## 1 Introduction  
Periodontium as a component of the masticatory organ surrounds and immobilizes the tooth. It consists of root cement, alveolar bone with periosteum, periodontitis, and gingiva [1]. During orthodontic treatment, permanent forces applied to the tooth are transferred to the periodontium. With a significant load on it, immediate movement within the periodontal space is prevented by tissue fluid. During the first second of pressure on the tooth, a small amount of tissue fluid is squeezed out of the periodontal space. If the pressure on the tooth persists, the fluid is squeezed out quickly, and the tooth moves inside the periodontal gap by pressing the periodontal ligament to the adjacent bone. Normally, 3-5 s after applying a great force, pain is felt, which indicates that the tissue fluid has been squeezed out and the crushing pressure acts on the periodontal ligament itself [2]. The periodontal ligament, due to the special arrangement of collagen fibers, is well adapted to resist forces that act briefly, such as chewing forces, which reach 700-1000 N within molars [3, 4, 5]. The maximal bite force clearly depends on many factors such as gender, number of interdental contacts in the occlusion, and muscles size [6]. However, these are intermittent forces--during chewing, tooth contact lasts a maximum of 1s. Constant forces cause such a strong displacement of the tooth within the periodontal gap that the tissue fluid is squeezed out of the periodontal space. Orthodontic force, acting for a long time,despite low intensity, causes periodontal remodeling, resulting in resorption and aposition of bone tissue belonging to the periodontium. The response to orthodontic force applied to the teeth is a function of the magnitude of the force [2; 7; 8; 9; 10; 11]. After applying orthodontic forces, the tooth moves in the periodontal ligament under the force of pressure from one side of the tooth root and pulling on the other. These forces change the blood flow within the blood vessels--the pressure of the tooth on the periodontal gap decreases the blood flow and pulling increases by changing the cross-section of the blood vessels. Changes in blood flow in the oppressed area cause a decrease in oxygen levels, and in the tense part of the ligament, it increases. The appropriate proportions of metabolites change within a few minutes. After 1-2 s, the fluid is already partly squeezed out, and the tooth moves within the periodontal space. The blood vessels within the periodonotin are partially narrowed on the compressed side 3-5 s from the application of force and widened on the stretched side; the fibers and periodonotin cells are mechanically twisted, which is a sign of toothache. After a few minutes, the blood flow changes, oxygen pressure begins to change, and prostaglandandins and cytokines are released [12]. The action of force affects the systemic remodeling of the appendix and periodontitis up to 14 days from the application of force due to the activation of cells responsible for resorption and bone superstructure [13]. From the point of view of physiology, periodic metabolic activity during tooth movement is associated with limited inflammation of the above tissues. The temperature of a healthy gingiva measured subgingivally in the space between the marginal gingiva and the connecting epithelium is on average 36.1 \({}^{\circ}\)C [14]. Considering this fact, the following studies hypothesized that a constant orthodontic force applied to the teeth, by changing the blood flow and affecting the release of proinflammatory cytokines, affects the change in periodontal temperature and thus also the gingiva. Theoretically, within the part of the pulled periodontal ligament, the temperature should change differently than in the part where collagen fibers and vessels are compressed.