## 2 Materials and Methods
### Results  
The corresponding pairs of strain gauge and optical digital measurements showed statistically clear concordances for each case in the intraclass correlation. The smallest relative difference in mean values between the measurement methods was found for the case of strain gauge 1 when measuring the bone surface at an applied force of 100 N across the bridge made of PEEK. There was a difference of 0.043% and 0.3 \(\upmu\)m/m, respectively. For strain gauge 2, this was also the case at an applied force of 100 N and the bridge made of PEEK. The deviation in this case was 0.09% or 0.4 \(\upmu\)m/m. The largest relative mean deviation in relation to strain gauge 1 occurred at a force of 100 N with the bridge made of non-precious metal alloy. This amounted to 4.3% or 28.7 \(\upmu\)m/m, respectively. In the case of strain gauge 2, the largest relative mean deviation was found to be 2.52% and 23.5 \(\upmu\)m/m for the combination of a force of 150 N and the bridge made of ceramic. In Table 1, the results of the measurements related to strain gauges 1 and 2 are summarized descriptively. The \(p\)-values of the equivalence tests and the results of the intraclass correlation (ICC) are shown in Tables 2 and 3. Figure 3: Experimental setup showing the upper horizontal surface with superstructure as well as the optical measuring surface above strain gauge 2 at increasing mastocatory forces from left to right. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & & \multicolumn{8}{c}{**Strain Gauge 1 (\(\mu\)/m)**} & \multicolumn{8}{c}{**Strain Gauge 2 (\(\mu\)/m)**} \\ \hline
**Material** & **Load** & **Method** & **Mean** & **SD** & **Min.** & **Max.** & **Mean** & **SD** & **Min.** & **Max.** \\ \hline \multirow{8}{*}{ceramics} & \multirow{2}{*}{50 N} & Optical & 282.5 & 39.9 & 218 & 355 & 225.4 & 44.6 & 143 & 277 \\ \cline{3-11}  & & SG & 273.3 & 38.6 & 198 & 348 & 223.7 & 38.4 & 155 & 278 \\ \cline{3-11}  & & Optical & 639.7 & 54.6 & 560 & 738 & 571.6 & 62.0 & 471 & 672 \\ \cline{3-11}  & & SG & 640 & 51.8 & 562 & 719 & 582.0 & 57.2 & 494 & 686 \\ \cline{3-11}  & & Optical & 1078.7 & 50.1 & 986 & 1153 & 910.4 & 60.5 & 804 & 1009 \\ \cline{3-11}  & & SG & 1073.9 & 43.6 & 997 & 1172 & 933.9 & 50.7 & 862 & 1014 \\ \cline{3-11}  & & Optical & 1544.2 & 36.1 & 1449 & 1598 & 1252.1 & 15.2 & 1221 & 1278 \\ \cline{3-11}  & & SG & 1536.5 & 31.7 & 1436 & 1567 & 1259.4 & 10.2 & 1231 & 1273 \\ \hline \multirow{8}{*}{npm} & \multirow{2}{*}{50 N} & Optical & 312.3 & 54.9 & 239 & 406 & 195.1 & 47.5 & 88 & 253 \\ \cline{3-11}  & & SG & 271.1 & 48.2 & 202 & 359 & 187.9 & 46.6 & 91 & 248 \\ \cline{3-11}  & & Optical & 703.5 & 60.6 & 563 & 791 & 556.8 & 60.2 & 448 & 647 \\ \cline{3-11}  & & SG & 674.8 & 42.6 & 609 & 760 & 564.4 & 59.2 & 457 & 653 \\ \cline{3-11}  & & Optical & 1143.3 & 75.6 & 1002 & 1233 & 861.9 & 46.3 & 802 & 970 \\ \cline{3-11}  & & SG & 119.6 & 69.3 & 1002 & 1223 & 867.1 & 47.3 & 813 & 973 \\ \cline{3-11}  & & Optical & 1575.7 & 41.2 & 1461 & 1628 & 1168.1 & 22.7 & 1104 & 1197 \\ \cline{3-11}  & & SG & 1564.9 & 31.4 & 1462 & 1591 & 1178.8 & 28.7 & 1109 & 1252 \\ \hline \multirow{8}{*}{PEEK} & \multirow{2}{*}{50 N} & Optical & 304.4 & 74.7 & 142 & 421 & 152.2 & 27.7 & 108 & 208 \\ \cline{3-11}  & & SG & 272.5 & 55.1 & 142 & 341 & 147.7 & 31.4 & 107 & 207 \\ \cline{1-1} \cline{2-11}  & & SG & 697.7 & 109.2 & 517 & 994 & 434.5 & 39.8 & 361 & 499 \\ \cline{1-1} \cline{2-11}  & & SG & 698.0 & 85.3 & 529 & 808 & 434.1 & 36.5 & 366 & 495 \\ \cline{1-1} \cline{2-11}  & & Optical & 1170.3 & 124.4 & 949 & 1405 & 639.1 & 20.5 & 611 & 667 \\ \cline{1-1} \cline{2-11}  & & SG & 1176.9 & 92.5 & 1052 & 1329 & 641.7 & 20.5 & 612 & 668 \\ \cline{1-1} \cline{2-11}  & & Optical & 1613.5 & 104.5 & 1426 & 1731 & 832.5 & 8.4 & 817 & 843 \\ \cline{1-1} \cline{2-11}  & & SG & 1616.9 & 67 & 528 & 1686 & 834.3 & 8.2 & 818 & 847 \\ \hline \hline \end{tabular}
\end{table}