Osseointegration and its experimental background
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Repositioning accuracy of the implant- and abutment-level prosthetic components used in conventional and digital workflows
2024, Journal of DentistryTo evaluate the repositioning accuracy of the implant- and abutment-level impression components (impression abutments and implant scan bodies) and implant abutments (with and without anti-rotational hex index); also, to estimate the tightening torque influence on the positional stability of abutments.
Seven types of prosthetic components (n = 7) [impression pick-up copings (PC), implant scan bodies (ISB), non‑hex and hex titanium base implant abutments (TB H and TB NH), multi-unit impression copings (MU PC), multi-unit implant scan bodies (MU ISB), and multi-unit caps (MU C) (Medentika GmbH)] were tested. For repositioning accuracy tests a coordinate measuring machine (CMM) was used. During assembly 15 Ncm torque for all components was applied. After measurement, only hex and non‑hex abutments were torqued to 25 Ncm and their coordinates were again recorded to assess torque influence. The procedure was repeated 7 times for each component. Linear and 3D deviations, angulation to the vertical axis, and axial rotation were calculated. The Kruskal-Wallis test was used to compare the measurements between the groups. A post-hoc test (Mann–Whitney U test) was used for pairwise comparison to determine the influence of the torque (α=0.05).
Implant- and abutment-level components used for digital scans showed different positional discrepancies compared to ones used for conventional impressions and ranged from 10 to 37 µm. Hex abutments demonstrated statistically significantly lower 3D deviations (4.4 ± 7.1 µm) compared to non‑hex abutments (8.7 ± 6.1 µm). Torque influence was significantly lower for hex abutments than for non‑hex abutments.
Repositioning inaccuracies were found in all implant- and abutment-level impression components (impression abutments and implant scan bodies) and all abutments (with and without anti-rotational hex index) tested. Final tightening of the components could cause further positional discrepancies.
The misfit of the prosthetic components used in conventional and digital workflows stays in the clinically acceptable range. Even when multiple connections and disconnections on the track of the laboratory preparation is needed, it should not have a negative influence for single teeth reconstructions. However, in the complex cases with multiple implants, repetitive repositioning of the prosthetic components may lead to the accumulation of vertical, horizontal and rotational errors leading to the clinical problems with the passive fit of the final framework.
Biomechanical behavior of a new design of dental implant: Influence of the porosity and location in the maxilla
2024, Journal of Materials Research and TechnologyThe biomechanical performance of dental implants determines their clinical success. In this work, the stress and deformation distribution of a new implant design (dense and porous) was evaluated by the Finite Element Method. Furthermore, the effect of the location of the dental implant in the maxillary zone, as well as the mechanical response in the peri-implant maxillary tissue (cortical and trabecular) is discussed in detail. Before carrying out the computational study of the dental implant, Ti6Al4V cylindrical preforms obtained by conventional powder metallurgy and space-holder technique were characterized, to choose the most appropriate porosity (percentage and size) to achieve the biomechanical and biofunctional balance of the dental implant investigated. The novel porous dental implant under investigation exhibits 40% porosity in the region in contact with the trabecular bone, featuring inclined pores at 60 and 120° with a diameter of 200 μm. Our findings revealed that the cortical bone experienced the highest stress values, whereas the trabecular bone exhibited the highest levels of strain. Notably, the location of dental implants in the maxilla highlighted as the most influential factor affecting the maximum values of von Mises equivalent stress and strain. Furthermore, in the second molar location, the stress and strain levels exceeded the recommended thresholds for maintaining peri-implant bone density. Additionally, the porous implants generated significantly higher levels of stress and strain in the peri-implant trabecular bone than dense implants.
A comparative analysis of the passivity of fit of complete arch implant-supported frameworks fabricated using different acquisition techniques
2024, Journal of Prosthetic DentistryThe accuracy of intraoral scanners (IOSs) in recording edentulous jaws has improved recently. However, improvement in accuracy does not necessarily imply the clinical validity of the scans, and limited information is available regarding the manufacture of passively fitting prostheses.
The purpose of this in vitro study was to analyze the passivity of complete arch screw-retained frameworks fabricated using different acquisition techniques.
A 3-dimensional maxillary edentulous model to receive all-on-4 screw-retained frameworks was prototyped. Eighteen polymethylmethacrylate (PMMA) frameworks were fabricated with a 5-axis milling machine and divided into 3 groups according to the acquisition technique (n=6): scanned by using an IOS (CEREC Primescan; Dentsply Sirona), scanned with the aid of an auxiliary device by using the same IOS, and by using a conventional impression and then scanning the stone cast with an extraoral scanner (EOS). The passivity of fit of the frameworks was tested with the 1-screw test, the terminal screw of the framework assembly was tightened on the multiunit abutment (MUA), and the vertical marginal gap (µm) was measured at the other 3 framework-to-abutment interfaces by using a digital microscope at ×40 magnification. A modification to the 1-screw test was analyzed by tightening all screws and then unscrewing all except 1 of the anterior abutments. Data were explored for normality by using the theoretical quantile-quantile (Q-Q) plots and the Shapiro-Wilk test of normality. The Friedman test compared data between the different acquisition techniques; the tightening methods and locations (buccal and palatal) were used as the block variable. The post hoc Dunn test was used when the Friedman test was significant. The Kruksal-Wallis test compared the data from the 2 groups of the tightening methods and the 2 location groups. The aligned rank transformation (ART) ANOVA test was used for the interaction effects among the 3 variables. A multiway ANOVA was applied to the ranked data. (α=.05 for all tests).
Significant differences were found among all groups (P<.001). Regarding the passivity of fit, the mean vertical marginal gap was 50 µm for frameworks fabricated from an intraoral scan with the aid of an auxiliary device, 62 µm for frameworks fabricated by using an IOS, and 140 µm for frameworks fabricated by using an EOS. No significant difference was found among all groups regarding the tightening method (P=.355) or location measured (P=.175).
Digital scanning with the aid of an auxiliary device resulted in the best fit; however, digital approaches with or without the auxiliary device resulted in a more accurate fit with a smaller marginal gap than with the conventional impression.
Modulation of SEMA4D-modified titanium surface on M2 macrophage polarization via activation of Rho/ROCK-mediated lactate release of endothelial cells: In vitro and in vivo
2024, Colloids and Surfaces B: BiointerfacesSEMA4D-modified titanium surfaces can indirectly regulate macrophages through endothelial cells to achieve an anti-inflammatory effect, which is beneficial for healing soft tissues around the gingival abutment. However, the mechanism of surface-induced cellular phenotypic changes in SEMA4D-modified titanium has not yet been elucidated. SEMA4D activates the RhoA signaling pathway in endothelial cells, which coordinates metabolism and cytoskeletal remodeling. This study hypothesized that endothelial cells inoculated on SEMA4D-modified titanium surfaces can direct M2 polarization of macrophages via metabolites. An indirect co-culture model of endothelial cells and macrophages was constructed in vitro, and specific inhibitors were employed. Subsequently, endothelial cell adhesion and migration, metabolic changes, Rho/ROCK1 expression, and inflammatory expression of macrophages were assessed via immunofluorescence microscopy, specific kits, qRT-PCR, and Western blotting. Moreover, an in vivo rat bilateral maxillary implant model was constructed to evaluate the soft tissue healing effect. The in vitro experiments showed that the SEMA4D group had stronger endothelial cell adhesion and migration, increased Rho/ROCK1 expression, and enhanced release of lactate. Additionally, decreased macrophage inflammatory expression was observed. In contrast, the inhibitor group partially suppressed lactate metabolism and motility, whereas increased inflammatory expression. The in vivo analyses indicated that the SEMA4D group had faster and better angiogenic and anti-inflammatory effects, especially in the early stage. In conclusion, via the Rho/ROCK1 signaling pathway, the SEMA4D-modified titanium surface promotes endothelial cell adhesion and migration and lactic acid release, then the paracrine lactic acid promotes the polarization of macrophages to M2, thus obtaining the dual effects of angiogenesis and anti-inflammation.
Accuracy assessment of robot-assisted implant surgery in dentistry: A systematic review and meta-analysis
2024, Journal of Prosthetic DentistryThe systematic assessment of accuracy of robot-assisted implant surgery is lacking.
The purpose of this systematic review and meta-analysis was to evaluate the accuracy of robot-assisted implant surgery and compare it with computer-aided implant surgery in partially and completely edentulous patients and human phantoms.
The studies were selected from ScienceDirect, Web of science, Cochrane Library, PubMed, and CNKI databases. The risk of bias of the included studies was evaluated with the risk of bias in nonrandomized studies of interventions tool. The mean and standard deviation of global coronal, apical, and angular deviations of implants were the primary outcome. Meta-analysis was conducted to evaluate the accuracy of the robot-assisted implant surgery and compare it with computer-aided implant surgery in dental implantation (α=.05).
Eleven in vitro studies with 809 implants and 10 clinical studies with 257 implants were included. For the in vitro studies, the mean global coronal, apical, and angular deviations of robot-assisted implant surgery were 0.7 mm (95% CI: 0.6 to 0.8), 0.8 mm (95% CI: 0.6 to 1.0), and 1.8 degrees (95%CI: 1.2 to 2.5), respectively. For the clinical studies, the average global coronal, apical, and angular deviations of robot-assisted implant surgery were 0.6 mm (95% CI: 0.5 to 0.8), 0.7 mm (95% CI: 0.6 to 0.8), and 1.6 degrees (95%CI: 1.1 to 2.0), respectively. For the in vitro studies, the robot-assisted implant surgery group showed significantly more decrease in global coronal deviation than the computer-assisted implant surgery group (P=.012). The robot-assisted implant surgery group offered smaller global apical deviation (P=.001) and angular deviation (P<.001) than the computer-assisted implant surgery group.
Robot navigation is a clinically reliable method of implant placement. Significantly lower global coronal, apical, and angular deviations were observed for robot-assisted implant surgery compared with computer-assisted implant surgery in human phantoms.
Computer guided root tip extraction and implant placement: A clinical report
2024, Journal of Prosthetic DentistryExtraction of a residual root tip and implant placement can be challenging because of the complexity and invasiveness of the procedure. Improvised application of a guided implant surgery may avoid such challenges. This clinical report presents an innovative technique combining a 3-dimensionally printed surgical guide with conventional instrumentation for a residual root tip extraction in a minimally invasive and predictable way.
Presented at the Toronto Conference on Osseointegration in Clinical Dentistry, Toronto, Ont., Canada, and the Academy of Denture Prosthetics, San Diego, Calif.
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Professor and Head, Laboratory of Experimental Biology, Department of Anatomy.