A preliminary comparison between the effects of red and infrared laser irradiation on viability and proliferation of SHED

Effect of photobiomodulation therapy with 660 and 980 nm diode lasers on differentiation of periodontal ligament mesenchymal stem cells

This study aimed to compare the effects of photobiomodulation therapy (PBMT) with 660 and 980 nm diode lasers on differentiation of periodontal ligament mesenchymal stem cells (PDLMSCs). In this in vitro, experimental study, PDLMSCs were obtained from the Iranian Genetic Bank and cultured in osteogenic medium. They were then subjected to irradiation of 660 and 980 nm diode lasers, and their viability was assessed after one, two, and three irradiation cycles using the methyl thiazolyl tetrazolium (MTT) assay. The cells also underwent DAPI staining, cell apoptosis assay by using the Annexin V/PI, Alizarin Red staining, and real-time polymerase chain reaction (PCR) for assessment of the expression of osteogenic genes. Data were analyzed by two-way ANOVA. The two laser groups had no significant difference in cell apoptosis according to the results of DAPI staining. Both laser groups showed higher cell viability in the MTT assay at 4 and 6 days compared with the control group. Annexin V/PI results showed higher cell viability in both laser groups at 4 days compared with the control group. Rate of early and late apoptosis was lower in both laser groups than the control group at 4 days. Necrosis had a lower frequency in 980 nm laser group than the control group on day 6. Alizarin Red staining showed higher cell differentiation in both laser groups after 3 irradiation cycles than the control group. The highest expression of osteopontin (OPN), osteocalcin (OCN), and Runt-related transcription factor 2 (RUNX2) was noted in 660 nm laser group with 3 irradiation cycles at 14 days, compared with the control group. PBMT with 660 and 980 nm diode lasers decreased apoptosis and significantly increased PDLMSC differentiation after 3 irradiation cycles.

Analysis of dentin wear and biological properties promoted by experimental inoffice desensitizing materials

BACKGROUND

This study aimed to evaluate dentin wear and biological performance of desensitizing materials.

METHODS

Seventy bovine root dentin blocks were sectioned. Half of the surface of each specimen was untreated (control) and the other half was immersed in EDTA and treated with the following desensitizing materials: placebo varnish (PLA), fluoride varnish (FLU), sodium fluoride (NaF) varnish + sodium trimetaphosphate (TMP), universal adhesive (SBU), S-PRG varnish (SPRG), biosilicate (BIOS), and amelotin solution (AMTN). After application, the specimens were submitted to an erosive-abrasive challenge and the wear analyzed by optical profilometer. Serial dilutions of extracts obtained from the culture medium containing discs impregnated with those desensitizers were applied on fibroblasts and odontoblasts-like cells cultures. Cytotoxicity and production of total protein (TP) by colorimetric assays were determined after 24 h. Data were statistically analyzed using Kruskal-Wallis, Dunn's, One-way ANOVA and Tukey tests (p ≤ 0.05).

RESULTS

No dentin wear was observed only for SBU. The lowest dentin wear was observed for AMTN and TMP. Cell viability was significantly reduced after treatment with undiluted extracts of PLA, FLU, TMP and SBU in fibroblasts and TMP and SBU in odontoblast-like cells. SPRG, BIOS and AMTN were cytocompatible at all dilutions tested. Considering TP results, no statistical difference was observed among the groups and high levels for TP were observed after TMP and FLU treatments.

CONCLUSIONS

Universal adhesive system may protect dentin with opened tubules from wear after challenge. Extracts of adhesive and fluoride varnishes presented cytotoxic mainly on fibroblasts. The enamel protein may be a future alternative to treat dentin with opened tubules because it may cause low wear under erosive-abrasive challenge with low cytotoxic effects.

Influence of Different Photobiomodulation Parameters on Multi-Potent Adipose Tissue Mesenchymal Cells In Vitro

Objective: Investigating the effect of different parameters of photobiomodulation (PBM) with low-power laser on multi-potent mesenchymal stem cells (MSCs) derived from adipose tissue in terms of proliferation and cell death. Methods: MSCs were submitted to PBM applications with combinations of the following physical parameters: control group (no intervention), wavelengths of 660 and 830 nm; energy of 0.5, 2, and 4 J; and power of 40 and 100 mW. MSC analysis was performed using MetaXpress® software at 24, 48, and 72 h. Results: Irradiation promoted a significant increase in cell proliferation (p < 0.05), with 830 nm laser, 100 mW, with energy of 0.5, 2, and 4 J in relation to the control group at all times. PBM with 660 nm, power of 40 mW, and energy of 0.5, 2, and 4 J produced greater cell death at 24 h compared with the control group. At the time of 72 h, there was no significant difference concerning cell death. Conclusions: According to the results found, we can conclude that both wavelengths were effective; however, the 830 nm laser was more effective in terms of cell proliferation compared with the 660 nm laser. The 660 nm wavelength showed a significant increase in cell death when compared with the 830 nm laser.

The Role of Photobiomodulation on Dental-Derived Stem Cells in Regenerative Dentistry: A Comprehensive Systematic Review

BACKGROUND

Photobiomodulation therapy involves exposing tissues to light sources, including light-emitting diodes or low-level lasers, which results in cellular function modulation. The molecular mechanism of this treatment is revealed, demonstrating that depending on the light settings utilized, it has the potential to elicit both stimulatory and inhibitory reactions.

OBJECTIVE

The current systematic review aimed to evaluate the impact of photobiomodulation therapy on dental stem cells and provide an evidence-based conclusion in this regard.

METHODS

This systematic review was performed and reported based on the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) revised guidelines. PICO(S) components were employed to define the inclusion criteria. Web of Science, Scopus, Medline as well as grey literature, and google scholar were searched up to September 2021 to retrieve relevant papers.

RESULTS

Photobiomodulation therapy showed promising effects on the proliferation, viability, and differentiation of dental stem cells. This finding was based on reviewing related articles with a low risk of bias.

CONCLUSION

Despite the positive benefits of photobiomodulation therapy on dental stem cells, the current data do not provide a definitive conclusion on the best physical parameters for enhancing cell viability, proliferation, and differentiation.

Chemical, morphological and microhardness analysis of coronary dentin submitted to internal bleaching with hydrogen peroxide and violet LED

BACKGROUND

Violet LED has been used for internal bleaching, however its implications on coronary dentin composition are unclear. The present study aims to evaluate the effect of bleaching with violet LED, either associated with 35 % hydrogen peroxide or not, on microhardness, chemical composition, and morphological characteristics of coronal dentin.

METHODS

Thirty maxillary canines were selected to obtain 30 blocks of coronal dentin, distributed in 3 groups (n = 10): 35 % hydrogen peroxide (HP); violet LED (LED); HP 35 % + LED, (HP+LED). The chemical analysis was performed by FTIR and the morphological evaluation of the dentin structure by confocal laser scanning microscopy before (T0) and after treatment (T1). The microhardness analysis was performed by microdurometer after bleaching. The data were submitted to repeated measures ANOVA test (P> 0.05).

RESULTS

The intensity of the inorganic peaks decreased after bleaching for all groups (P = 0.003). There was an increase in the organic peak intensity after bleaching with HP, a decrease for LED, while HP+LED did not change the intensity (P = 0.044). Moreover, the inorganic/organic ratio decreased for HP (P = 0.022), while for LED and HP+LED there was no significant changes (P>0.05). HP and HP+LED showed lower microhardness values compared to LED (P< 0.05). Regarding morphological changes, an increase in the perimeter of the dentinal tubules was found for all groups, with the smallest increase being observed for LED.

CONCLUSION

HP bleaching decreased the chemical stability and microhardness of the coronal dentin, while the violet LED treatments had no significant impact on dentin stability. In all groups, there was an increase in exposure of the dentinal tubules after bleaching, which was less pronounced with the violet LED bleaching.

Ligand-based design, synthesis, computational insights, and in vitro studies of novel N-(5-Nitrothiazol-2-yl)-carboxamido derivatives as potent inhibitors of SARS-CoV-2 main protease

The global outbreak of the COVID-19 pandemic provokes scientists to make a prompt development of new effective therapeutic interventions for the battle against SARS-CoV-2. A new series of N-(5-nitrothiazol-2-yl)-carboxamido derivatives were designed and synthesised based on the structural optimisation principle of the SARS-CoV Mpro co-crystallized WR1 inhibitor. Notably, compound 3b achieved the most promising anti-SARS-CoV-2 activity with an IC50 value of 174.7 µg/mL. On the other hand, compounds 3a, 3b, and 3c showed very promising SARS-CoV-2 Mpro inhibitory effects with IC50 values of 4.67, 5.12, and 11.90 µg/mL, respectively. Compound 3b docking score was very promising (-6.94 kcal/mol) and its binding mode was nearly similar to that of WR1. Besides, the molecular dynamics (MD) simulations of compound 3b showed its great stability inside the binding pocket until around 40 ns. Finally, a very promising SAR was concluded to help to design more powerful SARS-CoV-2 Mpro inhibitors shortly.

NIR irradiation of human buccal fat pad adipose stem cells and its effect on TRP ion channels

The effect of near infrared (NIR) laser irradiation on proliferation and osteogenic differentiation of buccal fat pad-derived stem cells and the role of transient receptor potential (TRP) channels was investigated in the current research. After stem cell isolation, a 940 nm laser with 0.1 W, 3 J/cm² was used in pulsed and continuous mode for irradiation in 3 sessions once every 48 h. The cells were cultured in the following groups: non-osteogenic differentiation medium/primary medium (PM) and osteogenic medium (OM) groups with laser-irradiated (L +), without irradiation (L -), laser treated + Capsazepine inhibitor (L + Cap), and laser treated + Skf96365 inhibitor (L + Skf). Alizarin Red staining and RT-PCR were used to assess osteogenic differentiation and evaluate RUNX2, Osterix, and ALP gene expression levels. The pulsed setting showed the best viability results (P < 0.05) and was used for osteogenic differentiation evaluations. The results of Alizarin red staining were not statistically different between the four groups. Osterix and ALP expression increased in the (L +) group. This upregulation abrogated in the presence of Capsazepine, TRPV1 inhibitor (L + Cap); however, no significant effect was observed with Skf96365 (L + Skf).

A Comparative Analysis of Photobiomodulation-Mediated Biological Effects of Single Versus Double Irradiation on Dental Pulp Stem Cells: An In Vitro Study

Objective: In recent years, fractionated irradiation protocols, rather than a simple plan of exposure, have been proposed as a more effective method in the field of tissue regeneration. Thus, this study aimed at a comparative analysis of single versus double irradiation of an 808-nm diode laser, in terms of dental pulp stem cells' (DPSCs) viability and proliferation in vitro. Methods: Subcultured DPSCs were either irradiated, or not (control group), with energy densities of 3, 7, and 12 J·cm^-2 in a single- or double-session manner (24 h apart). On 0, 12, 24, 48, and 72 h postirradiation, cell viability and proliferation were evaluated through Trypan Blue and alamarBlue assays, respectively. Results: During the first 48 h postirradiation, the highest rates of DPSC proliferation were assigned to double irradiation at 3 or single exposure to 7 J⋅cm^-2, with no cytotoxic effects on cell viability. Inversely, single irradiation at 12, or a double session of exposure to 7 or 12 J⋅cm^-2, led to a significant descent in the rates of proliferation and cell viability. Conclusions: Within the limitations of this study, evidence suggests a positive impact on the biological responses of DPSCs following double session of exposure to lower energy densities as well as a single irradiation at a higher energy dosage.

Newly synthesized series of oxoindole–oxadiazole conjugates as potential anti-SARS-CoV-2 agents: in silico and in vitro studies

The pharmacophoric features of the novel series of 1,3,4-oxadiazole–oxoindole conjugates (IVa–g) as potential anti-SARS-CoV-2 agents based on the reported Mpro inhibitor (Ia) are presented.

Photobiomodulation of inflamed dental pulp stem cells under different nutritional conditions

Aim: The present study aimed to investigate photobiomodulation's (PBM) effect on inflamed dental pulp stem cells (IDPSCs) under different nutritional conditions. Methods: Cell proliferation and odontogenic differentiation were evaluated using the MTT assay and real-time quantitative reverse transcription PCR, respectively after laser PBM of cells in 5 or 10% fetal bovine serum (FBS) culture conditions. Results: A significant positive effect of laser irradiation on cell proliferation under both nutritional conditions after 24 and 48 h was observed. DMP-1 gene expression increased in the groups with laser irradiation and 5% FBS. Comparison of gene expression levels in the four groups revealed no statistically significant stimulatory effect. The highest gene expression was observed in the non-laser group with 5% FBS. Conclusion: Further studies are required to obtain an irradiation setup to ideally improve inflamed dental pulp stem cells' proliferation and differentiation.

Effect of Different Energy Densities of 915 nm Low Power Laser on The Biological Behavior of Human Gingival Fibroblast Cells in-vitro

Photobiomodulation is recognized as an effective method for adjunct therapy in periodontal treatments. our purpose in this study was to investigate the effects of different energy densities of 915nm diode laser on the viability and viability capacity of human gingival fibroblast cells. cell samples were examined in 5 groups, including 4 irradiation groups with low-level diode laser 915nm, 1,2,3,4 J/cm² , and a control group (no Laser irradiation). Cell viability and viability were measured 1, 3 and 5 days after irradiation by MTT and DAPI assay. Statistical differences between groups at any time were analyzed by one-way ANOVA and a post hoc Turkey's test. The cell viability and viability capacity increased on the third day at an energy density of 3 J/cm² ; (P-value = 0.007) and the fifth day at energy densities of 2,3 and 4 J/cm² was recorded compared to the control group (P-value =0.000). Also, a significant decrease in the viability and viability of irradiated cells with an energy density of 1 J/cm² was found. (P-value =0.033). according to our results, Photobiomodulation with 915nm diode laser has a positive stimulating effect on the viability and viability capacity of human gingival fibroblast cells.

β-Blockers bearing hydroxyethylamine and hydroxyethylene as potential SARS-CoV-2 Mpro inhibitors: rational based design, in silico, in vitro, and SAR studies for lead optimization

The global COVID-19 pandemic became more threatening especially after the introduction of the second and third waves with the current large expectations for a fourth one as well. This urged scientists to rapidly develop a new effective therapy to combat SARS-CoV-2. Based on the structures of β-adrenergic blockers having the same hydroxyethylamine and hydroxyethylene moieties present in the HIV-1 protease inhibitors which were found previously to inhibit the replication of SARS-CoV, we suggested that they may decrease the SARS-CoV-2 entry into the host cell through their ability to decrease the activity of RAAS and ACE2 as well. Herein, molecular docking of twenty FDA-approved β-blockers was performed targeting SARS-CoV-2 Mpro. Results showed promising inhibitory activities especially for Carvedilol (CAR) and Nebivolol (NEB) members. Moreover, these two drugs together with Bisoprolol (BIS) as an example from the lower active ones were subjected to molecular dynamics simulations at 100 ns. Great stability across the whole 100 ns timeframe was observed for the top docked ligands, CAR and NEB, over BIS. Conformational analysis of the examined drugs and hydrogen bond investigation with the pocket's crucial residues confirm the great affinity and confinement of CAR and NEB within the Mpro binding site. Moreover, the binding-free energy analysis and residue-wise contribution analysis highlight the nature of ligand-protein interaction and provide guidance for lead development and optimization. Furthermore, the examined three drugs were tested for their in vitro inhibitory activities towards SARS-CoV-2. It is worth mentioning that NEB achieved the most potential anti-SARS-CoV-2 activity with an IC50 value of 0.030 μg ml-1. Besides, CAR was found to have a promising inhibitory activity with an IC50 of 0.350 μg ml-1. Also, the IC50 value of BIS was found to be as low as 15.917 μg ml-1. Finally, the SARS-CoV-2 Mpro assay was performed to evaluate and confirm the inhibitory effects of the tested compounds (BIS, CAR, and NEB) towards the SARS-CoV-2 Mpro enzyme. The obtained results showed very promising SARS-CoV-2 Mpro inhibitory activities of BIS, CAR, and NEB (IC50 = 118.50, 204.60, and 60.20 μg ml-1, respectively) compared to lopinavir (IC50 = 73.68 μg ml-1) as a reference standard.

Anti-SARS-CoV-2 activities of tanshinone IIA, carnosic acid, rosmarinic acid, salvianolic acid, baicalein, and glycyrrhetinic acid between computational and in vitro insights

Six compounds namely, tanshinone IIA (1), carnosic acid (2), rosmarinic acid (3), salvianolic acid B (4), baicalein (5), and glycyrrhetinic acid (6) were screened for their anti-SARS-CoV-2 activities against both the spike (S) and main protease (Mpro) receptors using molecular docking studies. Molecular docking recommended the superior affinities of both salvianolic acid B (4) and glycyrrhetinic acid (6) as the common results from the previously published computational articles. On the other hand, their actual anti-SARS-CoV-2 activities were tested in vitro using plaque reduction assay to calculate their IC₅₀ values after measuring their CC₅₀ values using MTT assay on Vero E6 cells. Surprisingly, tanshinone IIA (1) was the most promising member with IC₅₀ equals 4.08 ng μl^-1. Also, both carnosic acid (2) and rosmarinic acid (3) showed promising IC₅₀ values of 15.37 and 25.47 ng μl^-1, respectively. However, salvianolic acid (4) showed a weak anti-SARS-CoV-2 activity with an IC₅₀ value equals 58.29 ng μl^-1. Furthermore, molecular dynamics simulations for 100 ns were performed for the most active compound from the computational point of view (salvianolic acid 4), besides, the most active one biologically (tanshinone IIA 1) on both the S and Mpro complexes of them (four different molecular dynamics processes) to confirm the docking results and give more insights regarding the stability of both compounds inside the SARS-CoV-2 mentioned receptors, respectively. Also, to understand the mechanism of action for the tested compounds towards SARS-CoV-2 inhibition it was necessary to examine the mode of action for the most two promising compounds, tanshinone IIA (1) and carnosic acid (2). Both compounds (1 and 2) showed very promising virucidal activity with a most prominent inhibitory effect on viral adsorption rather than its replication. This recommended the predicted activity of the two compounds against the S protein of SARS-CoV-2 rather than its Mpro protein. Our results could be very promising to rearrange the previously mentioned compounds based on their actual inhibitory activities towards SARS-CoV-2 and to search for the reasons behind the great differences between their in silico and in vitro results against SARS-CoV-2. Finally, we recommend further advanced preclinical and clinical studies especially for tanshinone IIA (1) to be rapidly applied in COVID-19 management either alone or in combination with carnosic acid (2), rosmarinic acid (3), and/or salvianolic acid (4).

The effectiveness of hydroxyapatite-beta tricalcium phosphate incorporated into stem cells from human exfoliated deciduous teeth for reconstruction of rat calvarial bone defects

OBJECTIVE

To investigate the effects of stem cells from the pulp of human exfoliated deciduous teeth (SHED) on biphasic calcium phosphate granules (BCP) to repair rat calvarial defects as compared to autogenous bone grafting.

MATERIALS AND METHODS

A defect with a 6-mm diameter was produced on the calvaria of 50 rats. BCP granules were incorporated into SHED cultures grown for 7 days in conventional (CM) or osteogenic (OM) culture media. The animals were allocated into 5 groups of 10, namely: clot, autogenous bone, BCP, BCP+SHED in CM (BCP-CM), and BCP+SHED in OM (BCP-OM). The presence of newly formed bone and residual biomaterial particles was assessed by histometric analysis after 4 and 8 weeks.

RESULTS

The autogenous group showed the largest newly formed bone area at week 8 and in the entire experimental period, with a significant difference in relation to the other groups (P < 0.05). At week 8, BCP-CM and BCP-OM groups showed homogeneous new bone formation (P = 0.13). When considering the entire experimental period, the BCP group had the highest percentage of residual particle area, with no significant difference from the BCP-CM group (P = 0.06) and with a significant difference from the BCP-OM group (P = 0.01). BCP-CM and BCP-OM groups were homogeneous throughout the experimental period (P = 0.59).

CONCLUSIONS

BCP incorporated into SHED cultures showed promising outcomes, albeit less pronounced than autogenous grafting, for the repair of rat calvarial defects.

CLINICAL RELEVANCE

BCP incorporated into SHED cultures showed to be an alternative in view of the disadvantages to obtain autogenous bone graft.

Photobiomodulation Effect of Different Diode Wavelengths on the Proliferation of Human Gingival Fibroblast Cells

This study is focused on comparing the effect of various energy densities and wavelengths of diode lasers on the proliferation of human gingival fibroblast (HGF) cells in vitro. In this study, 204 sample cells were examined in 4 test groups (laser radiation) and 1 control group (non-laser radiation). The proliferation rate of radiated cells with wavelengths of 635, 660, 808 and 980 nm and the densities of 1, 1.5, 2.5 and 4 J cm^-2 was measured after 1, 3 and 5 days using the MTT assay. The proliferation rate of human gingival fibroblast (HGF) cells in test groups was increased on day 1 at wavelengths of 635, 808 and 980 nm and on day 3 at the wavelength of 980 nm compared with the control group. Our findings denoted that the photobiomodulation therapy increased the proliferation rate of HGF. The most desirable laser radiation setting, which led to the highest proliferation rate of the cells, included 980 nm wavelength with 1, 1.5 and 4 J cm^-2 energy densities and 635 nm wavelength with 4 J cm^-2 energy density.

Could the photobiomodulation therapy induce angiogenic growth factors expression from dental pulp cells?

This study aimed to evaluate the effect of different photobiomodulation (PBM) radiant exposures on the viability, proliferation, and gene expression of pulp fibroblasts from human primary teeth (HPF) involved in the pulp tissue repair. HPF were irradiated with Laser InGaAlP (Twin Flex Evolution, MMOptics®) at 660-nm wavelength (red); single time, continuous mode, 0.04-cm² laser tip area, and 0.225-cm laser tip diameter, keeping the distance of 1 mm between the laser beam and the cell culture. The doses used were between 1.2 and 6.2 J/cm² and were evaluated at the 6 h, 12 h, and 24 h after PBM. MTT and crystal violet assays evaluated the cell viability and proliferation. RT-PCR verified VEGF and FGF-2 mRNA expression. A blinded examiner analyzed the data through two-way ANOVA followed by Tukey test (p < 0.05). The groups with higher powers (10 mW, 15 mW, 20 mW, and 25 mW), shortest application periods (10 s), and radiant exposures between 2.5 and 6.2 J/cm² exhibited statistically higher viability than that of the groups with small power (5 mW), longer application period (50 s), and radiant exposure of 6.2 J/cm² (p < 0.05). VEGF and FGF-2 mRNA expression were observed at the three evaluated periods (6 h, 12 h, and 24 h) and the highest expression was in the shortest period (p < 0.05). All radiant exposures maintained HPF viable. The period of 6 h after irradiation showed statistically greater gene expression for both growth factors than other periods. VEGF mRNA had no differences among the dosimetries studied. The best radiant exposures for FGF-2 gene expression were 2.5 J/cm² and 3.7 J/cm².

Angiogenic protein synthesis after photobiomodulation therapy on SHED: a preliminary study

This study evaluated the viability, proliferation, and protein expression after photobiomodulation (PBM) of stem cell from human exfoliated deciduous teeth (SHED). The groups were the following: G1 (2.5 J/cm2), G2 (3.7 J/cm2), and control (not irradiated). According to the groups, cells were irradiated with InGaAlP diode laser at 660 nm wavelength, continuous mode, and single time application. After 6 h, 12 h, and 24 h from irradiation, the cell viability and proliferation, and the protein expression were analyzed by MTT, crystal violet, and ELISA multiplex assay, respectively. Twenty-four hours after PBM, SHED showed better proliferation. Over time in the supernatant, all groups had an increase at the levels of VEGF-C, VEGF-A, and PLGF. In the lysate, the control and G2 exhibited a decrease of the VEGF-A, PECAM-1, and PLGF expression, while control and G3 decreased VEGF-C, VEGF-A, and PDGF expression. The dosimetries of 2.5 J/cm2 and 3.7 J/cm2 maintained viability, improved proliferation, and synthesis of the angiogenic proteins in the supernatant in the studied periods on SHED.

Effect of single and multiple doses of low-level laser therapy on viability and proliferation of stem cells from human exfoliated deciduous teeth (SHED)

The present study aimed to evaluate in vitro whether the low-level laser (LLL) delivering fractionated total energy (multiple irradiation) or single irradiation stimulates regeneration-associated events (viability and proliferation) in stem cells from human exfoliated deciduous teeth (SHED). Cells received LLL irradiation (InGaAlP-660 nm), according to the following experimental groups: G1 (single irradiation 2.5 J/cm², 10 mW, 10 s, 0.10 J), G2 (single irradiation 5.0 J/cm², 10 mW, 20 s, 0.20 J), G3 (single irradiation 7.5 J/cm², 10 mW, 30 s, 0.30 J), G4 (two irradiations 2.5 J/cm², 10 mW, 10 s; total energy 0.20 J), G5 (three irradiations 2.5 J/cm², 10 mW, 10 s; total energy 0.30 J), and G6 (non-irradiated). Cell viability was assessed by MTT and trypan blue exclusion (TBE) methods, while cell proliferation was evaluated by crystal violet (CV) and sulforhodamine B (SRB) assays after 24, 48, and 72 h after the first irradiation. By MTT, there was no difference between groups at 24 and 72 h. At 48 h, the groups subjected to multiple irradiation (G4 and G5) presented higher cell viability rates. The average percentages of viable cells for all groups by TBE method were 91.04%, 96.63%, and 97.48% at 24, 48, and 72 h, respectively. By CV, there was no significant difference between groups at 24 and 48 h; at 72 h, G2, G3, and G4 presented higher cell proliferation. By SRB, G1 and G4 presented lower proliferation rates in all the periods. When the groups presenting the same total energy were compared, G2 (0.20 J) presented lower cell viability rates and higher cell proliferation rates in comparison with G4; G3 (0.30 J) presented similar results to those of G5, with higher cell viability and proliferation. The application of laser delivering fractionated total energy (two or three applications of 2.5 J/cm²) induced higher cell viability at 48 h, while the single irradiation with 2.5 J/cm² did not stimulate metabolic activity in such period and the proliferation over time. The 5.0 and 7.5 J/cm² single doses and the three applications of 2.5 J/cm² maintained cell viability and stimulated proliferation of SHED at 72 h.