Acute and Chronic Pain from Facial Skin and Oral Mucosa: Unique Neurobiology and Challenging Treatment

Nociceptor Neurons Facilitate Orthodontic Tooth Movement via Piezo2 in Mice

Multiple sensory afferents, including mechanosensitive and nociceptive nerves, are projected to the periodontium. Peptidergic afferents expressing transient receptor potential vanilloid 1 (TRPV1), a receptor for capsaicin, mediate pain caused by orthodontic forces. However, their role in orthodontic force-induced alveolar bone remodeling is poorly understood as is the contribution of mechanosensitive ion channels such as Piezo2 in nociceptive nerves. To investigate this role, we studied orthodontic tooth movement and alveolar bone remodeling using neural manipulations and genetic mouse models. Chemical ablation of TRPV1-expressing afferents localized to the trigeminal ganglia decreased orthodontic force-induced tooth movement and the number of osteoclasts in alveolar bone on the compression side. The extent of the force-induced increase in the ratio of receptor activator of nuclear factor kappa-B ligand/osteoprotegerin in the periodontium was modestly decreased in the chemical ablation group. Furthermore, chemogenetic silencing of TRPV1-lineage afferents reduced orthodontic tooth movement and the number of osteoclasts. Piezo2 was expressed in most periodontal afferents, and chemogenetic inhibition of Piezo2-expressing neurons decreased orthodontic tooth movement and the number of osteoclasts. In addition, the conditional knockout of Piezo2 in TRPV1-lineage afferents decreased orthodontic tooth movement and the number of osteoclasts. Overall, these results suggest that nociceptor neurons play critical roles in orthodontic force-induced alveolar bone remodeling and that the mechanical activation of neuronal Piezo2 in nociceptive nerves facilitates orthodontic tooth movement and associated alveolar bone remodeling.

Ageing-Related Macrophage Polarisation in the Trigeminal Ganglion Enhances Incisional Intraoral Pain

OBJECTIVE

Although macrophage polarisation in the trigeminal ganglion (TG) is crucial in orofacial pain hypersensitivity, the effect of ageing-related changes and their involvement in intra-oral nociception remains unclear. We assessed the effect of ageing-related macrophage polarisation in TG on intra-oral mechanical pain hypersensitivity following palatal mucosal incision using senescence-accelerated mice (SAM)-prone8 (SAMP8) and SAM-resistant 1 (SAMR1).

MATERIALS AND METHODS

Mechanical head-withdrawal reflex threshold (MHWRT) of the palatal mucosa was measured for 21 days after palatal mucosal incision. On days 3 and 14, the abundance of Iba-1-immunoreactive (IR) cells, CD11c-IR cells (pro-inflammatory macrophages (M1)), C-C motif chemokine ligand 2 (CCL2)-IR M1-macrophages, CD206-IR cells (anti-inflammatory macrophages (M2)) and transforming growth factor-β (TGF-β)-IR M2-macrophages in the TG was analysed. The effect of continuous intra-TG administration of CCL2-neutralising antibody or recombinant-CCL2 on MHWRT was examined.

RESULTS

Incision-induced decrease in MHWRT was enhanced in SAMP8 compared with that in SAMR1. On days 3 and 14, the number of CCL2-IR M1-macrophages in TG was increased in SAMP8 compared with that in SAMR1. CCL2-neutralising antibody suppressed, whereas recombinant-CCL2 increased pain hypersensitivity in SAMP8.

CONCLUSIONS

Mechanical pain hypersensitivity after oral mucosal injury is potentiated and sustained by age-related enhancement of CCL2 signalling via M1-macrophage hyperactivation in TG.

Therapeutic effectiveness of keratinized mucosa augmentation for functioning dental implants: A systematic review and meta-analysis

PURPOSE

This study aimed to provide the latest updates on the therapeutic effectiveness of keratinized mucosa (KM) augmentation using autogenous soft tissue grafts for dental implants retaining prostheses.

STUDY SELECTION

A systematic search of electronic databases was conducted on autogenous soft tissue grafts to create and/or augment KM for functioning dental implants. Two investigators independently extracted data from the selected 11 clinical studies, including 290 participants, from the initially retrieved 573 publications.

RESULTS

A lack of KM surrounding dental implants was associated with greater mucosal inflammation. A free gingival graft (FGG) was used to increase the KM width, and a connective tissue graft (CTG) was used to manage peri-implant mucosal recession (MR). The weighted mean gain in KM was 2.6 mm from the selected FGG studies, with a significant reduction in mucosal inflammation and no changes in crestal bone levels for up to 4 years. The weighted mean reduction in MR was 2 mm in selected CTG studies.

CONCLUSIONS

A lack of KM negatively affects soft tissue health around dental implants. FGG was effective in increasing KM and reducing mucosal inflammation, whereas CTG was effective in decreasing MR.

Melatonin alleviates oral epithelial cell inflammation via Keap1/Nrf2 signaling

BACKGROUND

Oral mucosal diseases manifest primarily as inflammatory conditions. These diseases affect approximately half a billion people worldwide.

OBJECTIVE

Novel and effective strategies for treating inflammatory diseases of the oral mucosa have great potential for improving patient outcomes, and warrant study.

METHODS

The impact of melatonin on inflammation was investigated using RAW264.7 macrophages and HOEC and HSC-3 oral epithelial cells.

RESULTS

Melatonin decreased macrophage-induced inflammation by acting through the melatonin receptor MTNR1A. Additionally, melatonin mitigated macrophage-induced inflammation in oral epithelial cells. Importantly, the results demonstrated that the effects of melatonin on oral epithelial inflammation were mediated through the KEAP1/Nrf2 signaling pathway.

CONCLUSION

These findings will contribute to the development of innovative therapies for inflammatory conditions affecting the oral epithelium.

Methylcobalamin as a candidate for chronic peripheral neuropathic pain therapy: review of molecular pharmacology actiona

Chronic peripheral neuropathic pain therapy currently focuses on modulating neuroinflammatory conditions. Methylcobalamin (MeCbl), a neuroregenerative agent, modulates neuroinflammation. This review aimed to explore the molecular pharmacology action of MeCbl as a chronic peripheral neuropathic pain therapeutic agent. MeCbl plays a role in various cellular processes and may have therapeutic potential in neurodegenerative diseases. Intracellular MeCbl modulates inflammation by regulating the activity of T lymphocytes and natural killer cells as well as secretion of inflammatory cytokines, namely, tumor necrosis factor-α, interleukin-6, interleukin-1β, epidermal growth factor, and neuronal growth factor. MeCbl can reduce pain symptoms in chronic neuropathic pain conditions by decreasing excitation and hyperpolarization-induced ion channel activity in medium-sized dorsal root ganglion (DRG) neurons and the expression of transient receptor potential ankyrin 1, transient receptor potential cation channel subfamily M member 8, phosphorylated p38MAPK, transient receptor potential cation channel subfamily V members 1 and 4 in the DRG, and the voltage-gated sodium channel in axons.

Evaluating the Influence of Acute and Chronic Orofacial Pains on the Overall Comprehensive Quality of Life

Background Orofacial discomfort refers to various disorders that affect the mouth, jaws, and face. These conditions may substantially influence a person's quality of life (QoL). This kind of pain may be categorised into two primary classifications: acute and chronic. Acute orofacial pain (OFP) usually occurs suddenly and lasts for a short period. It is commonly caused by specific factors such as dental treatments, traumas, or infections. Hence, this study aimed to assess the influence of acute and chronic orofacial discomfort on the overall QoL. Methodology This research used a convenience sample to gather data from the five groups. It was conducted as a cross-sectional study. Four categories of OFP syndromes were utilised: temporomandibular disorders (TMDs), atypical dental pain (ADP), trigeminal neuralgia (TN), and persistent dentoalveolar pain disorder (PDAP). In addition, a control group consisting of individuals who did not experience any discomfort was also included in the study. Participants received a standardised explanation of the questionnaires utilised, and in most instances, they completed them at the clinic under the supervision of one of the investigators. Results The correlations between each version of the Oral Health Impact Profile (OHIP) were statistically significant (p < 0.001), with correlation values ranging from 0.92 to 0.97. When comparing the occurrence of OHIP items across the four pain types, we identified 18 variations that exceeded the 35% prevalence threshold we established for identifying important items that frequently occur out of the 315 comparisons. The question "Have you had a painful aching in your mouth?" showed a low frequency in patients with TN, TMD, and ADP but a significant prevalence in patients with PDAP (90%). This difference in prevalence across pain types was the biggest seen. The question that seemed to distinguish between the pain categories most effectively was "Have you experienced a toothache?" This question had a high occurrence in PDAP (65%) and ADP (60%), perhaps allowing for differentiating these two diseases from TN and TMD. The highest prevalence differences, over 30%, were most often seen when PDAP was included as one of the disorders being compared. ADP had the fewest variances, over 30%, occurring just seven times. Conclusion Both acute and chronic OFPs have a major negative influence on QoL, but they affect it differently and to differing extents. Injury-related acute pain obviously poses rapid and severe restrictions on physical function and causes temporary psychological distress and temporary social exclusion. On the other hand, chronic pain for the patient always implies being locked in a physical world that does not allow him or her to bypass physical limitations, psychological disorders remain constant, and isolation from other people persists for life.

Sublingual Dissolving Microneedle (SLDMN)-Based Vaccine for Inducing Mucosal Immunity against SARS-CoV-2

The coronavirus pandemic has accelerated the development of next-generation vaccination technology to combat future pandemic outbreaks. Mucosal vaccination effectively protects the mucosal surfaces, the primary sites of viral entry, by inducing the secretion of immunoglobulin A (IgA) and humoral IgG. Here, a dissolving microneedle (DMN) is adopted as a mucosal vaccine delivery platform to directly penetrate the sublingual site, which is rich in antigen-presenting cells (APCs) and lymphoid tissues. The sublingual dissolving microneedle (SLDMN) vaccination platform comprised a micropillar-based compartment and a 3D-printed SLDMN applicator as a substitute for the DMN patch. The penetration efficacy of SLDMNs is assessed using in vitro optical coherence tomography (OCT) and in vivo histological analysis. The efficacy of SLDMN is also evaluated in a vaccine form using the recombinant spike (S1) protein of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Furthermore, SLDMN is used to challenge transgenic mice expressing human angiotensin-converting enzyme 2 (hACE2) receptors. Its effects are evaluated on antibody production, survival rate, and inflammation attenuation after infection compared to the intramuscular (IM) injections. Overall, SLDMN effectively induced mucosal immunity via IgA secretion, attenuated lung inflammation, and lowered the levels of cytokines and chemokines, which may prevent the "cytokine storm" after SARS-CoV-2 infection.

Functional drug-delivery hydrogels for oral and maxillofacial wound healing

The repair process for oral and maxillofacial injuries involves hemostasis, inflammation, proliferation, and remodeling. Injury repair involves a variety of cells, including platelets, immune cells, fibroblasts, and various cytokines. Rapid and adequate healing of oral and maxillofacial trauma is a major concern to patients. Functional drug-delivery hydrogels play an active role in promoting wound healing and have shown unique advantages in wound dressings. Functional hydrogels promote wound healing through their adhesive, anti-inflammatory, antioxidant, antibacterial, hemostatic, angiogenic, and re-epithelialization-promoting properties, effectively sealing wounds and reducing inflammation. In addition, functional hydrogels can respond to changes in temperature, light, magnetic fields, pH, and reactive oxygen species to release drugs, enabling precise treatment. Furthermore, hydrogels can deliver various cargos that promote healing, including nucleic acids, cytokines, small-molecule drugs, stem cells, exosomes, and nanomaterials. Therefore, functional drug-delivery hydrogels have a positive impact on the healing of oral and maxillofacial injuries. This review describes the oral mucosal structure and healing process and summarizes the currently available responsive hydrogels used to promote wound healing.

Transoral endoscopic thyroidectomy vestibular approach as a safe and feasible alternative to open thyroidectomy: a systematic review and meta-analysis

BACKGROUND

Transoral endoscopic thyroidectomy vestibular approach (TOETVA) is a scarless alternative to open thyroidectomy (OT). This systematic review and meta-analysis aimed to synthesize evidence comparing the intraoperative and postoperative outcomes of TOETVA and OT.

METHODS

A systematic literature search of PubMed, Web of Science, the Cochrane Library, and Google Scholar was performed to identify studies comparing the outcomes of TOETVA and OT published before February 2023. The outcomes of interest were operative time, intraoperative blood loss, hospital stay, postoperative pain, number of central lymph nodes retrieved, number of metastatic central lymph nodes, and incidences of transient and permanent recurrent laryngeal nerve injury, transient and permanent hypocalcemia, hematoma, and infection.

RESULTS

Thirteen studies published between 2016 and 2022, involving a total of 2889 patients (TOETVA, n =1085; OT, n =1804) were included in this systematic review and meta-analysis. Meta-analysis showed that the TOETVA group had a significantly longer overall operative time (weighted mean difference [WMD] 55.19; 95% CI, 39.15, 71.23; P <0.001), longer hospital stay (WMD, 0.27; 95% CI, 0.14, 0.39; P <0.001), and lower pain scores on postoperative day 1 (WMD, -1.41; 95% CI, -2.79, -0.03; P =0.04) than the OT group. Other intraoperative and postoperative outcomes were not significantly different between the groups.

CONCLUSION

TOETVA has a similar safety profile to OT with less postoperative pain, making it an appropriate and more cosmetically appealing alternative to OT for select patients.

Effectiveness of Photobiomodulation in Reducing Pain of Oral Mucosal Diseases: A Case Series

Introduction

Pain management becomes important in the treatment of oral mucosal diseases since it can impair the quality of life. Photobiomodulation (PBM) as an alternative therapy, has potency in reducing pain through several mechanisms targeting peripheral nerves in the target tissue.

Purpose

To discuss the effectiveness of PBM in the management of four cases of oral mucosal diseases.

Case

Four patients, two females and two males, with an age ranging from 24 to 63 years came to the Oral Medicine Department complaining of painful lesions in their oral cavity. Three cases showed ulceration of the oral mucosa and had been diagnosed with recurrent aphthous stomatitis, recalcitrant chronic ulcer, and non-specific chronic sialadenitis. One patient who complained of intense pain and swelling on the right side of the face was diagnosed with post-herpetic neuralgia (PHN).

Case Management

PBM was administered in all four cases (976 nm diode laser, three cases with spot size 0.01 cm², fluency 10 J/cm², and one case with spot size 0.5 cm²; fluency 3 J/cm²). Visual analog scale (VAS) control was performed before and after the PBM at each visit. The recorded VAS results show a reduction in pain that started at the post-laser time, with VAS before PBM ranging from 5 to 7 and after PBM ranging from 0 to 4. Three patients were given triamcinolone acetonide 0.1%, chlorhexidine gluconate 0.2% mouthwash, petroleum jelly, and multivitamins. One patient was given mefenamic acid and multivitamins.

Conclusion

PBM can be a useful adjunctive treatment to relieve the pain of oral mucosal diseases due to its ability to reduce pain intensity.

Substance P aggravates ligature-induced periodontitis in mice

Periodontitis is one of the most common oral diseases in humans, affecting over 40% of adult Americans. Pain-sensing nerves, or nociceptors, sense local environmental changes and often contain neuropeptides. Recent studies have suggested that nociceptors magnify host response and regulate bone loss in the periodontium. A subset of nociceptors projected to periodontium contains neuropeptides, such as calcitonin gene-related peptide (CGRP) or substance P (SP). However, the specific roles of neuropeptides from nociceptive neural terminals in periodontitis remain to be determined. In this study, we investigated the roles of neuropeptides on host responses and bone loss in ligature-induced periodontitis. Deletion of tachykinin precursor 1 (Tac1), a gene that encodes SP, or treatment of gingiva with SP antagonist significantly reduced bone loss in ligature-induced periodontitis, whereas deletion of calcitonin related polypeptide alpha (Calca), a gene that encodes CGRP, showed a marginal role on bone loss. Ligature-induced recruitment of leukocytes, including neutrophils, and increase in cytokines leading to bone loss in periodontium was significantly less in Tac1 knockout mice. Furthermore, intra-gingival injection of SP, but not neurokinin A, induced a vigorous inflammatory response and osteoclast activation in alveolar bone and facilitated bone loss in ligature-induced periodontitis. Altogether, our data suggest that SP plays significant roles in regulating host responses and bone resorption in ligature-induced periodontitis.

In Vivo Calcium Imaging of Neuronal Ensembles in Networks of Primary Sensory Neurons in Intact Dorsal Root Ganglia

Ca2+ imaging can be used as a proxy for cellular activity, including action potentials and various signaling mechanisms involving Ca2+ entry into the cytoplasm or the release of intracellular Ca2+ stores. Pirt-GCaMP3-based Ca2+ imaging of primary sensory neurons of the dorsal root ganglion (DRG) in mice offers the advantage of simultaneous measurement of a large number of cells. Up to 1,800 neurons can be monitored, allowing neuronal networks and somatosensory processes to be studied as an ensemble in their normal physiological context at a populational level in vivo. The large number of neurons monitored allows the detection of activity patterns that would be challenging to detect using other methods. Stimuli can be applied to the mouse hindpaw, allowing the direct effects of stimuli on the DRG neuron ensemble to be studied. The number of neurons producing Ca2+ transients as well as the amplitude of Ca2+ transients indicates sensitivity to specific sensory modalities. The diameter of neurons provides evidence of activated fiber types (non-noxious mechano vs. noxious pain fibers, Aβ, Aδ, and C fibers). Neurons expressing specific receptors can be genetically labeled with td-Tomato and specific Cre recombinases together with Pirt-GCaMP. Therefore, Pirt-GCaMP3 Ca2+ imaging of DRG provides a powerful tool and model for the analysis of specific sensory modalities and neuron subtypes acting as an ensemble at the populational level to study pain, itch, touch, and other somatosensory signals.

The degeneration-pain relationship in the temporomandibular joint: Current understandings and rodent models

Temporomandibular disorders (TMD) represent a group of musculoskeletal conditions involving the temporomandibular joints (TMJ), the masticatory muscles and associated structures. Painful TMD are highly prevalent and conditions afflict 4% of US adults annually. TMD include heterogenous musculoskeletal pain conditions, such as myalgia, arthralgia, and myofascial pain. A subpopulations of TMD patients show structural changes in TMJ, including disc displacement or degenerative joint diseases (DJD). DJD is a slowly progressing, degenerative disease of the TMJ characterized by cartilage degradation and subchondral bone remodeling. Patients with DJD often develop pain (TMJ osteoarthritis; TMJ OA), but do not always have pain (TMJ osteoarthrosis). Therefore, pain symptoms are not always associated with altered TMJ structures, which suggests that a causal relationship between TMJ degeneration and pain is unclear. Multiple animal models have been developed for determining altered joint structure and pain phenotypes in response to various TMJ injuries. Rodent models of TMJOA and pain include injections to induce inflammation or cartilage destruction, sustained opening of the oral cavity, surgical resection of the articular disc, transgenic approaches to knockout or overexpress key genes, and an integrative approach with superimposed emotional stress or comorbidities. In rodents, TMJ pain and degeneration occur during partially overlapping time periods in these models, which suggests that common biological factors may mediate TMJ pain and degeneration over different time courses. While substances such as intra-articular pro-inflammatory cytokines commonly cause pain and joint degeneration, it remains unclear whether pain or nociceptive activities are causally associated with structural degeneration of TMJ and whether structural degeneration of TMJ is necessary for producing persistent pain. A thorough understanding of the determining factors of pain-structure relationships of TMJ during the onset, progression, and chronification by adopting novel approaches and models should improve the ability to simultaneously treat TMJ pain and TMJ degeneration.

Capsaicin-induced depolymerization of axonal microtubules mediates analgesia for trigeminal neuropathic pain

ABSTRACT

Capsaicin is a specific agonist of transient receptor potential vanilloid 1 (TRPV1), which is enriched in nociceptors. Capsaicin not only produces acute pain but also leads to long-lasting analgesia in patients with chronic pain. Although capsaicin-induced TRPV1 and Ca 2+ /calpain-dependent ablation of axonal terminals is necessary for long-lasting analgesia, the mechanisms underlying capsaicin-induced ablation of axonal terminals and its association with analgesia are not fully understood. Microtubules are composed of tubulin polymers and serve as a main axonal cytoskeleton maintaining axonal integrity. In this study, we hypothesized that capsaicin would increase the depolymerization of microtubules and lead to axonal ablation and analgesia for trigeminal neuropathic pain. Paclitaxel, a microtubule stabilizer, decreased capsaicin-induced ablation of axonal terminals in time-lapsed imaging in vitro. Capsaicin increases free tubulin in dissociated sensory neurons, which was inhibited by paclitaxel. Consistently, subcutaneous injection of paclitaxel prevented capsaicin-induced axonal ablation in the hind paw skin. Capsaicin administration to the facial skin produced analgesia for mechanical hyperalgesia in mice with chronic constriction injury of the infraorbital nerve, which was prevented by the coadministration of paclitaxel and capsaicin. Whole-mount staining of facial skin showed that paclitaxel reduced capsaicin-induced ablation of peptidergic afferent terminals. Despite the suggested involvement of TRPV1 Ser801 phosphorylation on microtubule integrity, capsaicin-induced analgesia was not affected in TRPV1 S801A knock-in mice. In conclusion, capsaicin-induced depolymerization of axonal microtubules determined capsaicin-induced ablation of nociceptive terminals and the extent of analgesia. Further understanding of TRPV1/Ca 2+ -dependent mechanisms of capsaicin-induced ablation and analgesia may help to improve the management of chronic pain.

Sucrose alleviates capsaicin-induced tongue burning: An in vivo study

Background

Spicy foods are flavorful and stimulate salivation, which is beneficial for individuals with poor appetite. They are also ubiquitous in many regional cuisines, but the chemical compounds in such foods, especially capsaicin from chili peppers, can cause tissue inflammation and generate intolerable burning pain in the oral cavity.

Material and Methods

To identify a potential method to reduce capsaicin-induced burning pain without influencing food flavor, we tested the effects of mouth rinsing with various concentrations of sucrose. Inclusion criteria were good general and oral health, while exclusion criteria were poor baseline smell or taste, capsaicin allergy, and current orofacial pain complaints. To define an appropriate capsaicin dose, participants placed filter paper strips impregnated with 0.003%–0.3% capsaicin on the tip of the tongue and rated burning sensation by visual analog scale (VAS) score.

Results

A 0.1% capsaicin solution induced tongue burning in the midrange (VAS = 6.33 ± 0.52) and so was used for subsequent tests. We then examined the efficacy concentration of sucrose for reducing tongue burning by recording VAS scores at multiple time points following a 15-s oral rinse with various aqueous sucrose solutions (5%, 10%, and 20%), milk, or pure water (control) after 0.1% capsaicin application. Scores were compared at each time point by one-way ANOVA with post hoc Dunnett’s tests. A 15-s rinse with 20% sucrose significantly alleviated burning pain compared to water rinse at 45, 60, 120, and 180 s after capsaicin exposure.

Conclusions

Thus, periodic rinsing with 20% aqueous sucrose may help promote spicy food consumption among individuals with poor appetite.

Key words:Capsaicin, sucrose, burning sensation.

Insight into the Role of Psychological Factors in Oral Mucosa Diseases

With the development of psychology and medicine, more and more diseases have found their psychological origins and associations, especially ulceration and other mucosal injuries, within the digestive system. However, the association of psychological factors with lesions of the oral mucosa, including oral squamous cell carcinoma (OSCC), burning mouth syndrome (BMS), and recurrent aphthous stomatitis (RAS), have not been fully characterized. In this review, after introducing the association between psychological and nervous factors and diseases, we provide detailed descriptions of the psychology and nerve fibers involved in the pathology of OSCC, BMS, and RAS, pointing out the underlying mechanisms and suggesting the clinical indications.

Natural Products for the Prevention and Treatment of Oral Mucositis-A Review

Cancer, a major world public health problem, is associated with chemotherapy treatments whose administration leads to secondary concerns, such as oral mucositis (OM). The OM disorder is characterized by the presence of ulcers in the oral mucosa that cause pain, bleeding, and difficulty in ingesting fluids and solids, or speaking. Bioactive compounds from natural sources have arisen as an effective approach for OM. This review aims to summarize the new potential application of different natural products in the prevention and treatment of OM in comparison to conventional ones, also providing a deep insight into the most recent clinical studies. Natural products, such as Aloe vera, Glycyrrhiza glabra, Camellia sinensis, Calendula officinalis, or honeybee crops, constitute examples of sources of bioactive compounds with pharmacological interest due to their well-reported activities (e.g., antimicrobial, antiviral, anti-inflammatory, analgesic, or wound healing). These activities are associated with the bioactive compounds present in their matrix (such as flavonoids), which are associated with in vivo biological activities and minimal or absent toxicity. Finally, encapsulation has arisen as a future opportunity to preserve the chemical stability and the drug bioa vailability of bioactive compounds and, most importantly, to improve the buccal retention period and the therapeutic effects.