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Clin Implant Dent Relat Res. 2017 Aug;19(4):671-680. doi: 10.1111/cid.12494. Epub 2017 May 10.

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

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Dental School, Pontifical Catholic University of Rio Grande do Sul (PUCRS), Porto Alegre, Brazil.
Dental School, Federal University of Santa Catarina (UFSC), Florianópolis, Brazil.



The use of short implants is still not a consensus for challenging clinical situations, such as unfavorable crown-to-implant (C/I) ratio.


This 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.


Forty-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.


The mean follow-up time was 45 ± 9 (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.


The 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.


crown-to-implant ratio; dental implants; peri-implant bone loss; prospective clinical study; prosthetic complications; short implants

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