## 2 Materials and Methods  
The study sample consisted of 23 female patients, with a mean age of 24.3 years. Mini-implants were scheduled to be placed in the maxilla between the first molar and second premolar to facilitate anchorage purposes (in most cases, the right and left maxillary buccal region), and 43 sites were evaluated. The inclusion criteria were: periodontically healthy patients, with a CBCT imaging of the upper jaw, which was acquired for diagnostic and safety purposes (mainly impacted teeth were involved, or questionable tooth movements). Patients who presented poor oral hygiene, periodontal pathology, metabolic disease (diabetes), or deciduous teeth, or who smoked, were excluded from the study. The patients (or their representatives) were informed of the aim and procedures of the study, and they signed a consent form regarding the need for mini-implants, and the reasons for acquiring a three-dimensional X-ray (CBCT). This research is part of a protocol that was validated by the Ethics and Scientific Committee of 401 General Army Hospital in Athens, Greece (ref: No. 10/8-12-2020). Prior to the mini-implant placement, CBCT imaging of the upper jaw was acquired (Planmeca ProMax(r) CBCT system, Planmeca Oy, Helsinki, Finland, 90 kVp/4-10 mA, 200-400 um voxel size). The width of the attached gingiva in the maxillary arch, between the first molar and second premolar, was measured during the clinical examination of the patient, with the help of a periodontal probe (Figure 1a), utilizing the visual method, and study casts were constructed. The clinical procedure was applied to the patient's cast, and the attached gingiva was marked by two lines. The first represented the mucoginguival junction, and the wavy second one, the upper (apical) border of the free gingiva. A third straight line, connecting the upper borders of the second wavy line, was drawn, and so was a fourth line, in the middle of the first and third lines (Figure 1b). All the lines were engraved into the plaster model. All the plaster models were scanned with Carestream 3600 digital oral scanner (Carestream Dental, LLC, Atlanta, GA, USA), and a stereolithography (STL) file was acquired (Figure 1c). Figure 1: Measurement of the attached gingiva with (**a**) periodontal probe. (**b**) The four lines in the attached gingiva, engraved into the plaster model. (**c**) The STL file of the plaster model. Digital Imaging and Communications in Medicine (DICOM) files from the CBCT imaging and STL files were combined, using several matching points, to build a digital model on an open-source software (Blue Sky Plan V4.9.4 64 bit, Libertyville, IL, USA). On that digital model, the teeth, the supporting bone, and the mucosa could be evaluated at the same time. In the program panel, five interacting perspectives of the digital model could be inspected at the same time: 3D, panoramic, cross-sectional, axial, and implant/tangential (Figure 2). The orientation of the digital model was set so that the palatal plane would be parallel to the horizontal axis, and the nasal septum would be parallel to the vertical axis, provided by the software, accordingly to the method of [PERSON] et al. [28]. The region for bone evaluation was on the midline between the first molar and second premolar on the right and left side of the upper jaw, where the mini-implants were scheduled to be placed. This region of interest was spotted on the panoramic and axial panel of the program. On the 3D panel, three axial slices were defined on the digital model, representing the first, third, and fourth engraved lines on the casts. The cortical bone thickness and density, and trabecular bone density were measured at the three defined levels on the corresponding coronal slice and panel, at the midline between the first molar and second premolar (Figure 3).