Short versus longer implants in augmented mandibles – A systematic review of RCTs with 5-year follow-up

Background

Often in atrophic jaws it is not possible to place dental implants of ìadequate lengthî because there is less than 8 mm of residual vertical bone height. Clinicians are faced with the dilemma whether to augment the bone or to place short implants having an intra-bony length of 8 mm or less.

Aim/Hypothesis

To compare the clinical outcome of fixed prostheses supported by 4 to 8 mm-long implants with prostheses supported by longer implants placed in vertically augmented atrophic mandibles after a follow-up of 5 years in function.

Material and Methods

The Cochrane Central Register of Controlled Trials (CENTRAL) and MEDLINE were searched up to 1st September 2018 for Randomised Controlled Trials (RCTs) with a follow-up of at least 5 years in function comparing fixed prostheses supported by 4 to 8 mm-long implants with prostheses supported by longer implants placed in vertically augmented atrophic mandibles. Outcome measures were prosthesis failure, implant failures, augmentation procedure failures, complications, and peri-implant marginal bone level changes. Screening of eligible studies, assessment of the risk of bias and data extraction were conducted in duplicate and independently by two review authors. The statistical unit of the analysis was the prosthesis. Results were expressed as random-effects models using mean differences for continuous outcomes and risk ratios (RR) for dichotomous outcomes with 95% confidence intervals (CIs).

Results

Four eligible RCTs, which included originally 135 patients, were included. Two RCTs had a parallel group design and two a split-mouth design. Short implants were 5 to 6.6 mm-long and were compared with longer implants placed in posterior mandibles augmented with interpositional blocks of bone substitutes. All trials were judged at unclear risk of bias. Twelve (14%) bone augmentation procedures failed to achieve the planned bone height to allow placement of implants with the planned length. Five years after loading 28 patients (21%) dropped from the four RCTs. There were no differences for patients having prosthesis (P = 0.47) or implant (P = 1.00) failures between the two interventions, but there were more patients experiencing complications (P < 0.00001) and peri-implant marginal bone loss (P < 0.00001) at longer implants in augmented bone.

Conclusion and Clinical Implications

Five years after loading, prosthetic and implant failures were similar between the two interventions, but complications and peri-implant marginal bone loss were higher and more severe at longer implants placed in vertically augmented mandibles. Larger trials and longer follow-ups up to 10 years after loading are needed to confirm or reject the present preliminary findings. However, in the meantime short implants could be the preferable option.