## 5 Conclusions  
Following the comparative study performed, several conclusions can be drawn:  
* The torsional behavior of all three types of instruments included in the present study is similar from the point of view of the maximum tangential stresses recorded. * The fractographic analysis of the sections indicated that the failure mode of all three types of instruments is similar. * From the perspective of withstanding torsional loads, the cross-sectional shape of E instruments is superior to the other two considered in the comparison. * By improving the qualities of NiTi alloys, the deficiency due to the shape of the instrument design (i.e., cross-section) can be partially compensated. * While the more robust instruments (Type E) appear to be more torsion-resistant, the others compensate through higher elasticity due to the M-wire alloy. Thus, one can conclude that both hypotheses made in the Introduction were confirmed. Future work in this direction includes studies of cross-sections and instruments such as those considered in this work using scanning electron microscopy (SEM) [55], but also on-site optical coherence tomography (OCT) investigations, as we have demonstrated that the latter can replace the gold standard of SEM for the study of metallic fractures [56; 57]. This also comes in the context that, due to its complementarity with the most common dental radiography, we have demonstrated that OCT is able to become part of current dental practice [58; 59]. Conceptualization, A.-S.B.-P., C.S., V.-F.D., M.-L.N., D.I.S. and L.M.N. ; methodology, A.-S.B.-P., C.S., V.-F.D., D.I.S. and M.-L.N. ; optical microscopy, D.I.S. and C.O. ; sample preparation, A.-S.B.-P. and D.I.S. ; sample testing, D.I.S. ; data and statistical analysis, D.I.S. and C.O. ; supervision and project administration, C.S. and V.-F.D. ; writing--original draft, A.-S.B.-P., O.-A.V.-B., L.O., R.M.H. and V.-F.D. ; writing--review and editing, V.-F.D., A.-S.B.-P. and D.I.S. ; funding, V.-F.D. All authors have read and agreed to the published version of the manuscript. This research was supported by the Romanian Ministry of Research, Innovation and Digitization, CNCS/CCCDI-UEFISCDI, project PN-III-P2-2.1-PED-2020-4423, within PNCDI III ([http://3 om-group-optomechatronics.ro/](http://3 om-group-optomechatronics.ro/), accessed on 1 June 2021). Data Availability Statement: Data supporting reported results can be obtained from A.-S.B.-P.  
Acknowledgments: The evaluations were performed in the Department of Mechanics and Strength of Materials, \"Politehnica\" University of Timisoara, 1 Mihai Viteazu Ave., 30022 Timisoara, Romania. The support of [PERSON] with the statistical analysis is gratefully acknowledged. This paper is based on a presentation prepared for the '1 st International Conference-Advances in 3 OM: Opto-Mechatronics, Opto-Mechanics, and Optical Metrology', 13-16 December 2021, Timisoara, Romania. Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results. References  
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