30 July 2021

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Immediate loading of 3 mm-diameter implants as an alternative to horizontal bone augmentation for placing 4 mm-diameter implants: one-year post-loading results from a multicentre randomised controlled trial

Authors: Marco Esposito, Carlo Barausse, Roberto Pistilli, Pierantonio Bellini, Jacopo Buti, Pietro Felice

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PURPOSE
To evaluate the effectiveness of immediately loaded 3 mm-diameter implants as an alternative to horizontal bone augmentation procedures to allow placement of implants with a conventional diameter of 4 mm. 

MATERIALS AND METHODS
Forty-five partially edentulous patients with between 4 and 5 mm of bone width 3 mm below the crest in areas requiring one to three adjacent implants were randomised, according to a parallel-group design, to receive one to three 3.0 mm-diameter implants to be loaded immediately (23 patients) or horizontal crest augmentation with a granular bone substitute covered with a bone lamina for placing, and, after 6 months of healing, one to three 4 mm-diameter implants (22 patients) at two centres. Implants at augmented sites were left to heal unloaded for 4 months. Four mm-diameter implants were restored using provisional screw-retained reinforced acrylic prostheses, replaced after 4 months by definitive prostheses. Three mm-diameter implants were loaded immediately with definitive metal-composite prostheses if the insertion torque was ≥ 35 Ncm, or otherwise after 4 months. Patients were followed-up to 1 year post-loading. Outcome measures were: prosthesis and implant failures, any complication, peri-implant marginal bone level changes, and patient satisfaction. 

RESULTS
Two patients dropped out of the augmentation group. In three patients, five 3 mm-diameter implants could not be inserted with a torque of 35 Ncm, so they were submerged unloaded for 4 months. Two implants failed in two patients from the augmentation group (P = 0.2333; difference in proportion = -0.09; CI 95% -0.24 to 0.07) and neither patient was fitted with a prosthesis. Five patients with narrow-diameter implants were affected by six complications versus 11 augmented patients with 12 complications, the difference being statistically significant (P = 0.0477; difference in proportion = -0.28; CI 95% -0.52 to 0). One year after loading, patients with 3 mm-diameter implants lost on average 0.14 mm of peri-implant bone, while augmentation patients lost 0.52 mm. The difference in bone loss between the two groups was statistically significant (mean difference = 0.38 mm, 95% CI 0.10 to 0.66, P = 0.0112). Five 3-mm group patients versus two augmentation group patients (mean difference = 0.12 mm, 95% CI -0.12 to 0.32, P = 0.4205) and one 3-mm group patient versus two augmentation group patients (mean difference = -0.06 mm, 95% CI -0.23 to 0.12, P = 0.5900) were partially satisfied with function and aesthetics, respectively, all remaining patients being fully satisfied. All patients would undergo the same procedure again.

CONCLUSIONS
One year after loading, patients treated with 3 mm-diameter implants exhibited better results than those receiving horizontal augmentation for placement of 4 mm-diameter implants. Three mm-diameter implants might therefore be the preferable choice with respect to horizontal bone augmentation, the treatment being less invasive, faster, cheaper, and associated with less morbidity and peri-implant marginal bone loss; however, 5- to 10-year post-loading data will be necessary before reliable recommendations can be made.