Short versus standard implants for single-crown restorations in the posterior region: A systematic review and meta-analysis

Statement of problem. Whether implant-supported crowns on short or standard implants have similar clinical outcomes in the posterior alveolar bone is unclear. Purpose. The purpose of this systematic review and meta-analysis was to compare clinical outcomes, including survival rates, marginal bone loss (MBL), and complications associated with short implants and standard implants supporting a single crown in the posterior alveolar bone. Material and methods. This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) principles and was registered with PROSPERO (CRD42018112978). The authors identified eligible trials published before August 2019 by searching PubMed, EMBASE, and the Cochrane Library. Only randomized controlled trials (RCTs) were included in the study, and quality assessment was performed by using the Cochrane Collaboration Risk of Bias tool. Relevant information was extracted by using a standardized form, and a meta-analysis was performed by using a software program. Results. A total of 1954 references were identified. Five eligible trials were included in the quantitative synthesis. The survival rate of the short implants (<= 6 mm) was similar to that of longer implants (>6 mm) in the short term (P=.72; RR: 0.99; 95% CI: 0.97-1.02); however, long-term follow-up showed that short implants had a poorer survival rate than standard implants (P=.01; RR: 0.94; 95% CI: 0.90-0.99). There was no significant difference in the MBL (P=.94; MD: 0.00; 95% CI:-0.10 to 0.11). Conclusions. The present study suggested that, although short implants have a higher crown-toimplant (C/I) ratio, they do not affect MBL. However, long-term follow-up comparisons indicated that short implants (<= 6 mm) have a poorer survival rate than standard implants (>6 mm) (P=.01). Nonsplinted crowns supported by short implants should be used with caution in the posterior alveolar bone.