Risk factors for single crowns supported by short (6-mm) implants in the posterior region: A prospective clinical and radiographic study

BackgroundThe use of short implants is still not a consensus for challenging clinical situations, such as unfavorable crown-to-implant (C/I) ratio. PurposeThis prospective study evaluated the rates of prosthetic complications and implant failure, the mean marginal bone loss of 6-mm dental implants with single crowns in posterior regions and the potential risk factors. Materials and MethodsForty-six dental implants, 6-mm long and 4.1-mm wide, were placed in the posterior region in 20 patients. Patients were clinically and radiographically examined after the restoration with single crowns and on a yearly basis. Potential risk factors (arch, bruxism, maximum bite force, anatomical and clinical C/I ratios, and occlusal table area) were analyzed according to the following outcomes: implant survival, bone loss, and prosthetic complications. ResultsThe mean follow-up time was 459 (16-57) months. There was no early loss of implants. After prosthetic loading, 4 implants were lost (2 in the mandible and 2 in the maxilla; 91.3% survival), and there were 13 prosthetic complications (28.3%), yielding a 65.2% success rate. The frailty term showed a 95% greater chance of loss in the mandible than the maxilla. Mean peri-implant bone loss was of 0.2 +/- 0.4 mm, 0.1 +/- 0.2 mm, 0.1 +/- 0.3 mm, and 0.2 +/- 0.4 mm in the first, second, third, and fourth years, respectively, with a mean cumulative loss of 0.3 +/- 0.5 mm at 48 months. In the multilevel model, the effects of the clinical C/I ratio and time were significant for bone loss (P<.001). It was estimated that a mean bone loss of 0.1 mm is associated with both a one-unit increase in time (12 months) and a 0.1 increase in the clinical C/I ratio. The other potential risk factors showed no significant relationship with the outcomes. ConclusionsThe 6-mm implants supporting single crowns performed well, but the mandible shows a higher risk of failure. The time and clinical C/I ratio are predictors for bone loss.