Quantitative and Qualitative i n vivo Analysis of Metal Residuals in the Saliva of Subjects with and without Fixed Orthodontic Appliances

Metal the Abstract Aim of the Work: The aim of this work was to evaluate Ni e Cr ions in the saliva of subjects with and without fixed orthodontic appliances. Materials and Methods: This was a prospective, non-randomized study of 100 patients, so selected: 50 have undergone fixed orthodontic appliance at least from 24 months; others 50 subjects as control-group, without any fixed and/or removable orthodontic appliance It was conducted according to the Declaration of the World Medical Association of Helsinki. The two selected groups were compatible for age, sex, absence of restoration in amalgam or other metals in the oral cavity. The saliva of all the subjects was collected with standardized sterile methods. The samples were analyzed with an atomic absorption spectrophotometer instrument. Results: Absolute values of the salivary metal ions in the subjects with fixed orthodontic appliances are more than the values observed in the control group, but these values are within the normal range. Conclusion: The results show a greater presence in saliva of Ni and Cr ions in the group with fixed orthodontic device. This research must be deepened because ions released in saliva can have effects both locally and in distant districts.


Introduction
Fixed orthodontic appliances including brackets, orthodontic bands and arches are commonly made of stainless steel and nickel titanium. These materials are generally biocompatible, but many studies have shown the possibility releasing nickel ions and some side effects both locally and in distant districts [1][2][3][4]. The presence of oxides on the external and internal surface of the metal alloys is responsible for the micro-fissures of the crystal lattice. The corrosion processes can be activated even in depth, making the metal alloy a microporous support that favors the adhesion of the bacterial plaque and through this the process of corrosion can occur even severely, making the metal alloy a microporous support, able to foster the adhesion of bacterial plaque which is then in turn responsible for low pH values, facilitating the corrosion process through oxides present in the metal [5][6][7][8]. In food, in tobacco, as in water, aggressive substances such as chlorides and sulphides can be present, which trigger even marked oxidation phenomena [9,10].
Most fixed orthodontic appliances contain metals of various kinds and in varying quantities . These components are constantly subjected to the action of the salivary fluid, but also undergo the chemical and physical action of food. Various Authors [1,[11][12][13][14][15][16][17] have stated that the orthodontic appliances released in the oral cavity the ions metals and they create electric currents how due from the difference in electrical potential between the metals immersed in the salivary fluid. The oral environment can conducive to corrosion with release of ions because of the constantly wet mouth environment, constant temperature, and pH changes in the mouth. Among these ions, nickel has been the subject of major research for its harmful effects on cells, tissues and organs. In these studies it has been re-ported that Ni complexes, in the form of arsenides and sulfides, can be allergenic, carcinogenic, and act as mutant substances [18][19][20][21][22][23][24][25][26]. In fact, 10% of the population has a hypersensitivity reaction to nickel [11,13,14,27]. Some authors have shown that the amounts of nickel released by orthodontic appliances in saliva or serum are significantly lower than the average dietary intake [27,28]. The release of ions varies during the different period of orthodontic treatment and depends on the pH level of the saliva itself. In vitro corrosion studies show different results from the studies conducted in vivo [30][31][32][33].
The purpose of the current work is the quantitative and qualitative analysis of the Ni and Cr ions released in the saliva in subjects wearing fixed orthodontic appliances. A number of factors influencing the metal releasing are also assessed.

Material and Methods
Eligible patients for this study were selected from the Depart-

Results
The quantitative values of the Ni and Cr metals expressed As can be seen from the graph, the Ni values of subjects with fixed orthodontic appliances (in green) are higher than control subjects (in orange). In particular, 4 subjects exceed the limit value of 5 μg / l while other 6 remain just below this threshold of a few μg. Among the control subjects, however, there are no particularly high values, and no one exceeds the limit value of 5 μg / l Graph 1: Shows the average values of the Nickel ions, in the group with fixed appliance and in the control group.  c) The mechanical stress that triggers stress corrosion.
d) The oxygen tension that varies between exposed and internal areas of the devices [28].
Therefore, the oral environment being a galvanic cell, the metals of orthodontic appliances create potential differences in the mouth from 200 up to 1000 milliVolts, going to corrosion. The same microorganisms interacting with the metal surfaces, they also create variations in oxygen tension, pH and local chemistry, contributing to the metallic alteration The combination of these chemical and physical phenomena involves the passage of weak currents in the tissues with dispersion in the oral cavity and in the tissues of metal ions [34]. Cellular and tissue metabolism, both local and systemic, also influences the onset and progression of corrosion phenomena.

Conclusion
The study is conducted on patients with fixed orthodontic appliances therapy compared with patients without orthodontic appliance. The results show to increased levels of Ni and Cr ions in the saliva of patients in therapy. we can find this ions also in soft tissues, and even organs.