Short implants versus longer implants in the posterior alveolar region after an observation period of at least five years: A systematic review and meta-analysis

Objectives: This meta-analysis compared clinical outcomes, including survival rate, marginal bone loss (MBL), and technical and biological complications of short implants (<7 mm) and long implants (>= 7 mm) placed in the posterior alveolar bone. Sources: Electronic (via PubMed, EMBASE, Cochrane Library) and manual searches were performed for articles published prior to November 29, 2019. Study selection: The review protocol was registered with PROSPERO (CRD42019140718). Only randomized controlled trials (RCTs) comparing short implants and standard implants in the same study after an observation period of at least five years were included. Data: Nine RCTs were included in this study. The survival rates of short implants (<7 mm) ranged from 86.7 %-98.5 %, whereas the survival rates of longer implants (>= 7 mm) were 95.1%-100% with follow-up ranging from 5 to 10 years. Dichotomous variables were compared using the Mantel-Haenszel (MH) method, and continuous variables were compared using the inverse variance (IV) method. The random effects model and the fixed effects model were used. Meta-analyses showed that short implants had a poorer survival rate than longer implants (P = 0.008). Short implants were associated with lower MBL than longer implants (P < 0.001). The biological complications of short implants were lower (P < 0.001) and the technical complications were higher, than those of long implants (P = 0.006). Conclusions: The results indicate that although the survival rate of short implants in the maxilla may be lower than that of long implants, the survival rate of short implants in the mandible is similar to that of long implants, and short implants can result in a lower rate of biological complications. The conclusions should be interpreted with caution due to the limited numbers of participants and implants. Clinical Significance: When selecting the length of implants, surgeons should consider survival rate, the location of implant placement, their own clinical experience, and the incidence of complications.