Gluma etch 35 gel

The labial surface of the maxillary incisor was prepared by a high-speed turbine hand piece to remove its enamel and expose the dentine (Fig. 1A and B). Then, the labial surface of the prepared incisor was etched with 37% phosphoric acid gel (Gluma Etch 35 Gel, Heraeus Kulzer GmbH, Germany) for 15 second and the surface was rinsed with a large volume of deionized water. After these two steps, the acid-etched labial dentine surface of the maxillary incisor was formed.

The rats in the EO and SE groups were anesthetized by an intraperitoneal injection of 2% ketamine hydrochloride 2 mL/kg (Jiangsu Hengrui Medicine Co Ltd, Lianyungang, People’s Republic of China) during setting and adjusting of the orthodontic appliance. Once anesthetized, the rats were kept supine on the operating table, with the extremities and head fixed. The maxillary modulus of the rats was taken using a homemade tray to achieve an individual impression and the working model. According to the model, a stainless steel orthodontic wire (0.014 inch heat-treated arch wire, AJ Wilcock Pty Ltd, Whittlesea, Australia) was bent into a rectangular form with two opening loops (Figure 1A). After the appliances were bonded to the first and second maxillary molars on both sides, light-cured adhesive (Gluma Comfort Bond, Heraeus Kulzer GmbH, Hanau, Germany) was attached to the molars of the rats after etching the teeth with acid etch (Gluma Etch 35 Gel, Heraeus Kulzer GmbH). The initial expansive force was adjusted to 0.98 N, measured with a strain gauge (Hangzhou Aosu Medical Device Co, Hangzhou, People’s Republic of China). The occlusal view of the orthodontic appliance in the maxilla of the rat is shown in Figure 1B. During surgery, the rats were kept warm by lighting in order to maintain body temperature, and vital signs were closely observed until the rats were fully awake.