Tatsuya Matsuzaki

Purpose: To analyze how the taper angle (defined here as the half‑angle per side) influences the mechanics of the implant–abutment connection using finite element analysis. Methods: Three‑dimensional finite element models (implant body, abutment, and screw) with taper angles of 8°, 15°, 18°, and 22° were established in ABAQUS/CAE. All components were modeled as linearly elastic Ti‑6Al‑4 V (E = 110 GPa, ν = 0.35). Frictional contact (μ = 0.3) was assigned at the taper and screw interfaces. A bolt load of 605 N (equivalent to 35 Ncm) was applied and then released to assess the press‑fit retention. Under the maintained preload, 100-N vertical and horizontal loads (unidirectional and bidirectional) were applied for five cycles. The primary outcomes are the abutment axial displacement, implant von Mises stress, bolt load change, and microgap size. Results: Smaller taper angles (8°, 15°) retained press‑fit after preload release, whereas larger angles (18°, 22°) lost press‑fit contact. As the taper angle decreased, the abutment axial displacement, implant stresses, and bolt load loss increased. The effect of the loading direction follows the order: vertical < horizontal (unidirectional) < horizontal (bidirectional). Microgaps decreased with smaller taper angles and cycling. Conclusion: Taper angle differences affect press-fit, abutment axial displacement, screw loosening, stress distribution, and microgap formation.

Purpose: To compare abutment and scan body subsidence and determine the appropriate tightening torque value for a scan body that can accurately replicate abutment subsidence.Methods: An internally tapered connection implant was placed in a bone model. The titanium abutment (Ti Abut), polyetheretherketone scan body (PEEK SB), and titanium scan body (Ti SB) were tightened to torque values of 10 or 35 Ncm, with the 10 Ncm models used as reference models. Both the 10 and 35 Ncm models were scanned using a laboratory scanner. The vertical displacements of the Ti Abut, PEEK SB, and Ti SB at each torque value were determined using three-dimensional analysis software.Results: Upon tightening the scan bodies and abutment to 35 Ncm, the displacement was significantly greater than when tightened to 10 Ncm (P < 0.01). At 35 Ncm, Ti SB and Ti Abut showed significantly greater displacements than PEEK SB, whereas no significant difference was observed between Ti SB and Ti Abut.Conclusions: The titanium scan bodies, when tightened at 35 Ncm, accurately replicated titanium abutment subsidence, unlike the PEEK scan bodies.

This retrospective study aimed to investigate the survival rate of implants from 5 to 10 years after the placement of implant-supported fixed dental prostheses (ISFDPs) and the management of implant loss in the elderly population. Elderly patients (≥65 years old) who had been treated with ISFDPs and followed up with for at least 5 years between October 2009 and March 2020 were enrolled. Patient profiles and implant-related data were extracted. The survival rate of implants up to 5 years as well as the 10-year cumulative survival rate were evaluated. The management of implant loss and prosthetic interventions were also investigated. In total, 195 patients (mean age: 70.1 ± 4.5 years old) and 687 implants (287 ISFDPs) were assessed. The 5-year survival rate was 99.0% and the 10-year cumulative survival rate was 98.1%. Seven of the eleven implants lost were lost due to peri-implantitis. Only three implants in two patients were placed after the loss of the implants; most were restored using non-invasive procedures. Two patients underwent a conversion from ISFDPs to removable prostheses. This study showed that high survival rates were observed in an elderly population with ISFDPs and that non-invasive procedures were often applied after the loss of an implant.

There are some spaces between abutment and implant body which can be a reservoir of toxic substance, and they can penetrate into subgingival space from microgap at the implant–abutment interface. This penetration may cause periimplantitis which is known to be one of the most important factors associated with late failure. In the present study, three kinds of abutment connection system, external parallel connection (EP), internal parallel connection (IP), and internal conical connection (CC), were studied from the viewpoint of microleakage from the gap between the implant and the abutment and in connection with the loosening of abutment screw. We observed dye leakage from abutment screw hole to outside through microgap under the excessive compressive and tensile load and evaluated the anti-leakage characteristics of these connection systems. During the experiment, one abutment screw for EP and two screws for IP, out of seven samples in each group, were fractured. After the 2000 cycles of compressive tensile loadings, removal torque value (RTV) of abutment screw represented no statistical differences among three groups. Standard deviation was largest in the RTV of EP and smallest in that of CC. The results of microleakage of toluidine blue from implant–abutment connection indicated that microleakage generally increased as loading procedure progressed. The amount of microleakage was almost plateau at 2000 cycles in CC, but still increasing in other two groups. The value of microleakage greatly scattered in EP, but the deviation of that in CC is significantly smaller. At 500 cycles of loading, there were no significant differences in the amount of microleakage among the groups, but at 1000, 1500, and 2000 cycles of loading, the amount of microleakage in CC was significantly smaller than that in IP. Throughout the experiment, the amount of microleakage in EP was largest, but no statistical difference was indicated due to the high standard deviation. Within the limitation of the present study, CC was stable even after the loading in the RTV of abutment screw and it prevented microleakage from the microgap between the implant body and the abutment, among the three tested connections.