Involvement of nitric oxide in orthodontic tooth movement in rats

Osteocyte Mechanotransduction in Orthodontic Tooth Movement

PURPOSE OF REVIEW

Orthodontic tooth movement is characterized by periodontal tissue responses to mechanical loading, leading to clinically relevant functional adaptation of jaw bone. Since osteocytes are significant in mechanotransduction and orchestrate osteoclast and osteoblast activity, they likely play a central role in orthodontic tooth movement. In this review, we attempt to shed light on the impact and role of osteocyte mechanotransduction during orthodontic tooth movement.

RECENT FINDINGS

Mechanically loaded osteocytes produce signaling molecules, e.g., bone morphogenetic proteins, Wnts, prostaglandins, osteopontin, nitric oxide, sclerostin, and RANKL, which modulate the recruitment, differentiation, and activity of osteoblasts and osteoclasts. The major signaling pathways activated by mechanical loading in osteocytes are the wingless-related integration site (Wnt)/β-catenin and RANKL pathways, which are key regulators of bone metabolism. Moreover, osteocytes are capable of orchestrating bone adaptation during orthodontic tooth movement. A better understanding of the role of osteocyte mechanotransduction is crucial to advance orthodontic treatment. The optimal force level on the periodontal tissues for orthodontic tooth movement producing an adequate biological response, is debated. This review emphasizes that both mechanoresponses and inflammation are essential for achieving tooth movement clinically. To fully comprehend the role of osteocyte mechanotransduction in orthodontic tooth movement, more knowledge is needed of the biological pathways involved. This will contribute to optimization of orthodontic treatment and enhance patient outcomes.

Salivary oxidative stress during and after rapid maxillary expansion

Objectives:

The objectives of the study were to evaluate oxidative stress biomarkers during a rapid maxillary expansion (RME).

Material and Methods:

Fourteen patients were treated with an acrylic RME device, and after treatment, all were followed for 3 months. Saliva samples were collected before activation (baseline), 1st, 10th days after the first activation, and after retention. Periodontal indexes were recorded at baseline and after retention. Nitric oxide (NO) and malondialdehyde (MDA) levels were evaluated.

Results:

NO levels were elevated on the 10th day compared to baseline (P < 0.01), revealing a decrease after retention (P < 0.01). MDA levels were increased on the 10th day and after retention periods compared to baseline (P < 0.01, respectively). Both plaque and gingival indexes increased after retention relative to baseline (P < 0.01, respectively).

Conclusion:

Initial stages of orthopedic force increased salivary oxidative stress biomarkers. Long-term results showed decreased levels of NO, but still high MDA levels. The initially increased NO expression decreased after retention, despite the increase in microbial load at this period which might show the effect of mechanical stimuli to be more effective than the microbial load. MDA levels remained at high levels during the post-retention period, arising a possible consideration for the impact of material properties or deficiencies of oral hygiene. Future long-term evaluations for oxidative stress status and orthodontic appliances would be useful.

Control of Orthodontic Tooth Movement by Nitric Oxide Releasing Nanoparticles in Sprague-Dawley Rats

Orthodontic treatment commonly requires the need to prevent movement of some teeth while maximizing movement of other teeth. This study aimed to investigate the influence of locally injected nitric oxide (NO) releasing nanoparticles on orthodontic tooth movement in rats.

MATERIALS AND METHODS

Experimental tooth movement was achieved with nickel-titanium alloy springs ligated between the maxillary first molar and ipsilateral incisor. 2.2 mg/kg of silica nanoparticles containing S-nitrosothiol groups were injected into the mucosa just mesial to 1^st molar teeth immediately prior to orthodontic appliance activation. NO release from nanoparticles was measured in vitro by chemiluminescence. Tooth movement was measured using polyvinyl siloxane impressions. Bones were analyzed by microcomputed tomography. Local tissue was assessed by histomorphometry.

RESULTS

Nanoparticles released a burst of NO within the first hours at approximately 10 ppb/mg particles that diminished by 10 × to approximately 1 ppb/mg particles over the next 1-4 days, and then diminished again by tenfold from day 4 to day 7, at which point it was no longer measurable. Molar but not incisor tooth movement was inhibited over 50% by injection of the NO releasing nanoparticles. Inhibition of molar tooth movement occurred only during active NO release from nanoparticles, which lasted for approximately 1 week. Molar tooth movement returned to control levels of tooth movement after end of NO release. Alveolar and long bones were not impacted by injection of the NO releasing nanoparticles, and serum cyclic guanosine monophosphate (cGMP) levels were not increased in animals that received the NO releasing nanoparticles. Root resorption was decreased and periodontal blood vessel numbers were increased in animals with appliances that were injected with the NO releasing nanoparticles as compared to animals with appliances that did not receive injections with the nanoparticles.

CONCLUSION

Nitric oxide (NO) release from S-nitrosothiol containing nanoparticles inhibits movement of teeth adjacent to the site of nanoparticle injection for 1 week. Additional studies are needed to establish biologic mechanisms, optimize efficacy and increase longevity of this orthodontic anchorage effect.

Role of nitric oxide in orthodontic tooth movement (Review)

Nitric oxide (NO) is an ubiquitous signaling molecule that mediates numerous cellular processes associated with cardiovascular, nervous and immune systems. NO also plays an essential role in bone homeostasis regulation. The present review article summarized the effects of NO on bone metabolism during orthodontic tooth movement in order to provide insight into the regulatory role of NO in orthodontic tooth movement. Orthodontic tooth movement is a process in which the periodontal tissue and alveolar bone are reconstructed due to the effect of orthodontic forces. Accumulating evidence has indicated that NO and its downstream signaling molecule, cyclic guanosine monophosphate (cGMP), mediate the mechanical signals during orthodontic-related bone remodeling, and exert complex effects on osteogenesis and osteoclastogenesis. NO has a regulatory effect on the cellular activities and functional states of osteoclasts, osteocytes and periodontal ligament fibroblasts involved in orthodontic tooth movement. Variations of NO synthase (NOS) expression levels and NO production in periodontal tissues or gingival crevicular fluid (GCF) have been found on the tension and compression sides during tooth movement in both orthodontic animal models and patients. Furthermore, NO precursor and NOS inhibitor administration increased and reduced the tooth movement in animal models, respectively. Further research is required in order to further elucidate the underlying mechanisms and the clinical application prospect of NO in orthodontic tooth movement.

Moving towards precision orthodontics: An evolving paradigm shift in the planning and delivery of customized orthodontic therapy

Advances in precision medicine portend similar progress in orthodontics and will be increasingly harnessed to achieve customized treatment approaches and enhance treatment efficiencies. Our goal is to provide a background on emerging advances in computer technologies and biomedicine and highlight their current and likely future applications to precision orthodontics. A review of orthodontically relevant technologies and advances in pertinent biological research was undertaken. Innovations in computer hardware and software, and 3D imaging technologies offer the ability for customized treatment and biomechanical planning that will be more fully realized within the next few decades. These technologies combined with 3D printing are already being applied to customized appliance fabrication such as aligners and retainers. The future prospects for custom fabrication of orthodontic brackets of appropriate material properties and smart devices are highly desirable and compelling goals. Within biomedicine, the fundamental understanding of cartilage growth and bone biology is currently being tested in animal models to modify mandibular growth and modulate tooth movement, respectively. Some of these discoveries will ultimately have clinical applications in orthodontics including for growth modification, accelerating orthodontic tooth movement, and enhancing anchorage or retention of teeth. Additional genomic and proteomic information will add to further customization of orthodontic diagnosis and treatments. Over the coming decades, precision orthodontics will continue to benefit from advances in many fields and will require the integration of advances in technology, and biomedical and clinical research to deliver optimal, efficient, safe, and reproducible personalized orthodontic treatment.

Nitric oxide in human gingival crevicular fluid after orthodontic force application

Nitric oxide (NO) is involved in bone remodelling and has been shown to play a role in regulating the rate of orthodontic tooth movement (OTM) in rat models. In humans, however, the role of NO in OTM remains less clear. In this study, NO concentration in gingival crevicular fluid (GCF) was measured in patients undergoing orthodontic treatment. Thirteen male participants (ages 11-18 years) planned for non-extraction fixed orthodontic therapy were recruited. Samples of GCF were collected from each maxillary central incisor and first and second molar immediately before (T0), 1h after (T1), and 3-4 days after (T2) application of light orthodontic forces. The maxillary second molars were not included in the appliance and served as controls. Measureable NO levels were consistently obtained from all sampled sites. Total NO levels showed significantly higher NO levels (p<0.05) at T1 at the buccal surfaces of the central incisors when compared to the first and second molars. The results indicate a possible role for NO in OTM at the pressure sites of incisors at early time points. Further studies are required to determine whether NO levels in the periodontal ligament tissues of human teeth during OTM are affected by a force gradient and the magnitude of the applied force.

Effect of low-level laser therapy (LLLT) on orthodontic tooth movement

The aim of this study is to evaluate the effects of low-level laser therapy (LLLT) on (1) the velocity of orthodontic tooth movement and (2) the nitric oxide levels in gingival crevicular fluid (GCF) during orthodontic treatment. The sample consisted of 20 patients (14 girls, six boys) whose maxillary first premolars were extracted and canines distalized. A gallium-aluminum-arsenide (Ga-Al-As) diode laser was applied on the day 0, and the 3rd, 7th, 14th, 21st, and 28th days when the retraction of the maxillary lateral incisors was initiated. The right maxillary lateral incisors composed the study group (the laser group), whereas the left maxillary lateral incisors served as the control. The teeth in the laser group received a total of ten doses of laser application: five doses from the buccal and five doses from the palatal side (two cervical, one middle, two apical) with an output power of 20 mW and a dose of 0.71 J /cm(2). Gingival crevicular fluid samples were obtained on the above-mentioned days, and the nitric oxide levels were analyzed. Bonferroni and repeated measures variant analysis tests were used for statistical analysis with the significance level set at p ≤ 0.05. The application of low-level laser therapy accelerated orthodontic tooth movement significantly; there were no statistically significant changes in the nitric oxide levels of the gingival crevicular fluid during orthodontic treatment.

In-vitro study of cellular viability and nitric oxide production by J774 macrophages stimulated by interferon gamma with ceramic, polycarbonate, and polyoxymethylene brackets

INTRODUCTION

Ceramic brackets are chemically inert in the oral cavity, whereas polycarbonate and polyoxymethylene brackets can degrade and release bisphenol-A and formaldehyde, respectively. More reliable tests are needed to assess the potential toxicity of these materials. In addition to traditional cytotoxicity tests, the study of nitric oxide (NO) cellular production stimulated by a specific material has been shown to be a reliable tool for evaluating cytotoxic potential. The purpose of this study was to assess, with esthetic brackets, cellular viability by 3,(4,5-dimethylthiazol-2-yl)-2,5diphenyltetrazolium bromide assay (Sigma, St. Louis, Mo) in the macrophage cell line J774 stimulated with interferon gamma. Interferon gamma is a key cytokine in the activation of macrophages, plays an important role in immunologic processes, and also quantifies NO production by these macrophages.

METHODS

Well plates were seeded with 2 x 104 J774 cells per well, in a volume of 100 microL, resuspended in Roswell Park Memorial Institute Supplemented Medium 1640. The macrophage cell line J774 was stimulated with interferon gamma. Ceramic, polycarbonate, and polyoxymethylene brackets were added and kept in the culture for 24, 48, or 72 hours in 5% carbon dioxide at 37 degrees C; the control samples did not include brackets. At the end of each incubation period, the supernatant was collected for posterior NO quantification, and the cells were evaluated for cytotoxicity.

RESULTS

Cellular viability in all groups was higher at 72 hours than at 24 hours. The final means in the bracket groups did not show significant differences compared with the control group. NO production was significantly greater in all groups at the final time than at the initial time. However, the brackets with the interferon gamma stimulation did not result in greater NO production than did the cells in the control group.

Local delivery of EGF-liposome mediated bone modeling in orthodontic tooth movement by increasing RANKL expression

AIMS

It has long been demonstrated that epidermal growth factor (EGF) has catabolic effects on bone. Thus, we examined the role of EGF in regulating mechanically induced bone modeling in a rat model of orthodontic tooth movement.

MAIN METHODS

The maxillary first molars of rats were moved mesially using an orthodontic appliance attached to the maxillary incisor teeth. Rats were randomly divided into 4 groups: (G1) administration of PBS (phosphate buffer saline) solution (n=24); (G2) administration of empty liposomes (n=24); (G3) administration 20ng of EGF solution (n=24); and (G4) 20ng of EGF-liposomes solution (n=24). Each solution was injected in the mucosa of the left first molar adjacent to the appliance. At days 5, 10, 14 and 21 after drug administration, 6 animals of each group were sacrificed. Histomorphometric analysis was used to quantify osteoclasts (Tartrate-resistant acid phosphatase (TRAP)+cells) and tooth movement. Using immunohistochemistry assay we evaluated the RANKL (receptor activator of nuclear factor kappaB ligand) and epidermal growth factor receptor (EGFR) expression.

KEY FINDINGS

The EGF-liposome administration showed an increased tooth movement and osteoclast numbers compared to controls (p<0.05). This was correlated with intense RANKL expression. Both osteoblasts and osteoclasts expressed EGFR.

SIGNIFICANCE

Local delivery of EGF-liposome stimulates osteoclastogenesis and tooth movement.

Expression of Nitric Oxide Synthases in Orthodontic Tooth Movement

Objective: To investigate differential expression of NOS isoforms in periodontal ligament (PDL) and bone in tension and pressure sides using a rat model of orthodontic tooth movement (OTM).

Materials and Methods: Immunohistochemistry with NOS isoform (iNOS, eNOS, and nNOS) antibodies was performed on horizontal sections of the first maxillary molars subjected to 3 and 24 hours of OTM. The PDL and adjacent osteocytes of the distopalatal root at pressure and tension areas were analyzed for expression of these proteins. The contralateral molar served as a control. Results were analyzed with one-way ANOVA and with two-way ANOVA.

Results: Expression of all isoforms was increased in the tension side. iNOS and nNOS expression in the pressure side with cell-free zone was decreased but in the pressure side without cell-free zone was increased. The number of eNOS-positive cells did not change, but the intensity of the staining was visibly increased in the tension side. Duration of OTM changed only the pattern of nNOS expression. Osteocyte NOS expression did not change significantly in response to OTM.

Conclusions: All NOS isoforms are involved in OTM with different expression patterns between tension and pressure sides, with nNOS being more involved in early OTM events. NOS expression did not change in osteocytes, suggesting that PDL cells rather than osteocytes are the mechanosensors in early OTM events with regard to NO signaling.

Inhibition of osteocyte apoptosis by fluid flow is mediated by nitric oxide

Bone unloading results in osteocyte apoptosis, which attracts osteoclasts leading to bone loss. Loading of bone drives fluid flow over osteocytes which respond by releasing signaling molecules, like nitric oxide (NO), that inhibit osteocyte apoptosis and alter osteoblast and osteoclast activity thereby preventing bone loss. However, which apoptosis-related genes are modulated by loading is unknown. We studied apoptosis-related gene expression in response to pulsating fluid flow (PFF) in osteocytes, osteoblasts, and fibroblasts, and whether this is mediated by loading-induced NO production. PFF (0.7+/-0.3Pa, 5Hz, 1h) upregulated Bcl-2 and downregulated caspase-3 expression in osteocytes. l-NAME attenuated this effect. In osteocytes PFF did not affect p53 and c-Jun, but l-NAME upregulated c-Jun expression. In osteoblasts and fibroblasts PFF upregulated c-Jun, but not Bcl-2, caspase-3, and p53 expression. This suggests that PFF inhibits osteocyte apoptosis via alterations in Bcl-2 and caspase-3 gene expression, which is at least partially regulated by NO.

Local delivery of osteoprotegerin inhibits mechanically mediated bone modeling in orthodontic tooth movement

INTRODUCTION

The RANKL-OPG axis is a key regulator of osteoclastogenesis and bone turnover activity. Its contribution to bone resorption under altered mechanical states, however, has not been fully elucidated. Here we examined the role of OPG in regulating mechanically induced bone modeling in a rat model of orthodontic tooth movement.

METHODS

The maxillary first molars of male Sprague-Dawley rats were moved mesially using a calibrated nickel-titanium spring attached to the maxillary incisor teeth. Two different doses (0.5 mg/kg, 5.0 mg/kg) of a recombinant fusion protein (OPG-Fc), were injected twice weekly mesial to the first molars. Tooth movement was measured using stone casts that were scanned and magnified. Changes in bone quantity were measured using micro-computed tomography and histomorphometric analysis was used to quantify osteoclasts and volumetric parameters. Finally, circulating levels of TRAP-5b (a bone resorption marker) was measured using enzyme-linked immunosorbent assay.

RESULTS

The 5.0 mg/kg OPG-Fc dose showed a potent reduction in mesial molar movement and osteoclast numbers compared to controls (p<0.01). The molar movement was inhibited by 45.7%, 70.6%, and 78.7% compared to controls at days 7, 14, and 21 respectively, with the high dose of OPG. The 0.5 mg dose also significantly (p<0.05) inhibited molar movement at days 7 (43.8%) and 14 (31.8%). While incisor retraction was also decreased by OPG-Fc, the ratio of incisor to molar tooth movement was markedly better in the high-dose OPG group (5.2:1, p<0.001) compared to the control group (2.3:1) and the low-dose OPG group (2.0:1).

CONCLUSIONS

Local delivery of OPG-Fc inhibits osteoclastogenesis and tooth movement at targeted dental sites.

Parathyroid hormone modifies human periodontal ligament cell proliferation and survival in vitro

BACKGROUND AND OBJECTIVE

Periodontal ligament (PDL) cells show traits that are typical of osteoblasts, such as osteoblastic marker gene expression and the ability to respond to parathyroid hormone (PTH) stimulation in an osteoblast-like manner with respect to differentiation and local factor production. In the present study, we hypothesized that human PDL cells might respond to PTH stimulation with changes in proliferation and cell survival and thereby provide another mechanism by which PTH might affect the reparative potential of PDL cells. We speculated that the maturation state of the cells and the mode of PTH(1-34) administration would have an impact on the cellular response.

MATERIAL AND METHODS

PDL cells were challenged with PTH(1-34) intermittently or continuously at different maturation states. Cell number, 5-bromo-2-deoxyuridine (BrdU) incorporation, DNA fragmentation, nitric oxide production and the duration of the PTH(1-34) effect were determined.

RESULTS

Intermittent PTH(1-34) treatment of preconfluent cells caused a significant increase in proliferation and DNA fragmentation, whereas in more mature cells, proliferation was less enhanced while apoptosis was more pronounced than in immature cells. Continuous PTH(1-34) exposure did not alter proliferation in any maturation state but increased DNA fragmentation in preconfluent cells. PTH(1-34) prevented etoposide-induced apoptosis after 6 h but no longer after 24 h. Nitric oxide production was unaffected.

CONCLUSION

These results indicate that human PDL cells respond to PTH(1-34) with changes in proliferative and apoptotic signaling in a maturation-state-dependent manner. Besides changes in local factor production, these findings provide a further possible mechanism to support the idea that PDL cells possess the potential to be involved in the regulation of dental hard tissue repair.

Fluid shear stress inhibits TNFalpha-induced osteocyte apoptosis

Bone tissue can adapt to orthodontic load. Mechanosensing in bone is primarily a task for the osteocytes, which translate the canalicular flow resulting from bone loading into osteoclast and osteoblast recruiting signals. Apoptotic osteocytes attract osteoclasts, and inhibition of osteocyte apoptosis can therefore affect bone remodeling. Since TNF-alpha is a pro-inflammatory cytokine with apoptotic potency, and elevated levels are found in the gingival sulcus during orthodontic tooth movement, we investigated if mechanical loading by pulsating fluid flow affects TNF-alpha-induced apoptosis in chicken osteocytes, osteoblasts, and periosteal fibroblasts. During fluid stasis, TNF-alpha increased apoptosis by more than two-fold in both osteocytes and osteoblasts, but not in periosteal fibroblasts. One-hour pulsating fluid flow (0.70 +/- 0.30 Pa, 5 Hz) inhibited (-25%) TNF-alpha-induced apoptosis in osteocytes, but not in osteoblasts or periosteal fibroblasts, suggesting a key regulatory role for osteocyte apoptosis in bone remodeling after the application of an orthodontic load.

Clodronate inhibits PGE(2) production in compressed periodontal ligament cells

Periodontal ligament (PDL) cells play an essential role in orthodontic tooth movement. We recently reported that clodronate, a non-N-containing bisphosphonate, strongly inhibited tooth movement in rats, and thus could be a useful adjunct for orthodontic treatment. However, it is not clear how clodronate affects the responses of PDL cells to orthodontic force. In this study, we hypothesized that clodronate prevents the mechanical stress-induced production of prostaglandin E(2) (PGE(2)), interleukin-1beta (IL-1beta), and nitric oxide (NO) in human PDL cells. A compressive stimulus caused a striking increase in PGE(2) production, while the responses of IL-1beta and NO were less marked. Clodronate concentration-dependently inhibited the stress-induced production of PGE(2). Clodronate also strongly inhibited stress-induced gene expression for COX-2 and RANKL. These results suggest that the inhibitory effects of clodronate on tooth movement and osteoclasts may be due, at least in part, to the inhibition of COX-2-dependent PGE(2) production and RANKL expression in PDL cells.

Cellular, molecular, and tissue-level reactions to orthodontic force

Remodeling changes in paradental tissues are considered essential in effecting orthodontic tooth movement. The force-induced tissue strain produces local alterations in vascularity, as well as cellular and extracellular matrix reorganization, leading to the synthesis and release of various neurotransmitters, cytokines, growth factors, colony-stimulating factors, and metabolites of arachidonic acid. Recent research in the biological basis of tooth movement has provided detailed insight into molecular, cellular, and tissue-level reactions to orthodontic forces. Although many studies have been reported in the orthodontic and related scientific literature, a concise convergence of all data is still lacking. Such an amalgamation of the rapidly accumulating scientific information should help orthodontic clinicians and educators understand the biological processes that underlie the phenomenon of tooth movement with mechanics (removable, fixed, or functional appliances). This review aims to achieve this goal and is organized to include all major findings from the beginning of research in the biology of tooth movement. It highlights recent developments in cellular, molecular, tissue, and genetic reactions in response to orthodontic force application. It reviews briefly the processes of bone, periodontal ligament, and gingival remodeling in response to orthodontic force. This review also provides insight into the biological background of various deleterious effects of orthodontic forces.

Nitric oxide synthase expression is increased by occlusal force in rat periodontal ligament

OBJECTIVES

The goal of this study was to investigate the role of nitric oxide synthase (NOS) in occlusal force-induced signal transduction in rat periodontal ligament (PDL).

DESIGN

Rats were fitted with a bite plate and a metal cap to the maxillary and mandibular incisors, respectively, to eliminate the occlusal forces on rat molars. One group was sacrificed at 7 days (exclusion group), while the remaining rats had their appliances removed to reestablish molar occlusal contact (reload group) and were sacrificed 7 days thereafter. Another group of rats (normal group) were left completely untreated. Frozen cross sections of the upper first molars were stained with NADPH-diaphorase to quantify NOS activity. The distal sides of the disto-palatal roots of the upper first molars were examined, and the number and the area of stained cells in the PDL were measured.

RESULTS

In the normal group, NOS expression was detected in blood vessels, monocyte-macrophages, fibroblastic cells and osteoclastic cells. NOS expression was lower in the exclusion group when compared with the normal group or the reload group (p < 0.05), and the exclusion group exhibited occluded blood vessels and a narrowing of PDL. In contrast, in the reload group the PDL and blood vessel structure had recovered and NOS expression was increased to the level of the controls.

CONCLUSION

Occlusal force resulted in increased NOS expression. NO may mediate changes in PDL structure in response to occlusal force.

Effect of nitric oxide on the recovery of the hypofunctional periodontal ligament

The relationship between occlusal stimuli and a hypofunctional periodontal ligament (PDL) structure has been reported, though changes in occlusal recovery conditions were still unclear. Nitric oxide (NO) produced by NO synthase (NOS) is considered a factor for vascular and immune system control, and it increases according to mechanical stimuli. The objective of this study was to examine the relationship between NOS and occlusal stimuli in PDL by comparing hypofunction with occlusal recovery. The study focused on the expression of endothelial NOS (eNOS) and inducible NOS (iNOS). Their expression significantly decreased in occlusal hypofunction compared with the control group and increased close to normal in an occlusal recovery group. The change in the immunopositive area was more dramatic than the immunopositive cell number. Moreover, the rate of iNOS increase was higher than that of eNOS. This study suggests that NO plays an important role in the recovery of the hypofunctional PDL.