior alveolar anesthetic injection for periodontal procedures in the maxilla

Periodontal procedures require adequate anesthesia not only to ensure the patient's comfort but also to enhance the operator's performance and minimize chair time. In the maxilla, anesthesia is often achieved using highly traumatic nerve blocks, apart from multiple local infiltrations through the buccal vestibule. In recent years, anterior middle superior alveolar (AMSA) field block has been claimed to be a less traumatic alternative to several of these conventional injections, and it has many other advantages. This critical review of the existing literature aimed to discuss the rationale, mechanism, effectiveness, extent, and duration of AMSA injections for periodontal surgical and non-surgical procedures in the maxilla. It also focused on future prospects, particularly in relation to computer-controlled local anesthetic delivery systems, which aim to achieve the goal of pain-free anesthesia. A literature search of different databases was performed to retrieve relevant articles related to AMSA injections. After analyzing the existing data, it can be concluded that this anesthetic technique may be used as a predictable method of effective palatal anesthesia with adequate duration for different periodontal procedures. It has additional advantages of being less traumatic, requiring lesser amounts of local anesthetics and vasoconstrictors, as well as achieving good hemostasis. However, its effect on the buccal periodontium appears highly unpredictable.

Effect of 8% lidocaine spray on the sensory and pain thresholds of the skin of the face and hands evaluated by quantitative sensory testing

Background

Recently, we examined the effects of 2% lidocaine gel on the tactile sensory and pain thresholds of the face, tongue and hands of symptom-free individuals using quantitative sensory testing (QST); its effect was less on the skin of the face and hands than on the tongue. Consequently, instead of 2% lidocaine gel, we examined the effect of 8% lidocaine spray on the tactile sensory and pain thresholds of the skin of the face and hands of healthy volunteers.

Methods

Using Semmes-Weinstein monofilaments, QST of the skin of the cheek and palm (thenar skin) was performed in 20 healthy volunteers. In each participant, two topical sprays were applied. On one side, 0.2 mL of 8% lidocaine pump spray was applied, and on the other side, 0.2 mL of saline pump spray was applied as control. In each participant, QST was performed before and 15 min after each application. Pain intensity was measured using a numeric rating scale (NRS).

Results

Both the tactile detection threshold and filament-prick pain detection threshold of the cheek and thenar skin increased significantly after lidocaine application. A significant difference between the effect of lidocaine and saline applications was found on the filament-prick pain detection threshold only. NRS of the cheek skin and thenar skin decreased after application of lidocaine, and not after application of saline.

Conclusion

The significant effect of applying an 8% lidocaine spray on the sensory and pain thresholds of the skin of the face and hands can be objectively scored using QST.

Involvement of transient receptor potential vanilloid 2 in intra-oral incisional pain

OBJECTIVE

To examine whether transient receptor potential vanilloid 2 (TRPV2) contributes to the changes in intra-oral thermal and mechanical sensitivity following the incision of buccal mucosa.

MATERIALS AND METHODS

Buccal mucosal pain threshold was measured after the incision. Changes in the number of TRPV2-immunoreactive (IR) trigeminal ganglion (TG) neurons which innervate the whisker pad skin and buccal mucosa, changes in the number of isolectin B4-negative/isolectin B4-positive TRPV2-IR TG neurons which innervate the whisker pad skin and the buccal mucosa, and the effect of peripheral TRPV2 antagonism on the pain threshold of incisional whisker pad skin and buccal mucosa were examined after these injuries.

RESULTS

Buccal mucosal pain hypersensitivities were induced on day 3 following the incision. The total number of TRPV2-IR TG neurons and the number of isolectin B4-negative TRPV2-IR TG neurons which innervate the whisker pad skin and buccal mucosa were increased. Buccal mucosal TRPV2 antagonism completely suppressed the heat and mechanical hypersensitivities, but not cold hypersensitivity. TRPV2 antagonist administration to the incisional whisker pad skin only partially suppressed pain hypersensitivities.

CONCLUSION

The increased expression of TRPV2 in peptidergic TG neurons innervating the incisional buccal mucosa is predominantly involved in buccal mucosal heat hyperalgesia and mechanical allodynia following buccal mucosal incision.

Mechanical sensitivity and psychological factors in patients with burning mouth syndrome

OBJECTIVES

The aim of this study was to compare mechanical sensitivity on the tongue using quantitative sensory testing (QST) and psychological factors using the General Health Questionnaire (GHQ) between burning mouth syndrome (BMS) patients and healthy participants.

MATERIALS AND METHODS

Participants comprised 20 female BMS patients (68.1 ± 7.4 years) and 20 healthy females (65.4 ± 4.6 years). Psychological factors were evaluated with GHQ. Tactile detection thresholds (TDT) and filament-prick pain detection thresholds (FPT) were used to evaluate mechanical sensitivity on the tongue in all participants. TDT and FPT were measured on the tongue within both the painful area and the non-painful area in BMS patients, and on the tongue on both sides in healthy participants. As controls, TDT and FPT were measured with Semmes-Weinstein monofilaments on the skin of the mentum and palm in all participants.

RESULTS

GHQ scores were significantly higher in BMS patients than in healthy participants (P = 0.024). No significant differences in TDT or FPT on the tongue, mentum, or palm were seen between BMS patients and healthy participants (P > 0.05). BMS patients showed no significant differences in TDT or FPT between the painful and non-painful areas on the tongue (P > 0.05). There were no significant correlations among TDT/FPT and GHQ score in BMS patients (P > 0.05).

CONCLUSIONS

These findings could indicate a more important role for psychological factors than mechanical sensitivity in BMS pathophysiology.

CLINICAL RELEVANCE

Pain on the tongue in elderly female patients with BMS may be more related to psychological factors.

Sensory function in cluster headache: an observational study comparing the symptomatic and asymptomatic sides

BACKGROUND

Based on inconsistent sensory alterations demonstrated in cluster headache (CH), the aim of this study was to determine whether patients with CH develop sensory changes in the symptomatic side compared to the asymptomatic side.

METHODS

Quantitative sensory testing (QST), including pressure pain threshold (PPT), tactile detection threshold (TDT), prick detection threshold (PDT), and two-point detection threshold (2PDT), was evaluated in 16 patients (seven women; age 41.9±6.8 years) with CH. Test sites included the first, second, and third divisions of the trigeminal nerve, cervical spine, and thenar eminence in the symptomatic and asymptomatic sides.

RESULTS

The symptomatic side, compared to the asymptomatic side, presented significantly decreased PPT in the first (P=0.011; 423.81±174.05 kPa vs 480.13±214.99 kPa) and second (P=0.023; 288.88±140.80 kPa vs 326.38±137.33 kPa) divisions of the trigeminal nerve, significantly increased TDT in the first (P=0.002; 2.44±0.40 vs 1.74±0.24) and second (P=0.016; 1.92±0.34 vs 1.67±0.09) divisions, and increased 2PDT in the first division (P=0.004; 18.13±4.70 mm vs 15.0±4.92 mm) and neck (P=0.007; 45.31±20.65 mm vs 38.44±16.10 mm).

CONCLUSION

These results support the prior evidence suggesting a specific pattern of alteration of sensory function with alterations in the symptomatic side compared to the asymptomatic side.

Quantitative sensory testing for assessment of somatosensory function in human oral mucosa: a review

OBJECTIVE

This narrative review provides an overview of the quantitative sensory testing (QST) to assess somatosensory function in human oral mucosa.

MATERIAL AND METHODS

A literature search was conducted in the PubMed database to identify studies in vivo on human oral mucosa using QST methods. A list of 149 articles was obtained and screened. A total of 36 relevant articles remained and were read in full text. Manual search of the reference lists identified eight additional relevant studies. A total of 44 articles were included for final assessment.

RESULTS

The included studies were divided into six categories according to the study content and objective. In each category, there was a great variety of aims, methods, participants and outcome measures. The application of QST has nevertheless helped to monitor somatosensory function in experimental models of intraoral pain, effects of local anesthesia, after oral and maxillofacial surgery and after prosthodontic and orthodontic treatment.

CONCLUSIONS

QST has been proved to be sufficiently stable and reliable, and valuable information has been obtained regarding somatosensory function in healthy volunteers, special populations and orofacial pain patients. However, as most of the studies were highly heterogeneous, the results are difficult to compare quantitatively. A standardized intraoral QST protocol is recommended and expected to help advance a mechanism-based assessment of neuropathies and other intraoral pain conditions.

Changes in shoulder muscle activity pattern on surface electromyography after breast cancer surgery

BACKGROUND AND OBJECTIVES

Alterations in muscle activation and restricted shoulder mobility, which are common in breast cancer patients, have been found to affect upper limb function. The purpose of this study was to determine muscle activity patterns, and to compare the prevalence of abnormal patterns among the type of breast surgery.

METHODS

In total, 274 breast cancer patients were recruited after surgery. Type of breast surgery was divided into mastectomy without reconstruction (Mastectomy), reconstruction with tissue expander/implant (TEI), latissimus dorsi (LD) flap, or transverse rectus abdominis flap (TRAM). Activities of shoulder muscles were measured using surface electromyography. Experimental analysis was conducted using a Gaussian filter smoothing method with regression.

RESULTS

Patients demonstrated different patterns of muscle activation, such as normal, lower muscle electrical activity, and tightness. After adjusting for BMI and breast surgery, the odds of lower muscle electrical activity and tightness in the TRAM are 40.2% and 38.4% less than in the Mastectomy only group. The prevalence of abnormal patterns was significantly greater in the ALND than SLNB in all except TRAM.

CONCLUSIONS

Alterations in muscle activity patterns differed by breast surgery and reconstruction type. For breast cancer patients with ALND, TRAM may be the best choice for maintaining upper limb function.

Effect of topical lidocaine in the oral and facial regions on tactile sensory and pain thresholds

OBJECTIVE

The aim of the present study was to examine the effect of lidocaine application to the face, tongue and hand on sensory and pain thresholds of symptom-free subjects.

DESIGN

Eighteen females (mean age 25.7 years, range 22-38) participated. Using Semmes-Weinstein monofilaments, the tactile detection threshold (TDT) and the filament-prick pain detection threshold (FPT) were measured on the cheek skin (CS), tongue tip (TT) and palm side of the thenar skin (TS). Subjects were tested in 2 sessions at a 1week interval in randomised order. Lidocaine (session A) or placebo gel (session B) was applied for 5min. The TDT and FPT were measured before and after application.

RESULTS

The TDT at all sites in session A significantly increased after 5min, but a significant session effect on the TDT was only found at the TT (P<0.01). On the other hand, there were significant session effects on the FPT at all sites (P<0.01).

CONCLUSION

These results indicate that the pain threshold (FPT) is more susceptible to local anesthetics than the sensory threshold (TDT), but further study is needed to use topical lidocaine for the control of oral and facial pain in the clinic.

Assessment of periodontal mechano-nociceptive function in healthy Chinese individuals

OBJECTIVE

Few clinical techniques are available for the description of mechano-nociceptive function in human periodontal tissues. The objective of this study was to test a new technique for assessment of periodontal mechano-nociceptive function by direct application of controlled forces to the teeth and quantify site, side and gender differences in healthy individuals.

DESIGN

Twenty healthy young adults (ten males and ten females) participated. A handheld pressure algometer was used to assess pressure pain threshold (PPT) on the maxillary and mandibular central incisors, canines and first premolars on the left and the right side from two directions: lateral and vertical. Statistical analysis was performed using analyses of variance (ANOVA) with repeated measures to compare data.

RESULTS

There were significant gender differences of PPT for both lateral (P_lateral=0.007) and vertical (P_vertical=0.001) directions with lower thresholds in females (higher sensitivity) than in males. A significant site effect (P_lateral=0.002, P_vertical<0.001) was observed with less sensitivity at the first premolar compared to the anterior teeth. No significant right-to-left side differences (P=0.082) were found for the PPTs. There were significant PPT differences between maxillary and mandibular teeth (P_lateral=0.020, P_vertical=0.041,) and significant differences between lateral and vertical direction (P<0.001).

CONCLUSION

The novel application of PPTs directly to the teeth indicated an adequate and practical method with potential value for clinical assessment of painful conditions affecting the periodontal ligament.

The Anesthetic Effect of Anterior Middle Superior Alveolar Technique (AMSA)

Anesthesia of the soft and hard tissues of the maxilla may require up to 5 injections. Thus, the aim of this study was to evaluate the anesthetic efficacy of the anterior middle superior alveolar (AMSA) and supraperiosteal injection techniques during subgingival scaling and root planing (SRP). Thirty individuals with periodontitis were scheduled for SRP on the buccal aspect of teeth in the anterior maxilla. Before SRP, on a randomly chosen side of the maxilla, the supraperiosteal injection was performed in 1 session, while the AMSA injection was conducted in the contralateral side of the same patient in another session. Immediately after each SRP session, patients rated their pain perception during the procedure with a visual analog scale. No statistically significant differences in mean pain ratings during SRP were found after both anesthetic techniques (P > .05). This preliminary study demonstrated that the AMSA and supraperiosteal injection techniques provided similar anesthetic comfort during SRP. The AMSA injection could be an alternative to anesthetize the buccal aspect of maxilla, without the undesirable effects on facial structures such as the upper lip, nostrils, and lower eyelids. However, further randomized clinical trials with larger samples are necessary to confirm such results.

Regulation of transient receptor potential vanilloid 1 expression in trigeminal ganglion neurons via methyl-CpG binding protein 2 signaling contributes tongue heat sensitivity and inflammatory hyperalgesia in mice

Background

Pain hypoalgesia has been reported in Rett syndrome patients, a severe neurodevelopmental disorder which can be attributed to mutations in the methyl-CpG binding protein 2 (MeCP2). Here, we examined the role of MeCP2 signaling in tongue heat sensitivity in the normal and inflamed state using Mecp2 heterozygous (Mecp2^+/−) mice.

Results

Heat hypoalgesia of the tongue occurred in Mecp2^+/− mice and submucosal injection of complete Freund’s adjuvant into the tongue produced a long-lasting heat hyperalgesia at the inflamed site in wild-type mice but not in Mecp2^+/− mice. Transient receptor potential vanilloid 1 was expressed in a large number of MeCP2-immunoreactive trigeminal ganglion neurons innervating the tongue in both wild-type and Mecp2^+/− mice (70.9% in wild type; 72.1% in Mecp2^+/−). The number of transient receptor potential vanilloid 1-immunoreactive trigeminal ganglion neurons innervating the tongue was smaller in Mecp2^+/− mice relative to wild-type mice (30.5% in wild type; 20.2% in Mecp2^+/−). Following complete Freund’s adjuvant injection, the number of transient receptor potential vanilloid 1- and MeCP2-immunoreactive trigeminal ganglion neurons innervating the tongue, as well as MeCP2 protein expression in trigeminal ganglion, was significantly increased in wild-type mice but not in Mecp2^+/− mice. Additionally, tongue heat hyperalgesia following complete Freund’s adjuvant injection was completely suppressed by the administration of SB366791, a transient receptor potential vanilloid 1 antagonist, in the tongue.

Conclusions

These findings indicate that tongue heat sensitivity and hypersensitivity are dependent on the expression of transient receptor potential vanilloid 1 which is regulated via MeCP2 signaling in trigeminal ganglion neurons innervating the tongue.

Involvement of TRPV1 and TRPA1 in incisional intraoral and extraoral pain

Thermal and mechanical hypersensitivity in the injured region is a common complication. Although it is well known clinically that thermal and mechanical sensitivity of the oral mucosa is different from that of the skin, the mechanisms underlying injured pain of the oral mucosa remain poorly understood. The transient receptor potential (TRP) vanilloid 1 (TRPV1) and TRP ankyrin 1 (TRPA1) in primary afferent neurons are known to contribute to pathological pain. Therefore, we investigated whether TRPV1 and/or TRPA1 contribute to thermal and mechanical hypersensitivity following oral mucosa or whisker pad skin incision. Strong heat and mechanical and cold hypersensitivity was caused in the buccal mucosa and whisker pad skin following incisions. On day 3 after the incisions, the number of TRPV1-immunoreactive (IR) and TRPA1-IR trigeminal ganglion (TG) neurons innervating the buccal mucosa and whisker pad skin was significantly increased, and the number of TRPV1/TRPA1-IR TG neurons innervating whisker pad skin, but not the buccal mucosa, was significantly increased. Administration of the TRPV1 antagonist, SB366791, to the incised site produced a significant suppression of heat hyperalgesia in both the buccal mucosa and whisker pad skin, as well as mechanical allodynia in the whisker pad skin. Administration of the TRPA1 antagonist, HC-030031, to the incised site suppressed mechanical allodynia and cold hyperalgesia in both the buccal mucosa and whisker pad skin, as well as heat hyperalgesia in the whisker pad skin. These findings indicate that altered expressions of TRPV1 and TRPA1 in TG neurons are involved in thermal and mechanical hypersensitivity following the buccal mucosa and whisker pad skin incision. Moreover, diverse changes in the number of TRPV1 and TRPA1 coexpressed TG neurons in whisker pad skin-incised rats may contribute to the intracellular interactions of TRPV1 and TRPA1 associated with whisker pad skin incision, whereas TRPV1 and TRPA1 expression in individual TG neurons is involved in buccal mucosa-incised pain.

Pressure pain threshold of the cervico-facial muscles in healthy elderly people: the role of gender, age and dominance

OBJECTIVE

The aim of this study was to assess the impact of age on pressure pain threshold (PPT) of cervico-facial muscles in healthy geriatric subjects and to investigate the role of gender and dominance on nociception.

BACKGROUND

Musculo-skeletal pain is common in the elderly, but being subjective, it risks to be underdiagnosed and undertreated. A useful method for assessment of local pain is determining PPT through pressure algometry. Ageing process seems to increase PPTs, but reference values for the assessment of pain in geriatric subjects are lacking.

METHODS

In this study, PPTs in temporal muscle, masseter, sternocleidomastoid, occipital and splenius capitis of 97 healthy elderly subjects were measured using Fischer algometer. Participants were divided by age in four classes (years 65-69; 70-74; 75-79; ≥80).

RESULTS

Women had lower PPTs in all muscles compared with men. Comparing PPTs obtained from the right and the left side, no significant differences were recorded neither in men nor in women. When dividing subjects by age class and education, in both genders no significant differences were observed in PPTs among the groups, neither in the right nor in the left sides.

CONCLUSION

In conclusion, the present study reports reference PPT values for the cervico-facial muscles that can be applied to a population of healthy elderly subjects. After 65 years of age, further ageing does not influence PPTs in cervico-facial muscles whereas female gender has lower PPTs.

Somatosensory profiling of intra-oral capsaicin and menthol in healthy subjects

This study was designed to investigate the effect of surrogate orofacial pain models on the quantitative sensory testing (QST) profile in healthy participants. Capsaicin, menthol, or saline (control) were applied topically onto the gingiva of 15 healthy subjects for 15 min. During application, the subjects rated pain intensity on a score of 0-10, on an electronic visual analog scale (VAS). A standardized intra-oral QST protocol was performed before and immediately after application. Data obtained before and after application were compared using rank-sum tests, and QST profiles were made after Z-transformation. Application of capsaicin caused moderate levels of pain (VAS(peak)  = 6.0 ± 0.7), and application of menthol produced mild levels of pain (VAS(peak)  = 1.8 ± 0.6). Capsaicin induced hypersensitivity to warmth, heat pain and cold pain and hyposensitivity to mechanical stimuli. Menthol induced hypersensitivity to cold and warmth. Saline caused hypersensitivity to heat pain and hyposensitivity to mechanical stimuli. However, somatosensory profiles from Z-scores demonstrated sensory gains regarding warmth detection and heat pain only after application of capsaicin. In conclusion, a standardized battery of QST showed somatosensory changes after application of capsaicin, menthol and saline to the gingiva. However, the Z-score-based profiles may only reflect the most prominent somatosensory changes and thus represent a conservative approach for evaluation of data.

Effect of a mixed solution of sodium hyaluronate and carboxymethyl cellulose on upper limb dysfunction after total mastectomy: a double-blind, randomized clinical trial

Restricted shoulder mobility is a major upper limb dysfunction related to lower quality of life and disability after breast cancer surgery. We hypothesized that sodium hyaluronate-carboxymethyl cellulose (HA-CMC) applied to the surface of the pectoralis major muscle after mastectomy would significantly reduce pain and improve range of motion (ROM) of the shoulder in breast cancer patients. We conducted a double-blind, randomized controlled study to evaluate the clinical efficacy and safety of HA-CMC in the prevention of upper limb dysfunction after total mastectomy (TM). A total of 99 women with breast cancer were randomly assigned to one of two groups. In the HA-CMC group (n = 50), a mixed HA-CMC was applied to the surface of the pectoralis major and serratus anterior muscle after TM. In the control group (n = 49), TM was performed without the use of HA-CMC. The primary outcomes were ROM of the shoulder and motion-related pain assessed using a numeric rating scale measured before surgery (T0) and 3 (T1) and 6 months (T2) after surgery. Secondary outcomes included disabilities of the arm, shoulder, and hand (DASH) and the pectoralis minor length test. Compared with the control group, the HA-CMC group showed greater reductions in postoperative restriction of total shoulder ROM (sum of flexion and horizontal abduction) at 3 months (10.20°, P = 0.004). Mean pain levels related to flexion and horizontal abduction were significantly lower in the HA-CMC group (-1.32 and -0.93, respectively, P < 0.05). The DASH score was lower (-4.94; P = 0.057) in the HA-CMC group at T2. No adverse effect was observed in either group. These results provide evidence that HA-CMC may provide pain relief and improve ROM of the shoulder without causing adverse effects. The effect on pectoralis tightness should be investigated in further studies.

The effect of nonfunctional tooth contact on sensory and pain perception in patients with myofascial pain of the jaw muscles

PURPOSE

The aim of this study was to examine the effect of nonfunctional tooth contact on sensory threshold (tactile detection threshold: TDT) and pain thresholds (filament-prick pain detection threshold: FPT; pressure pain threshold: PPT) in the orofacial region of patients with myofascial pain of the jaw muscles.

METHODS

The study was performed on 36 subjects: 20 normal subjects and 16 patients. Using a stair-case method, TDT and FPT were measured by Semmes-Weinstein monofilaments, on the cheek skin (CS) overlying the masseter muscles (MM) and on the skin overlying the palm side of the thenar skin (TS). PPT was measured at the central part of the MM using a pressure algometer. Each parameter was measured before and after keeping light tooth contact for 5 min (session 1) and keeping the jaw relaxed for 5 min (session 2) as a control.

RESULTS

There were significant effects of experimental condition (before-after 5 min) on the TDT and FPT at several sites: after 5 min, TDT was higher in all measurement sites except the left CS of the patients in session 2. As for the FPT, the reactions between CS and TS were quite opposite in both sessions: after 5 min, the FPT at the CS decreased and/or remained, but the FPT at the TS increased and/or remained. Significant session effects (session 1-session 2) were only found on the FPT at the CS in patients.

CONCLUSION

Sensitivity to FPT was more susceptible to tooth contact condition, especially in the patients.

A systematic literature review of 10 years of research on sex/gender and experimental pain perception - part 1: are there really differences between women and men?

The purpose of this systematic review was to summarize and critically appraise the results of 10 years of human laboratory research on pain and sex/gender. An electronic search strategy was designed by a medical librarian and conducted in multiple databases. A total of 172 articles published between 1998 and 2008 were retrieved, analyzed, and synthesized. The first set of results (122 articles), which is presented in this paper, examined sex difference in the perception of laboratory-induced thermal, pressure, ischemic, muscle, electrical, chemical, and visceral pain in healthy subjects. This review suggests that females (F) and males (M) have comparable thresholds for cold and ischemic pain, while pressure pain thresholds are lower in F than M. There is strong evidence that F tolerate less thermal (heat, cold) and pressure pain than M but it is not the case for tolerance to ischemic pain, which is comparable in both sexes. The majority of the studies that measured pain intensity and unpleasantness showed no sex difference in many pain modalities. In summary, 10 years of laboratory research have not been successful in producing a clear and consistent pattern of sex differences in human pain sensitivity, even with the use of deep, tonic, long-lasting stimuli, which are known to better mimic clinical pain. Whether laboratory studies in healthy subjects are the best paradigm to investigate sex differences in pain perception is open to question and should be discussed with a view to enhancing the clinical relevance of these experiments and developing new research avenues.

Organization of hyperactive microglial cells in trigeminal spinal subnucleus caudalis and upper cervical spinal cord associated with orofacial neuropathic pain

The aim of this study was to evaluate spatial organization of hyperactive microglial cells in trigeminal spinal subnucleus caudalis (Vc) and upper cervical spinal cord (C1), and to clarify the involvement in mechanisms underlying orofacial secondary hyperalgesia following infraorbital nerve injury. We found that the head-withdrawal threshold to non-noxious mechanical stimulation of the maxillary whisker pad skin was significantly reduced in chronic constriction injury of the infraorbital nerve (ION-CCI) rats from day 1 to day 14 after ION-CCI. On day 3 after ION-CCI, mechanical allodynia was obvious in the orofacial skin areas innervated by the 1st and 3rd branches of the trigeminal nerve as well as the 2nd branch area. Hyperactive microglial cells in Vc and C1 were observed on days 3 and 7 after ION-CCI. On day 3 after ION-CCI, a large number of phosphorylated extracellular signal-regulated kinase (pERK)-immunoreactive (IR) cells were observed in Vc and C1. Many hyperactive microglial cells were also distributed over a wide area of Vc and C1 innervated by the trigeminal nerve. The intraperitoneal administration of minocycline significantly reduced the activation of microglial cells and the number of pERK-IR cells in Vc and C1, and also significantly attenuated the development of mechanical allodynia. Furthermore, enhanced background activity and mechanical evoked responses of Vc wide dynamic range neurons in ION-CCI rats were significantly reversed following minocycline administration. These findings suggest that activation of microglial cells over a wide area of Vc and C1 is involved in the enhancement of Vc and C1 neuronal excitability in the early period after ION-CCI, resulting in the neuropathic pain in orofacial areas innervated by the injured as well as uninjured nerves.

Duloxetine in patients with central neuropathic pain caused by spinal cord injury or stroke: a randomized, double-blind, placebo-controlled trial

The mechanisms underlying central neuropathic pain are poorly understood. Pain inhibitory mechanisms including sertononergic and norepinephrine systems may be dysfunctional. In this randomized, double-blinded, placebo-controlled trial we evaluated the effects of duloxetine on pain relief (spontaneous pain and evoked pain), tolerability, health status, and quality of life in patients with central pain related to cerebrovascular lesions or spinal cord lesions. At baseline and eight weeks following start of treatment subjects were evaluated with standard measures of efficacy: pain intensity (primary efficacy variable), quantitative sensory testing, health status and quality of life (secondary efficacy variables). Forty-eight patients received escalating doses of either duloxetine (60 and 120mg/day) or matching placebo capsules. In both groups, patients started with 1 capsule per day. If pain relief was insufficient, patients were titrated to a higher dose. A trend towards a decrease in mean pain score after eight weeks was observed for duloxetine treatment (p=0.056). Duloxetine alleviated dynamic (p=0.035) and cold allodynia (p<0.001) significantly better than placebo. Tactile pain and pressure pain thresholds did not improve significantly. The duloxetine group showed a significant improvement for the bodily pain domain of the SF36 (p=0.035). No significant differences were observed in the other domains of the SF36, the Pain Disability Index, and the EQ-5D. While this trial showed no significant effect on pain intensity, duloxetine revealed a biologic effect. It would be worthwhile to suspend our judgement and to perform more studies to evaluate the role of duloxetine in modulation of the symptoms of central neuropathic pain.

Involvement of peripheral ionotropic glutamate receptors in orofacial thermal hyperalgesia in rats

Background

The purpose of the present study was to elucidate the mechanisms that may underlie the sensitization of trigeminal spinal subnucleus caudalis (Vc) and upper cervical spinal cord (C1-C2) neurons to heat or cold stimulation of the orofacial region following glutamate (Glu) injection.

Results

Glu application to the tongue or whisker pad skin caused an enhancement of head-withdrawal reflex and extracellular signal-regulated kinase (ERK) phosphorylation in Vc-C2 neurons. Head-withdrawal reflex and ERK phosphorylation were also enhanced following cold stimulation of the tongue but not whisker pad skin in Glu-injected rats, and the head-withdrawal reflex and ERK phosphorylation were enhanced following heat stimulation of the tongue or whisker pad skin. The enhanced head-withdrawal reflex and ERK phosphorylation after heat stimulation of the tongue or whisker pad skin, and those following cold stimulation of the tongue but not whisker pad skin were suppressed following ionotropic glutamate receptor antagonists administration into the tongue or whisker pad skin. Furthermore, intrathecal administration of MEK1/2 inhibitor PD98059 caused significant suppression of enhanced head-withdrawal reflex in Glu-injected rats, heat head-withdrawal reflex in the rats with Glu injection into the tongue or whisker pad skin and cold head-withdrawal reflex in the rats with Glu injection into the tongue.

Conclusions

The present findings suggest that peripheral Glu receptor mechanisms may contribute to cold hyperalgesia in the tongue but not in the facial skin, and also contribute to heat hyperalgesia in the tongue and facial skin, and that the mitogen-activated protein kinase cascade in Vc-C2 neurons may be involved in these Glu-evoked hyperalgesic effects.

Guidelines and recommendations for assessment of somatosensory function in oro-facial pain conditions--a taskforce report

The goals of an international taskforce on somatosensory testing established by the Special Interest Group of Oro-facial Pain (SIG-OFP) under the International Association for the Study of Pain (IASP) were to (i) review the literature concerning assessment of somatosensory function in the oro-facial region in terms of techniques and test performance, (ii) provide guidelines for comprehensive and screening examination procedures, and (iii) give recommendations for future development of somatosensory testing specifically in the oro-facial region. Numerous qualitative and quantitative psychophysical techniques have been proposed and used in the description of oro-facial somatosensory function. The selection of technique includes time considerations because the most reliable and accurate methods require multiple repetitions of stimuli. Multiple-stimulus modalities (mechanical, thermal, electrical, chemical) have been applied to study oro-facial somatosensory function. A battery of different test stimuli is needed to obtain comprehensive information about the functional integrity of the various types of afferent nerve fibres. Based on the available literature, the German Neuropathic Pain Network test battery appears suitable for the study of somatosensory function within the oro-facial area as it is based on a wide variety of both qualitative and quantitative assessments of all cutaneous somatosensory modalities. Furthermore, these protocols have been thoroughly described and tested on multiple sites including the facial skin and intra-oral mucosa. Standardisation of both comprehensive and screening examination techniques is likely to improve the diagnostic accuracy and facilitate the understanding of neural mechanisms and somatosensory changes in different oro-facial pain conditions and may help to guide management.

Effect of lingual nerve block on burning mouth syndrome (stomatodynia): a randomized crossover trial

Burning mouth syndrome (stomatodynia) is associated with changes of a neuropathic nature the main location of which, peripheral or central, remains unknown. A randomised, double-blind crossover design was used to investigate the effects of lingual nerve block on spontaneous burning pain and a possible correlation with the effects of topical clonazepam, the patient's response to a psychological questionnaire, and the taste and heat thresholds. The spontaneous burning was measured with a visual analogue scale (VAS) just before and 15 min after injection. The decreases in VAS score after lidocaine or saline injection were not significantly different (2.7+/-3.9 and 2.0+/-2.6, respectively; n=20). However, two groups of patients could be identified: in a "peripheral group" (n=10) the VAS decrease due to lingual nerve injection was 4.3+/-3.1cm after lidocaine and 0.9+/-0.3 cm after saline (p=0.02). In a "central group" (n=7), there were an increase in pain intensity score (-0.8+/-2.6 cm) after lidocaine and a decrease (1.5+/-3.0 cm) after saline (p=0.15). An increase in the hospital anxiety and depression (HAD) score and a decreased taste sensitivity and heat pain threshold of painful oral area were seen in patients compared with age-and-sex-matched controls (p<0.05). Topical clonazepam treatment tended to be more effective (p=0.07) and HAD score lower (p<0.03) in the peripheral than in the central group. These results suggest that the neuropathic disorder associated with stomatodynia may be predominantly peripheral, central or mixed depending on the individual. Topical application of clonazepam and HAD may serve as indicators of which mechanism is dominating.

Sex, gender, and pain: a review of recent clinical and experimental findings

Sex-related influences on pain and analgesia have become a topic of tremendous scientific and clinical interest, especially in the last 10 to 15 years. Members of our research group published reviews of this literature more than a decade ago, and the intervening time period has witnessed robust growth in research regarding sex, gender, and pain. Therefore, it seems timely to revisit this literature. Abundant evidence from recent epidemiologic studies clearly demonstrates that women are at substantially greater risk for many clinical pain conditions, and there is some suggestion that postoperative and procedural pain may be more severe among women than men. Consistent with our previous reviews, current human findings regarding sex differences in experimental pain indicate greater pain sensitivity among females compared with males for most pain modalities, including more recently implemented clinically relevant pain models such as temporal summation of pain and intramuscular injection of algesic substances. The evidence regarding sex differences in laboratory measures of endogenous pain modulation is mixed, as are findings from studies using functional brain imaging to ascertain sex differences in pain-related cerebral activation. Also inconsistent are findings regarding sex differences in responses to pharmacologic and non-pharmacologic pain treatments. The article concludes with a discussion of potential biopsychosocial mechanisms that may underlie sex differences in pain, and considerations for future research are discussed.

PERSPECTIVE

This article reviews the recent literature regarding sex, gender, and pain. The growing body of evidence that has accumulated in the past 10 to 15 years continues to indicate substantial sex differences in clinical and experimental pain responses, and some evidence suggests that pain treatment responses may differ for women versus men.