Perceptual distortion of the tongue by lingual nerve block and topical application of capsaicin in healthy women

Role of dairy proteins in the reduction of capsaicin-induced oral burning pain

Capsaicin-induced burning sensation in the oral mucosa can be relieved by skimmed and whole milk. The mechanism behind this effect, however, is unknown. This study aimed to asses the role of milk proteins in reducing capsaicin-induced oral burning sensation. 24 healthy participants were included in this single-blinded cross-over study consisting of four sessions. In each sessions, mucosal burning sensation was evoked by having the participants dip their tongues in a cup containing 0.1% capsaicin gel for a total of 8 min. The perceived levels of unpleasantness and burning intensity were scored on two different numerical rating scales. After capsaicin exposure, the participants rinsed their mouth for 10 s with a different solution in each session (3.5% casein, 3.5% whey, 3.5% lactose (non-protein control) and skimmed milk (active/positive control)). Mechanical (64, 128 and 256 mN pinprick) and thermal (5, 40, 45 and 50 ̊C) sensitivity of the tongue was measured using semi-quantative sensory testing at baseline, immediately after capsaicin exposure and when the scores for unpleasantness and burning intensity reached the minimum value of 0. Thermographic images of the tongue were taken at the same time-points. Overall, no statistically significant difference in unpleasantness and burning intensity was found between the four sessions (P ≥ 0.070). Explorative pair-wise comparisons, however, showed slight short-term reduction in unpleasantness and burning intensity when comparing the casein solution with the lactose solution (P ≤ 0.020). Scores for burning intensity and unpleasantness varied over time (P ≤ 0.001). Statistically significant changes in heat and mechanical sensitivity was observed between time-points (P < 0.001) but not sessions (P ≥ 0.410). An increased sensitivity towards heat and a decreased sensitivity towards mechanical stimuli was observed after capsaicin exposure compared with baseline (P < 0.001). Similarly, changes in thermographic temperature of the tongue was observed between time-points (P < 0.001), but not sessions (P ≥ 0.827). An increased maximum, minimum and average temperature of the tongue was observed immediately after capsaicin exposure compared with baseline (P < 0.001). In conclusion, short-term rinsing with room temperature milk proteins did not robustly alter capsaicin-induced oral burning sensation, unpleasantness, somatosensory changes or tongue temperature compared with control. Further studies exploring the effects of increased rinsing time and concentrations are needed in the future.

Effect of aging and tooth loss on sensory function of alveolar mucosa

BACKGROUND

Maintain Quality of Life of elderly denture wearers is one of the most crucial tasks for dentists in the super-aged society. Although external mechanical load on removable dentures has been investigated to minimize a risk of soreness caused by dentures, sensory perception of the alveolar mucosa remains obscure.

OBJECTIVES

This study aimed to investigate effect of aging and tooth loss in sensory function on the alveolar mucosa for deep understanding of the characteristics of pain sensitivity in edentulous individuals.

METHODS

Eighteen edentulous participants(ED), as well as 18 age-matched dentate participants(EC) and 18 young dentate participants(YC), participated in this study. Tactile detection threshold(TDT) and pain threshold(PT) were measured with von Frey filaments (0.125-512 mN). Mechanical pain sensitivity(MPS) after a 2-sec application of 1 kg palpation was assessed with a 0-50-100 Numerical Rating Scale(NRS) (0: no pain, 50: slight pain, and 100: the worst pain imaginable). Furthermore, entropy scores of TDT, PT, and NRS on MPS were calculated.

RESULTS

In both maxilla and mandible, EC showed significantly higher TDT and PT, compared to YC, whereas ED showed significantly lower TDT and PT, compared to EC. NRS on MPS in ED was significantly higher than that in EC. The entropy scores of all the outcome parameters showed no significant difference between groups.

CONCLUSION

Both aging and tooth loss can alter tactile and pain perception in the oral mucosa. This suggest that it might be beneficial to assess sensory function of the alveolar mucosa in edentulous patients clinically in prior to denture fabrication.

Neuropathic and Psychogenic Components of Burning Mouth Syndrome: A Systematic Review

The pathophysiology of primary burning mouth syndrome (BMS) has been extensively debated but is poorly understood despite a large number of hypotheses attempting to explain its etiopathogenic mechanisms. The aim of the present work was to systematically review papers that could provide arguments in favour of the neuropathic and psychogenic components of primary BMS for a better understanding of the disease. This systematic review (SR) was registered in PROSPERO (CRD42021224160). The search was limited to articles in English or French from 1990 to 01 December 2020. A total of 113 articles were considered for data extraction. We divided them into four subgroups: pharmacological and nonpharmacological management studies (n = 23); neurophysiological studies (n = 35); biohistopathological studies (n = 25); and questionnaire-based studies (n = 30). Several of these studies have shown neuropathic involvement at various levels of the neuraxis in BMS with the contribution of quantitative sensory testing (QST), functional brain imaging, and biohistopathological or pharmacologic studies. On the other hand, the role of psychological factors in BMS has also been the focus of several studies and has shown a link with psychiatric disorders such as anxiety and/or depression symptoms. Depending on the patient, the neuropathic and psychogenic components may exist simultaneously, with a preponderance of one or the other, or exist individually. These two components cannot be dissociated to define BMS. Consequently, BMS may be considered nociplastic pain.

Unilateral lingual nerve transection alters jaw-tongue coordination during mastication in pigs

During chewing, movements and deformations of the tongue are coordinated with jaw movements to manage and manipulate the bolus and avoid injury. Individuals with injuries to the lingual nerve report both tongue injuries due to biting and difficulties in chewing, primarily because of impaired bolus management, suggesting that jaw-tongue coordination relies on intact lingual afferents. Here, we investigate how unilateral lingual nerve (LN) transection affects jaw-tongue coordination in an animal model (pig, Sus scrofa). Temporal coordination between jaw pitch (opening-closing) and 1) anteroposterior tongue position (i.e., protraction-retraction), 2) anteroposterior tongue length, and 3) mediolateral tongue width was compared between pre- and post-LN transection using cross-correlation analyses. Overall, following LN transection, the lag between jaw pitch and the majority of tongue kinematics decreased significantly, demonstrating that sensory loss from the tongue alters jaw-tongue coordination. In addition, decrease in jaw-tongue lag suggests that, following LN transection, tongue movements and deformations occur earlier in the gape cycle than when the lingual sensory afferents are intact. If the velocity of tongue movements and deformations remains constant, earlier occurrence can reflect less pronounced movements, possibly to avoid injuries. The results of this study demonstrate that lingual afferents participate in chewing by assisting with coordinating the timing of jaw and tongue movements. The observed changes may affect bolus management performance and/or may represent protective strategies because of altered somatosensory awareness of the tongue.NEW & NOTEWORTHY Chewing requires coordination between tongue and jaw movements. We compared the coordination of tongue movements and deformation relative to jaw opening-closing movements pre- and post-lingual nerve transection during chewing in pigs. These experiments reveal that the timing of jaw-tongue coordination is altered following unilateral disruption of sensory information from the tongue. Therefore, maintenance of jaw-tongue coordination requires bilateral sensory information from the tongue.

Multisensory modulation of experimentally evoked perceptual distortion of the face

BACKGROUND

Chronic oro-facial pain patients often perceive the painful face area as "swollen" without clinical signs, that is a perceptual distortion (PD). Local anaesthetic (LA) injections in healthy participants are also associated with PD.

OBJECTIVE

The aim was to explore whether PD evoked by LA into the infraorbital region could be modulated by adding mechanical stimulation (MS) to the affected area.

METHODS

Mechanical stimulation was given with a brush and a 128-mN von Frey filament. Firstly, sixty healthy participants were randomly divided into three groups: (i) LA control, (ii) LA with MS, (iii) isotonic solution (ISO) with MS as an additional control condition. To further examine the role of a multisensory modulation, an additional experiment was conducted. Twenty participants received LA with MS (filament) in addition to visual feedback of their distorted face. The results of the two experiments are presented together.

RESULTS

All three LA groups experienced PD; per contra, PD was not reported in the ISO group. MS alone did not change the magnitude of PD: brush (P = .089), filament (P = .203). However, when the filament stimulation was combined with additional visual information of a distorted face, there was observable decrease in PD (P = .002).

CONCLUSION

The findings indicate the importance of multisensory integration for PD and represent a significant step forward in the understanding of the factors that may influence this common condition. Future studies are encouraged to investigate further the cortical processing for possible implications for PD in pain management.