Evaluation of marginal bone loss in short implants with different smooth neck length: a retrospective clinical study

Aim The aim of the study was to compare peri-implant bone resorption in two implant systems and to evaluate if there is a correlation between the distance bone-implant-abutment junction (IAJ) and bone loss over time. Materials and methods A multi-centre retrospective study was carried out to compare 2 implant systems in which the implant body had the same micro- and macro-morphology but with different neck morphologies. The short (Kt) and ultra-short (Kx) implants were 8.3 and 6 mm in length, respectively, with a smooth neck of 1.3 and 0.7 mm, respectively. We investigated the relationship between insertion depth and bone loss. Bone margin level was evaluated at the time of insertion and at follow-up and mean bone loss (MBL) were calculated. Survival and success rates were also evaluated. Results A total of 52 implants in 40 patients were analysed, with a mean follow-up of about 4 years. Overall survival rate was 100% and success rate was 98.1%. MBL (±SD) was 0.39 mm (±0.40) with Kx implants and 0.43 mm (±0.85) with Kt implants; there was no statistically significant difference in bone resorption between the two implant types. Implant insertion depth was correlated with the MBL at follow-up. Conclusion Despite the difference in neck morphology, the two implant systems showed comparable results at the 4-year follow-up. The positioning depth of the smooth neck portion of the implant appears to affect medium-term bone resorption.