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

Evaluating the effect of strontium ranelate and photobiomodulation on cementogenic and osteogenic differentiation of buccal fat pad-derived stem cells: An in vitro study

This study aimed to analyze the impact of strontium ranelate (Str), photobiomodulation (PBM), or their combination of the proliferation, osteogenic differentiation, and cementogenic differentiation of buccal fat pad-derived stem cells. BFPdSCs were exposed to one of the following interventions: (1) PBM (660 nm), (2) PBM (660 nm) + Str, (3) PBM (880 nm), (4) PBM (880 nm) + Str, (5) Str. All study groups had significantly higher osteogenic differentiation than the control group (p < 0.05), and no significant difference existed between the 660 and 808 nm groups (p = 0.97). Compared to the Str group, 660 nm and 880 nm group samples had significantly lower osteogenic differentiation (p < 0.0001), while other groups did not show a significant difference. Regarding cementogenic differentiation, the 660 nm group showed higher values than the 808 nm group (p < 0.01). Compared with the Str group, 660 nm, 660 nm + Str, and 808 nm + Str groups showed significantly higher gene expression (p < 0.05). In the case of osteogenic differentiation, although photobiomodulation alone had a lower inducing effect than strontium ranelate, combining 808 nm diode lasers and strontium ranelate may provide the best results. Moreover, using a 660 nm diode laser and exposing stem cells to strontium ranelate can be the most effective approach to induce cementogenic differentiation.

Impact of Photobiomodulation and Melatonin on Periodontal Healing of Periodontitis in Immunosuppressed Rats

Introduction: Periodontitis is an inflammatory disease due to bacterial origin; it has a chronic course and progresses by immunosuppressive therapy. However, adjuvant therapies such as photobiomodulation (PBM) and melatonin can reduce the severity of the inflammation and inhibit the progression of periodontitis. Therefore, the present study evaluated the effects of PBM (PBM) and melatonin, as adjuvant therapies, on periodontal healing in immunosuppressed rats with periodontitis. Methods: Random allocation was performed on 36 albino Wistar rats, divided into the following groups: control, periodontitis, immunosuppressant only, immunosuppressant+PBM, immunosuppressant+melatonin, and immunosuppressant+melatonin+PBM. Periodontitis caused by ligature in all groups, except for the control group. Subcutaneous administration of dexamethasone was performed in the immunosuppressant groups for immunosuppression. All the groups except the control group received scaling and root planning (SRP). Each group was subdivided into three equal subgroups according to the evaluation period: (A), one week, (B) two weeks (C), 4 weeks. Histological examination was done with haematoxylin & eosin and Masson's Trichrome for inflammation and periodontal healing. Statistical Analysis of the data was done by using the chi-square test. The significance level was set at P≤0.05. Results: Regarding the inflammatory response and periodontal healing, histological examination revealed statistically significant difference in all treated groups in comparison with the control untreated immunosuppressed group (P<0.001). The combined application of melatonin and PBM resulted in a best histological response presented by lower inflammatory response and better periodontal healing, when compared with all other treated groups (P<0.001). Conclusion: After considering the circumstances of this research, the combination of melatonin and PBM by a 650 nm diode laser with output power of 100 mw for one minute for three sessions appeared to be a beneficial adjunct in periodontal healing in immunosuppressed rats with periodontitis.

Cytotoxicity of dilutions of bioceramic materials in stem cells of human exfoliated deciduous teeth

OBJECTIVE

Several materials have been developed to preserve pulp vitality. They should have ideal cytocompatibility characteristics to promote the activity of stem cells of human exfoliated deciduous teeth (SHED) and thus heal pulp tissue.

OBJECTIVE

To evaluate the cytotoxicity of different dilutions of bioceramic material extracts in SHED.

METHODOLOGY

SHED were immersed in αMEM + the material extract according to the following experimental groups: Group 1 (G1) -BBio membrane, Group 2 (G2) - Bio-C Repair, Group 3 (G3) - MTA Repair HP, Group 4 (G4) - TheraCal LC, and Group 5 (G5) - Biodentine. Positive and negative control groups were maintained respectively in αMEM + 10% FBS and Milli-Q Water. The methods to analyze cell viability and proliferation involved MTT and Alamar Blue assays at 24, 48, and 72H after the contact of the SHED with bioceramic extracts at 1:1 and 1:2 dilutions. Data were analyzed by the three-way ANOVA, followed by Tukey's test (p<0.05).

RESULTS

At 1:1 dilution, SHED in contact with the MTA HP Repair extract showed statistically higher cell viability than the other experimental groups and the negative control (p<0.05), except for TheraCal LC (p> 0.05). At 1:2 dilution, BBio Membrane and Bio-C showed statistically higher values in intra- and intergroup comparisons (p<0.05). BBio Membrane, Bio-C Repair, and Biodentine extracts at 1:1 dilution showed greater cytotoxicity than 1:2 dilution in all periods (p<0.05).

CONCLUSION

MTA HP Repair showed the lowest cytotoxicity even at a 1:1 dilution. At a 1:2 dilution, the SHED in contact with the BBio membrane extract showed high cell viability. Thus, the BBio membrane would be a new non-cytotoxic biomaterial for SHED. Results offer possibilities of biomaterials that can be indicated for use in clinical regenerative procedures of the dentin-pulp complex.

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.

Effect of LASER photobiomodulation on the cell viabilities of periodontal ligament fibroblasts of older and younger individuals - An in vitro study

Background and Objectives

Fibroblasts form the major cell type of the periodontal ligament and most often studied for periodontal regeneration. The aim of the present study was to investigate the effects of photobiomodulation (PBM) on aged periodontal fibroblasts and compare the viability of periodontal fibroblasts of older and younger individuals.

Materials and Methods

A total of 32 patients were divided into four groups: A, B, C, and D. Groups A and C and B and D comprised of extracted teeth of older (>60 year) and younger individuals (<25 year), respectively. Extracted teeth from Groups A and B received PBM, (diode laser, 660 nm, 100 mW at 4J) whereas Groups C and D did not. Tissue from extracted teeth of all groups was processed and cultured and subjected to 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay to assess their viability.

Results

The difference between the groups in terms of viability was significant (P < 0.0001). The mean viability of A and B (PBM) was 1.04 and 1.19, respectively. The mean viability for C and D (non-PBM) was 0.95 and 0.85, respectively.

Conclusion

Older fibroblasts have lower viability than younger fibroblasts. PBM improves viability in both older and younger fibroblasts and more so in younger fibroblasts. However, more than one PBM would be required to sustain the effect longer.

Effects of Two Protocols of Low-Level Laser Therapy on the Proliferation and Differentiation of Human Dental Pulp Stem Cells on Sandblasted Titanium Discs: An In Vitro Study

Introduction: Stem cell activities have different effects on tissue response and its outcomes. Low-level laser therapy (LLLT) can be considered a trigger to modify stem cell activities. The objective of the present experimental investigation was to study the effects of two protocols of LLLT on the proliferation and differentiation of human dental pulp stem cells (hDPSCs) cultured on sandblasted titanium discs. Methods: Cells obtained from human dental pulp were seeded/cultured on titanium discs and were set in 2 main groups: (i) Radiated cells using the gallium-aluminium-arsenide (GaAlAs) diode laser at a continuous wavelength of 808 nm at 3 J/cm² for 12 sec or 5 J/cm² for 20 seconds, and (ii) Non-irradiated cells serving as control groups. The impact of LLLTs on hDPSC-proliferation and viability was investigated using the MTT assay after 24, 72 and 96 hours. The alkaline phosphatase activity was studied with p-nitrophenylphosphate after 14 and 28 days. The ability of hDPSCs to express osteocalcin was investigated using real-time polymerase chain reaction after 28 days, while their attachment was observed under a scanning electron microscope (SEM) after 14 and 28 days. Results: Our study showed that LLLTs caused maximum cell proliferation in 96 hours (P<0.001) with 3 J/cm² resulting in a higher proliferation rate. The highest activity of alkaline phosphatase and osteocalcin expression was observed in the laser radiation groups after 28 days. Conclusion: The outcomes of the current study showed that cultured hDPSCs on sandblasted titanium discs had a tendency towards increased cellular activity in response to LLLTs. Thus, LLLTs could regulate the activities of hDPSCs on bone repair surrounding the sandblasted titanium discs.

The effects of combination therapy by solid lipid nanoparticle and dental stem cells on different degenerative diseases

Stem cells have multiple therapeutic applications, as well as solid lipid nanoparticles. Solid lipid nanoparticle has appeared as a field of nano lipid technology with various potential applications in drug delivery, clinical medicine and research. Besides, the stem cells have a high proliferation rate and could differentiate into a variety of tissues. Stem cells derived from human dental pulp tissue differ from other sources of mesenchymal stem cells due to their embryonic neural crest source and neurotrophic potential. These consist of both dental pulp stem cells from dental pulp tissues of human permanent teeth and stem cells from human exfoliated deciduous teeth. With the emergence of stem cell banks, stem cells are considering for tissue engineering with respect to therapies attitude and regenerative medicine. The present study aimed to evaluate the advantages and disadvantages of the solid lipid nanoparticle and stem cells combination therapy in different therapeutic applications. The solid lipid nanoparticles have anticancer activity against tumors, induce neural differentiation in pluripotent stem cells, and regulate the mesenchymal stem cells. They also have immunomodulatory effects on human mesenchymal stem cells, the gene transfection efficiency, osteogenic differentiation and bone regeneration. But, the crucial health hazards related to stem cell transplantation such as immune rejection reactions and the interaction with other tissues and the effect of solid lipid nanoparticles must not be neglected. Overall, more experiments need to approve the synergism and antagonism effects of the stem cells and solid lipid nanoparticle combination therapy on different degenerative diseases.

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.

The therapeutic effects of stem cells from human exfoliated deciduous teeth on clinical diseases: a narrative review study

INTRODUCTION

Stem cells isolated from human dental pulp tissue are different from other sources of Mesenchymal stem cells because of their embryonic neural crest sources and neuro-trophic potential. These stem cells consist of dental pulp stem cells from human permanent teeth and stem cells from human exfoliated deciduous teeth.

AIM

In this study, we survey the advantages and disadvantages of these stem cells with therapies attitude.

MAIN TEXT

Stem cells from human exfoliated deciduous teeth with a high proliferation rate could distinguish into a wide types of cells. After stem cell banking appearance, stem cells from human exfoliated deciduous teeth can preserve and use for treatment, especially in regenerative medicine. But the crucial health hazards related to stem cell transplantation, such as immune rejection reactions and the interaction with other tissues, should not be neglected.

CONCLUSION

Further experiments are required to approve the impact of these stem cells on different human disorders.

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.

Photobiomodulation has rejuvenating effects on aged bone marrow mesenchymal stem cells

The plasticity and proliferative capacity of stem cells decrease with aging, compromising their tissue regenerative potential and therapeutic applications. This decline is directly linked to mitochondrial dysfunction. Here, we present an effective strategy to reverse aging of mouse bone marrow mesenchymal stem cells (BM-MSCs) by restoring their mitochondrial functionality using photobiomodulation (PBM) therapy. Following the characterization of young and aged MSCs, our results show that a near-infrared PBM treatment delivering 3 J/cm2 is the most effective modality for improving mitochondrial functionality and aging markers. Furthermore, our results unveil that young and aged MSCs respond differently to the same modality of PBM: whereas the beneficial effect of a single PBM treatment dissipates within 7 h in aged stem cells, it is lasting in young ones. Nevertheless, by applying three consecutive treatments at 24-h intervals, we were able to obtain a lasting rejuvenating effect on aged MSCs. Our findings are of particular significance for improving autologous stem cell transplantation in older individuals who need such therapies most.

Protective effect of low-level laser irradiation on lipopolysaccharide-mediated inflammatory injury of human periodontal ligament fibroblasts

OBJECTIVES

To study the effect and mechanism of low-level laser irradiation (LLLI) on lipopolysaccharide (LPS)-induced inflammatory injury of human periodontal ligament fibroblasts (hPDLFs).

METHODS

hPDLFs were inoculated into well plates and randomly divided into the normal group, LPS group, and LPS+LLLI group. The cells in the normal group were cultured in conventional medium. The hPDLFs in the LPS and LPS+LLLI groups were cultured in RPMI1640 medium containing 1 mg·L^-1 LPS. The three subgroups of the LPS+LLLI group were exposed to different LLLI. After 4 days, the cell apoptosis, viability, and intracellular free Ca²⁺ concentration of each group were measured. The contents of tumor necrosis factor-α (TNF-α), interleukin (IL)-8, IL-1β, and IL-6 were measured by enzyme linked immunosorbent assay (ELISA). Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot were used to detect the expression of matrix metalloproteinase (MMP)-2, MMP-3, and MMP-9 genes and proteins of hPDLFs in each group.

RESULTS

Compared with the normal group, the LPS group showed increased apoptosis rate of hPDLFs and intracellular free Ca²⁺concentration and decreased cell viability (P<0.05). The TNF-α, IL-8, IL-1β, and IL-6 levels were higher in the cell supernatant (P<0.05), and the expression of MMP-2, MMP-3, and MMP-9 genes and proteins of hPDLFs was significantly increased (P<0.05). Compared with the LPS group, the LPS+LLLI group showed significantly decreased apoptosis rate and intracellular free Ca²⁺ concentration and significantly increased cell viability (P<0.05). The TNF-α, IL-8, IL-1β, and IL-6 levels in the supernatant of cells and the expression of MMP-2, MMP-3, and MMP-9 genes and proteins of hPDLFs were significantly decreased (P<0.05).

CONCLUSIONS

LLLI has a protective effect on the inflammatory injury of hPDLFs induced by LPS, and the effect is most obvious when the irradiation intensity is 4 J·cm^-2.

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.

Cytotoxic, Migration, and Angiogenic Effects of Photodynamic Therapy and Photobiomodulation Associated with a Revascularization Protocol

INTRODUCTION

This study evaluated photodynamic therapy (PDT) and photobiomodulation therapy (PBM) as adjuncts to pulp revascularization using cultures of apical papilla cells (APCs) and endothelial cells (HUVECs).

METHODS

The root canal and apical foramen of 2 mandibular first premolars were enlarged to simulate immature teeth. The canal of 1 tooth was filled with 1 mL 0.005% methylene blue (MB). After that, the canals of both teeth were irrigated with 20 mL 1.5% sodium hypochlorite (NaOCl) and 20 mL 17% EDTA. The resulting solutions were diluted in cell culture media at a concentration of 0.5% (0.5% MB + NaOCl + EDTA and 0.5% NaOCl + EDTA). After PDT (0.5% MB + NaOCl + EDTA + PDT) and PBM (0.5% NaOCl + EDTA + PBM) applications, the effects were evaluated to determine cytotoxicity, polarity index, APC migration, and HUVEC sprouting, and results were compared with those of their controls (solutions without laser application). Cell culture media (CT) was also used as a control. Data were analyzed using 1-way analysis of variance and the Tukey post hoc test (P ≤ .05).

RESULTS

PDT and PBM promoted greater APC viability than their controls, and PDT had greater cell viability than CT (P < .05). All protocols reduced APC migration when compared with CT (P < .05). HUVEC sprouts grown out of spheroids in PBM had a greater ratio area than their control (P ≤ .01), and the PDT ratio of the spheroid area was similar to that of its control (P > .05).

CONCLUSIONS

PBM and PDT seem to be potentially effective adjuncts to revascularization in nonvital immature teeth.

Laser-Induced Differentiation of Human Adipose-Derived Stem Cells to Temporomandibular Joint Disc Cells

BACKGROUND AND OBJECTIVES

Temporomandibular disorder (TMD) is an incapacitating disease with temporomandibular joint (TMJ) disc degenerative changes in patients. Despite several research attempts to find a definitive treatment, there is no evidence of a permanent solution. The objective of the current study was to observe the role of 660 nm diode laser in the differentiation of human adipose-derived stem cells (ADSCs) to fibroblasts and chondrocytes.

STUDY DESIGN/MATERIALS AND METHODS

After irradiation, the morphology, viability, and adenosine triphosphate (ATP) proliferation of the ADSCs were analyzed at different time intervals. The differentiation of ADSCs toward fibroblastic and chondrogenic phenotypes was supported using flow cytometry and immunofluorescence at 1- and 2-week post-irradiation.

RESULTS

More than 90% of viable cells were observed in all experimental groups, with an increase in ATP proliferation. Flow cytometry analyses and immunofluorescence demonstrated the presence of chondrogenic and fibroblastic cell surface markers at 1- and 2-week post-irradiation.

CONCLUSION

This study has demonstrated methods to induce the differentiation of ADSCs toward fibroblastic and chondrogenic phenotypes with a 660 nm diode laser. The study also proposes a future alternative method of treatment for patients with degenerative TMJ disc disorders and presents a positive prospect in the application of photobiomodulation and ADSCs in the treatment of degenerative TMJ disc. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

Review on the Cellular Mechanisms of Low-Level Laser Therapy Use in Oncology

Photobiomodulation (PBM) using low-level laser therapy (LLLT) is a treatment that is increasingly used in oncology. Studies reported enhancement of wound healing with reduction in pain, tissue swelling and inflammatory conditions such as radiation dermatitis, oral mucositis, and lymphedema. However, factors such as wavelength, energy density and irradiation frequency influence the cellular mechanisms of LLLT. Moreover, the effects of LLLT vary according to cell types. Thus, controversy arose as a result of poor clinical response reported in some studies that may have used inadequately planned treatment protocols. Since LLLT may enhance tumor cell proliferation, these will also need to be considered before clinical use. This review aims to summarize the current knowledge of the cellular mechanisms of LLLT by considering its effects on cell proliferation, metabolism, angiogenesis, apoptosis and inflammation. With a better understanding of the cellular mechanisms, bridging findings from laboratory studies to clinical application can be improved.

Comparative evaluation of low-level laser therapy on proliferation of long-term cryopreserved human dental pulp cells isolated from deciduous and permanent teeth

The aim of the current study was to evaluate the proliferative effect of low-level laser therapy on long-term cryopreserved dental pulp stem cells (DPSC_S) and stem cells from human exfoliated deciduous teeth (SHED_S). The DPSC_S and SHED_S were divided into 2 main groups according to gallium aluminum arsenide (GaAIAs) diode laser irradiation densities as 5 J/cm² and 7 J/cm². Each main group was further divided into 4 groups according to laser irradiation periods as 0, 24, 48, 72 h groups. During the incubation periods, cells received laser irradiation in every 24 h according to their groups and were put into incubator after irradiation. Cell groups that were not subjected to laser irradiation were served as control groups. Viabilities of cells were determined via MTT assay at the end of all incubation periods, and data were statistically analyzed. Laser irradiation demonstrated significant effects on proliferation rate of DPSCs and SHEDs in comparison with control. Intragroup comparison data of DPSC_S revealed that repetitive laser irradiation for long term (72 h) increased the cellular viability significantly in comparison with all other treatment groups; however, no significant differences were found when energy densities were compared within each time interval, except for 48 h group at which irradiation with 7 J/cm² provided significantly higher cell viability rates of SHED_S. DPSCs showed significantly higher cellular viability than SHEDs only for the 7 J/cm² energy density in 72 h. Longer term (72 h) repetitive laser irradiation with energy densities of 5 and 7 J/cm² (wavelength of 980 nm) may be recommended to induce the proliferative effect on long-term cryopreserved DPSC_S and SHED_S.