03 June 2021

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Four-mm-long versus longer implants in augmented bone in atrophic posterior jaws: 3 year post loading results from a multicentre randomised controlled trial

Authors: Pietro Felice, Carlo Barausse, Roberto Pistilli, Zamira Kalemaj, Marco Esposito

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PURPOSE
To evaluate whether 4-mm-long dental implants could be an alternative to bone augmentation with xenografts and placement of implants of length at least 10 in posterior atrophic jaws.

MATERIALS AND METHODS
Forty patients with atrophic posterior (premolar and molar areas) mandibles having 5 to 6 mm bone height above the mandibular canal and 40 patients with atrophic maxillae having 4 to 5 mm bone height below the maxillary sinus were randomised according to a parallel-group design to receive one to three 4.0-mm-long implants or one to three implants of length at least 10 mm in augmented bone at two points. All implants had a diameter of 4.0 or 4.5 mm. Mandibles were vertically augmented with interpositional equine bone blocks and resorbable barriers. Implants were placed 4 months after grafting. Maxillary sinuses were augmented with particulated porcine bone via a lateral window covered with resorbable barriers, and implants were placed simultaneously. Implants were not submerged, and were loaded after 4 months with provisional prostheses. Four months later, screw-retained reinforced acrylic restorations were fitted, and replaced after 4 months by definitive screw-retained metal-composite prostheses. Patients were followed up to 3 years post-loading. Outcome measures were: prosthesis and implant failures, any complications, and peri-implant marginal bone level changes. 

RESULTS
Nine patients dropped out, six from the augmentation group and three from the short implant group. In six augmented mandibles (30%) it was not possible to place implants of length at least 10.0 mm, so shorter implants had to be placed instead. In mandibles, two implants from the augmentation group failed in two patients, versus two 4.0-mm-long implants in two patients from the short implant group. In maxillae, four short implants failed in three patients versus seven long implants in four patients (two long implants and one short implant dropped into the maxillary sinus). Three prostheses on short implants (one mandibular and two maxillary) failed or were placed at a later stage due to implant failure, versus eight prostheses (three mandibular and five maxillary) at augmented sites. There were no statistically significant differences in implant failures (P [Fisher’s exact test] = 0.159; difference in proportion = 0.05; CI 95% -0.11 to 0.21) or prostheses failures (P [Fisher’s exact test] = 0.919; difference in proportion = 0.02; CI 95% -0.14 to 0.18). There were more patients affected by complications in the augmentation group (18 patients affected by 30 complications versus 8 patients affected by 10 complications), but the difference was not statistically significant (P [Fisher’s exact test] = 0.587; difference in proportion = -0.72; CI 95% -0.29 to 0.14). At 3 years post-loading, average peri-implant bone loss was 0.62 mm at 4-mm-long mandibular implants, 0.71 mm at 10-mm or longer mandibular implants, 1.14 mm at short maxillary implants and 0.73 mm at long maxillary implants. The difference was not statistically significant in mandibles (mean difference -0.08 mm, 95% CI -0.37 to 0.20, P [ANCOVA] = 0.568), but was significant in maxillae, with greater bone loss at short implants (mean difference 0.41 mm, 95% CI -0.04 to 0.87, P [ANCOVA] = 0.037).

CONCLUSIONS
Three years after loading, 4.0-mm-long implants yielded similar, if not better, results than longer implants in augmented jaws, but were affected by fewer complications. Hence, short implants may be preferable to bone augmentation, especially in mandibles, since the treatment is less invasive, faster, cheaper, and associated with less morbidity. However, 5- to 10-year post-loading data will be necessary to make reliable recommendations.