Marginal bone loss around external hex and Morse-taper implants – 5-years prospective clinical trial

Background

The biological width formation, the inflammatory reactions due to the implant-abutment microgap contamination, the periimplant stress strain concentration causing bone microdamage accumulation and or a foreign body response, characterized by a chronic inflammation in soft tissue, have been suggested to explain early periimplant bone loss. However, it is yet not well understood to which extent the implant-abutment connection type may influence the remodeling process around dental implants.

Aim/Hypothesis

to evaluate clinical, bacteriological and biomechanical parameters related to periimplant bone loss at the crestal region, comparing external hexagon (EH) and Morse-taper (MT) connections.

Material and Methods

Twelve patients received two custom made Ø 3.8 x 13 mm implants, EH or MT, 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 months follow-up. Samples of the subgingival microbiota were collected 1, 3 and 6 months after implant loading. DNA were extracted and used for the quantification of Tf, Aa, Pi and Fn. Comparison among multiple periods of observation were 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 the results for the peak EQV strain in periimplant bone were interpreted by means of ANOVA.

Results

The variation in periimplant bone loss assessed by means of radiographs was significantly different between the connection types (P < 0.001). Mean IT-FBIC was 1.66 ± 0.83 mm for EH, and 0.48 ± 0.70 mm for MT, considering all evaluated time periods. All clinical parameters presented not significant differences. No significant microbiological differences could be observed between both connection types. 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 = 0.005) was found for EH (mean 3,438.65 με) compared to MT (mean 840.98 με) connection.

Conclusion and Clinical Implications

Varying implant-abutment connection type will result in diverse periimplant bone remodeling. Clinical and microbiological conditions could not be demonstrated as responsible for marginal bone loss, after the first year of implant function. The present findings suggest that a Morse-taper connection is more efficient to prevent long-term periimplant bone loss, compared to an external hexagon connection.