Immunomodulatory Activities of Periodontal Ligament Stem Cells in Orthodontic Forces-Induced Inflammatory Processes: Current Views and Future Perspectives

Adjunctive therapies in orthodontics: a scoping systematic review

BACKGROUND

Orthodontic tooth movement (OTM) induces physiological and sometimes pathological inflammation in periodontal tissues. This review evaluates the effectiveness of low-level laser therapy (LLLT), vibrational therapy, and probiotics as adjunctive treatments for managing inflammation, pain, and the duration of OTM.

METHODS

Medline via OVID, Cochrane, EMBASE, and Web of Science databases were utilized to identify randomized controlled trials (RCTs) published between January 1990 and November 2023. Studies were selected based on their evaluation of LLLT, vibrational therapy, and probiotics as adjuncts in fixed orthodontic treatment.

RESULTS

LLLT shows promise in enhancing orthodontic tooth movement by accelerating tooth movement and potentially reducing pain. However, disparate study outcomes indicate a need for standardized application protocols. The efficacy of vibrational therapy as an adjunct in OTM remains inconclusive. Some studies in this regard indicate a significant acceleration in OTM but most did not. Probiotic therapy shows potential to improve oral microbiota balance and inflammation but requires more rigorous studies to determine its efficacy and optimal administration methods.

CONCLUSION

Future research should focus on establishing standardized guidelines and protocols to achieve consistent and reliable outcomes across these adjunctive therapies.

Inflammatory Modulation of Toll-like Receptors in Periodontal Ligament Stem Cells: Implications for Periodontal Therapy

Toll-like receptors (TLRs) play a crucial role in the innate immune response, mediating cellular interactions with the microenvironment and influencing periodontal disease progression. This in vitro study aimed to comprehensively characterize the TLR expression profile of periodontal ligament mesenchymal stem/progenitor cells (PDLSCs) and investigate its modulation by inflammatory stimuli associated with periodontal disease. PDLSCs (n = 6) were isolated, selected using anti-STRO-1 antibodies, and cultured to evaluate their colony-forming abilities and stem/progenitor characteristics. Baseline and inflammation-induced TLR expressions were evaluated using RT-PCR and protein analyses following cytokine-mediated stimulation. PDLSCs exhibited the expected stem cell characteristics and expressed multiple TLRs under both conditions. Notably, inflammatory stimulation significantly upregulated TLR1 and TLR2 while downregulating TLR10 (p < 0.05). These findings provide a comprehensive characterization of TLR expression in PDLSCs and demonstrate how inflammation modulates their innate immune profile. The observed shifts in TLR expression may influence PDLSC responses to microbial pathogens and impact their immunomodulatory and regenerative properties in periodontal tissues. Understanding these interactions could contribute to developing targeted strategies for improving PDLSC-based therapies in periodontal disease.

Enhancing Periodontal Ligament Regeneration via PDLSC Delivery Using Electrospun PCL/Collagen/Cellulose Acetate Scaffolds and Collagen Hydrogel Incorporated with Curcumin-Loaded ZIF-8 Nanoparticles

Background

Regenerating periodontal ligament (PDL) tissue is a vital challenge in dentistry that aims to restore periodontal function and aesthetics. This study explores a tissue engineering strategy that combines polycaprolactone (PCL)/collagen/cellulose acetate electrospun scaffolds with collagen hydrogels to deliver curcumin-loaded ZIF-8 nanoparticles fand periodontal ligament stem cells (PDLSCs).

Methods

Scaffolds were fabricated via electrospinningand collagen hydrogels incorporated PDLSCs and curcumin-loaded ZIF-8 nanoparticles (CURZIF-8) were developed using cross-linking. In vitro assays evaluated biocompatibility, anti-inflammatory, and antioxidative properties. In vivo efficacy was assessed in a rat PDL injury model using histological and ELISA analyses examining tissue regeneration and inflammatory cytokine modulation.

Results

In vitro studies demonstrated that the scaffolds effectively supported PDLSC viability and migration. CURZIF-8 hydrogels enhanced anti-inflammatory and antioxidative activities. In vivo study showed that the combined scaffold-hydrogel system significantly promoted PDL regeneration. Tissue levels of bFGF, HGF, and TGF-β that are crucial for tissue repair, angiogenesis, and cell proliferation were evaluated. Whereas, pro-inflammatory cytokines TNF-α and IL-6=were downregulated. Histological analysis confirmed the formation of organized PDL structures and improved bone-cementum integration that arekey indicators of successful periodontal regeneration.

Conclusion

The developed scaffold-hydrogel system facilitates PDL regeneration by modulating inflammation and promoting pro-healing factor expression. This approach shows promise for advancing periodontal tissue engineering and warrants further investigation in clinical settings.

Inflammation and mechanical force-induced bone remodeling

Periodontitis arises from imbalanced host-microbe interactions, leading to dysbiosis and destructive inflammation. The host's innate and adaptive immune responses produce pro-inflammatory mediators that stimulate destructive events, which cause loss of alveolar bone and connective tissue attachment. There is no consensus on the factors that lead to a conversion from gingivitis to periodontitis, but one possibility is the proximity of the inflammation to the bone, which promotes bone resorption and inhibits subsequent bone formation during coupled bone formation. Conversely, orthodontic tooth movement is triggered by the mechanical force applied to the tooth, resulting in bone resorption on the compression side and new bone formation on the tension side. However, the environment around orthodontic brackets readily retains dental plaque and may contribute to inflammation and bone remodeling. The immune, epithelial, stromal, endothelial and bone cells of the host play an important role in setting the stage for bone remodeling that occurs in both periodontitis and orthodontic tooth movement. Recent advancements in single-cell RNA sequencing have provided new insights into the roles and interactions of different cell types in response to challenges. In this review, we meticulously examine the functions of key cell types such as keratinocytes, leukocytes, stromal cells, osteocytes, osteoblasts, and osteoclasts involved in inflammation- and mechanical force-driven bone remodeling. Moreover, we explore the combined effects of these two conditions: mechanical force-induced bone remodeling combined with periodontal disease (chronic inflammation) and periodontally accelerated osteogenic orthodontics (acute transient inflammation). This comprehensive review enhances our understanding of inflammation- and mechanical force-induced bone remodeling.

Mechanical force modulates inflammation and immunomodulation in periodontal ligament cells

Mechanical forces control a multitude of biological responses in various cells and tissues. The periodontal ligament, located between the tooth's root and alveolar bone, is a major tissue compartment that is incessantly subjected to such mechanical stimulation through either normal or abnormal oral functionality. It is now known that mechanical stimulation activates periodontal ligament stem cells (PDLSCs) to modulate periodontal immunity and regulate inflammation - a basic feature of periodontal disease that affects virtually every human during their lifetime. For instance, shear stress induces the expression of immunomodulatory-related gene, indoleamine 2,3-dioxygenase (IDO). IDO cleaves l-tryptophan, resulting in increased l-kynurenine levels that, in turn, further promote regulatory T-cell differentiation and inhibit T cell proliferation. These and other related data reinforce the notion that mechanical stimulation plays a crucial role in controlling inflammation and immunomodulation of periodontal tissues. Further investigations, however, are warranted to evaluate the immunomodulatory features of PDLSCs so as to understand the pathological basis of periodontal disease and translate these into clinical interventions.

Breaking a dogma: orthodontic tooth movement alters systemic immunity

BACKGROUND

The prevailing paradigm posits orthodontic tooth movement (OTM) as primarily a localized inflammatory process. In this study, we endeavor to elucidate the potential ramifications of mechanical force on systemic immunity, employing a time-dependent approach.

MATERIALS AND METHODS

A previously described mouse orthodontic model was used. Ni-Ti. springs were set to move the upper 1st-molar in C57BL/6 mice and the amount of OTM was. measured by µCT. Mice were allocated randomly into four experimental groups, each. corresponding to clinical phases of OTM, relative to force application. Terminal blood. samples were collected and a comprehensive blood count test for 7 cell types as well as. proteome profiling of 111 pivotal cytokines and chemokines were conducted. Two controls. groups were included: one comprised non-treated mice and the other mice with inactivated springs.

RESULTS

Serum immuno-profiling unveiled alterations in cellular immunity, manifesting as. changes in percentages of leukocytes, monocytes, macrophages, neutrophils, and. lymphocytes, alongside key signaling factors in comparison to both control groups. The systemic cellular and molecular alterations triggered by OTM mirrored the dynamics previously described in the local immune response.

CONCLUSIONS

Although the exact interplay between local and systemic immune responses to orthodontic forces require further elucidation, our findings demonstrate a tangible link between the two. Future investigations should aim to correlate these results with human subjects, and strive to delve deeper into the specific mechanisms by which mechanical force modulates the systemic immune response.

Systematic review on effects of experimental orthodontic tooth displacement on brain activation assessed by fMRI

BACKGROUND

Orthodontic treatment is often accompanied by discomfort and pain in patients, which are believed to be a result of orthodontic tooth displacement caused by the mechanical forces exerted by the orthodontic appliances on the periodontal tissues. These lead to change blood oxygen level dependent response in related brain regions.

OBJECTIVE

This systematic review aims to assess the impact of experimental orthodontic tooth displacement on alterations in central nervous system activation assessed by tasked based and resting state fMRI.

MATERIALS AND METHODS

A literature search was conducted using online databases, following PRISMA guidelines and the PICO framework. Selected studies utilized magnetic resonance imaging to examine the brain activity changes in healthy participants after the insertion of orthodontic appliances.

RESULTS

The initial database screening resulted in 791 studies. Of these, 234 were duplicates and 547 were deemed irrelevant considering the inclusion and exclusion criteria. Of the ten remaining potential relevant studies, two were excluded during full-text screening. Eight prospective articles were eligible for further analysis. The included studies provided evidence of the intricate interplay between orthodontic treatment, pain perception, and brain function. All of the participants in the included studies employed orthodontic separators in short-term experiments to induce tooth displacement during the early stage of orthodontic treatment. Alterations in brain activation were observed in brain regions, functional connectivity and brain networks, predominantly affecting regions implicated in nociception (thalamus, insula), emotion (insula, frontal areas), and cognition (frontal areas, cerebellum, default mode network).

CONCLUSIONS

The results suggest that orthodontic treatment influences beyond the pain matrix and affects other brain regions including the limbic system. Furthermore, understanding the orthodontically induced brain activation can aid in development of targeted pain management strategies that do not adversely affect orthodontic tooth movement. Due to the moderate to serious risk of bias and the heterogeneity among the included studies, further clinical trials on this subject are recommended.

Molecular signaling and mechanisms of low-level laser-induced gene expression in cells involved in orthodontic tooth movement

BACKGROUND

The study aimed to observe molecular signaling, including reactive oxygen species (ROS) and mitochondrial membrane potential (ΔΨm), to evaluate the alteration of gene expression by low-level laser therapy (LLLT) and the correlation between its mechanisms and the NF-kB pathway in cells involved in orthodontic tooth movement.

METHODS

Osteoblast-like cells (MG63), immortalized periodontal ligament cells (iPDL), and M1 macrophage-like cells were irradiated by 980-nm LLLT with energy densities of 1 and 10 J/cm2 ΔΨm and intracellular ROS were monitored using fluorescent probes. The changes of mRNA expression were assessed using reverse transcription polymerase chain reaction (RT-PCR). NF-kB inhibitor, ROS scavenger, and ΔΨm suppressor were used to analyze signals associated with the regulation of gene expression. Finally, Western blot analysis was performed to confirm NF-kB signaling after LLLT.

RESULTS

We found the increases of ΔΨm and ROS in all three cell types after LLLT, but no significant difference was observed between 1 and 10 J/cm2 LLLT. Regarding gene expression, some target genes were upregulated in MG63 6 h, 12 h, and 1 day after LLLT and in iPDL cells 12 h and 1 day after LLLT. However, no changes occurred in M1 cells. The inhibitor that significantly reduced most changes in gene expression was NF-kB inhibitor. Western blot analysis showed the increase in p-IkBα level after LLLT in iPDL and MG63, but not in M1.

CONCLUSION

The 980-nm LLLT increased ΔΨm and ROS production in all three cell types. However, changes in gene regulation were found only in MG63 and iPDL cells, which related to the NF-kB pathway.

Osteoimmunology in Periodontitis and Orthodontic Tooth Movement

PURPOSE OF REVIEW

To review the role of the immune cells and their interaction with cells found in gingiva, periodontal ligament, and bone that leads to net bone loss in periodontitis or bone remodeling in orthodontic tooth movement.

RECENT FINDINGS

Periodontal disease is one of the most common oral diseases causing inflammation in the soft and hard tissues of the periodontium and is initiated by bacteria that induce a host response. Although the innate and adaptive immune response function cooperatively to prevent bacterial dissemination, they also play a major role in gingival inflammation and destruction of the connective tissue, periodontal ligament, and alveolar bone characteristic of periodontitis. The inflammatory response is triggered by bacteria or their products that bind to pattern recognition receptors that induce transcription factor activity to stimulate cytokine and chemokine expression. Epithelial, fibroblast/stromal, and resident leukocytes play a key role in initiating the host response and contribute to periodontal disease. Single-cell RNA-seq (scRNA-seq) experiments have added new insight into the roles of various cell types in the response to bacterial challenge. This response is modified by systemic conditions such as diabetes and smoking. In contrast to periodontitis, orthodontic tooth movement (OTM) is a sterile inflammatory response induced by mechanical force. Orthodontic force application stimulates acute inflammatory responses in the periodontal ligament and alveolar bone stimulated by cytokines and chemokines that produce bone resorption on the compression side. On the tension side, orthodontic forces induce the production of osteogenic factors, stimulating new bone formation. A number of different cell types, cytokines, and signaling/pathways are involved in this complex process. Inflammatory and mechanical force-induced bone remodeling involves bone resorption and bone formation. The interaction of leukocytes with host stromal cells and osteoblastic cells plays a key role in both initiating the inflammatory events as well as inducing a cellular cascade that results in remodeling in orthodontic tooth movement or in tissue destruction in periodontitis.