Extra-short implants (≤ 6.5 mm in length) in atrophic and non-atrophic sites to support screw-retained full-arch restoration: a retrospective clinical study

Abstract Purpose Increasing scientific evidence support extending the application of short dental implants to non-atrophic dental arches. The purpose of this study has been the evaluation of extra-short implants (≤ 6.5 mm in length) that were placed in atrophic and non-atrophic anatomical sites to support the same prosthesis. Methods For that, a retrospective study was conducted by including complete dentures that were solely supported by extra-short implants in the maxilla and/or the mandible. Clinical data about patients, implants, anatomy, and prosthesis were obtained. Statistical analysis was performed to assess implant- and prosthesis-survival, changes in the marginal bone level and prosthetic complications. Results A total of 87 implants in 15 screw-retained complete dentures were assessed. None of the prostheses nor the extra-short implant failed during the follow-up of 27.2 ± 15.4 months. The changes in the mesial and distal marginal bone level were + 0.15 ± 0.51 mm and + 0.11 ± 0.50 mm, respectively. Comparing the implants according to the availability of sufficient bone to place longer implants, indicated the absence of significant differences in the changes of the mesial marginal bone level. However, the changes in the distal marginal bone level showed a statistically significant difference in favor of implants that were placed in non-atrophic sites. Two events of screw loosening were reported that were resolved by retightening the screws. Conclusions Implant- and prosthesis-related outcomes support the use of extra-short implants in atrophic and non-atrophic site to support complete prosthesis. Graphical Abstrac

Impact of proportional resonant controller parameters of VSC connected to AC grids with variable X/R characteristic on the small signal stability

The purpose of this paper is to assess the impact of proportional resonant controller (PR) parameters of a Voltage Source Converter (VSC) and AC grid topology on the small signal stability of a VSC-AC system. Based on this, a small signal model is constructed, step by step, and validated against EMT simulations. Following this validation, several scenarios containing different PR controller gains are proposed and compared by means of trajectory of eigenvalues. A discussion of the best adequacy of PR controller parameters and AC grid strength in combination with inductive-resistive characteristic (X/R) is developed to ensure the stability of the system. The previous eigenvalue analysis is verified in time domain by means of EMT simulations. The analysis performed concludes that, while the AC grid strength in combination with PR controller parameters plays an important role in determination of stability, variations in the inductive-resistive AC grid characteristic need to be included in the analysis, since further instabilities can appear even when the PR controller is well designed for a specific AC grid configuration.The authors thank the support from the Basque Government (projects: ELKARTEK KK-2017/00083 and Road2DC. KK-2018/00083 and research group GISEL ref. IT1083-16) and from the Ministry of Economy, Industry and Competitiveness (project ENE2016-79145-R AEFI/FEDER, UE)