## 1 Introduction  
Orthodontic treatment with fixed braces and aligners requires special preparation of the enamel surface for fixing attachments necessary for orthodontic tooth movement. The enamel quality and thickness have a direct impact on the bond strength between a composite material and the tissue surface and indirectly affect the bond strength between an orthodontic abument and the composite material [1]. The bond strength between the enamel surface and the material is also influenced by other factors, such as the details of the acid etching (acid organic/inorganic composition and concentration, process time), pH reaction, enamel structure (morphology, calcium phosphate concentration, enamel site), etchant viscosity and rinsing time [2,3].  
On the other hand, the bond strength affects enamel damage that occurs during debracketing and the amount of remnant composite material that has to be removed in order to restore the enamel to its pre-treatment condition. Thus, the amount affects the length and aggressiveness of enamel cleaning, which can also lead to tissue damage.  
The procedure for attaching orthodontic abutments to the enamel surface involves etching the enamel with 36% orthophosphoric acid, followed by the application of resin and a composite material. Enamel etching has become a breakthrough method for keeping abutments on the enamel surface; their resistance to the pulling force comes from the arc, and the pushing force comes from the aligners, thus providing an effective treatment process [4; 5; 6]. However, enamel etching is associated with tissue loss ranging from 5 to 60 \(\upmu\)m, showing significant iatrogenic effects [5; 6; 7; 8]. Changes in enamel thickness after orthodontic treatment due to the method of gluing the abutments, their type, and the applied force necessary to remove them has already been investigated in a previous paper by [PERSON] et al. [1; 9; 10] and depends on initial condition and etching time. Enamel is highly mineralized and and is the hardest tissue in the human body, consisting of 96% inorganic substances, 2% organic substances and 2% water [11]. Tissue etching results in removing the organic substances, making the surface structure rough. Another procedure related to orthodontic treatment with fixed appliances, i.e., enamel cleaning after abutment removal, may also cause surface roughness, depending on the tool with which the enamel is cleaned [12; 13]. The aim of the present study was to determine the changes in the surface topography, i.e., roughness and morphology, as well as the nanomechanical properties, such as adhesion and Young's modulus, associated with the procedure of attachment and removal of orthodontic abutments as well as enamel cleaning.  
Due to its structure and nanomechanical properties, enamel withstands the enormous pressure generated by chewing forces, showing an average elasticity modulus of 70-120 GPA [14]. These properties can be assessed by AFM (atomic force microscopy) imaging, which enables spatial observation of the topography of biological specimens. The correlation of topographic images with nanomechanical properties allows for the assessment of morphology and properties at the micro- and nano-meter level in three dimensions simultaneously without the need for enamel preparation [15; 16; 17]. Atomic force microscopy (AFM) was used to study the structural topography of enamel crystals in healthy and affected enamel [18; 19; 20; 21].  
The aim of the study was to map the mechanical properties of enamel surfaces during orthodontic treatment.  
The specific aim of the study was to evaluate  
* whether enamel etching results in removing organic substances of the tissue,
* whether the use of resin changes the surface of the etched tissue,
* after which procedure the enamel has the highest hardness, and
* after which procedure the enamel smoothness is the greatest.  
The research hypothesis was the assumption that in orthodontic procedures the nanomechanical properties of the tissue are changing.