Trueness of the Combined Intra- and Extraoral Scanning Technique for Transferring Subgingival Contours from Provisional Restorations to Definitive Restorations

PURPOSE: To compare the morphologic trueness of provisional and definitive restorations constructed with conventional custom impression techniques to those constructed with intra- and extraoral scanning (IEOS), which can digitally transfer the subgingival morphology of the provisional restoration to the definitive restoration. MATERIALS AND METHODS: Provisional restorations were fabricated on typodonts in which implants were placed. In the conventional method, a customized impression coping was produced by using polymethyl methacrylate resin to transfer the subgingival contour of the provisional restoration. Impressions were taken with silicone impression material, and definitive restorations were made by CAM. The IEOS technique was performed as previously reported. In brief, three individually scanned stereolithography (STL) files were superimposed in CAD software to transfer the morphology of the provisional restoration to the definitive restoration. Definitive restorations were then made by CAM. The provisional and definitive restorations were both scanned by IOS. Scanned data files were superimposed with morphometry software, and the distortions were measured. Student t test was used for statistical analysis. RESULTS: The subgingival morphologies of definitive restorations prepared by the conventional method showed significant negative distortions compared to definitive restorations prepared by the IEOS technique. CONCLUSION: The IEOS technique can more accurately transfer the subgingival contour of provisional restorations to definitive restorations compared to the conventional customized impression coping technique.

Prognosis of Implants with Implant-Supported Fixed Dental Prostheses in the Elderly Population: A Retrospective Study with a 5- to 10-Year Follow-Up.

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.

Effect of post-osseointegration loading magnitude on the dynamics of peri-implant bone: a finite element analysis and in vivo study.

PURPOSE: Much research has been invested in determining the effects of postoperative loading of implants and whether this loading contributes to implant failure, but the issue remains controversial. The present study aimed to elucidate whether cyclic lateral loading of an implant causes bone resorption or bone formation at various loading magnitudes, using a finite element method (FEM) and peri-implant morphologic and morphometric analyses. METHODS: An FEM model was created using Digital Imaging and Communications in Medicine (DICOM) data of rabbit tibia. For the animal study, implants were inserted into rabbit tibia and, after osseointegration, were subjected to lateral cyclic loading of 20N, 40N or 60N. RESULTS: Bone-implant contact was significantly higher in both 40N and 60N groups. Bone-abutment contact (BAC) was extraordinarily observed in all experimental groups. Bone height was higher than the implant platform level at higher levels of loading (60N). Among the three experimental groups, those receiving 40N loading had the highest bone height and BAC. Larger BAC values were observed on the compressive side than the tensile side. CONCLUSIONS: Peri-implant bone formation was enhanced with increased loading, with bone formation predominantly on the compressive side. BAC was highest in the 40N group, implying existence of a loading threshold for peri-implant bone formation and resorption.

The influence of implant-abutment connection on the screw loosening and microleakage.

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

A comparison of the peri-implant bone stress generated by the preload with screw tightening between 'bonded' and 'contact' model.

A number of finite element analyses (FEAs) for the dental implant were performed without regard for preload and with all interfaces 'fixed-bonded'. The purpose of this study was comparing the stress distributions between the conventional FEA model with all contacting interfaces 'fixed-bonded' (bonded model) and the model with the interfaces of the components in 'contact' with friction simulated as a preloaded implant (contact model). We further verified the accuracy of the result of the FEA using model experiment. In the contact model, the stress was more widely distributed than in the bonded model. From the model study, the preload induced by screw tightening generated strain at the peri-implant bone, even before the application of external force. As a result, the bonded model could not reproduce the mechanical phenomena, whereas the contact model is considered to be appropriate for analysing mechanical problems.

Comparative stress analysis of delayed and immediate loading of a single implant in an edentulous maxilla model.

Stress distribution in peri-implant bone in an edentulous maxilla following delayed and immediate loading implant and the effect of implant length on the maximum stress were evaluated by using two kinds of finite element analyses. A threaded implant was loaded with a 100 N vertical force, either immediately or delayed, and examined by finite element analysis with a simple contact relation or a bonding interaction between the implant and the bone, respectively. Higher stresses were observed in cortical bone around the implant neck following delayed loading and in the trabecular bone around the implant threading in the immediate loading model. The maximum stress in the immediate loading model was dramatically higher than in delayed loading. Increased implant length caused decrease in bone stresses in both loading models. Though the stress level was higher, the decrease in the maximum trabecular bone stress in immediate loading was profound.