Relevant aspects of implant design on periimplant bone loss ‐ 5‐years prospective clinical trial

Abstract

Background : Periimplant bone loss can jeopardize both the functional and esthetical outcomes of implant treatment. Several biological (i.e. formation of biological width, implant-abutment gap bacterial contamination) and biomechanical (i.e stress strain concentration caused by an excessive dynamic loading) hypothesis for changes in crestal bone height have been suggested. However, the relative contribution of relevant aspects of implant design on marginal bone loss has not been determined.Aim/Hypothesis : To evaluate clinical, bacteriological, and biomechanical parameters related to marginal bone loss, comparing external hex (EH) and Morse-taper (MT) connections, threaded (Th) and non-threaded (nTh) crestal modules and crestal module with and without (wT) surface treatment.Material and Methods : Twelve patients received four custom made Ø 3.8 x 13 mm implants (MT Th, MT nTh, EH Th, MT Th wT), randomly placed based on a split-mouth design. Clinical parameters were evaluated at 6 sites around the implants, at a 12-month follow-up. The distance from the top of the implant to the first bone-to-implant contact -IT-FBIC was evaluated on standardized digital peri-apical radiographs acquired at 1-, 3-, 6-, 12-, 36-, and 60-month follow-up. Samples of the subgingival microbiota were collected 1, 3 and 6 months after implant loading. DNA was extracted and used for the quantification of Tf, Aa, Pi and Fn. Comparison among multiple periods of observation was performed using repeated-measures Analysis of Variance (ANOVA), followed by a Tukey post hoc test, while two-period based comparisons were made using paired t-test. Further, 36 computer-tomographic based finite element (FE) models were accomplished and relevant biomechanical aspects were interpreted by means of ANOVA.Results : After 5-year follow-up, the variation in periimplant bone loss assessed from the radiographs was different between all aspects of crestal module design ( P < 0.001), except for MT Th and MT Th wT ( P = 0.1672). Mean IT-FBIC was 0.48 ± 0.70 mm for MT Th, 0.65 ± 0.57 mm for MT Th wT, 0.99 ± 0.29 mm for MT nTh, 1.66 ± 0.83 mm for EH Th. All clinical parameters did not present significant differences. No significant microbiological differences could be observed between evaluated parameters. Most of the collected samples had very few pathogens, meaning that these regions were healthy from a microbiological point of view. In FE analysis, a significantly higher peak of EQV strain ( P < 0.001) was found for EH Th (mean 3438.65 με), followed for MT Th wT (mean 1681.1 με), MT Th (mean 840.98 με), and MT nTh (mean 767.1 με). The MT nTh (mean 1.54 ± 1.25 mm 3 ) implant presented the highest bone volume affected by a shear stress above 5 MPa, comparing to the other implant designs. Conclusion and clinical implications :Varying the implant design at crestal module will lead to diverse periimplant bone loss extension.Clinical and microbiological conditions could not be demonstrated as responsible for early marginal bone loss. A singular loading transmission thro...