Matrix-metalloproteinases and bone loss at implants restored according to the platform switching concept: a randomized controlled trial on the influence of different mismatching

Background and Aim: Matrix metalloproteinases (MMPs) are important mediators of tissue degradation. This randomized controlled clinical trial aimed to evaluate bone responses to implants restored with different implant/abutment mismatching and to assess the correlation between peri-implant bone remodeling and peri-implant sulcular fluid levels of matrix metalloproteinases. Materials and Methods: A total of 80 implants (Global®, Sweden & Martina, Italy) were divided according to platform diameter in 4 groups: 3.8 (ControlGroup), 4.3 (TestGroup1), 4.8 (TestGroup2) and 5.5mm (TestGroup3), 20 implants each group. They were randomly placed in the posterior maxilla of 30 patients. Two months later, all implants were connected to a 3.8mm diameter abutment and definitive prosthetic rehabilitation was performed. Radiographic bone levels were measured independently by two calibrated examiners immediately after implant placement (baseline) and every six months after loading using an image analysis software. Patients were followed up for 30 months after prosthetic loading. At the last follow-up visit, in addition to a standard clinical and radiographic exam, peri-implant sulcular fluid samples were obtained. Activated matrix metalloproteinase-8 (aMMP-8) was quantified by ELISA (Dentognostics, Jena, Germany). Results: Five patients were lost to follow up after 33 months. A total of seventy implants remained in the study and all of them were clinically osseointegrated. Radiographic analysis showed a mean bone loss of 0.97mm (SD = 0.42mm) for TestGroup1, 0.77mm (SD = 0.43mm) for TestGroup2, 0.64mm (SD = 0.32mm) for TestGroup3. These values were statistically significant lower (p < 0.005) than the ControlGroup mean values (1.48mm, SD = 0.42mm). There was an inverse correlation between the amount of bone loss and the degree of mismatching (-0.63, p < 0.001). For MMP-8, the respective mean values were: 4.139ng (SD: 3.25ng) for the ControlGroup; TestGroup1: 2.894ng (SD: 3.17ng); TestGroup2: 3.534ng (SD: 3.64ng), TestGroup3: 3.278ng (SD: 3.25) and 2.80ng (SD: 4.45ng) for samples from adjacent control teeth (probing depth ≤ 3 mm). No significant differences between the groups and no significant correlation between MMP-8 levels and the extent of past bone loss at individual sites was observed. Conclusion This study confirmed an inverse correlation between that extent of implant/abutment mismatching and the amount of peri-implant bone loss. Longitudinal monitoring of peri-implant sulcular levels of MMP-8 may be warranted to determine their suitability as predictors for future peri-implant attachment loss.