## 4 Discussion
In contrast, application of the stimulated method, in which saliva is stimulated with chewing gum or paraffin, results in a different salivary composition because all the salivary glands are stimulated and at least half of all the saliva is secreted by the parotid salivary glands. Therefore, stimulation may alter the protein composition of the saliva, and nickel has a high affinity for protein, thus affecting the nickel content of the saliva [26]. The movement and friction of the parts of the brackets can lead to corrosion and the release of metals into saliva [17]. In the oral cavity, the release of ions is influenced by many factors: saliva, which has a dynamic composition; physiological differences, such as diet, pH, physical condition, and the chemical properties of food; and the qualitative composition of the saliva and the rate of its release [27]. The daily intake of nickel and chromium ions is about 300-600 ug/day and50-200 \(\upmu\)g/day, respectively. The main sources of nickel and chromium ions are vegetables, cereals, and nuts [28]. The normal range of metal ions in the body is 300-600 \(\upmu\)g for nickel and 50-200 \(\upmu\)g for chromium [14], which is higher than the levels of these ions found in the saliva of the patients in this study. The age of the patient also has a significant influence on the qualitative and quantitative changes in the saliva. In adolescence, an increase in saliva can be observed due to hormonal changes during puberty. However, it has been shown that salivary secretion gradually decreases over time in adult patients, as age-related changes may inhibit the salivary glands. In all the studies, healthy patients with no dental or oral disease and no metal restorations were included in order to limit the effects of these variables [29]. In the study by [PERSON] et al. [16], the aim was to completely eliminate environmental factors; therefore, a same-sex brother or sister was chosen in the treatment and control groups. Chemical processes in the oral cavity can lead to a certain degree of corrosion and the release of metal ions [30] In ten studies, orthodontic treatment was followed by an increase in nickel and chromium ion levels, which could be due to corrosion on the surface of the brackets, metal archives, and ligatures [31]. Nickel is a cathode and causes corrosion on the surface of stainless steel alloys during the first days of orthodontic treatment, after which these chemical reactions decrease. A chromium oxide layer is formed on the metal parts, and the chromium can be released into the oral cavity under the influence of physical and chemical factors [32]. A detailed medical and dental history is needed in order to create a personalized orthodontic treatment plan and to select the optimal appliances. For patients who are allergic to nickel, alternative orthodontic appliances are recommended, consisting of materials such as ceramics, polycarbonates, and metal alloys coated with epoxy resins, as well as brackets made of titanium, vanadium, cobalt-chrome, and aluminum [2]. In the event of even mild signs and symptoms of allergy during orthodontic treatment, it is necessary to carry out detailed examinations and to make a decision about modifying the orthodontic treatment and the continued use of the particular appliance [29]. However, in the future, our findings should be supported by more substantial research.