POSTERIOR JAW REHABILITATION USING PARTIAL PROSTHESES SUPPORTED BY IMPLANTS 4.0 X 4.0 MM OR LONGER: THREE-YEAR POST- LOADING RESULTS OF A MULTICENTRE RANDOMISED CONTROLLED TRIAL

PURPOSE. To evaluate whether 4.0 x 4.0-mm dental implants could be viable alternatives to implants of length at least 8.5 mm when placed in posterior jaws with adequate bone volumes.

MATERIALS AND METHODS. One hundred and fifty patients with posterior (premolar and molar areas) jaws having at least 12.5 mm bone height above the mandibular canal or 11.5 mm below the maxillary sinus, as applicable, were randomised according to a parallel-group design and received one to three 4.0 mm-long implants or one to three implants which were at least 8.5 mm long at three treatment centres. All implants had a diameter of 4.0 mm. Implants were loaded with permanent screw-retained prostheses after 4 months. Patients were followed up until 3-year post loading, and outcome measures considered were prosthesis and implant failure, any complications, and changes in peri-implant marginal bone levels.

RESULTS. Seventy-five patients were randomly allocated to each group. Drop-outs at 3-year post-loading assessment were five patients from the long implant group and three from the short implant group. Up to 3 years post-loadings, three patients lost one 4.0 mm-long implant each, in comparison to two patients who lost one long implant each (difference in proportion = -0.013; 95% CI: -0.079 to 0.054; P = 1). All failures occurred before loading; failed implants were replaced, delaying delivery of two prostheses in each group by several months (difference in proportion = 0; 95% CI: -0.061 to 0.062; P = 1). Five short-implant patients experienced six complications versus the three complications seen in three long implant patients (difference in proportion = -0.026; 95% CI: -0.103 to 0.053; P = 0.719). There were no statistically significant differences between groups in prosthesis failures, implant failures or complications. Patients with short implants lost on average 0.55 mm of peri-implant bone, and patients with longer implants lost 0.61 mm. There were no statistically significant differences between short and long implants in bone level changes up to 3 years (mean difference = 0.05 mm; 95% CI: -0.05 to 0.16; P = 0.221).

CONCLUSIONS. Outcomes 3 years after loading were similar with 4.0 x 4.0 mm-long implants and 8.5 x 4.0 mm or longer implants in posterior jaws, in the presence of adequate bone volumes. However, 5 to 10-year post-loading data will be necessary before reliable recommendations can be made.