Variability in Capsaicin-stimulated Calcitonin Gene-related Peptide Release from Human Dental Pulp

Prevalence of Endodontically Treated Teeth in Patients Undergoing Treatment for Painful Temporomandibular Disorders: An Observational Study

INTRODUCTION

Temporomandibular disorders (TMDs) and endodontic pain often present overlapping symptoms, complicating the diagnosis and treatment of patients experiencing orofacial pain.

METHODS

This observational retrospective cohort study aims to determine the prevalence of endodontically treated teeth on the side of pain complaint in patients with TMD, and to explore the association between TMD diagnoses and the presence of endodontically treated teeth. Dental records of patients treated at the TMD and Pain clinic at the Federal University of Uberlândia was reviewed. The study included 85 patients, and demographic data, TMD diagnosis, and the side of referred pain were extracted from the records. Diagnostic imaging exams, including panoramic and periapical radiographs, and cone-beam computed tomography, were analyzed to count the number of endodontically treated teeth on each side of the mouth.

RESULTS

The study population consisted of 88% (n = 70) women, with a mean age of 40.5 ± 16.3 years. A significant association was found between the side of TMD pain and the number of endodontically treated teeth, with more treated teeth on the side of pain complaint (median = 1) compared to the pain-free side (median = 0), with P < .001. When analyzing specific TMD diagnoses, the association was significant in muscle-related and mixed TMD diagnoses but not in joint-related TMD pain. Additionally, a binary analysis confirmed this association, showing that patients were significantly more likely to have at least 1 endodontically treated tooth on the side of TMD pain compared to the nonpain side (χ2 = 13.06, P = .0003).

CONCLUSION

This study underscores the importance of comprehensive diagnostic evaluations in patients with orofacial pain to avoid unnecessary endodontic treatments and ensure appropriate care. Further research is needed to explore the underlying mechanisms linking endodontic and TMD pain and to validate these findings in diverse populations.

Neural Regulations in Tooth Development and Tooth-Periodontium Complex Homeostasis: A Literature Review

The tooth-periodontium complex and its nerves have active reciprocal regulation during development and homeostasis. These effects are predominantly mediated by a range of molecules secreted from either the nervous system or the tooth-periodontium complex. Different strategies mimicking tooth development or physiological reparation have been applied to tooth regeneration studies, where the application of these nerve- or tooth-derived molecules has been proven effective. However, to date, basic studies in this field leave many vacancies to be filled. This literature review summarizes the recent advances in the basic studies on neural responses and regulation during tooth-periodontium development and homeostasis and points out some research gaps to instruct future studies. Deepening our understanding of the underlying mechanisms of tooth development and diseases will provide more clues for tooth regeneration.

Interplay of Oral, Mandibular, and Facial Disorders and Migraine

PURPOSE OF THE REVIEW

Migraine and other primary headache disorders can be localized in the face resembling facial or dental pain, indicating the influence of the trigeminovascular system in the structures innervated by the maxillary (V2) and mandibulary (V3) branches of the trigeminal nerve. Disorders of oral and craniofacial structures may influence primary headache disorders. In the current article, we review the potential links of this interplay.

RECENT FINDINGS

This interplay may be related to anatomy, with the trigeminal pathway and the involvement of both peripheral and central mechanisms, and the presence of calcitonin gene-related peptide (CGRP), a key mediator in migraine pathophysiology. CGRP is also involved in the pathophysiology of temporomandibular disorders (TMD) and their comorbidity with migraine and is also implicated in dental and periodontal pathology. Inflammatory and pathological processes of these structures and their trigeminal nociceptive pathways may influence the trigeminovascular system and consequently may exacerbate or even potentially trigger migraine.

Exploring the effect of the "quaternary regulation" theory of "peripheral nerve-angiogenesis-osteoclast-osteogenesis" on osteoporosis based on neuropeptides

Osteoporosis is a common bone metabolic disease among the middle-aged and elderly, with its high incidence rate and a major cause of disability and mortality. Early studies found that bone metabolic homeostasis is achieved through osteogenesis-osteoclast coupling. Although current anti-osteoporosis drugs can attenuate bone loss caused by aging, they present specific side effects. With the discovery of CD31^hi Emcn^hi blood vessels in 2014, the effect of H-type blood vessels on bone metabolism has been valued by researchers, and the ternary regulation theory of bone metabolism of "Angiogenesis-Osteoclast-Osteogenesis" has also been recognized. Nowadays, more studies have confirmed that peripheral nerves substantially impact bone metabolism. However, due to the complex function of peripheral nerves, the crosstalk mechanism of "Peripheral nerve-Angiogenesis-Osteoclast-Osteogenesis" has not yet been fully revealed. Neuropeptide serves as signaling molecules secreted by peripheral nerves that regulate blood vessels, osteoblasts, and osteoclasts' functions. It is likely to be the breakthrough point of the quaternary regulation theory of "Peripheral nerve-Angiogenesis-Osteoclast-Osteogenesis". Here, we discuss the effect of peripheral nerves on osteoporosis based on neuropeptides.

CGRP release in an experimental human trigeminal pain model

Background

Migraine and trigemino-autonomic cephalalgia attacks are associated with an increase of α-calcitonin-gene related peptide levels in the ipsilateral jugular vein. It is however unknown whether trigeminal pain stimulation in healthy subjects without headache disorders also induces increase of calcitonin-gene related peptide levels.

Findings

We measured α-calcitonin-gene related peptide levels in eight healthy subjects after subcutaneous injection of capsaicin in the forehead and in the mandibular region and after injection of sodium chloride in the forehead. We observed a significant increase of α-calcitonin-gene related peptide level only after injection of capsaicin in the forehead (i.e. first trigeminal branch). We also observed trigemino-autonomic activation (lacrimation, rhinorrhea etc.) only after injection of capsaicin in the forehead.

Conclusion

Increase of α-calcitonin-gene related peptide levels do not only occur in primary headache attacks but also after experimental trigeminal pain of the first branch. This finding suggests that α-calcitonin-gene related peptide elevation is, at least an additional, unspecific effect of first trigeminal branch stimulation following pain activation and not a specific mechanism of idiopathic headache disorders.

Effects of CGRP-Primed Dental Pulp Stem Cells on Trigeminal Sensory Neurons

Dental pulp stem cells (DPSCs) are important in tooth physiology, contributing to development, repair, regeneration, and immunomodulatory processes. However, their role in inflammatory mechanisms underlying pulpitis is not well understood. We evaluated the influence of DPSCs stimulated with calcitonin gene-related peptide (CGRP), a proinflammatory neuropeptide, on the expression of mediators released from DPSCs and the effect of these mediators on sensory neuron activity. Human DPSCs were treated with either control media or media containing CGRP (10^-8 M) for 7 d, and the conditioned media (CM) containing DPSC-released mediators was collected. The expression of cytokines and chemokines from DPSCs was evaluated by reverse transcription quantitative polymerase chain reaction. The effects of the CM from CGRP-primed DPSCs (primed DPSC-CM) were evaluated on sensory afferents by using primary cultures of mouse trigeminal neurons and an organotypic model of cultured human pulp slices. Mouse trigeminal neurons and human pulp explants were pretreated for 24 h with control or primed DPSC-CM and then stimulated with capsaicin. Afferent activity was measured by quantifying the response to capsaicin via live cell calcium imaging in mouse neurons and CGRP released from pulp explants. Gene expression analysis showed that primed DPSCs overexpressed some proinflammatory cytokines and chemokines, including chemokines CXCL1 and CXCL8, which are both agonists of the receptor CXCR2 expressed in sensory neurons. Primed DPSC-CM increased human pulp sensory afferent activity as compared with control DPSC-CM. Similarly, primed DPSC-CM increased the intensity of calcium responses in cultured mouse trigeminal neurons. Furthermore, the CXCR2 antagonist SB225002 prevented trigeminal neuron sensitization to capsaicin induced by primed DPSC-CM. In conclusion, mediators released by DPSCs, primed with the proinflammatory mediator CGRP, induce neuronal sensitization through CXCR2 receptor. These data suggest that DPSCs might contribute to pain symptoms that develop in pulpitis.

Dental nerves: a neglected mediator of pulpitis

As one of the most densely innervated tissues, the dental pulp contains abundant nerve fibres, including sensory, sympathetic and parasympathetic nerve fibres. Studies in animal models and human patients with pulpitis have revealed distinct alterations in protein expression and histological appearance in all types of dental nerve fibres. Various molecules secreted by neurons, such as classical neurotransmitters, neuropeptides and amino acids, not only contribute to the induction, sensitization and maintenance of tooth pain, but also regulate non-neuronal cells, including fibroblasts, odontoblasts, immune cells and vascular endothelial cells. Dental nerves are particularly important for the microcirculatory and immune responses in pulpitis via their release of a variety of functional substances. Further, nerve fibres are found to be involved in dental soft and hard tissue repair. Thus, understanding how dental nerves participate in pulpitis could have important clinical ramifications for endodontic treatment. In this review, the roles of dental nerves in regulating pulpal inflammatory processes are highlighted and their implications for future research on this topic are discussed.

Effect of intracanal diode laser application and low-level laser therapy on CGRP change

The aim of this study was to investigate the effect of a placebo, intracanal diode laser application, and low-level laser therapy (LLLT) on the change of the total amount of calcitonin gene-related peptide (CGRP) in the gingival crevicular fluid (GCF) (split-mouth study design). GCF sampling was performed on a contralateral tooth and experimental tooth (root canal-treated tooth) of thirty-nine patients. The patients were divided into three groups (n = 13), as follows: placebo (mock laser application), intracanal laser application, and LLLT. GCF sampling was repeated at the same sites (experimental and control teeth) one week after root canal treatment. The data were analyzed using the Pearson's correlation analysis and the independent-samples t-tests (p=0.05). In the placebo group, the total CGRP level changes in the GCF before and after treatment was significantly higher for experimental teeth than for control teeth (p<0.05). However, there was no significant difference between experimental and control teeth in the intracanal laser application and LLLT groups (p > 0.05). Intracanal laser application and low-level laser therapy have immunomodulation effects linked to the modulation of the total amount of CGRP in the GCF.

TRPV1-Like Immunoreactivity in the Human Locus K, a Distinct Subregion of the Cuneate Nucleus

The presence of transient receptor potential vanilloid type-1 receptor (TRPV1)-like immunoreactivity (LI), in the form of nerve fibres and terminals, is shown in a set of discrete gray matter subregions placed in the territory of the human cuneate nucleus. We showed previously that those subregions share neurochemical and structural features with the protopathic nuclei and, after the ancient name of our town, collectively call them Locus Karalis, and briefly Locus K. TRPV1-LI in the Locus K is codistributed, though not perfectly overlapped, with that of the neuropeptides calcitonin gene-related peptide and substance P, the topography of the elements immunoreactive to the three markers, in relation to each other, reflecting that previously described in the caudal spinal trigeminal nucleus. Myelin stainings show that myelinated fibres, abundant in the cuneate, gracile and trigeminal magnocellular nuclei, are scarce in the Locus K as in the trigeminal substantia gelatinosa. Morphometric analysis shows that cell size and density of Locus K neurons are consistent with those of the trigeminal substantia gelatinosa and significantly different from those of the magnocellular trigeminal, solitary and dorsal column nuclei. We propose that Locus K is a special component of the human dorsal column nuclei. Its functional role remains to be determined, but TRPV1 appears to play a part in it.