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.
Effects of implant design and surface on bone regeneration and implant stability: an experimental study in the dog mandible
Purpose: The current study set out to investigate whether an alteration to implant surface texture by means of grit-blasting and/or the addition of retention elements as a MicroThread'" would influence the healing of marginal bone defects and the associated implant stability.
Materials and Methods: Three implant types were employed in the study, these were BrSnemark System 3.75 X 8.5 mm (BS) which were machine prepared, and Astra Tech ST 4.5 X 9 mm (ATST) and Astra Tech MicroThread" 4.0 X 9 mm (ATM), which both present with a titanium grit-blasted surface and so-called MicroThread'" in the coronal third of the implant. The ATST implants also present with a tapered coro-nal collar.
One of each implant was immediately inserted into the socket of either P2 or P3 premolars, which were extracted bilaterally in each one of six greyhound dogs, under anaesthesia. Crestobuccal bone defects measuring 3x3 mm were created adjacent to the implants on one side only (test side), with the contralateral alveolus being left intact to act as control. A transducer was attached to all implants in order to measure their baseline resonance frequency (ISQ value) to assess their interfacial stiffness, before flaps were repositioned and implants benefited from submerged healing for 4 months.
After the healing period a second ISQ value was recorded. Thereafter all animals were sacrificed and implant specimens were removed en bloc and fixed in formalin. Specimens were embedded, sectioned and ground to 10 pm prior to staining with toluidine blue 1% and Pyronin-G. Histomorphometric evaluation was carried out on both sides of each specimen to measure the percentage bone-to-implant contact (BIC), the percentage bone area in all threads (BA), and the distance from each implant's reference point to the most coronal bone contact.
Results: Healing was uneventful and all implants showed some degree of bone regeneration at the defect sites. When considering the ISQ values there was a typical increase in stiffness for all implants as a result of osseointegration in both test and control groups, which tended to be more significant for ATST and ATM. In addition the change in ISQ at 4 months compared to baseline for test implants compared to control implants reached statistical significance for both Astra Tech implant types (p < 0.05).
Histomorphometry revealed a statistically significant increase in mean BIC for Astra Tech implants compared to the BrSnemark implant with 4-month values measuring 51% (ATM) > 47.4% (ATST) > 23.6% (BS) for test and control implants combined. Mean BA measured 38.9% (ATST) > 36.7% (ATM) > 32.5% (BS) for test implants and 42.1% > 41.3% > 34.8% for control implants respectively.
The mean distance from each implant's reference point to the most coronal bone contact was significantly longer for the Branemark implants compared to the Astra Tech implants (p < 0.05) measuring 2.70 mm (BS) 2.20 mm (ATM) > 2.18 mm (ATST).
Discussion: The finding in this study that implants with a roughened surface result in an increased BIC is supported in the literature from human, animal and in vitro studies. It is also interesting to note that the distance to the most coronal bone at defect sites was notably shorter for these same roughened implants. This may also be related to the MicroThread. Increase in ISQ values was mostly attributable to osseointegration, however some notable relative increase in ISQ was seen for roughened implants. Whether new bone filling in the defects provides any additional stability can not be verified. Data would suggest this to be unlikely, either due to lack of integration or possibly due to its immature structure.
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