Are <7-mm long implants in native bone as effective as longer implants in augmented bone for the rehabilitation of posterior atrophic jaws? A systematic review and meta-analysis

Purpose: To compare clinical and radiographic outcomes of <7 mm short (SH) implants inserted in native bone vs longer (ST) implants placed in vertically augmented partially edentulous posterior jaws. A further aim was to evaluate if the residual bone dimension plays a role in the outcomes of SH and extra-SH implants. Materials and Methods: This review was registered with PROSPERO. An electronic literature search was performed on PubMed, Scopus and Web of Science. Randomized controlled trials (RCTs) with at least 1-year follow-up, comparing fixed prostheses supported by SH vs ST implants in augmented sites were included. Marginal bone level (MBL) changes, implant survival rate, and complications were evaluated through a meta-analysis. Subgroup analysis was performed dividing the SH implants according to length at each follow-up (1-, 3-, 5-year of function). Results: Twenty-five articles fulfilled the inclusion criteria, featuring a total of 650 SH implants placed in 415 patients and 685 ST implants placed in 403 patients. There was a trend for a significantly lower MBL associated with SH implants respect to ST implants at each follow-up, whilst there was no evidence of a difference in failure rates between SH and ST implants, for any SH length considered and at any follow-up. There was evidence for a lower incidence of complications in favor of SH implants at both 1-year (P <.0001) and 3-year follow-up (P =.01), while at 5-year follow-up there was no evidence of a difference between SH and ST groups (P =.30). Conclusion: SH implants supporting partial fixed rehabilitations represent a valuable alternative to augmentation procedures in the medium term. While the performance of implants at least 5-mm long is well documented, more studies with at least 5-year follow-up are needed to confirm the promising outcomes observed with <5 mm-long fixtures.