Retrospective Study of Short and Extra-Short Implants Placed in Posterior Regions: Influence of Crown-to-Implant Ratio on Marginal Bone Loss

AIM: The aim of this study is to evaluate the influence of crown-to-implant (CI) ratio as well as other surgical, prosthetic and biomechanical variables on marginal bone loss (MBL) and on the survival rates of implant-supported prostheses in short implants (≤8.5 mm in length) placed in posterior areas of maxilla and mandible. MATERIAL & METHODS: This was a retrospective study based on clinical charts and follow-up recordings from a single private practice over a period of 10 years. Patients rehabilitated in the posterior region of the jaws by means of prostheses supported by implants of ≤8.5 mm length were included. Patients-related, surgery-related. and implant-related variables, as well as other prosthetic and biomechanical variables. were registered. The data were split into two groups according to the value of CI ratio (CI < 2 and CI ≥ 2). MBL was measured from radiographs using an image analysis software. Implant and prosthesis survival rates were recorded. RESULTS: One hundred twenty-eight short implants placed in 63 patients were evaluated. The mean follow-up period was 21.88 months (standard deviation (SD): 22.9, range 7-113 months). Eighty-six implants (67.2%) had a CI ratio of <2, whereas it was ≥2 in 42 implants (32.8%). The mean value of CI ratio was 1.82 (SD: 0.42; range 1.04-3.31). The average MBL after 1 year of follow-up was 0.35 (SD: 0.50), and it was 0.45 (SD: 0.46) mm for subsequent evaluations. Survival rates of implants and prosthesis were 100%. The presence of a cantilever had a negative influence on the first year MBL (p < .05). CONCLUSIONS: The CI ratio had not a significant influence on MBL in Biotechnology Institute (BTI; Vitoria, Spain) short implants humidified with PRGF-Endoret and placed in posterior areas. The only variable that showed a significant negative influence on first year postloading MBL was the use of cantilever for rehabilitations.