Less marginal bone loss around bone-level implants restored with long abutments: A systematic review and meta-analysis.

The aim of this study was to investigate the biological outcomes of bone-level implants restored with long vs. short abutments, with regard to the 'one abutment at one time' protocol. The systematic search was performed in five databases: MEDLINE (PubMed), EMBASE, Web of Science, Scopus, and CENTRAL for randomized controlled trials up to January 14, 2023. Data were collected for marginal bone loss, bleeding on probing, and probing pocket depth by two reviewers. As effect size measure, mean difference (MD), and risk ratio (RR) were used for continuous and categorical outcomes, R-statistics software was used for conducting statistical analyses. For quality and certainty assessment, Risk of Bias Tool 2, ROBINS-I, and GRADE approach were used. The search resulted in 4055 records without any duplicates. After title, abstract, and full-text analysis, eight articles were found eligible for inclusion. Bone-level and platform-switched implants presented less marginal bone loss after 6 months and 1 year as well, when long abutments were used (MD 0.63, 95% CI: [-0.16; 1.42]) and (MD 0.26, 95% CI: [-0.02; 0.53]). However, subgroup analysis revealed no difference in marginal bone loss when applying 'one abutment at one time' protocol (p = 0.973). Bleeding on probing and probing pocket depth presented similarly good results in both groups without almost any differences (RR 0.97, 95% CI: [0.76; 1.23]) and (MD -0.05, 95% CI: [-1.11; 1.01]). Longer abutments on bone-level implants seem to be a favorable choice for decreasing early marginal bone loss, irrespective of connection timing.