Experimental orthodontic pain drives anxiety state through the induction of alterations to the neuronal architecture in hippocampus.

Background: To explore the effect and mechanism of hippocampus on experimental orthodontic pain-induced anxiety.

Methods: Herein, we document a novel modeling method whereby the nickel-titanium (Ni-Ti) orthodontic wire was fixed stably in the oral cavity of mice with a ligation technique to induce stable distal movement of maxillary incisors to mimic orthodontic tooth movement. At the experimental endpoint, serum corticosterone assay, Golgi staining and Micro-CT were performed in each group after oral-facial mechanical pain sensitivity assessment and open field test.

Results: The mechanical pain sensitivity of experimental tooth movement pain (ETMP) mice had an apparent increased elicited following tooth movement. And anxiety-like behavior was developed: reduced the time proportion of center zone and the total moving distance in the open field test and the elevated serum corticosterone levels in ETMP mice relative to control group mice. The Golgi staining in ventral hippocampal CA1 revealed that neural spine density, dendritic length and number of dendrites are reduced markedly in ETMP mice compared with the control group.

Conclusion: Experimental orthodontic pain drives emotional anxiety through the plasticity changes in decreased neuronal complexity and reduced spine density in ventral hippocampal CA1 in mice.