Introduction: Biocompatibility is the ability of a material to elicit an appropriate biological response in the oral cavity, without harming the patient's health, causing toxic reactions, allergies, or inflammation. It must also be stable and durable, as it is constantly exposed to the complex environment of the oral cavity, which includes mechanical stress, changes in pH levels, and the presence of bacteria and saliva. Metallic alloys such as stainless steel and cobalt-chromium (CoCr) alloys are used due to their excellent mechanical properties, such as high strength and corrosion resistance. Numerous studies have shown surface changes in both new and used metal alloys due to corrosion processes. Purpose: The aim of this thesis is to present cobalt-chromium alloys and stainless steel, which are used in a digitally manufactured orthodontic appliance for rapid maxillary expansion. Since the surface properties of materials from used digitally manufactured orthodontic appliances for rapid maxillary expansion have not yet been described in the literature, the goal is also to evaluate the surfaces and biocompatibility of the materials used in the appliance. Methods: The thesis is based on a descriptive method of collecting, reviewing, and analyzing existing literature. Literature was searched across several databases, including PubMed, ScienceDirect, Medline, Google Scholar, Cinahl, Cochrane, and COBBIS, which provides access to library resources. The study included a used digitally manufactured rapid maxillary expansion appliance made from CoCrMoW alloy and stainless steel. Surface properties were analyzed using a scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS) for surface chemistry, XRD for chemical analysis, and XPS for surface analysis. Results: For the purpose of the thesis, a digitally manufactured rapid maxillary expansion appliance was designed and planned using the 3Shape Ortho Analyzer software. Scanning electron microscopy and energy-dispersive spectroscopy analysis showed that the CoCr alloy produced using additive technology is suitable for use in orthodontic appliances. After six months of clinical use, no changes in microstructure, chemical composition, signs of degradation, or porosity were observed. The XPS method was used to analyze the chemical composition of the surface and the oxide layers up to a depth of 50 nm. The Cr₂O₃ oxide layer on the surface of the appliance was 20 nm thick. Discussion and conclussion: The chemical surface analysis showed that the composition of the CoCrMoW material did not change after use and remains within the values prescribed by the ASTM standard. Microstructural investigations revealed no signs of porosity or inhomogeneity, indicating a high level of manufacturing technology and material quality. After six months of exposure to the oral environment, no signs of material degradation were observed. The results of the thesis confirmed that both the cobalt-chromium alloy (CoCrMoW) and stainless steels are suitable materials for use in orthodontic appliances. After six months of clinical use, no changes in microstructure, chemical composition, or signs of degradation were observed, confirming their high resistance to stress in the aggressive oral environment and their compliance with expected biocompatibility.
|
