Occlusal Disharmony in Mice

Five-week-old male C57BL/6J mice were obtained from Sankyo Labo Service Co., Ltd. (Tokyo, Japan). Mice were maintained in our animal care facility under room temperature (21 ± 1 °C), with a 12-h light/12-h dark cycle. The experimental procedures were reviewed and approved by the Institutional Animal Care and Use Committee of the Tokyo Medical and Dental University (Tokyo, Japan, approved number; #0130279A) and all experiments were performed in accordance with relevant guidelines and regulations. Since the mice in the occlusal disharmony group could not easily eat the standard (pellet) diet, the standard diet was changed to a powdered diet on the third day after the standard diet was provided. The mice had three- and six-day acclimation periods, respectively, to adapt to the powdered diet and single cages prior to the experimental intervention (day 0; Fig. 1).
Mice were randomly divided into two groups: a control group (n = 5) and an occlusal disharmony (disharmony) group (n = 5). In the disharmony group, the occlusal height was increased by 0.5 mm, using a composite resin (MI FIL, GC Co. Ltd., Tokyo, Japan), with the mice under anaesthesia, as per methods that have previously been described, but with some modifications^{2 (link),3 (link)} (Fig. 1). The mice were subjected to anaesthesia using medetomidine hydrochloride (0.5 mg/kg; Domitor, Meijiseika, Tokyo, Japan) and ketamine hydrochloride (50 mg/kg; Ketalar, Sankyo, Tokyo, Japan). The same anaesthetic was used in mice in the control group, without any intervention. Atipamezole hydrochloride (the antagonist of medetomidine hydrochloride, 2.5 mg/kg; Nippon Zenyaku Kogyo Co., Ltd., Japan) was administered to all animals to reduce the stress from the anaesthesia^{29 (link)}.