Short versus longer implants: a 5-year randomised controlled trial

PURPOSE: To evaluate whether 6.6 mm long implants could be a suitable alternative to longer implants placed in vertically augmented atrophic posterior mandibles. METHODS AND MATERIALS: Sixty partially edentulous patients having 7–8 mm of residual crestal height and at least 5.5 mm thickness measured on CT scans above the mandibular canal were randomised according to a parallel group design either to receive 1–3 submerged 6.6 mm long implants or 9.6 mm or longer implants (30 patients per group) placed in vertically augmented bone. Bone was augmented with interposition anorganic bovine bone blocks covered by resorbable barriers. Grafts were left to heal for 5 months before implant placement. Four months after provisional acrylic prostheses were delivered, replaced, after 4 months, by definitive metal-ceramic prostheses. Outcome measures were: prosthesis and implant failures, complications, and radiographic peri-implant marginal bone level changes. All patients were followed up to 5 year after loading. RESULTS: Five years after loading 8 patients dropped out: 3 from the short implant group and 5 from the augmented group. The augmentation procedure failed in 2 patients and only 6.6mm long implants could be inserted. There were no statistically significant differences for prosthesis and implant failures. Five prostheses failed in 4 patients of the short implant group versus 5 prostheses in 5 patients in the augmented group. Five short implants failed in 3 patients versus 3 long implants in 3 patients. There were statistically more complications in augmented patients (25 complications in 21 augmented patients versus 6 complications in 6 patients of the short implant group). Both groups gradually lost peri-implant bone in a statistically significant way. Five years after loading, short implant group patients lost an average of 1.49 mm peri-implant bone compared with 2.34 mm in the augmented group. Short implants experienced statistically significantly less bone loss (0.82 mm, CI95% 0.48; 1.16, P < 0.0001) than long implants. CONCLUSION: When residual bone height over the mandibular canal is between 7 and 8 mm, 6.6 mm short implants could be an interesting alternative to vertical augmentation in posterior atrophic mandibles since the treatment is faster, cheaper and associated with less morbidity. Longer follow-ups may still be needed to confirm these results, however the medium- term prognosis (5 years after loading) of short implants is at least as good as those of longer implants in placed vertically augmented mandibles.