Infrared LED irradiation photobiomodulation of oxidative stress in human dental pulp cells

Histological effects of photobiomodulation on delayed tooth replantation: a systematic review

This systematic review evaluated preclinical studies to assess whether PBM has a more favorable histological response than other treatments used before delayed replantation of avulsed teeth. This review followed the PRISMA checklist and was registered in PROSPERO. MEDLINE (PubMed), Embase, Scopus and Web of Science were searched from their inception to July 14, 2022. Data were independently extracted by two reviewers. Data were collected about species, number of animals, number and type of teeth, groups evaluated, extra-alveolar time, parameters for PBM and other study groups, presence and characteristics of containment, observation time points, evaluation methods, characteristics evaluated, and significant results. The ARRIVE and SYRCLE tools were used to assess the methodological quality and risk of bias (RoB) of the studies. After screening, six studies were included in the review synthesis. Three of the four studies that evaluated root resorption as an outcome found that PBM decreases its occurrence after delayed tooth replantation. A meta-analysis was not conducted because some data were missing in the included studies. Half of the studies evaluating ankylosis found an increase in its occurrence after PBM. Two studies evaluated inflammatory responses and found a reduction of inflammation after PBM. In general, studies had high methodological heterogeneity, intermediate reporting quality and high RoB. Despite the methodological quality and RoB limitations of the studies, the histological responses after delayed tooth replantation were more favourable in the PBM groups. Preclinical studies supported by guidelines should define laser parameters for future clinical studies.

A systematic review of trends in photobiomodulation in dentistry between 2018 and 2022: advances and investigative agenda

Background

Photobiomodulation (PBM) involves laser therapy utilized in medical sciences to modulate biological processes acting as a palliative and immune response-enhancing treatment. This study conducts a comprehensive bibliometric analysis to explore current trends in PBM-related scientific production, encompassing publications, citations, impact, keywords and clusters. Additionally, it aims to predict future research trends in this domain.

Methods

The data for this quantitative and qualitative bibliometric analysis were obtained from 608 scientific documents retrieved in November 2022, with 123 sourced from Web of Science and 485 from Scopus, Utilizing Excel, the data was processed in Excel to extract essencial information. Productivity and impact were evaluated for eligibility, and VOSviewer aided in determining associativity for the bibliometric analysis.

Results

The findings of this study demostrate that the scientific production related to PBM adheres to a growth power law, exhibiting characteristics of both exponential and linear phases. Notably, recent research trends emphasize critical concepts such as laser therapy, orthodontics, and dental pulp stem cells. Particularly significant is the burgeoning interest in utilizing PBM within dentistry as a complementary alternative to existing protocols.

Conclusions

PBM stands as a promising laser therapy within medical applications. Through a detailed bibliometric analysis, this study underscores the increasing significance of PBM, especially within the realm of dental treatments. These insights offer a glimpse into the evolving landscape of PBM research and provide valuable guidance for potential future directions of study.

Effect of Photobiomodulation in Suppression of Oxidative Stress on Retinal Pigment Epithelium

As the world undergoes aging, the number of age-related diseases has increased. One of them is disease related to retinal pigment epithelium (RPE) degeneration, such as age-related macular degeneration, causing vision loss without physical damage in the ocular system. It is the leading cause of blindness, with no cure. Although the exact pathogenesis is still unknown, the research shows that oxidative stress is one of the risk factors. Various molecules have been reported as anti-oxidative materials; however, the disease has not yet been conquered. Here, we would like to introduce photobiomodulation (PBM). PBM is a non-invasive treatment based on red and near-infrared light and has been used to cure various diseases by regulating cellular functions. Furthermore, recent studies showed its antioxidant effect, and due to this reason, PBM is arising as a new treatment for ocular disease. In this study, we confirm the antioxidant effect of PBM in retinal pigment epithelium via an RPE model with hypoxia. The function of RPE is protected by PBM against damage from hypoxia. Furthermore, we observed the protective mechanism of PBM by its suppression effect on reactive oxygen species generation. These results indicate that PBM shows great potential to cure RPE degeneration to help patients with blindness.

Effect of Humid Air Exposed to IR Radiation on Enzyme Activity

Water vapor absorbs well in the infra-red region of the electromagnetic spectrum. Absorption of radiant energy by water or water droplets leads to formation of exclusion zone water that possesses peculiar physico-chemical properties. In the course of this study, normally functioning and damaged alkaline phosphatase, horseradish peroxidase and catalase were treated with humid air irradiated with infrared light with a wavelength in the range of 1270 nm and referred to as coherent humidity (CoHu). One-minute long treatment with CoHu helped to partially protect enzymes from heat inactivation, mixed function oxidation, and loss of activity due to partial unfolding. Authors suggest that a possible mechanism underlying the observed effects involves altering the physicochemical properties of aqueous media while treatment of the objects with CoHu where CoHu acts as an intermediary.

Photobiomodulation therapy upregulates the growth kinetics and multilineage differentiation potential of human dental pulp stem cells-an in vitro Study

This study aims to evaluate the impact of red LED irradiation on the viability, proliferation, colonogenic potential, markers expression along with osteogenic and chondrogenic differentiation of dental pulp stem cells. DPSCs were isolated from sound human permanent teeth using enzymatic digestion method and seeded with regular culture media. Cells at P4 were irradiated using red LED Light (627 nm, 2 J/cm²) and examined for growth kinetics, and multilineage differentiation using the appropriate differentiation media. The irradiated groups showed an increase in cellular growth rates, cell viability, clonogenic potential, and decrease in population doubling time compared to the control group. Cells of the irradiated groups showed enhanced differentiation towards osteogenic and chondrogenic lineages as revealed by histochemical staining using alizarin red and alcian blue stains. Photobiomodulation is an emerging promising element of tissue engineering triad besides stem cells, scaffolds, and growth factors.

Specific parameters of infrared LED irradiation promote the inhibition of oxidative stress in dental pulp cells

OBJECTIVES

The present study aimed to assess the oxidative stress and the viability of dental pulp cells stimulated by lipopolysaccharide (LPS) and submitted to photobiomodulation (PBM) with infrared light-emitting diode (LED, 850 nm).

DESIGN

Three healthy primary teeth (n = 3) were collected and seeded in 24-well plates with 10 µg/mL of LPS to induce inflammatory mediator formation. The cells were irradiated (850 nm, 40 mW/cm² and 80 mW/cm²) at the proposed radiant exposures of 0 (control), 4, 15, and 30 J/cm² shortly after LPS supplementation. The tests were performed 24 h after irradiation to assess mitochondrial activity (MTT assay), the number of viable cells (Trypan Blue), cell morphology (Scanning Electron Microscopy - SEM), and the quantification of Nitric Oxide (NO) and Reactive Oxygen Species (ROS). The data were analyzed using Kruskal-Wallis and Dunn's tests (p < 0.05).

RESULTS

The irradiated groups showed larger viable cells number than the non-irradiated group with LPS (p < 0.0001). All irradiation parameters decreased ROS concentrations after LPS application compared to the non-irradiated group (p < 0.05). All irradiation parameters enhanced the NO values compared to those of the control group (p < 0.05). The SEM images showed cells with regular morphology that adhered to the substrate.

CONCLUSIONS

According to the parameters used in this study, the radiant exposure of 15 J/cm² and irradiance of 40 mW/cm² were the most effective irradiation parameters to stimulate and modulate oxidative stress in the primary teeth-derived dental pulp cells.

Photobiomodulation effect of red LED (630 nm) on the free radical levels produced by pulp cells under stress conditions

The aim of this study was to assess the ability of red light emitting diodes (LED) to modulate oxidative stress in human dental pulp fibroblasts (HDPFs) when different irradiation parameters are employed. Cells from primary teeth were seeded (100,000 cells/well) in 24-well plates in culture medium (DMEM). At 24 h after incubation, the culture medium was replaced with DMEM containing 10 μg/mL lipopolysaccharide (LPS). Thereafter, the cells were irradiated (LED 630 nm, 0.04 W/cm² and 0.08 W/cm²) at 0 J/cm² (control group), 4 J/cm², 15 J/cm², and 30 J/cm²; and their viability (MTT assay), number (Trypan Blue), synthesis of nitric oxide (NO) (Griess reagent), and reactive oxygen species (ROS) (fluorescence probe, DCFH-DA) were assessed. The Kruskal-Wallis and Mann-Whitney statistical tests using Bonferroni correction were employed (significance level of 5%). Compared to that in control fibroblasts, increased viability was observed in HDPFs exposed to LPS and irradiated with 15 J/cm² and 30 J/cm² at 0.04 W/cm² and 4 J/cm² and 15 J/cm² at 0.08 W/cm² (p < 0.05). Exposure to 4 J/cm² at 0.04 W/cm² and 15 J/cm² and 30 J/cm² at 0.08 W/cm² modulated the oxidative stress in cells relative to that observed in non-irradiated LPS-treated pulp cells (p < 0.05). It was concluded that the irradiation strategies of using red LED with radiant exposures of 15 J/cm² and 30 J/cm² at 0.04 W/cm² and 15 J/cm² at 0.08 W/cm² were the best parameters to decrease NO and ROS concentration and to stimulate viability of HDPFs exposed to LPS challenge.

Effects of zinc oxide and calcium-doped zinc oxide nanocrystals on cytotoxicity and reactive oxygen species production in different cell culture models

Objectives

This study aimed to synthesize nanocrystals (NCs) of zinc oxide (ZnO) and calcium ion (Ca²⁺)-doped ZnO with different percentages of calcium oxide (CaO), to evaluate cytotoxicity and to assess the effects of the most promising NCs on cytotoxicity depending on lipopolysaccharide (LPS) stimulation.

Materials and Methods

Nanomaterials were synthesized (ZnO and ZnO:xCa, x = 0.7; 1.0; 5.0; 9.0) and characterized using X-ray diffractometry, scanning electron microscopy, and methylene blue degradation. SAOS-2 and RAW 264.7 were treated with NCs, and evaluated for viability using the MTT assay. NCs with lower cytotoxicity were maintained in contact with LPS-stimulated (+LPS) and nonstimulated (−LPS) human dental pulp cells (hDPCs). Cell viability, nitric oxide (NO), and reactive oxygen species (ROS) production were evaluated. Cells kept in culture medium or LPS served as negative and positive controls, respectively. One-way analysis of variance and the Dunnett test (α = 0.05) were used for statistical testing.

Results

ZnO:0.7Ca and ZnO:1.0Ca at 10 µg/mL were not cytotoxic to SAOS-2 and RAW 264.7. +LPS and −LPS hDPCs treated with ZnO, ZnO:0.7Ca, and ZnO:1.0Ca presented similar NO production to negative control (p > 0.05) and lower production compared to positive control (p < 0.05). All NCs showed reduced ROS production compared with the positive control group both in +LPS and −LPS cells (p < 0.05).

Conclusions

NCs were successfully synthesized. ZnO, ZnO:0.7Ca and ZnO:1.0Ca presented the highest percentages of cell viability, decreased ROS and NO production in +LPS cells, and maintenance of NO production at basal levels.

The effect of photobiomodulation on human dental pulp-derived stem cells: systematic review

This systematic review assessed if photobiomodulation of human dental pulp tissue improved cell viability, proliferation, and/or differentiation compared with a placebo. This systematic review was conducted in line with PRISMA. PICO question was established; inclusion and exclusion criteria were established before a search had begun. A literature search was conducted through PubMed, Scopus, and Cochrane. Studies were included if published within the last 20 years in English language, or where translation was available; laser parameters were mentioned; human dental pulp tissue was studied in vitro. Studies were excluded if non-human dental pulp tissue was studied and where the study was an in vivo study. Out of the total 121 studies found, 109 were excluded. Of the twelve included studies, three full-text articles were not available despite attempts made to contact the respective authors, leaving nine studies. Four of the included studies reported the use of stem cells derived from human deciduous teeth (SHEDs), and five used those from human permanent teeth (DPSCs). Most included studies utilized InGaAlP laser with wavelengths 660 nm, and one study with 610 nm. Other types of lasers included LED InGaN, and GaAlAs. Out of all included studies, two had a moderate risk of bias, and the rest had a low risk of bias. All studies confirmed positive effects on proliferation. One study also found improved osteogenic differentiation of the stem cells derived from stem cells of deciduous teeth. After assessing SHEDs and DPSCs separately, it is found that photobiomodulation improved cell proliferation in both subgroups. Due to heterogeneity in design protocols and laser parameters, it was not possible to compare the studies together. However, this study indicated that cell viability and proliferation did improve with photobiomodulation.

Nitric Oxide in Dental Pulp Tissue: From Molecular Understanding to Clinical Application in Regenerative Endodontic Procedures

Nitric oxide (NO), which is synthesized by the enzyme NO synthase (NOS), is a versatile endogenous molecule with multiple biological effects on many tissues and organs. In dental pulp tissue, NO has been found to play multifaceted roles in regulating physiological activities, inflammation processes, and tissue repair events, such as cell proliferation, neuronal degeneration, angiogenesis, and odontoblastic differentiation. However, there is a deficiency of detailed discussion on the NO-mediated interactions between inflammation and reparative/regenerative responses in wounded dental pulp tissue, which is a central determinant of ultimate clinical outcomes. Thus, the purpose of this review is to outline the current molecular understanding on the roles of Janus-faced molecule NO in dental pulp physiology, inflammation, and reparative activities. Based on this knowledge, advanced physicochemical techniques designed to manipulate the therapeutic potential of NOS and NO production in endodontic regeneration procedures are further discussed. Impact statement The interaction between inflammation and reparative/regenerative responses is very important for regenerative endodontic procedures, which are biologically based approaches intended to replace damaged tissues. Inside dental pulp tissue, endogenous nitric oxide (NO) is generated mainly by immunocompetent cells and dental pulp cells and mediates not only inflammatory/immune activities but also signaling cascades that regulate tissue repair and reconstruction, indicating its involvement in both tissue destruction and regeneration. Thus, it is feasible that NO acts as one of the indicators and modulators in dental pulp repair or regeneration under physiological and pathological conditions.

Development and application of LED arrays for use in phototherapy research

Lasers/LEDs demonstrate therapeutic effects for a range of biomedical applications. However, a consensus on effective light irradiation parameters and efficient and reliable measurement techniques remain limited. The objective here is to develop, characterise and demonstrate the application of LED arrays in order to progress and improve the effectiveness and accuracy of in vitro photobiomodulation studies. 96-well plate format LED arrays (400-850 nm) were developed and characterised to accurately assess irradiance delivery to cell cultures. Human dental pulp cells (DPCs) were irradiated (3.5-142 mW/cm² : 15-120 s) and the biological responses were assessed using MTT assays. Array calibration was confirmed using a range of optical and analytical techniques. Multivariate analysis of variance revealed biological responses were dependent on wavelength, exposure time and the post-exposure assay time (P < 0.05). Increased MTT asbsorbance was measured 24 h post-irradiation for 30 s exposures of 3.5 mW/cm² at 470, 527, 631, 655, 680, 777, 798 and 826 nm with distinct peaks at 631 nm and 798 nm (P < 0.05). Similar wavelengths were also effective at higher irradiances (48-142 mW/cm² ). LED arrays and high throughput assays provide a robust and reliable platform to rapidly identify irradiation parameters which is both time- and cost-effective. These arrrays are applicable in photobiomodulation, photodynamic therapy and other photobiomedical research.

Dose-responses of Stem Cells from Human Exfoliated Teeth to Infrared LED Irradiation

Despite several reports regarding tissue regeneration, including pulp repair induced by different light sources, only limited data have been reported concerning the effects of light-emitting diodes (LED) on stem cells from human exfoliated deciduous teeth (SHEDs). The aim of this study was to evaluate the effects of different energy densities of infrared LED on the cell viability, number of cells and mineralized tissue production by SHEDs. SHEDs were obtained from near-exfoliation primary teeth (n=3), seeded in plain DMEM (104 cells/cm2), and irradiated by a LED prototype (LEDTable 850 nm, 40 mW/cm2) delivering 0 (control), 2, 4, 8, 15 or 30 J/cm2 (n=9). Cell viability (MTT assay), cell proliferation (trypan blue assay), and mineralized nodule (MN) formation (alizarin red stain) were assessed 12 and 72 h post-irradiation. Data were subjected to Kruskal-Wallis and Mann-Whitney tests (α=0.05). Cells irradiated with 2 or 4 J/cm2 exhibited higher metabolism at 72 h, and all energy densities provided increase in cell proliferation after 12 h. Regarding MN formation, the best results were observed at 72 h after SHED irradiation with 8 and 15 J/cm2. It was concluded that the cell viability, cell number and MN formation by pulp cells are enhanced after exposure to infrared LED irradiation. Overall, the greatest SHED biostimulation was obtained with 4 and 8 J/cm2.

Transdentinal photobiostimulation of stem cells from human exfoliated primary teeth

AIM

To evaluate the effects of infrared light-emitting diode (LED) irradiation on stem cells from human exfoliated deciduous teeth (SHEDs).

METHODOLOGY

Exfoliated primary teeth were obtained (n = 3), and SHEDs obtained from the teeth were seeded on the pulpal surface of 0.2-mm-thick dentine discs produced from permanent molars. The cells were incubated for 24 h by placing the discs in plain Dulbecco's modified Eagle's medium (DMEM). The DMEM was then replaced with new culture medium formulated for odontoblast differentiation. After 12 h in the second medium, SHEDs were irradiated through the dentine discs using an infrared LED (850 nm) with a power density of 80 mW cm^-2 . Energy doses (EDs) delivered to the occlusal surface of the dentine discs were 0 (control), 2 and 4 J cm^-2 (n = 6). Subsequent tests were performed 72 h after irradiation. These tests included cell viability (MTT), alkaline phosphatase activity (ALP), total protein production (TP), scanning electron microscopy (SEM), as well as gene expression for ALP, Col I, DSPP and DMP-1. Data were analysed using Kruskal-Wallis and Mann-Whitney t-tests (α = 0.05).

RESULTS

Both EDs (2 and 4 J cm^-2 ) significantly increased cell viability and ALP activity. For TP, ALP and Col I gene expression, only the 4 J cm^-2 group had significantly higher values compared to the control group. Cell morphology was not affected by irradiation.

CONCLUSION

Infrared LED irradiation was capable of biostimulating SHEDs through a 0.2 mm thickness of dentine, especially at the 4 J cm^-2 level.

Light-Emitting Diode Phototherapy Reduces Nocifensive Behavior Induced by Thermal and Chemical Noxious Stimuli in Mice: Evidence for the Involvement of Capsaicin-Sensitive Central Afferent Fibers

Low-intensity phototherapy using light fonts, like light-emitting diode (LED), in the red to infrared spectrum is a promising alternative for the treatment of pain. However, the underlying mechanisms by which LED phototherapy reduces acute pain are not yet well understood. This study investigated the analgesic effect of multisource LED phototherapy on the acute nocifensive behavior of mice induced by thermal and chemical noxious stimuli. The involvement of central afferent C fibers sensitive to capsaicin in this effect was also investigated. Mice exposed to multisource LED (output power 234, 390, or 780 mW and power density 10.4, 17.3, and 34.6 mW/cm², respectively, from 10 to 30 min of stimulation with a wavelength of 890 nm) showed rapid and significant reductions in formalin- and acetic acid-induced nocifensive behavior. This effect gradually reduced but remained significant for up to 7 h after LED treatment in the last model used. Moreover, LED (390 mW, 17.3 mW/cm²/20 min) irradiation also reduced nocifensive behavior in mice due to chemical [endogenous (i.e., glutamate, prostaglandins, and bradykinin) or exogenous (i.e., formalin, acetic acid, TRPs and ASIC agonist, and protein kinase A and C activators)] and thermal (hot plate test) stimuli. Finally, ablating central afferent C fibers abolished LED analgesia. These experimental results indicate that LED phototherapy reduces the acute painful behavior of animals caused by chemical and thermal stimuli and that LED analgesia depends on the integrity of central afferent C fibers sensitive to capsaicin. These findings provide new information regarding the underlying mechanism by which LED phototherapy reduces acute pain. Thus, LED phototherapy may be an important tool for the management of acute pain.

Nutritional deprivation and LPS exposure as feasible methods for induction of cellular - A methodology to validate for vitro photobiomodulation studies

Previous studies have demonstrated that high biostimulation takes place when cells under stress are subjected to phototherapy by laser or light-emitting-diode (LED) devices. Several studies selected nutritional deprivation by reducing the concentration of fetal bovine serum (FBS) in the culture medium or the exposure of cultured cells to lipopolysaccharide (LPS) as an in vitro cellular stress condition. However, there are no data certifying that these stimuli cause stressful conditions for cultured cells. This investigation assessed the induction of cellular stress by decreasing the concentration of FBS or adding LPS to culture medium. Odontoblast-like cells (MDPC-23) were cultured in complete culture medium (DMEM) containing 10% FBS. After a 12-hour incubation period, the DMEM was replaced by fresh medium containing 10% FBS (control), low concentrations of FBS (0, 0.2, 0.5, 2, or 5%) or LPS from Escherichia coli (10μg/ml). After an additional 12-hour incubation, cell viability, total cell-counting, total protein production, and gene expression of heat shock protein 70 (HSP70) were assessed. Data were statistically analyzed by ANOVA complemented by the Tukey test, with 5% considered significant. Cell viability was negatively affected only for 0% FBS, while reduced viable cell numbers and total protein production were detected for FBS concentrations lower than 2%. Higher HSP70 gene expression was also observed for FBS concentrations lower than 2% and for cells exposed to LPS. The nutritional deprivation model with culture medium lower than 2% of FBS can be safely used to induce cellular stress for in vitro photobiomodulation studies.

The dark art of light measurement: accurate radiometry for low-level light therapy

Lasers and light-emitting diodes are used for a range of biomedical applications with many studies reporting their beneficial effects. However, three main concerns exist regarding much of the low-level light therapy (LLLT) or photobiomodulation literature; (1) incomplete, inaccurate and unverified irradiation parameters, (2) miscalculation of ‘dose,’ and (3) the misuse of appropriate light property terminology. The aim of this systematic review was to assess where, and to what extent, these inadequacies exist and to provide an overview of ‘best practice’ in light measurement methods and importance of correct light measurement. A review of recent relevant literature was performed in PubMed using the terms LLLT and photobiomodulation (March 2014–March 2015) to investigate the contemporary information available in LLLT and photobiomodulation literature in terms of reporting light properties and irradiation parameters. A total of 74 articles formed the basis of this systematic review. Although most articles reported beneficial effects following LLLT, the majority contained no information in terms of how light was measured (73 %) and relied on manufacturer-stated values. For all papers reviewed, missing information for specific light parameters included wavelength (3 %), light source type (8 %), power (41 %), pulse frequency (52 %), beam area (40 %), irradiance (43 %), exposure time (16 %), radiant energy (74 %) and fluence (16 %). Frequent use of incorrect terminology was also observed within the reviewed literature. A poor understanding of photophysics is evident as a significant number of papers neglected to report or misreported important radiometric data. These errors affect repeatability and reliability of studies shared between scientists, manufacturers and clinicians and could degrade efficacy of patient treatments. Researchers need a physicist or appropriately skilled engineer on the team, and manuscript reviewers should reject papers that do not report beam measurement methods and all ten key parameters: wavelength, power, irradiation time, beam area (at the skin or culture surface; this is not necessarily the same size as the aperture), radiant energy, radiant exposure, pulse parameters, number of treatments, interval between treatments and anatomical location. Inclusion of these parameters will improve the information available to compare and contrast study outcomes and improve repeatability, reliability of studies.

Synthesis of dental matrix proteins and viability of odontoblast-like cells irradiated with blue LED

To evaluate the effect of irradiation with light-emitting diode (LED; 455 nm) on the viability and synthesis of dentin matrix proteins by odontoblast-like cells, MDPC-23 cells were cultivated (10(4) cells/cm(2)) in 24-well culture plates. After 12 h incubation in Dulbecco's modified Eagle's medium (DMEM), the cells were submitted to nutritional restriction by means of reducing the concentration of fetal bovine serum (FBS) for an additional 12 h. Cells were irradiated one single time with one of the following energy densities (EDs): 0.5, 2, 4, 10, or 15 J/cm(2) and irradiance fixed at 20 mW/cm(2). Non-irradiated cells served as control. After 72 h, cells were evaluated with regard to viability (methylthiazol tetrazolium technique (MTT)), mineralization nodule (MN) formation, total protein (TP) production, alkaline phosphatase activity (ALP), and collagen synthesis (Sircol), n = 8. The data were submitted to Kruskal-Wallis and Mann-Whitney tests (p > 0.05). There was no statistical difference between the viability of cells irradiated or not (control), for all the EDs. However, an increase in TP was observed for all the EDs when compared with the control group. A reduced ALP activity was seen in all irradiated groups, except for the ED of 0.5 J/cm(2), which did not differ from the control. There was no difference between the irradiated groups and control regarding collagen synthesis, with the exception of the ED of 10 J/cm(2), which inhibited this cell function. Significant reduction in MN occurred only for the EDs of 0.5 and 2 J/cm(2). The single irradiation with blue LED (455 nm), irradiance of 20 mW/cm(2), and energy densities ranging from 0.5 to 15 J/cm(2) exerted no effective biostimulatory capacity on odontoblast-like cells.

Metabolic activity of odontoblast-like cells irradiated with blue LED (455 nm)

Blue light emitting diodes (LEDs) are frequently used in dentistry for light activation of resin-based materials; however, their photobiostimulatory effects have not yet been fully investigated. This study aimed to investigate the effect of blue LED (455 nm) on the metabolism of odontoblast-like cells MDPC-23. Energy doses of 2 and 4 J/cm(2) were used at 20 mW/cm(2) fixed power density. MDPC-23 cells were seeded at 10,000 cells/cm(2) density in Dulbecco's modified Eagle's medium (DMEM) containing 10 % fetal bovine serum (FBS). After 12 h, the culture medium was replaced with new DMEM supplemented with 0.5 % of FBS, and the cells were incubated for further 12 h. After that, single irradiation was performed to the culture, under selected parameters. Cell viability evaluations (Alamar Blue Assay, n = 12), number of viable cells (Trypan Blue Assay, n = 12), morphological analysis by scanning electron microscopy (SEM, n = 2), gene expression (n = 6) of alkaline phosphatase (Alp), collagen (Col-1a1), and dental matrix protein (Dmp-1) (quantitative polymerase chain reaction (qPCR)) were performed 72 h after irradiation. Data were analyzed by Kruskal-Wallis, ANOVA, and Tukey tests (p < 0.05). Direct light application at 4 J/cm(2) energy dose had no negative effects on cell viability, while irradiation with 2 J/cm(2) reduced cell metabolism. None of doses affected the number of viable cells compared with the control group. The two energy doses downregulated the expression of Alp; however, expression of Col-1a1 and Dmp-1 had no alteration. Cells presented change in the cytoskeleton only when irradiated with 2 J/cm(2). In conclusion, the blue LED (455 nm) irradiation, under the evaluated parameters, had no biostimulatory effects on MDPC-23 cells.