# Impact of Implant Design and Bone Properties on the Primary Stability of Orthodontic Mini-Implants
## 2 Materials and Methods  
This experimental in vitro study examined three types of orthodontic mini-implants of different sizes and designs, produced by two manufacturers: Tomas-pin SD (Dentaurum, Ispringen, Germany) and Perfect Anchor (Hubit, Seoul, Korea). A total number of 40 mini-implants were tested (20 Tomas-pin mini-implants with a thread diameter of 1.6 mm and a thread length of 6 mm, and 20 Perfect Anchor mini-implants, of which 10 had a thread diameter of 1.4 mm and thread length of 8 mm, while 10 had a thread diameter of 1.6 mm and a thread length of 8 mm, according to the manufacturers' specifications). There are two properties that are common to all tested implants--one is the material of which they are made (titanium alloy Ti-6 Al-4V) and the other is the method of their insertion. The main difference between the mini-implants, which is why they have been selected as the subject of research in the first place, is reflected in their geometry or design. The implants differed in terms of length, diameter, body shape, head shape, and thread properties (Figure 1). Fresh pork ribs were used as the test model in this experiment. The total number of ribs corresponded to the total number of implants tested. The process of preparing the ribs included their scaling and cleaning by way of complete removal of soft tissues mechanically. The ribs were neither cut nor treated with any chemical agents, all with the aim of preserving the original bone structure, which would not be altered in any way. The study included four stages: (i) mini-implant geometry analysis; (ii) bone scanning; (iii) implant insertion; and (iv) pull-out test. The geometrical design analysis of orthodontic mini-implants included a series of measurement that covered the following parameters: thread length, pitch, thread bearing depth, multi-point thread diameters, and multi-point screw diameters based on which the degree of taper has been determined on the threaded section. Measurements of these parameters were performed with a Zeiss-ZKM 01-250 C universal two-coordinate measuring microscope (Figure 2). On the basis of the identified dimensions of the above parameters, the so-called thread shape factor (TSF) and the degree of thread taper were established (Figure 3 and Table 1). Cortical bone thickness (CBTC) measurements were performed at the mini-implant insertion point by using Cone-Beam computed tomography. Images of the prepared samples were taken by facescan on a GALILEOS Comfort plus device (Sirona Dental System GmbH Fabrikstrasse 31 D-64625 Behshein, Germany) (Figure 4a). The frame exposure parameters used were 98 kV and 10 mAs, exposure field 15 \(\times\) 15 cm, exposure time 12 s.  
CBTC measurements were performed by using the GALILEOS Implant Viewer, which allows different measurements of anatomical structures (bone density, length, and width of anatomical structures, etc.). Measurements of the pig rib CBTC were taken in a sagittal cross-section, at an angle of 90\({}^{\circ}\) to the wire (Figure 4b). Figure 1: Mini-implants (right-to-left: Perfect Anchor 1.4 \(\times\) 8 mm, 1.6 \(\times\) 8 mm, and Tomas-pin 1.6 \(\times\) 6 mm, respectively). Figure 3: Geometric parameters of the mini-implant threading: Perfect Anchor (**a**); Tomas-pin (**b**). This test was performed on a pig rib bone, with the aim of determining the load-bearing capacity of the bone-implant interface or the value of force that would result in extraction of the implant from the bone-implant interface. Prior to performing an experimental analysis of the mini-implant primary stability, it was necessary to prepare the sample adequately. Once the bone scan was completed, the bone was placed on a steel attachment pad designed for the purpose of this experiment. The attachment pad was designed in such a way so as to transfer the pull-out force from the clamp to the implant as directly as possible.