To study the effect of continuous static pressure on the endoplasmic reticulum of human periodontal ligament cells (hPDLCs) and the mechanism of osteogenic differentiation.

hPDLCs cultured in vitro were subjected to 1 g/cm² of continuous compressive pressure (CCP) by custom-made, round, glass panes for 0, 2, 4, and 6 h, respectively. Alkaline phosphatase staining was used to detect osteogenic differentiation, and real-time quantitative PCR was used to detect the expression of protein kinase receptor-like ER kinase (PERK), eukaryotic translation initiation factor 2α (eIF2α), and transcription activation factor 4 (ATF-4). The 0 h loading group was the control group.

After CCP treatment, the alkaline phosphatase staining of hPDLCs was blue-violet and significantly stronger than that of cells in the control group. The expression levels of PERK and ATF4 in the hPDLCs after CCP treatment were higher than those of cells in the control group (P < 0.05) and increased over time (P < 0.05). The expression of eIF2α was lower in the experimental groups than in the control group (P < 0.05) and decreased over time (P < 0.05).

Mechanical stimulation can activate ERS in hPDLCs, leading to enhanced PERK-eIF2α-ATF4 signaling and inducing osteogenic differentiation.

To evaluate the efficacy and related risk of low level laser therapy (LLLT) for accelerating tooth movement during orthodontic treatment.

An extensive electronic search was conducted by two reviewers. Randomized controlled trials (RCTs) and quasi-RCTs concerning the efficacy of LLLT for accelerating tooth movement during orthodontic treatment were searched in CENTRAL, PubMed, Medline, Embase, CBM, CNKI.

Six RCTs and three quasi-RCTs, involving 211 patients from six countries, were selected from 173 relevant studies. All nine articles were feasible for the systematic review and meta-analysis, five of which were assessed as moderate risk of bias, while the rest were assessed as high risk of bias. The mean difference and the 95 % confidence interval (95 % CI) of accumulative moved distance of teeth were observed among all the researches. The results showed that the LLLT could accelerate orthodontic tooth movement in 7 days (MD = 0.19, 95% CI 0.02-0.37, P = 0.03) and 2 months (MD = 1.08, 95% CI 0.16-2.01, P = 0.02). Moreover, a relatively lower energy density (2.5, 5 and 8 J/cm²) was seemingly more effective than 20 and 25 J/cm² and even higher ones.

This systematic review and meta-analysis demonstrated that LLLT might speed up the tooth movement in orthodontic treatment. A relatively lower energy density (2.5, 5, and 8 J/cm²) was seemingly more effective than higher ones. More qualified RCTs in human subjects are required.