Low-intensity pulsed ultrasound improves osseointegration of dental implant in mice by inducing local neuronal production of αCGRP

Objective: This study aimed to explore the effect of Low-intensity pulsed ultrasound (LIPUS) on implant osseointegration and elucidate the role of alpha-calcitonin gene-related peptide (alpha CGRP) in this process. Design: In vivo, alpha CGRP(+/+) (Wild-type model) mice and alpha CGRP(-/-) (Knock-out model) mice with implants immediately placed in the maxillary first molars extraction sockets were treated with LIPUS. We detected details of peri-implant bone tissues by micro-CT, real-time PCR and histological analysis. In vitro, alpha CGRP(+/+) and alpha CGRP(-/-) dorsal root ganglia (DRG) neurons were cultured and exposed to LIPUS. Then conditioned media from these neurons were collected and added to osteoblasts to analyze cell differentiation, mineralization and proliferation by real-time PCR, alkaline phosphatase (ALP) and cell counting kit-8 (CCK-8) assay. Besides, ELISA was performed to determine the effect of LIPUS on the alpha CGRP secretion in neurons. Results: In vivo tests revealed that alpha CGRP(-/-) mice displayed worse osseointegration when compared to alpha CGRP(+/+) mice. LIPUS could enhance implant osseointegration in alpha CGRP+/+ mice but had little effect on alpha CGRP(-/-) mice. Meanwhile, alpha CGRP was elevated during the osseointegration with LIPUS treatment. In vitro, LIPUS promoted alpha CGRP secretion in DRG neurons, thereby enhanced osteogenic differentiation and mineralization of osteoblasts. Also we proved that the effects of LIPUS was duty cycle-related and LIPUS of 80% duty cycle had the strongest impacts. Conclusions: Our findings demonstrated that LIPUS could enhance osseointegration of dental implant by inducing local neuronal production of alpha CGRP, providing a new idea to promote peri-implant osseointegration and bone regeneration.