Orthodontic Root Resorption in Spontaneously Hypertensive Rats: Modulation by β2-Adrenergic Receptor Blockade

Background/Objectives: Hypertension is associated with abnormal bone metabolism and enhanced bone resorption, and altered sympathetic/adrenergic signaling has been proposed as one contributing mechanism. Orthodontically induced inflammatory root resorption (OIRR) involves periodontal ligament inflammation, odontoclast induction, and the resorption of cementum and dentin. This study investigated whether the SHR phenotype is associated with greater OIRR and whether the pharmacological blockade of β2-adrenergic receptor (β2-AR) signaling with butoxamine (BTX) modulates these changes. Methods: A 50 gf Ni-Ti closed-coil spring was placed between the maxillary incisors and left first molar in SHRs and Wistar-Kyoto (WKY) rats for 21 days, beginning 7 days after BTX administration. Animals were assigned to WKY(control), WKY(BTX), SHR(control), and SHR(BTX) groups. The tooth-movement distance, root length, and root volume were assessed via micro-computed tomography. The odontoclast number and surface, TNF-α, IL-1β, and β2-AR immunoreactivity, cementocyte density, empty lacunae ratio, and TUNEL-positive cells within cementocyte lacunae were evaluated histologically. Results: Compared with WKY(control), SHR(control) showed greater tooth movement, a reduced root length and volume, an increased odontoclast number and surface, greater TNF-α- and IL-1β-positive areas, a lower cementocyte density, a higher empty lacunae ratio, and more TUNEL-positive cells within cementocyte lacunae. These root resorption- and inflammation-related changes were significantly attenuated in SHR(BTX) compared with SHR(control). Conclusions: The SHR phenotype was associated with increased OIRR, and the attenuation observed following β2-AR blockade supports a potential contribution of adrenergic signaling to this response.