Low-level laser therapy enhances the stability of orthodontic mini-implants via bone formation related to BMP-2 expression in a rat model

Objective: The aim of this study was to investigate the stimulatory effects of low-level laser therapy (LLLT) on the stability of mini-implants in rat tibiae. Background data: In adolescent patients, loosening is a notable complication of mini-implants used to provide anchorage in orthodontic treatments. Previously, the stimulatory effects of LLLT on bone formation were reported; here, it was examined whether LLLT enhanced the stability of mini-implants via peri-implant bone formation. Materials and methods: Seventy-eight titanium mini-implants were placed into both tibiae of 6-week-old male rats. The mini-implants in the right tibia were subjected to LLLT of gallium-aluminium-arsenide laser (830nm) once a day during 7 days, and the mini-implants in the left tibia served as nonirradiated controls. At 7 and 35 days after implantation, the stability of the mini-implants was investigated using the diagnostic tool (Periotest). New bone volume around the mini-implants was measured on days 3, 5, and 7 by in vivo microfocus CT. The gene expression of bone morphogenetic protein (BMP)-2 in bone around the mini-implants was also analyzed using real-time reverse-transcription polymerase chain reaction assays. The data were statistically analyzed using Student's t test. Results: Periotest values were significantly lower (0.79- to 0.65-fold) and the volume of newly formed bone was significantly higher (1.53-fold) in the LLLT group. LLLT also stimulated significant BMP-2 gene expression in peri-implant bone (1.92-fold). Conclusions: LLLT enhanced the stability of mini-implants placed in rat tibiae and accelerated peri-implant bone formation by increasing the gene expression of BMP-2 in surrounding cells.