Fe–N–C electrocatalysts have emerged as promising substitutes for Pt-based catalysts for the oxygen reduction reaction (ORR). However, their real catalytic active site is still under debate. The underlying roles of different types of coordinating N including pyridinic and pyrrolic N in catalytic performance require thorough clarification. In addition, how to understand the pH-dependent activity of Fe–N–C catalysts is another urgent issue. Herein, we comprehensively studied 13 different N-coordinated FeN x C configurations and their corresponding ORR activity through simulations which mimic the realistic electrocatalytic environment on the basis of constant-potential implicit solvent models. We demonstrate that coordinating pyrrolic N contributes to a higher activity than pyridinic N, and pyrrolic FeN4C exhibits the highest activity in acidic media. Meanwhile, the in situ active site transformation to *O-FeN4C and *OH-FeN4C clarifies the origin of the higher activity of Fe–N–C in alkaline media. These findings can provide indispensable guidelines for rational design of better durable Fe–N–C catalysts.
Background: During implantation planning, dentists should be able to make an informed decision regarding whether to use an implant template to assist the surgery.Purpose: The aim of this metaanalysis was to assess the results of implantation with or without an implant template based on the accuracy, survival rate, and other considerations.Materials and Methods: In January 2018, a systematic review was undertaken for randomized controlled trials and retrospective and prospective cohort studies with relevance to implant accuracy and the survival rate between the implant template and free-hand method. The odds ratios (ORs) of the survival rate and the mean difference of accuracy deviation from the selected papers were estimated by meta-analysis.Results: Of the 362 screened articles, 6 studies were included in the meta-analysis. Comparison of the survival rate of implant surgery with or without an implant template revealed no significant result (OR ¼ 1.71, 95% confidence interval [CI] 0.65-4.51). Significant differences in accuracy were observed in angular (mean difference ¼ −5.45 degrees, 95% CI −0.66 to −4.24 degrees) and apical deviation (mean difference ¼ −0.83 mm, 95% CI −1.12 to −0.54).Conclusions: With the technology of computer-aided surgical template, implant placement can be more accurate than free-hand operation. No significant difference is observed in the survival rate between template and freehand.
The aim of this systematic review was to compare the survival rate, marginal bone loss changes and complications between short implants (5‐8 mm) and long implants (≥10 mm) with a bone‐augmented procedure in the posterior jaw. An electronic search of the MEDLINE (PubMed), Embase and Cochrane Library databases through September 2018 was done to identify randomised controlled trials (RCT) assessing short implants and long implants with at least a 1‐year follow‐up period after loading. A quantitative meta‐analysis was conducted on the survival rate, marginal bone loss changes and complications. Ten RCTs met the inclusion criteria. There were no significant differences in the survival rate (RR: 1.01; 95% CI: [0.99, 1.03]; P = .32) and complications (RR: 0.48; 95% CI: [0.20, 1.17]; P = .11) between the two groups. Compared with the long implant group, the short implant group had a lower marginal bone loss change, and the effect measure was significant (mean difference: −0.13; 95% CI: [−0.20, −0.06]; P < .05). This systematic review showed no difference between the survival rates and complications of short implants (5‐8 mm) and long implants (≥10 mm). The marginal bone loss changes in short implants are lower than those in long implants.
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