Long-term studies have shown that there is no significant difference between the success rates of implants placed in natural alveolar bone and those placed in grafted bone. However bone graft techniques implies higher costs and risks of complications and may lead to an increased post-operative morbidity. In these cases, as an alternative, short implants can be used. The definition of short implant is still controversial. Recently they have been defined with a length less than 8mm. Recent studies have demonstrated that augmentation procedures have similar outcome in terms of implant failures than short implants. Furthermore the use of short implants implicates many advantages such as the possibility to avoid CT scans, a safer surgery and inferior costs. On the other hand some elements of debate (bone to implant contact, the c/i ratio and the crestal bone resorption) limit the use of short implants. In a randomised controlled trial published in EJOI in 2018, the authors compare survival and success rates of 6-mm and 10-mm long implants in partially edentulous posterior areas. Prosthetic and biomechanical variables on marginal bone loss (MBL) and on the survival rates of implant-supported prostheses were evaluated.
Materials and Methods
24 patients, with a partially edentulous area in the jaws were included in the study. Height and width of the bone should allow the positioning of 2 to 3 adjacent 10 × 4.1 mm implants without any bone graft procedure, as main inclusion criteria. Patients were randomly allocated according to a parallel group design to receive 6-mm long or 10-mm long implants. A total of 54 implants were placed (26 × 6 mm and 28 × 10 mm implants). Prosthesis were realised 8 weeks after surgery and were followed for 10 years. Outcome measures were prosthesis and implant survival, as well as marginal bone loss and complications.
After 10 years, 17 patients (eight with 6 mm implants and nine with 10 mm implants) were still available: three 6 mm and four 10 mm patients were lost to the follow-up. One 6 mm implant failed during the healing period but no other implants were lost after loading. Nine patients in the 6 mm group showed a total of 15 complications (two mucositis, six decementations and seven chippings). Ten patients in the 10 mm group showed a total of 13 complications (five mucositis, two decementations and six chippings). Generally, the difference for complications between the two groups was not statistically signiﬁcant (P = 0.22; difference in proportion = -0.02; 95% CI: -0.31 to 0.27). Decementations in the 6 mm group registered a value statistically significant higher than the 10 mm group (P = 0.04; difference in proportion = 0.39; 95% CI: 0.03 to 0.74). Marginal bone loss at 10 years was 0.84 and 0.37 mm with the 6 mm and 10 mm groups, respectively (difference between the two groups 0.49 mm; 95% CI -0.31; 1.29; not statistically signiﬁcant: t test P = 0.22)
From the study it’s not possible drawing general conclusions because of the limited sample. Overall survival rate of a prosthesis supported by 6 mm and 10 mm implants seem to be similar after 10 years. Marginal bone loss was similar. Prosthetic and biological complications rates showed high values in both groups. Rehabilitations supported by 6-mm or 10-mm long implants show comparable clinical outcomes in survival and success rates even if 6 mm implants show a tendency for decementations.
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