Posterior jaws rehabilitated with partial prostheses supported by 4.0 x 4.0 mm or by longer implants: Four-month post-loading data from a randomised controlled trial.

Purpose: To evaluate whether 4.0 x 4.0 mm dental implantscould be an alternative to implantsat least 8.5 mm long, which were placed in posterior jaws in the presence of adequate bone volumes. Materials and methods: One hundred and fifty patients with posterior (premolar and molar areas) mandibles having at least 12.5 mm bone height above the mandibular canalor 11.5 mm bone height below the maxillary sinus, were randomised according to a parallel group design, in order to receive one to three 4.0 mm-long implantsor one to three implantswhich were at least 8.5 mm long, at three centres. All implantshad a diameter of 4.0 mm. Implantswere loaded after 4 months with definitive screw-retained prostheses. Patients were followed up to 4-month post-loading and outcome measures were prosthesis and implant failures, any complications and peri-implantmarginal bone level changes. Results: No patients dropped-out before the 4-month evaluation. Three patients experienced the early failures of one 4.0 mm-long implanteach, in comparison to two patients who lost one long implanteach (difference in proportion = 0.01; 95% CI -0.06 to 0.09; P = 0.50). Consequently, two prostheses in each group could not be delivered as planned (difference in proportion = 0; 95% CI -0.07 to 0.07; P = 0.69), and one patient from each group is still waiting to have their prostheses delivered. Three short implantpatients experienced three complications versus two long implantpatients (difference in proportion = 0.01; 95% CI -0.06 to 0.09; P = 0.50). There were no statistically significant differences in prosthesis failures, implant failuresand complications. Patients with short implantslost on average 0.38 mm of peri-implantbone at 4 months and patients with long mandibular implantslost 0.42 mm. There were no statistically significant differences in bone level changes up to 4 months between short and long implants(mean difference = 0.04 mm; 95% CI: -0.041 to 0.117; P = 0.274). Conclusions: Four months after loading, 4.0 x 4.0 mm implantsachieved similar results as 8.5 x 4.0 mm-long or longer implantsin posterior jaws, however 5 to 10 years post-loading data are necessary before reliable recommendations can be made. Conflict-of-interest statement: Global D (Lyon, France) donated implantsand prosthetic components and Tecnoss (Coazze, Italy) donated the biomaterials used in this study. Data property belonged to the authors and by no means did the manufacturers interfere with the conduct of the trial or the publication of its results.