**5. Conclusions**

Within the limitations of this in vitro study, it can be concluded that none of the obturation techniques was able to provide pore-free root canal fillings in the apical 5 mm. Significantly higher porosity was observed in the MF and MF-UA groups as compared to the BR/SC and BR/SC-UA groups. The direct ultrasonic agitation had no considerable impact on the porosity distribution in BR/SC fillings, while MF fillings demonstrated significantly higher overall porosity after ultrasonic agitation.

**Author Contributions:** Conceptualization, S.D. and H.S.; methodology, S.D.; software, P.T.; validation, S.D., G.B. and H.S.; formal analysis, V.P.; investigation, S.D. and G.B.; resources, H.S.; data curation, G.B.; writing—original draft preparation, G.B. and S.D.; writing—review and editing, P.T., H.S. and V.P.; visualization, S.D.; supervision, H.S.; project administration, S.D. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Ethics Committee of Vilnius University Hospital Zalgirio Clinics (protocol no. EK-2, 2016 06 03).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** Data is contained within the article.

**Acknowledgments:** The authors would like to thank Leo J. van Ruijven for his help in operating the SkyScan 1272 μCT scanner and Septodont and Ultradent Products Inc. for the donation of the materials.

**Conflicts of Interest:** The authors declare no conflict of interest. The sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.
