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PURPOSE: This study compared the three-dimensional (3D) accuracy of conventional impressions with digital impression systems (intraoral scanners and dental laboratory scanners) for two different interimplant distances in maxillary edentulous arches. MATERIALS AND METHODS: Six impression systems comprising one conventional impression material(Impregum), two intraoral scanners (TRIOS and True Definition), and three dental laboratory scanners (Ceramill Map400, inEos X5, and D900) were evaluated on two completely edentulous maxillary arch master models (A and B) with six and eight implants, respectively. Centroid positions at the implant platform level were derived using either physical or virtual probe hits with a coordinate measuring machine. Comparison of centroid positions between master and test models (n = 5) defined linear distortions (dx, dy, dz), global linear distortions (dR), and 3D reference distance distortions between implants (ΔR). The two-dimensional (2D) angles between the central axis of each implant to the x- or y-axes were compared to derive absolute angular distortions (Absdθx, Absdθy). RESULTS: Model A mean dR ranged from 8.7 ± 8.3 µm to 731.7 ± 62.3 µm. Model B mean dR ranged from 16.3 ± 9 µm to 620.2 ± 63.2 µm. Model A mean Absdθx ranged from 0.021 ± 0.205 degrees to -2.349 ± 0.166 degrees, and mean Absdθy ranged from -0.002 ± 0.160 degrees to -0.932 ± 0.290 degrees. Model B mean Absdθx ranged from -0.007 ± 0.076 degrees to -0.688 ± 0.574 degrees, and mean Absdθy ranged from -0.018 ± 0.048 degrees to -1.052 ± 0.297 degrees. One-way analysis of variance (ANOVA) by Impression system revealed significant differences among test groups for dR and ΔR in both models, with True Definition exhibiting the poorest accuracy. Independent samples t tests for dR, between homologous implant location pairs in Model A versus B, revealed the presence of two to four significant pairings (out of seven possible) for the intraoral scanner systems, in which instances dR was larger in Model A by 110 to 150 µm. CONCLUSION: Reducing interimplant distance may decrease global linear distortions (dR) for intraoral scanner systems, but had no effect on Impregum and the dental laboratory scanner systems. Impregum consistently exhibited the best or second-best accuracy at all implant locations, while True Definition exhibited the poorest accuracy for all linear distortions in both Models A and B. Impression systems could not be consistently ranked for absolute angular distortions.

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PURPOSE: Prior studies have defined the accuracy of intraoral scanner (IOS) systems but the accuracy of the digital static interocclusal registration function of these systems has not been reported. This study compared the three-dimensional (3D) accuracy of the digital static interocclusal registration of 3 IOS systems using the buccal bite scan function. MATERIALS AND METHODS: Three IOS systems compared were 3MTM True Definition Scanner (TDS), TRIOS Color (TRC), and CEREC AC with CEREC Omnicam (CER). Using each scanner, 7 scans (n = 7) of the mounted and articulated SLA master models were obtained. The measurement targets (SiN reference spheres and implant abutment analogs) were in the opposing models at the right (R), central (C), and left (L) regions; abutments #26 and #36, respectively. A coordinate measuring machine with metrology software compared the physical and virtual targets to derive the global 3D linear distortion between the centroids of the respective target reference spheres and abutment analogs (dRR , dRC , dRL , and dRM ) and 2D distances between the pierce points of the abutment analogs (dXM , dYM , dZM ), with 3 measurement repetitions for each scan. RESULTS: Mean 3D distortion ranged from -471.9 to 31.7 µm for dRR , -579.0 to -87.0 µm for dRC , -381.5 to 69.4 µm for dRL , and -184.9 to -23.1 µm for dRM . Mean 2D distortion ranged from -225.9 to 0.8 µm for dXM , -130.6 to -126.1 µm for dYM , and -34.3 to 26.3 µm for dZM . Significant differences were found for interarch distortions across the three systems. For dRR and dRL , all three test groups were significantly different, whereas for dRC , the TDS was significantly different from the TRC and CER. For 2D distortion, significant differences were found for dXM only. CONCLUSIONS: Interarch and global interocclusal distortions for the three IOS systems were significantly different. TRC performed overall the best and TDS was the worst. The interarch (dRR , dRC , dRL ) and interocclusal (dXM ) distortions observed will affect the magnitude of occlusal contacts of restorations clinically. The final restoration may be either hyperoccluded or infraoccluded, requiring compensations during the CAD design stage or clinical adjustments at issue.

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In this work we investigate the potential of a polyethylene glycol-polypropylene glycol-polyethylene glycol, tri-block copolymer as a template for a hybrid carbon/silica membrane for use in the non-osmotic desalination of seawater. Silica samples were loaded with varying amounts of tri-block copolymer and calcined in a vacuum to carbonize the template and trap it within the silica matrix. The resultant xerogels were analyzed with FTIR, Thermogravimetric analysis (TGA) and N2 sorption techniques, wherein it was determined that template loadings of 10 and 20% produced silica networks with enhanced pore volumes and appropriately sized pores for desalination. Membranes were created via two different routes and tested with feed concentrations of 3, 10 and 35 ppk of NaCl at room temperature employing a transmembrane pressure drop of 85% (in most cases >95%) and fluxes higher than 1.6 kg m-2 h-1. Furthermore, the carbonized templated membranes displayed equal or improved performance compared to similarly prepared non-templated silica membranes, with the best results of a flux of 3.7 kg m-2 h-1 with 98.5% salt rejection capacity, exceeding previous literature reports. In addition, the templated silica membranes exhibited superior hydrostability demonstrating their potential for long-term operation.