## 2 Materials and Methods
### Calculation of the Strain \(\varepsilon\) for the Quarter-Bridge Circuit  
Here, an experimentally determined material constant k corresponds to the \"k-factor\" of the strain gauges and has a value of 1.98 for the strain gauge used, type 1-LY11-3/350(Hottinger Bruel and Kjaer GmbH, Darmstadt, Germany). U_E corresponds to the bridge supply voltage (V), U_A corresponds to the bridge output voltage (mV), and the quotient U_A/U_E of the two voltage values corresponds to the so-called \"bridge detuning\" (mV/V). \[\text{Strain }\varepsilon=4/\text{k}\cdot\text{U}\_\text{A}/\text{U}\_\text{E} \tag{1}\]  
For the calibration of the measuring amplifier, the so-called bridge detuning, a calibration signal of 1 mV/V was applied, and the gain was adjusted so that the output voltage of the measuring amplifier was 10 V.  
Calibration of the Measuring Amplifier:  
\[\text{10 V}\longmapsto 1\,\text{mV}/\text{V}\]  
\[\text{1 mV}\longmapsto 1\cdot[10^{-7}]\,\text{mV}/\text{V}\]  
If the calibration of the measuring amplifier is inserted into Equation (1), a signal of the measuring amplifier of 100 mV corresponds to a strain \(\varepsilon\) of 20.2 \(\upmu\)m/m. Based on this, a conversion factor of 202 was set in the ARAMIS Professional software so that the analog signals of the measuring amplifier fed into the software could be converted directly into technical strain values. The core of the test setup was the computer unit of the ARAMIS system, which had integrated within it the length changes of the strain gauges, the optical signals of the camera system, and the applied axial force of the universal testing machine. The camera system of the ARAMIS system was directly connected to the computer unit and was based on a photometric principle. For this purpose, two high-resolution cameras of the ARAMIS system, arranged at an angle of 25\({}^{\circ}\) to each other, were directed at the strain gauges. The synchronous recording of the measurement object by both cameras enabled a 3D calculation of the surface at any time during the test series. An exact distance of 350 mm between the lenses of the cameras and the bone block had to be maintained, as the camera system had a defined, unchanging focus used to perform the automatic triangular calculations. Figure 1 shows the test setup in the long view and the individual bridges on the implants placed in the bone block. The deformation of the surface could be calculated by the stochastic pattern applied in advance, which followed the deformation of the surface. The software was able to identify square image sections within the pattern by their respective gray value levels and track changes in their distances from each other in the image sequence. The centers of these squares were first converted by the software into 2D coordinate networks for each camera, which were then merged into a 3D coordinate system. Thus, the distance between all areas of the stochastic pattern could be traced at any time with reference to the applied axial force and synchronously with the change in length of the strain gauges. The calculation of surface deformations was performed virtually in the ARAMIS Professional software after the tests were performed. Prior to each series of measurements, the ARAMIS system was calibrated according to the manufacturer's specifications to ensure maximum measurement accuracy and consistency. Individual test series were performed for each of the three bridge materials. Each series consisted of 15 individual tests. A continuously increasing force was introduced from the universal testing machine via the bridge constructions and the implants into the artificial bone block, assuming a magnitude of 0-200 N. The shape changes were calculated for force magnitudes 50, 100, 150, and 200 N. Before each test series, the superstructures on the implants were tightened by hand using a ratchet with a force of 35 N/cm.