Effect of low-level laser irradiation on proliferation of human dental mesenchymal stem cells; a systemic review

Context: Identification of factors that enhance the proliferation of human dental mesenchymal stem cells (DMSCs) is vital to facilitate tissue regeneration. The role of low-level laser irradiation (LLLI) on proliferation of human DMSCs has not been well established. Objective: To assess the effect of LLLI on proliferation of human DMSCs when applied in-vitro. Data Sources: Electronic search of literature was conducted (2000-2016) on PubMed, Web of Science, and Scopus databases. Search terms included low-level light therapy, low-level laser irradiation, low-level light irradiation, LLLT, humans, adolescent, adult, cells, cultured, periodontal ligament, dental pulp, stem cells, dental pulp stem cells, mesenchymal stem cells, periodontal ligament stem cell, deciduous teeth, cell proliferation, adult stem cells, radiation, and proliferation. Results: The literature search identified 165 studies with 6 being eligible for inclusion; all used diode lasers; 5 studies used InGaAIP diode lasers; 4 used 660 nm, and the other two applied 810 nm or 980 nm wavelength LLLI. The distance between the DMSCs and the laser spot ranged between 0.5 mm to 2 mm. The time intervals of cell proliferation analysis ranged from 0 h to 7 days after LLLI. After 660 nm LLLI, an increase in the DMSC's proliferation was reported [DMSCs extracted from dental pulp of deciduous teeth (two irradiations, 3 J/cm(2), 20 mW was more effective than 40 mW), adult teeth (two irradiations, 0.5 and 1.0 J/cm2, 30 mW), and from adult periodontal ligament (two irradiations, 1.0 J/cm(2) was more effective than 0.5 J/cm(2), 30 mW)]. Similarly, an increase in the proliferation of DMSCs extracted from dental pulp of adult teeth was reported after 810 nm LLLI (7 irradiations in 7 days, 0.1 and 0.2 J/cm(2), 60 mW) or 980 nm LLLI (single irradiation, 3 J/cm(2), 100 mW). However, 660 nm LLLI in one study did not increase the proliferation of DMSCs (single irradiation, energy densities of 0.05, 0.30, 7, and 42 J/cm(2), 28 mW). Conclusion: There is limited evidence that in-vitro LLLI (660/810/980 nm, with energy densities of 0.1-3 J/cm(2)) increases the proliferation of DMSCs. Considering the limited evidence and their method heterogeneity it is difficult to reach a firm conclusion. Further research is necessary to identify the optimal characteristics of the LLLI setting (wave length, energy density, power output, frequency/duration of irradiations, distance between the cells and the laser spot/probe) to increase proliferation of DMSCs, and assess its impact on replicative senescence, as well as determine feasibility of the use in the clinical setting. (C) 2016 Elsevier B.V. All rights reserved.