Clinical effectiveness of short implants with versatile placement depths: a retrospective analysis over 5 years

Purpose: This retrospective study evaluated the long-term survival and success rates of 7-mm short implants and assessed the outcomes according to the placement depth. Materials and Methods: From March 2009 to November 2019, 111 short implants (7 mm length) were placed in 67 patients at the Apple Tree Dental Hospital and followed for 5 to 14 years (mean 7.4±2.2 years). The implants were categorized according to the placement depth for outcome analysis. Kaplan–Meier analysis was used to estimate the cumulative survival and success rates. Log-rank and Fisher's exact tests were performed for univariate analysis to assess the associations with various factors. Marginal bone loss (MBL) was evaluated radiographically. Results: Of the 111 implants, six were classified as failures (four removed and two ailing), resulting in overall implant survival and success rates of 96.4% and 94.6%, respectively. In univariate analysis, only the placement depth was significantly associated with survival (P<0.05). The implants in patients aged ≥70 years showed survival and success rates of 94.1%, which were similar to those in patients aged <70 years (97.4% and 94.8%, respectively). The long-term evaluation showed that supra-crestal placement had the lowest MBL (0.24±0.44 mm) and the highest cumulative success rate (98.0%). All MBL values across placement groups remained below the 2-mm clinical threshold, with gradual but limited progression from 0.16±0.37 mm at the early evaluation to 0.32±0.56 mm at the long-term evaluation. Conclusions: This study revealed the favorable long-term effectiveness of 7-mm short implants, with stable survival and success rates maintained for up to 14 years. Placement at the supra- or equi-crestal levels consistently produced favorable outcomes, and minimal MBL was observed regardless of the depth. These results support the predictable application of this short implant system under anatomically restricted conditions, including elderly patients with systemic comorbidities.