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Chapter 586in amount of total force necessary to remove more dorsally located teeth is eminent. The most dominant directions of forces seem to be the buccal side and extrusion for both upper and lower jaw. When the results are compensated for time (see appendix figures A.1, A.2 and A.3) the differences become less apparent. This means that some of the differences found in figure 3, 4 and 5 can be explained by the duration of the treatment. Other relevant findings in this study are the highest and lowest peak forces. A 10-fold increase was found in the measured peak forces between an upper second premolar (intrusive direction) and upper central incisor (extrusive direction). A large standard deviation was found in our outcomes, showing a high variance in forces, torques and time for removal even within groups of the same teeth. This finding was expected and corresponds well with our clinical experience. The amount of forces and their direction varies largely based on anatomic factors, such as the total root surface, amount and curvature of roots, but also of patient factors such as bone morphology and mineral density [14, 15]. Although metadata was present that could (partially) explain some of the variance, the dataset was too small to make any reliable conclusion in this matter. Most recent studies focused on measuring forces in limited directions and/or with only a selection of teeth. A useful comparison to previous literature is difficult since the existing scientific data is scarce and heterogeneous both in study design as in outcome. For example, Ahel et al.[4, 15] and Lethinen et al.[16] measured forces distinguishing between ‘twisting’ (rotational) and ‘rocking’ (buccolingual or buccopalatal) directions in an in vivo setup. Respectively, only incisors and teeth in the upper jaw were included. Cicciu et al., next to twisting and rocking forces, also distinguished ‘grasping’ forces in an in vivo study on the removal of a selection of premolars [17]. Dietrich et al. measured forces exerted with a unidirectional vertical extraction system in an in vivo setup, but molars were not included [14, 18]. Most recently, Sugahara et al. published data gained from simulating an extraction force performed by students and professionals in an in vitro laboratory setting. Forces were measured in three dimensions on a simulated mandibular molar [5]. Although the data in this study was of relatively high quality, it should be carefully interpreted in terms of clinical representativeness. This caution is related to the fact that the data was gathered ex vivo. Whilst the feedback from the surgeons was very positive in terms of clinical representativeness, it is not known in what way the freezing Tom van Riet.indd 86 26-10-2023 11:59