Influence of the abutment height on marginal bone level changes around two‐piece dental implants: Meta‐analysis and trial sequential analysis of randomized clinical trials

The focused question was: "In systemically healthy individuals with at least one two-piece dental implant, what is the efficacy of long (≥2 mm; intervention) compared with short (<2 mm; comparison) shoulder height abutments in peri-implant marginal bone level (MBL) changes at <1 year and ≥1 year reported by randomized controlled clinical trials?"An electronic and hand search was conducted to identify RCTs published up to August 2022. The primary outcome variable was changed in MBL from implant surgery to subsequent follow-ups. Mean values and standard deviations for each study were extracted. Weighted mean differences and 95% confidence intervals were calculated. Meta-analysis for MBL changes was performed through a random-effect restricted maximum-likelihood model at early (<1 year) and late (≥1 year) stages of bone remodeling. Publication bias and sensitivity tests were also applied. Subgroup analysis was performed to further explore possible sources of heterogeneity in the estimated treatment effect. Trial sequential analysis was performed to assess the required information and false-positive results.Six randomized clinical trials fulfilled the inclusion/exclusion criteria and were included in the qualitative and quantitative analysis with a follow-up range from 6 to 36 months after implant surgery. Meta-analysis revealed that long abutments significantly exhibited 0.27 mm (CI 95% -0.60, 0.06) and 0.33 mm (CI 05% -0.50, -0.16) lower MBL changes compared with short ones at <1 year and ≥1 year, respectively. Subgroup meta-analysis revealed that studies with implants placed in a more subcrestal position significantly exhibited less differences in MBL changes between long and short abutments. No meta-analysis was conducted for peri-implant clinical parameters, and soft-tissue changes provided that reported data were scarce. Trial sequential analysis revealed insufficient information size to provide a definitive answer on the effect of abutment height in MBL.It might be cautiously concluded that two-piece implants with long abutments (≥2 mm) may display a protective role against marginal bone loss when compared with short ones (<2 mm) at <1 year and ≥1 year. A more subcrestal implant position seemed to minimize the effect of the abutment height in terms of MBL.