## 3 Discussion  
The use of the ARAMIS system is well established in dental science but has not been used as presented here in prior years. Earlier work by [PERSON] et al. showed good repeatability and stable results for measuring micromovements of teeth [36; 37]. To date, one investigation of elongation behavior has been identified in connection with restorative composites [38]. Thus, in order to obtain as much information as possible, the present study evaluated strains as a function of different materials and forces. The current study is based on widely used and modern materials in dentistry: a non-precious metal alloy, ceramics (zirconia), and PEEK [39; 40; 41]. For comparison of the optical digital method with an already established method, the measurements performed by the ARAMIS system were compared with measurements from strain gauges taken in parallel. Strain gauges were selected because they made possible the integration with collected measured values. This comparison was not possible with the finite element method, as finite element simulations are based on geometrically simplified components [11]. Strain gauges are very technique sensitive in their use. For example, they must be bonded very carefully, and errors can occur [42; 43]. In addition, the changes in stress detected by the strain gauges are modified by a measurement amplifier, and they are then transferred to a computer unit for quantification of the change in length [22]. Strain gauge measurements of changes in length are made indirectly. The measured change in stress is first mathematically converted into a change in length per specific length by a given formula and then into an absolute change in length [42; 44]. Each of these aspects signifies a potential source of error, and it is necessary to account for sensor-related error sources of hysteresis and nonlinearity [31]. Moreover, regardless of measurement inaccuracy, measurements using linear strain gauges are fundamentally limited to one dimension. As a result, errors can add up in the combination of measurements when evaluating multidimensional processes [45]. In contrast, optical measurement technology has two disadvantages. First, only directly visible areas of a measured object can be examined using an optical method. Figure 6: Boxplots regarding the strain at different inserted forces and in the case of the superstructure made of PEEK. Transfers to in vivo experiments require complex adaptations to the set-up, but are in principle possible and will be presented in the future. Second, the surface to be measured must be prepared to allow the detection of surface changes by applying a stochastic pattern or GOM reference points [42; 43; 46]. Both methods have in common that only the surface of a test object can be examined. This leads to limitations of this measurement method, since no direct conclusions can be drawn about processes inside the test specimens. The computer-aided nature of the ARAMIS system allows for the investigation of different virtual measurement areas. In this study, a comparison of the measurement accuracies of the optical digital measurement system versus strain gauges was investigated using two virtual measurement areas corresponding to their respective contours. The positioning and extension of the measurement area correspond with high accuracy to those of the corresponding strain gauge. This eliminated errors due to different measurement ranges. Despite the limitation that the optical technique measures the surface of the strain gauges, the exact adaptation of the measurement ranges could have contributed to the statistically significant concordance between the two methods. In the present study, the materials used for the three superstructures were an oxide ceramic, a non-precious metal alloy, and PEEK. Overall, no significant difference in the elongation of the bone, both horizontally (DMS1) and vertical-axially (DMS2) to the implant, was observed between the non-precious metal alloy and the ceramic with either measurement method.