Synthetic aperture radar(SAR) has been widely used for reconnaissance. It provides high-resolution, day-and-night and weather-independent images for a multitude of applications [1] . Because SAR coherently combines many viewing angles to effectively create a large aperture(narrow beam) radar, the test-bed should be capable of moving straightly SAR sensor for the integration angle to meet resolution. This paper describes the test-bed developed to test and evaluate the SAR performance. It forms high-quality images in real time and saves the raw data for the purpose of post processing on the ground.

AimThis study aimed to investigate factors influencing the survival of replaced dental implants.Materials and MethodsCharts from 2005 to 2021 were reviewed. Replaced implants after removal for the first time were identified. Depending on their survival, the replaced group was divided into the surviving and second‐removal groups. Risk factors affecting survival of replaced implants were evaluated considering clustering of multiple implants within patients.ResultsThe present study included 464 replaced implants of 370 patients, of which 429 and 35 implants were categorized into the surviving group and the second‐removal group. The 5‐year survival rate was 90.2 ± 0.18% in replaced implants at sites with a periodontitis history and 97.0 ± 0.15% at sites without a periodontitis history (p = 0.008). The 5‐year survival rate was 89.1 ± 0.27% in replaced implants with guided bone regeneration (GBR) at first implant placement and 93.9 ± 0.14% at non‐GBR (p = 0.032). The 5‐year survival rate was 97.6 ± 0.13% in replaced implants with GBR and 90.3 ± 0.17% in replaced implants without GBR (p = 0.026). In the multivariable analysis adjusted for clinical variables, periodontitis history (adjusted hazard ratio [aHR] = 3.417; 95% confidence interval [CI] = 1.161–10.055), GBR at first implant placement (aHR = 2.152; 95% CI = 1.052–4.397) and non‐GBR at primary implant replacement (aHR = 0.262; 95% CI = 0.088–0.778) were identified as independent risk factors for second implant removal.ConclusionsPeriodontitis history, GBR at first implant placement and non‐GBR at primary implant replacement were identified as risk factors affecting the survival of replaced implants.

BackgroundGuided bone regeneration (GBR) is the most widely used technique for overcoming the deficiency of alveolar bone. However, the progression of peri‐implantitis in regenerative and pristine bone sites has not been fully investigated. The aim of this study is to compare experimental peri‐implantitis around implants placed in pristine bone and GBR sites.MethodsBilateral  mandibular first molars were extracted from six beagle dogs, and standardized horizontal ridge defect was simultaneously created at predetermined site in unilateral mandible. After 8 weeks, guided bone regeneration procedure was conducted at the defect site. After 16 weeks, implants (ϕ 3.6×8.0 mm) were placed at both extracted sites. This study included 3 months of active breakdown and another 3 months of spontaneous progression period. Radiographs were taken at each phase and specimens were obtained for histological, immunohistochemical, and polarized light microscopic analysis.ResultsMarginal bone loss around implant did not show the significant differences between pristine bone and GBR sites during spontaneous progression period. In immunohistochemical analysis, inflammatory and immune‐related cells were predominantly detected in peri‐implantitis‒affected area rather than unaffected area. In the polarized light microscopic analysis, substantial reductions in the amount and thickness of collagen fibers were observed in peri‐implantitis‒affected area compared with unaffected tissues. However, there were no significant differences in histological, immunohistochemical, polarized light microscopic outcomes between pristine bone and GBR sites.ConclusionPrevious hard tissue grafting at the implant sites did not affect experimental peri‐implantitis and exhibited similar radiographic, histological, immunohistochemical, and polarized light microscopic outcomes compared with those of pristine bone sites.