Response of osteoblastic cells to low-level laser treatment: a systematic review

Low-level laser therapy (LLLT)-induced photobiomodulation (PBM) stimulates bone tissue regeneration by inducing osteoblast differentiation and mitochondrial activation. However, the role of reactive oxygen species (ROS) in this process remains controversial. The aim of this systematic review was to collect and analyze the available literature on the cellular and molecular effects of LLLT on osteoblasts and the role of ROS in this process. A search was conducted in PubMed, ScienceDirect, Scopus, and Web of Science. Studies published in English over the past 15 years were selected. Fourteen articles were included with moderate (n = 9) and low risk of bias (n = 5). Thirteen studies reported the use of diode lasers with wavelengths (λ) between 635 and 980 nm. One study used an Nd:YAG laser (λ1064 nm). The most commonly used λ values were 808 and 635 nm. The energy densities ranged from 0.378 to 78.75 J/cm2, and irradiation times from 1.5 to 300 s. Most studies found increases in proliferation, ATP synthesis, mitochondrial activity, and osteoblastic differentiation related to moderate and dose-dependent increases in intracellular ROS levels. Only two studies reported no significant changes. The data presented heterogeneity owing to the variety of LLLT protocols. Although several studies have shown a positive role of ROS in the induction of proliferation, migration, and differentiation of different cell types, further research is required to determine the specific role of ROS in the osteoblastic cell response and the molecular mechanisms involved in triggering previously reported cellular events.