Increased Expression of TRPV1 in the Central Nucleus of the Amygdala Is Involved in Orthodontic Pain in Rats

Transient receptor potential vanilloid type 1 (TRPV1) is known to gate nociceptive signals, while the central amygdala (CeA) plays a key role in encoding pain and avoidance behaviors; however, whether TRPV1 within CeA mediate orthodontic tooth-moving pain remains unclear. To investigate this, we examined the role of TRPV1 in the CeA using a rat model of experimental tooth movement. A total of 118 Sprague-Dawley rats were divided into control, 30 g, 50 g, and 80 g force groups. Micro-CT confirmed successful tooth movement, and the 50 g force was selected as optimal. Pain was assessed by mechanical hypersensitivity using the von Frey test, face-grooming, and the Rat Grimace Scale (RGS). All measures showed maximal changes at day 1 and returned to baseline by day 7. Immunohistochemistry and western blot analysis in the 50 g group revealed upregulation of TRPV1 in the CeA following force application, a trajectory that paralleled the pain behavioral responses. These findings indicate that experimental tooth movement upregulates TRPV1 in the CeA and that this channel contributes to orthodontic pain.