MicroThread™ is the minute thread design on the neck of the Astra Tech implants, introduced as early as 1991. Scientific articles present the ability of MicroThread to ensure positive biomechanical bone stimulation and to maintain marginal bone levels in the long term. Summarized on the following pages, you will find articles about the continuous follow-up of the MicroThread.
Tissue characteristics at microthreaded implants an experimental study in dogs
Purpose: A degree of crestal bone loss is well established particularly within the first year of function
as well as a small but measurable on-going bone loss
thereafter. However in the case of an implant with a
smooth conical collar it has been reported that marginal bone loss is excessive and that this might be due to the geometric design of the implant. However data that has been gathered with the Astra Tech 4.5 mm implant would seem to demonstrate excellent bone maintenance, casting doubt on the theory that it is related to geometry. In the case of the Astra Tech implant it would appear that it might be related to the surface roughness and in particular to the MicroThread™ design of the collar. This study therefore set out to compare marginal bone response to implants with and without MicroThread on the collar.
Material and Methods: Mandibular premolars were extracted from six beagle dogs three months prior to implant installation, bilaterally. At time of implant insertion one test implant with microthreading and 2 control implants without microthreading were randomly inserted according to manufacturer's protocol with the implant/abutment junction (1AJ) being placed at the crest of the bone. All implants benefited from 3 months submerged healing prior to exposure and abutment connection. After a further 3 months, fixed gold prostheses were secured to the abutments by screwretention. In the opposing jaw fixed prostheses were cemented to previously prepared maxillary canines and premolars to provide appropriate occlusal function. At implant exposure and prosthesis insertion follow-up radiographs were taken and again after 10 months of functional loading. All radiographs were taken in custom holders using a paralleling technique and images were digitized and measurement carried out on the mesial and distal surfaces of each implant.
At the end of the study period all animals were sacrificed and implants removed en bloc for histological processing. Ground sections of 20 µm thickness were prepared, two from the mesio-distal and two from the bucco-lingual planes and stained with toluidine blue. Histometric evaluations were undertaken to measure percentage bone-to-implant contact (%BIC) of the neck portion, as well as the entire length of the implants, percentage bone density (% BD), and linear measurements between the landmarks: Mucosal Margin (MM), Bone Crest (BC), apex of Junctional Epithelium (aJE), and the Implant-Abutment-Junction (IAJ).
Results: In only one implant healing was compromised due to the formation of a small abscess leading to an infrabony defect. This site was excluded from the analysis.
Radiographic measurements revealed a total mean bone loss, measured from the IAJ, of -0.19 mm for control implants versus +0.05 mm for test implants. Bone levels were principally affected between insertion and abutment connection and then again after functional loading but only within the control group. These differences did not reach significance.
The % BIC measured at the neck of test implants was 81.8% compared to 72.8% for control implants, (p < 0.05) but overall % BIC was similar when measured over the entire implant length. The % BD varied for both test and control sites between 78.0% and 80.2%. Linear measurements revealed a longer distance of MM-BC and for IAJ-BC for control implants with MM-BC being statistically longer, 3.45 mm compared to 3.09 mm, (p < 0.05).
Discussion and Conclusions: In the current study there was a clear radiographic and histologic finding that test implants supported bone closer to the IAJ with a stable marginal bone level which remained at or even slightly above the microgap. These findings are in accordance with clinical results previously published.
It was of particular interest to note the statistically significant increase in % BIC for the neck portion of the test implants, compared to the entire implants, which for their remaining length were essentially the same. Given that all implants in the current study were loaded for an equal length of time it can be deduced that within the neck portion of the test implants the microthreading in some way enhanced and optimized osseointegration, encouraging a higher % BIC and greater marginal bone stability.
Astra Tech
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