## 4 Discussion  
The iatrogenic effect of orthodontic treatment on tooth tissues has been studied for many years. So far, studies have been carried out with the use of a profilometer, SEM [22], OCT [1] and AFM [23]. Various aspects of the negative impact of fixing orthodontic brackets have been investigated, such as the influence of etchants on the enamel (classic etching method, self-etching system) [24], the presence and type of abutments [13], contact time with the enamel and methods of their removal. The effects of cleaning of the composite resin remnants and the adhesive from the enamel with rotating tools [25] were also analysed. Figure 4: Graph of the averaged blade-surface adhesion force. The black dot means mean value. Figure 5: Graphs showing the values of functional parameters of the surface texture describing thicknesses of the surface components: core (Sk), peaks (Spk) and valleys (Svk). The research described in this paper focuses on the assessment of changes in the topography and nanomechanical properties of enamel during orthodontic treatment with fixed braces and aligners. Due to the use of additional attachments, the aligners also require enamel surface preparation in the same way as the attachments of fixed braces. The first stage of enamel preparation is etching. The effect of etching on the human enamel depends on nanomechanical and nanophysical interactions between acids and the enamel. These interactions may lead to the loss of hydroxyapatite crystals on the surface and the erosion process, resulting in a rough enamel surface [26]. AFM studies confirm the highest enamel roughness after etching. There are reports indicating that there is a significant difference in the acid etching patterns on different teeth, which suggests that in vitro tests should be performed on one tooth type or with the same number of different tooth types, which was done in the described experiment [27; 28; 29; 30]. The resin-coated surface showed slightly lower roughness than the intact enamel. The roughness parameter in the group of teeth with cleaned enamel was lower than in the intact enamel group and similar to the group of surfaces covered with resin. The results support the assumption that enamel etching removes organic matter, leaving a porous surface structure. Noteworthy is the strong surface development after etching, probably associated with removing all loosely connected elements and exposing the hard, porous structure of the sample. The applied resin refills the pores, which reduces the roughness and development ratio to previous values. An interesting result is the reduced roughness of the enamel after it has been cleaned of the orthodontic adhesive remnants using a rubber containing aluminum oxides. Many studies show an increase in surface roughness after using cemented carbide, composite or glass fibre drills [31; 32; 33]. This suggests that the use of rubbers with alumina, despite the extended cleaning time, is safer for the tissue surface than drills of any kind. Some studies [34] question the validity of using AFM to assess enamel roughness. Due to the fact that the pits between enamel crystals formed by acid etching are deeper than the AFM needle length, it is not possible to reach all the crystallite surfaces of the acid-etched enamel ends, and this leads to the profilometric underestimation of the roughness parameters of the acid-etched enamel. Therefore, AFM images at low magnification appear much smoother than SEM images at the appropriate magnification. However, at higher magnification, the AFM images of acid-etched enamel reflect the geometry of the probe tip. As a consequence, all roughness parameters measured with AFM on acid-etched tooth enamel surfaces are largely underestimated. However, the main advantage of AFM over other technologies is that it provides quantitative roughness data [15; 35]. This method has proven effective in assessing micro-damage on hard surfaces. The advantages of AFM include the simultaneous delivery of 2D and 3D images and minimal sample preparation.